David Liang, MD, PhD

All Publications

• Geometric perturbations in multiheaded papillary tip positions associated with acute ovine ischemic mitral regurgitation JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Timek, T. A., Lai, D. T., Bothe, W., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2015; 150 (1): 232-237

  Abstract

  Novel surgical approaches are focusing on the "ventricular disease" of ischemic mitral regurgitation (IMR), to correct altered papillary muscle (PM) tip positions (apical displacement) and ameliorate leaflet tethering. Due to the anatomic complexity of the subvalvular apparatus, however, the precise geometric perturbations of the multiheaded PM tips associated with IMR remain uncharacterized.In 6 adult sheep, we implanted 3 markers on each PM. To specifically identify distinct PM tips, 1 marker was placed on the PM origin of the dominant chord to the anterior, posterior, and commissural leaflets. Nine markers were placed on the edge of the posterior mitral leaflet, and 5 on the edge of the anterior mitral leaflet. Eight markers were sewn around the mitral annulus. Animals were studied immediately postoperatively, with biplane videofluoroscopy and transesophageal echocardiography, before and during acute snare occlusion of the proximal left circumflex coronary artery, to induce IMR. Papillary muscle tip and leaflet edge geometry was expressed as the orthogonal distance of each respective marker to the least-squares mitral annulus plane at end-systole. In addition, the distance from each PM tip marker to the mitral annulus "saddle horn" was calculated.Acute left circumflex occlusion significantly increased mitral regurgitation from a baseline of 0.7 ± 0.3 to 2.5 ± 0.5 (P < .05). The IMR was associated with posterior leaflet restriction near the central leaflet edge, with simultaneous prolapse of both leaflets near the posterior commissure. No apical displacement of PM tips was observed during IMR, although the posterior PM moved farther away from the midseptal annulus.During acute ischemia, no apical displacement of any PM tip was observed. Posterior PM movement away from the annular saddle horn, and toward the annulus, was associated with IMR and leaflet prolapse near the posterior commissure, and with restriction near the valve center. These data may help guide development of surgical interventions aimed at PM repositioning.

  View details for DOI 10.1016/j.jtcvs.2015.04.037

  View details for PubMedID 25998465

• Greater asymmetric wall shear stress in Sievers' type 1/LR compared with 0/LAT bicuspid aortic valves after valve-sparing aortic root replacement JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Stephens, E. H., Hope, T. A., Kari, F. A., Kvitting, J. E., Liang, D. H., Herfkens, R. J., Miller, D. C. 2015; 150 (1): 59-68

  Abstract

  To evaluate the role of commissure orientation on downstream blood flow patterns and ascending aortic wall shear stress (WSS) in patients with bicuspid aortic valves (BAV) after valve-sparing aortic root replacement (V-SARR).Nineteen BAV patients after V-SARR (9 Sievers' type 1/LR [type 1 valve with fusion of the left and right cusps] and 10 Sievers' type 0/LAT ["naturally perfect"; type 0 valve without the presence of a raphe, and with the 2 commissures oriented right-anterior-to-left-posterior]) were imaged using time-resolved 3-D phase contrast magnetic resonance imaging. A control group of 5 unoperated tricuspid aortic valve patients were used for comparison purposes. Wall shear stress and eccentricity of flow normalized to aortic diameter were measured in planes placed perpendicular to the axis of the ascending aorta at the level of the sinotubular junction (proximal ascending), main pulmonary artery (mid-ascending), and origin of the brachiocephalic (distal ascending).The ratio of WSS along the outer curvature to that along the inner curvature was greater in Sievers' type 1/LR patients compared with Sievers' type 0/LAT patients in the proximal (3.8 ± 1.6 vs 2.1 ± 0.9, P = .009) and mid- ascending aorta (4.5 ± 2.4 vs 2.4 ± 1.3, P = .027). Relative to control normal tricuspid patients, Sievers' type 1/LR BAV patients had a higher WSS ratio in the mid-ascending aorta (4.5 ± 2.4 vs 1.2 ± 1.2, P = .007). Conversely, WSS in Sievers' type 0/LAT patients was not different than in normal tricuspid patients.After V-SARR, BAV cusp morphology has a major impact on the pattern of blood flow and WSS in the ascending aorta.

  View details for DOI 10.1016/j.jtcvs.2015.04.020

  View details for PubMedID 25956338

• Defining "Severe" Secondary Mitral Regurgitation Emphasizing an Integrated Approach JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY Grayburn, P. A., Carabello, B., Hung, J., Gillam, L. D., Liang, D., Mack, M. J., McCarthy, P. M., Miller, D. C., Trento, A., Siegel, R. J. 2014; 64 (25): 2792-2801

  Abstract

  Secondary mitral regurgitation (MR) is associated with poor outcomes, but its correction does not reverse the underlying left ventricular (LV) pathology or improve the prognosis. The recently published American Heart Association/American College of Cardiology guidelines on valvular heart disease generated considerable controversy by revising the definition of severe secondary MR from an effective regurgitant orifice area (EROA) of 0.4 to 0.2 cm(2), and from a regurgitant volume (RVol) of 60 to 30 ml. This paper reviews hydrodynamic determinants of MR severity, showing that EROA and RVol values associated with severe MR depend on LV volume. This explains disparities in the evidence associating a lower EROA threshold with suboptimal survival. Redefining MR severity purely on EROA or RVol may cause significant clinical problems. As the guidelines emphasize, defining severe MR requires careful integration of all echocardiographic and clinical data, as measurement of EROA is imprecise and poorly reproducible.

  View details for DOI 10.1016/j.jacc.2014.10.016

  View details for Web of Science ID 000346734900012

• Tirone David procedure for bicuspid aortic valve disease: impact of root geometry and valve type on mid-term outcomes†. Interactive cardiovascular and thoracic surgery Kari, F. A., Kvitting, J. E., Stephens, E. H., Liang, D. H., Merk, D. R., Fischbein, M. P., Mitchell, R. S., Miller, D. C. 2014; 19 (3): 375-381

  Abstract

  A 180/180° configuration has been reported to increase repair durability after valve-sparing aortic root replacement (V-SARR) for bicuspid aortic valve (BAV) disease. We studied the impact of commissural angular configuration (CAC) and of BAV type on valve performance after V-SARR.A total of 85 BAV patients (68 males, age 44 ± 11 years) underwent Tirone David-V V-SARR between 1997 and 2013. BAV type was documented intraoperatively, and CAC determined from pre- and postoperative computed tomography scans as the angle subtended by the non-fused cusp. Transthoracic echocardiogram was performed at 6 ± 3 days and at 2.9 ± 2.1 years. Functional end-points included freedom from aortic regurgitation (AR) 1+, AR 2+ and freedom from AR progression (0 to 1+, or 1+ to 2+). Tested variables included preoperative CAC (>160 vs <160°) and changes in CAC after V-SARR (Δ > 30° vs Δ < 30°) and Sievers' BAV type (SØ or S1).CAC in SØ-BAV (n = 26) changed minimally from 164 ± 12 to 171 ± 11° (mean Δ = 7.2 ± 16°, P = 0.044), whereas in S1-BAV (n = 59) CAC changed substantially from 132 ± 19 to 156 ± 18° (mean Δ = 27 ± 21°, P < 0.001). Larger postoperative CAC angles were not linked to better mid-term valve performance, but Sievers' BAV type had a major effect on valve performance: mild AR in S1/i BAV progressed more often (76 vs 32% at 4 years, P = 0.017) and 1+ AR was more frequent (70 vs 36% at 4 years, P = 0.008) compared with SØ-BAV.BAV type, including number of raphes, sinuses and commissures (SØ superior to S1) but not commissure geometry within the neoroot alone, appears to be linked to functional outcomes after V-SARR for BAV.

  View details for DOI 10.1093/icvts/ivu123

  View details for PubMedID 24903440

• Relationship between Echocardiographic and Magnetic Resonance Derived Measures of Right Ventricular Size and Function in Patients with Pulmonary Hypertension. Journal of the American Society of Echocardiography Shiran, H., Zamanian, R. T., McConnell, M. V., Liang, D. H., Dash, R., Heidary, S., Sudini, N. L., Wu, J. C., Haddad, F., Yang, P. C. 2014; 27 (4): 405-412

  Abstract

  Transthoracic echocardiographic (TTE) imaging is the mainstay of clinical practice for evaluating right ventricular (RV) size and function, but its accuracy in patients with pulmonary hypertension has not been well validated.Magnetic resonance imaging (MRI) and TTE images were retrospectively reviewed in 40 consecutive patients with pulmonary hypertension. RV and left ventricular volumes and ejection fractions were calculated using MRI. TTE areas and indices of RV ejection fraction (RVEF) were compared.The average age was 42 ± 12 years, with a majority of women (85%). There was a wide range of mean pulmonary arterial pressures (27-81 mm Hg) and RV end-diastolic volumes (111-576 mL), RVEFs (8%-67 %), and left ventricular ejection fractions (26%-72%) by MRI. There was a strong association between TTE and MRI-derived parameters: RV end-diastolic area (by TTE imaging) and RV end-diastolic volume (by MRI), R(2) = 0.78 (P < .001); RV fractional area change by TTE imaging and RVEF by MRI, R(2) = 0.76 (P < .001); and tricuspid annular plane systolic excursion by TTE imaging and RVEF by MRI, R(2) = 0.64 (P < .001). By receiver operating characteristic curve analysis, an RV fractional area change < 25% provided excellent discrimination of moderate systolic dysfunction (RVEF < 35%), with an area under the curve of 0.97 (P < .001). An RV end-diastolic area index of 18 cm(2)/m(2) provided excellent discrimination for moderate RV enlargement (area under the curve, 0.89; P < .001).Echocardiographic estimates of RV volume (by RV end-diastolic area) and function (by RV fractional area change and tricuspid annular plane systolic excursion) offer good approximations of RV size and function in patients with pulmonary hypertension and allow the accurate discrimination of normal from abnormal.

  View details for DOI 10.1016/j.echo.2013.12.011

  View details for PubMedID 24444659

• Incidence and progression of mild aortic regurgitation after Tirone David reimplantation valve-sparing aortic root replacement JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Stephens, E. H., Liang, D. H., Kvitting, J. E., Kari, F. A., Fischbein, M. P., Mitchell, R. S., Miller, D. C. 2014; 147 (1): 169-?

  Abstract

  The study objective was to determine whether recurrent or residual mild aortic regurgitation, which occurs after valve-sparing aortic root replacement, progresses over time.Between 2003 and 2008, 154 patients underwent Tirone David-V valve-sparing aortic root replacement; 96 patients (62%) had both 1-year (median, 12 ± 4 months) and mid-term (62 ± 22 months) transthoracic echocardiograms available for analysis. Age of patients averaged 38 ± 13 years, 71% were male, 31% had a bicuspid aortic valve, 41% had Marfan syndrome, and 51% underwent aortic valve repair, predominantly cusp free margin shortening.Forty-one patients (43%) had mild aortic regurgitation on 1-year echocardiogram. In 85% of patients (n = 35), mild aortic regurgitation remained stable on the most recent echocardiogram (median, 57 ± 20 months); progression to moderate aortic regurgitation occurred in 5 patients (12%) at a median of 28 ± 18 months and remained stable thereafter; severe aortic regurgitation developed in 1 patient, eventually requiring reoperation. Five patients (5%) had moderate aortic regurgitation at 1 year, which did not progress subsequently. Two patients (2%) had more than moderate aortic regurgitation at 1 year, and both ultimately required reoperation.Although mild aortic regurgitation occurs frequently after valve-sparing aortic root replacement, it is unlikely to progress over the next 5 years and should not be interpreted as failure of the valve-preservation concept. Further, we suggest that mild aortic regurgitation should not be considered nonstructural valve dysfunction, as the 2008 valve reporting guidelines would indicate. We need 10- to 15-year follow-up to learn the long-term clinical consequences of mild aortic regurgitation early after valve-sparing aortic root replacement.

  View details for DOI 10.1016/j.jtcvs.2013.09.009

  View details for PubMedID 24176278

• Aortic wall thickness: an independent risk factor for aortic dissection? journal of heart valve disease Shiran, H., Odegaard, J., Berry, G., Miller, D. C., Fischbein, M., Liang, D. 2014; 23 (1): 17-24

  Abstract

  Aortic aneurysm size is known to portend a higher likelihood of aortic complications in patients with connective tissue disorders (CTD), but other objective tools are needed to determine which patients are at greatest risk of dissection, especially those which reflect the structural integrity and strength of the aortic wall.The aortic wall pathology was evaluated in CTD patients with and without acute aortic dissection to identify parameters that affect the risk of dissection. A retrospective review was performed of aneurysm pathology from patients with Marfan syndrome (MFS; n = 53) without dissection undergoing prophylactic aortic root surgery, and acute type A aortic dissection patients (AAAoD; n = 16). Patients without a cardiovascular cause of death (n = 19) served as controls. The minimal aortic medial wall thickness was measured, and medial myxoid degeneration (MMD) and the degree of elastin loss and fragmentation were graded.The mean minimal aortic wall thickness was 1,625 +/- 364 microm in controls, and 703 +/- 256 microm and 438 +/- 322 microm for MFS and AAAoD patients, respectively. Aortic root diameters did not correlate with aortic wall thickness. A comparison of aortic medial thickness showed that the media was significantly thinner among acute dissection patients than either elective surgical patients (p = 0.02) or controls (p < 0.001). Aortic size, degree of MMD, and elastin loss did not vary significantly between CTD patients.A diminished aortic wall medial thickness may be linked to aortic dissection. High-resolution imaging techniques in the future may lead to the morphological assessment of aortic medial wall thickness in vivo becoming a reality which, in theory, could provide a more refined risk prognostication for acute aortic dissection.

  View details for PubMedID 24779324

• Focused transthoracic echocardiography during critical care medicine training: curriculum implementation and evaluation of proficiency*. Critical care medicine Beraud, A., Rizk, N. W., Pearl, R. G., Liang, D. H., Patterson, A. J. 2013; 41 (8): e179-81

  Abstract

  OBJECTIVES:: We designed and implemented a focused transthoracic echocardiography curriculum for critical care medicine fellows participating in 1- and 2-year training programs. We quantitatively evaluated their proficiency in focused transthoracic echocardiography. DESIGN:: Prospective study evaluating curriculum implementation and objective assessment of focused transthoracic echocardiography proficiency. SETTING:: Medical and surgical ICUs at an academic teaching hospital. Simulation laboratory. SUBJECTS:: Eighteen critical care medicine fellows. INTERVENTIONS:: Training in focused transthoracic echocardiography followed by proficiency testing. MEASUREMENTS AND MAIN RESULTS:: We assessed the ability of critical care medicine fellows to obtain and interpret focused transthoracic echocardiography images from critically ill patients and a from transthoracic echocardiography simulator. Using a cognitive examination test, we also evaluated each fellow's knowledge with regard to focused transthoracic echocardiography and each fellow's ability to interpret prerecorded focused transthoracic echocardiography images. After training, critical care medicine fellows were able to rapidly obtain five essential focused transthoracic echocardiography views: parasternal long axis, parasternal short axis, apical four chamber, subcostal four chamber, and subcostal inferior vena cava. Fellows were also able to expeditiously identify four important abnormalities: asystole, left ventricular dysfunction, right ventricular dilation and dysfunction, and a large pericardial effusion. CONCLUSIONS:: A focused transthoracic echocardiography curriculum that includes quantitative measures of proficiency can be integrated into critical care medicine fellowship training programs.

  View details for DOI 10.1097/CCM.0b013e31828e9240

  View details for PubMedID 23760156

• Focused transthoracic echocardiography during critical care medicine training: curriculum implementation and evaluation of proficiency*. Critical care medicine Beraud, A., Rizk, N. W., Pearl, R. G., Liang, D. H., Patterson, A. J. 2013; 41 (8): e179-81

  View details for DOI 10.1097/CCM.0b013e31828e9240

  View details for PubMedID 23760156

• Race differences in ventricular remodeling and function among college football players. American journal of cardiology Haddad, F., Peter, S., Hulme, O., Liang, D., Schnittger, I., Puryear, J., Gomari, F. A., Finocchiaro, G., Myers, J., Froelicher, V., Garza, D., Ashley, E. A. 2013; 112 (1): 128-134

  Abstract

  Athletic training is associated with increases in ventricular mass and volume. Recent studies have shown that left ventricular mass increases proportionally in white athletes with a mass/volume ratio approaching unity. The objective of this study was to compare the proportionality in ventricular remodeling and ventricular function in black versus white National Collegiate Athletic Association Division I football players. From 2008 to 2011, football players at Stanford University underwent cardiovascular screening with a 12-point history and physical examination, electrocardiography, and focused echocardiography. Compared with white players, black players had on average higher left ventricular mass indexes (77 ± 11 vs 71 ± 11 g/m(2), p = 0.009), higher mass/volume ratios (1.18 ± 0.16 vs 1.06 ± 0.09 g/ml, p <0.001), and higher QRS vector magnitudes (3.2 ± 0.7 vs 2.7 ± 0.8, p = 0.002). Black race had an odds ratio of 14 (95% confidence interval 5 to 42, p <0.001) for a mass/volume ratio >1.2. Mass/volume ratio was inversely related to early diastolic tissue Doppler velocity e' (r = -0.50, p <0.001) but not to QRS vector magnitude (r = 0.065, p = 0.034). With regard to systolic indexes, there was no significant difference in the left ventricular ejection fraction, velocity of circumferential shortening, and isovolumic acceleration. In conclusion, black college football players exhibit more concentric ventricular remodeling, lower early diastolic annular velocities, and increased ventricular voltage compared with white players. Ventricular mass increases proportionally to volume in white players but not in black players.

  View details for DOI 10.1016/j.amjcard.2013.02.065

  View details for PubMedID 23602691

• Tirone David valve-sparing aortic root replacement and cusp repair for bicuspid aortic valve disease JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Kari, F. A., Liang, D. H., Kvitting, J. E., Stephens, E. H., Mitchell, R. S., Fischbein, M. P., Miller, D. C. 2013; 145 (3): S35-?

  Abstract

  The durability of valve-sparing aortic root replacement with or without cusp repair in patients with bicuspid aortic valve (BAV) disease is questioned. We analyzed the results of 75 patients with a BAV undergoing Tirone David reimplantation valve-sparing aortic root replacement.Average age was 45 ± 10 years; 80% were male; 31% had 2+ or greater aortic regurgitation (AR); annular diameter averaged 28 ± 3 mm; 32% had a Sievers' type 0 BAV, and 66% underwent concomitant cusp repair (usually cusp free margin shortening) to correct prolapse. Early (6 ± 3 days) and late (2.9 ± 1.7, 1-10 years) postoperative echocardiographic results were compared (cumulative echocardiographic follow-up, 190 patient-years; median late interval, 2 years [interquartile range, 0.68, 4.2]). Seven patients remained at risk beyond 6 years. Clinical outcome and valve function were analyzed using log-rank calculations.Actuarial survival was 99% ± 2%; freedom from reoperation was 90% ± 5%, infection 98% ± 2%, and stroke 100% at 6 years. After initial improvement in degree of AR (P < .001), minor subclinical progression of AR was observed (P > .5); however, freedom from AR of more than 2+ was 100%. Cusp free margin shortening was not associated with valve deterioration, but commissural suspensory polytetrafluoroethylene neochord creation (n = 4) portended a higher probability of recurrent AR (P = .025).After David procedure and cusp repair in patients with a BAV, midterm clinical and valve function outcomes were favorable out to 6 years. More follow-up is required to determine long-term valve durability and the hazard of other clinically important late adverse events, including eventual reoperation, to beyond 10 years.

  View details for DOI 10.1016/j.jtcvs.2012.11.043

  View details for PubMedID 23260433

• David valve-sparing aortic root replacement: Equivalent mid-term outcome for different valve types with or without connective tissue disorder JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Kvitting, J. E., Kari, F. A., Fischbein, M. P., Liang, D. H., Beraud, A., Stephens, E. H., Mitchell, R. S., Miller, D. C. 2013; 145 (1): 117-?

  Abstract

  Although implicitly accepted by many that the durability of valve-sparing aortic root replacement in patients with bicuspid aortic valve disease and connective tissue disorders will be inferior, this hypothesis has not been rigorously investigated.From 1993 to 2009, 233 patients (27% bicuspid aortic valve, 40% Marfan syndrome) underwent Tirone David valve-sparing aortic root replacement. Follow-up averaged 4.7 ± 3.3 years (1102 patient-years). Freedom from adverse outcomes was determined using log-rank calculations.Survival at 5 and 10 years was 98.7% ± 0.7% and 93.5% ± 5.1%, respectively. Freedom from reoperation (all causes) on the aortic root was 92.2% ± 3.6% at 10 years; 3 reoperations were aortic valve replacement owing to structural valve deterioration. Freedom from structural valve deterioration at 10 years was 96.1% ± 2.1%. No significant differences were found in survival (P = .805, P = .793, respectively), reoperation (P = .179, P = .973, respectively), structural valve deterioration (P = .639, P = .982, respectively), or any other functional or clinical endpoints when patients were stratified by valve type (tricuspid aortic valve vs bicuspid aortic valve) or associated connective tissue disorder. At the latest echocardiographic follow-up (95% complete), 202 patients (94.8%) had none or trace aortic regurgitation, 10 (4.7%) mild, 0 had moderate to severe, and 1 (0.5%) had severe aortic regurgitation. Freedom from greater than 2+ aortic regurgitation at 10 years was 95.3% ± 2.5%. Six patients sustained acute type B aortic dissection (freedom at 10 years, 90.4% ± 5.0%).Tirone David reimplantation valve-sparing aortic root replacement in carefully selected young patients was associated with excellent clinical and echocardiographic outcome in patients with either a tricuspid aortic valve or bicuspid aortic valve. No demonstrable adverse influence was found for Marfan syndrome or connective tissue disorder on durability, clinical outcome, or echocardiographic results.

  View details for DOI 10.1016/j.jtcvs.2012.09.013

  View details for PubMedID 23083792

• Comparison of Aortic Root Diameter to Left Ventricular Outflow Diameter Versus Body Surface Area in Patients With Marfan Syndrome AMERICAN JOURNAL OF CARDIOLOGY Shiran, H., Haddad, F., Miller, D. C., Liang, D. 2012; 110 (10): 1518-1522

  Abstract

  Aortic root dilation is important in the diagnosis of familial aortic syndromes, such as Marfan syndrome, and an important risk factor for aortic complications, such as dissection or rupture. Transthoracic echocardiography reliably measures the absolute aortic root size; however, the degree of abnormality of the measurement requires correction for the expected normal aortic root size for each patient. The expected normal size is currently predicted according to the body surface area (BSA) and age. However, the correlation between root size and BSA is imperfect, particularly for older patients. A potential exists to improve the diagnosis and treatment of patients with aortic disease, with an improved estimation of normal aortic root size. A reference size derived from within the cardiovascular system has been hypothesized to provide a more direct correlation with the aortic root size. Images from the Stanford echocardiography database were reviewed, and measurements of the aortic root and internal dimensions were performed in a control cohort (n = 150). The measurements were repeated in adult patients with Marfan syndrome (n = 70) on serial echocardiograms (145 total studies reviewed). Of the 150 control patients, excellent correlation was found between the aortic root and left ventricular outflow tract diameters, r(2) = 0.67, and r(2) = 0.34 with BSA (p <0.0001, for both). More importantly, using the left ventricular outflow tract to predict the normal aortic root size, instead of the BSA and age, improved the diagnostic accuracy of aortic root measurements for diagnosing Marfan syndrome. In conclusion, an internal cardiovascular reference, the left ventricular outflow tract diameter, can improve the diagnosis of aortic disease and might provide a better reference for the degree of abnormality.

  View details for DOI 10.1016/j.amjcard.2012.06.062

  View details for Web of Science ID 000311523900021

  View details for PubMedID 22858189

• VALIDATION OF A POWER LAW MODEL IN UPPER EXTREMITY VESSELS: POTENTIAL APPLICATION IN ULTRASOUND BLEED DETECTION ULTRASOUND IN MEDICINE AND BIOLOGY Wang, A. S., Liang, D. H., Bech, F., Lee, J. T., Zarins, C. K., Zhou, W., Taylor, C. A. 2012; 38 (4): 692-701

  Abstract

  Vascular ultrasound can provide quick and reliable diagnosis of arterial bleeding but it requires trained and experienced personnel. Development of automated sonographic bleed detection methods would potentially be valuable for trauma management in the field. We propose a detection method that (1) measures blood flow in a trauma victim, (2) determines the victim's expected normal limb arterial flow using a power law biofluid model where flow is proportional to the vessel diameter taken to a power of k and (3) quantifies the difference between measured and expected flow with a novel metric, flow split deviation (FSD). FSD was devised to give a quantitative value for the likelihood of arterial bleeding and validated in human upper extremities. We used ultrasound to demonstrate that the power law with k = 2.75 appropriately described the normal brachial artery bifurcation geometry and adequately determined the expected normal flows. Our metric was then applied to three-dimensional (3-D) computational models of forearm bleeding and on dialysis patients undergoing surgical construction of wrist arteriovenous fistulas. Computational models showed that larger sized arterial defects produced larger flow deviations. FSD values were statistically higher (paired t-test) for arms with fistulas than those without, with average FSDs of 0.41 ± 0.12 and 0.047 ± 0.021 (mean ± SD), respectively. The average of the differences was 0.36 ± 0.12 (mean ± SD).

  View details for DOI 10.1016/j.ultrasmedbio.2011.12.016

  View details for PubMedID 22341050

• A FAST SLAM APPROACH TO FREEHAND 3-D ULTRASOUND RECONSTRUCTION FOR CATHETER ABLATION GUIDANCE IN THE LEFT ATRIUM ULTRASOUND IN MEDICINE AND BIOLOGY Koolwal, A. B., Barbagli, F., Carlson, C. R., Liang, D. H. 2011; 37 (12): 2037-2054

  Abstract

  We present a method for real-time, freehand 3D ultrasound (3D-US) reconstruction of moving anatomy, with specific application towards guiding the catheter ablation procedure in the left atrium. Using an intracardiac echo (ICE) catheter with a pose (position/orientation) sensor mounted to its tip, we continually mosaic 2D-ICE images of a left atrium phantom model to form a 3D-US volume. Our mosaicing strategy employs a probabilistic framework based on simultaneous localization and mapping (SLAM), a technique commonly used in mobile robotics for creating maps of unexplored environments. The measured ICE catheter tip pose provides an initial estimate for compounding 2D-ICE image data into the 3D-US volume. However, we simultaneously consider the overlap-consistency shared between 2D-ICE images and the 3D-US volume, computing a "corrected" tip pose if need be to ensure spatially-consistent reconstruction. This allows us to compensate for anatomic movement and sensor drift that would otherwise cause motion artifacts in the 3D-US volume. Our approach incorporates 2D-ICE data immediately after acquisition, allowing us to continuously update the registration parameters linking sensor coordinates to 3D-US coordinates. This, in turn, enables real-time localization and display of sensorized therapeutic catheters within the 3D-US volume for facilitating procedural guidance.

  View details for DOI 10.1016/j.ultrasmedbio.2011.08.007

  View details for Web of Science ID 000297324700010

  View details for PubMedID 22014856

• Ectopia Lentis as the Presenting and Primary Feature in Marfan Syndrome AMERICAN JOURNAL OF MEDICAL GENETICS PART A Zadeh, N., Bernstein, J. A., Niemi, A. K., Dugan, S., Kwan, A., Liang, D., Hyland, J. C., Hoyme, H. E., Hudgins, L., Manning, M. A. 2011; 155A (11): 2661-2668

  Abstract

  Marfan syndrome (MFS) is a multisystem connective tissue disorder with primary involvement of the ocular, cardiovascular, and skeletal systems. We report on eight patients, all presenting initially with bilateral ectopia lentis (EL) during early childhood. These individuals did not have systemic manifestations of MFS, and did not fulfill the revised Ghent diagnostic criteria. However, all patients had demonstratable, disease-causing missense mutations in the FBN1 gene. Based on molecular results, cardiovascular imaging was recommended and led to the identification of mild aortic root changes in seven of the eight patients. The remaining patient had mitral valve prolapse with a normal appearing thoracic aorta. The findings presented in this paper validate the necessity of FBN1 gene testing in all individuals presenting with isolated EL. As we observed, these individuals are at increased risk of cardiovascular complications. Furthermore, we also noted that the majority of our patient cohort's mutations occurred in the 5' portion of the FBN1 gene, and were found to affect highly conserved cysteine residues, which may indicate a possible genotype-phenotype correlation. We conclude that in patients with isolated features of EL, FBN1 mutation analysis is necessary to aid in providing prompt diagnosis, and to identify patients at risk for potentially life-threatening complications. Additionally, knowledge of the type and location of an FBN1 mutation may be useful in providing further clinical correlation regarding phenotypic progression and appropriate medical management.

  View details for DOI 10.1002/ajmg.a.34245

  View details for PubMedID 21932315

• Effects of different annuloplasty ring types on mitral leaflet tenting area during acute myocardial ischemia JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Bothe, W., Kvitting, J. E., Stephens, E. H., Swanson, J. C., Liang, D. H., Ingels, N. B., Miller, D. C. 2011; 141 (2): 345-353

  Abstract

  The study objective was to quantify the effects of different annuloplasty rings on mitral leaflet septal-lateral tenting areas during acute myocardial ischemia.Radiopaque markers were implanted along the central septal-lateral meridian of the mitral valve in 30 sheep: 1 each to the septal and lateral aspects of the mitral annulus and 4 and 2 along the anterior and posterior mitral leaflets, respectively. Ten true-sized Carpentier-Edwards Physio, Edwards IMR ETLogix, and GeoForm annuloplasty rings (Edwards Lifesciences, Irvine, Calif) were inserted in a releasable fashion. Marker coordinates were obtained using biplane videofluoroscopy with ring inserted at baseline (RING_BL) and after 90 seconds of left circumflex artery occlusion (RING_ISCH). After ring release, another dataset was acquired before (No_Ring_BL) and after left circumflex artery occlusion (No_Ring_ISCH). Anterior and posterior mitral leaflet tenting areas were computed at mid-systole from sums of marker triangles with the midpoint between the annular markers being the vertex for all triangles.Compared with No_Ring_BL, mitral regurgitation grades and all tenting areas significantly increased with No_Ring_ISCH. Compared with No_Ring_ISCH, (1) all rings significantly prevented mitral regurgitation and reduced all tenting areas; (2) Edwards IMR ETLogix and GeoForm rings reduced posterior mitral leaflet area, but not anterior mitral leaflet tenting area, to a significantly greater extent than the Carpentier-Edwards Physio ring; and (3) Edwards IMR ETLogix and GeoForm rings affected tenting areas similarly.In response to acute left ventricular ischemia, disease-specific functional/ischemic mitral regurgitation rings (Edwards IMR ETLogix, GeoForm) more effectively reduced posterior mitral leaflet area, but not anterior mitral leaflet tenting area, compared with true-sized physiologic rings (Carpentier-Edwards Physio). Despite its radical 3-dimensional shape and greater amount of mitral annular septal-lateral downsizing, the GeoForm ring did not reduce tenting areas more than the Edwards IMR ETLogix ring, suggesting that further reduction in tenting areas in patients with FMR/IMR may not be effectively achieved on an annular level.

  View details for DOI 10.1016/j.jtcvs.2010.10.015

  View details for PubMedID 21241857

• Power Law as a Method for Ultrasound Detection of Internal Bleeding: In Vivo Rabbit Validation IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Wang, A. S., Abilez, O. J., Zarins, C. K., Taylor, C. A., Liang, D. H. 2010; 57 (12): 2870-2875

  Abstract

  New detection methods for vascular injuries can augment the usability of an ultrasound (US) imager in trauma settings. The goal of this study was to evaluate a potential-detection strategy for internal bleeding that employs a well-established theoretical biofluid model, the power law. This law characterizes normal blood-flow rates through an arterial tree by its bifurcation geometry. By detecting flows that deviate from the model, we hypothesized that vascular abnormalities could be localized. We devised a bleed metric, flow-split deviation (FSD), that quantified the difference between patient and model blood flows at vessel bifurcations. Femoral bleeds were introduced into ten rabbits (∼5 kg) using a cannula attached to a variable pump. Different bleed rates (0% as control, 5%, 10%, 15%, 20%, 25%, and 30% of descending aortic flow) were created at two physiological states (rest and elevated state with epinephrine). FSDs were found by US imaging the iliac arteries. Our bleed metric demonstrated good sensitivity and specificity at moderate bleed rates; area under receiver-operating characteristic curves were greater than 0.95 for bleed rates 20% and higher. Thus, FSD was a good indicator of bleed severity and may serve as an additional tool in the US bleed detection.

  View details for DOI 10.1109/TBME.2010.2058803

  View details for Web of Science ID 000284360100009

  View details for PubMedID 20639172

• Determinants of Evolution and Progression of Acute Ovine Ischemic Mitral Regurgitation JOURNAL OF HEART VALVE DISEASE Timek, T. A., Lai, D. T., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2010; 19 (4): 420-426

  Abstract

  The optimal treatment of moderate ischemic mitral regurgitation (IMR) remains contested. Thus, radiopaque markers were implanted on valvular structures to investigate the geometric and hemodynamic variables associated with the evolution and progression of acute ovine IMR.Eight adult sheep underwent implantation of five radiopaque markers on the edge of the posterior mitral leaflet (PML), and five on the edge of the anterior mitral leaflet (AML). Eight additional markers were sewn around the mitral annulus (MA). The animals were studied immediately after surgery, using biplane videofluoroscopy and transesophageal echocardiography. Data were acquired at Baseline and at two time points (IMR1 and IMR2) during acute snare occlusion of the proximal left circumflex coronary artery and progressive IMR. The orthogonal distance of each leaflet edge marker to the least-squares annular plane, mitral annular area (MAA), and septal-lateral diameter (SL) were calculated at end-systole. The leaflet tenting area (TA) was calculated at valve center (CENT) and near the anterior (ACOM) and posterior (PCOM) commissures.The degree of MR was 0.6 +/- 0.4, 1.8 +/- 0.7, and 2.8 +/- 0.7 for Baseline, IMR1, and IMR2, respectively (p < 0.005). IMR1 was associated with annular dilatation and leaflet restriction near the valve center, and prolapse near the PCOM versus Baseline. Although both left ventricular pressure (LVP) and left ventricular dP/dt decreased significantly from IMR1 to IMR 2, there were no differences in leaflet or annular geometry.The initiation of moderate IMR was associated with significant alterations in annular and leaflet geometry, but only a small decrease in LV systolic function, was needed for IMR progression. These data suggest that the surgical repair and optimization of LV function may be important in combination to treat moderate IMR, as only small hemodynamic deterioration and perturbations in valvular geometry are necessary for significant IMR progression.

  View details for Web of Science ID 000285280900003

  View details for PubMedID 20845887

• An Ultrasound-based Localization Algorithm for Catheter Ablation Guidance in the Left Atrium INTERNATIONAL JOURNAL OF ROBOTICS RESEARCH Koolwal, A. B., Barbagli, F., Carlson, C., Liang, D. 2010; 29 (6): 643-665

  View details for DOI 10.1177/0278364909105332

  View details for Web of Science ID 000276802100001

• Dyssynchrony Assessment with Tissue Doppler Imaging and Regional Volumetric Analysis by 3D Echocardiography Do Not Predict Long-Term Response to Cardiac Resynchronization Therapy. Cardiology research and practice Kuppahally, S. S., Fowler, M. B., Vagelos, R., Wang, P., Al-Ahmad, A., Hsia, H., Liang, D. 2010; 2011: 568918-?

  Abstract

  Background. Currently there are no reliable predictors of response to cardiac resynchronization therapy (CRT) before implantation. We compared pre-CRT left ventricular (LV) dyssynchrony by tissue Doppler imaging (TDI) and regional volumetric analysis by 3-dimensional transthoracic echocardiography (3DTTE) in predicting response to CRT. Methods. Thirty-eight patients (79% nonischemic cardiomyopathy) with symptomatic heart failure who underwent CRT were enrolled. Clinical and echocardiographic responses were defined as improvement in one NYHA class and reduction in LV end-systolic volume by ≥15% respectively. Functional status was assessed by Minnesota Living with Heart Failure questionnaire and 6-minute walk distance. Results. In 33 patients, after CRT for 7.86 ± 2.27 months, there were 24 (73%) clinical and 19 (58%) echocardiographic responders. Functional parameters, LV dimensions, volumes and synchrony by TDI and 3DTTE improved significantly in responders. There was no difference in the number of responders and nonresponders when cut-off values for dyssynchrony by different measurements validated in other trials were applied. Area under receiver-operating-characteristic curve ranged from 0.4 to 0.6. Conclusion. CRT improves clinical and echocardiographic parameters in patients with systolic heart failure. The dyssynchrony measurements by TDI and 3DTTE are not comparable and are unable to predict response to CRT.

  View details for DOI 10.4061/2011/568918

  View details for PubMedID 21234100

  View details for PubMedCentralID PMC3014673

• A probabilistic framework for freehand 3D ultrasound reconstruction applied to catheter ablation guidance in the left atrium INTERNATIONAL JOURNAL OF COMPUTER ASSISTED RADIOLOGY AND SURGERY Koolwal, A. B., Barbagli, F., Carlson, C. R., Liang, D. H. 2009; 4 (5): 425-437

  Abstract

  The catheter ablation procedure is a minimally invasive surgery used to treat atrial fibrillation. Difficulty visualizing the catheter inside the left atrium anatomy has led to lengthy procedure times and limited success rates. In this paper, we present a set of algorithms for reconstructing 3D ultrasound data of the left atrium in real-time, with an emphasis on automatic tissue classification for improved clarity surrounding regions of interest.Using an intracardiac echo (ICE) ultrasound catheter, we collect 2D-ICE images of a left atrium phantom from multiple configurations and iteratively compound the acquired data into a 3D-ICE volume. We introduce two new methods for compounding overlapping US data-occupancy-likelihood and response-grid compounding-which automatically classify voxels as "occupied" or "clear," and mitigate reconstruction artifacts caused by signal dropout. Finally, we use the results of an ICE-to-CT registration algorithm to devise a response-likelihood weighting scheme, which assigns weights to US signals based on the likelihood that they correspond to tissue-reflections.Our algorithms successfully reconstruct a 3D-ICE volume of the left atrium with voxels classified as "occupied" or "clear," even within difficult-to-image regions like the pulmonary vein openings. We are robust to dropout artifact that plagues a subset of the 2D-ICE images, and our weighting scheme assists in filtering out spurious data attributed to ghost-signals from multi-path reflections. By automatically classifying tissue, our algorithm precludes the need for thresholding, a process that is difficult to automate without subjective input. Our hope is to use this result towards developing 3D ultrasound segmentation algorithms in the future.

  View details for DOI 10.1007/s11548-009-0354-6

  View details for Web of Science ID 000207884900003

  View details for PubMedID 20033525

• Worsening of Left Ventricular End-Systolic Volume and Mitral Regurgitation without Increase in Left Ventricular Dyssynchrony on Acute Interruption of Cardiac Resynchronization Therapy ECHOCARDIOGRAPHY-A JOURNAL OF CARDIOVASCULAR ULTRASOUND AND ALLIED TECHNIQUES Kuppahally, S. S., Fowler, M. B., Vagelos, R., Wang, P., Al-Ahmad, A., Paloma, A., Liang, D. 2009; 26 (7): 759-765

  Abstract

  Responders to cardiac resynchronization therapy (CRT) have greater left ventricular (LV) dyssynchrony than nonresponders prior to CRT.We conducted this study to see whether the long term responders have more worsening of LV dyssynchrony and LV function on acute interruption of CRT.We identified 22 responders and 13 nonresponders who received CRT as per standard criteria for 23.73 +/- 7.9 months (median 24.5 months). We assessed the acute change in LV function, mitral regurgitation (MR) and compared LV dyssynchrony in CRT on and off modes.On turning off CRT, there was no significant worsening of LV dyssynchrony in both responders and nonresponders. The dyssynchrony measurements by SPWMD, TDI and 3D echocardiography did not correlate significantly. LVESV increased (p = 0.02) and MR (p = 0.01) worsened in CRT-off mode in responders only without significant change in LVEF or LV dimensions. Discussion andIn long-term responders to CRT, there is alteration in the function of remodeled LV with acute interruption of CRT, without significant worsening of LV dyssynchrony. The role of different echocardiographic parameters in the assessment of LV dyssynchrony remains controversial. Even after long-term CRT reversely remodels the LV, the therapy needs to be continued uninterrupted for sustained benefits.

  View details for DOI 10.1111/j.1540-8175.2008.00887.x

  View details for Web of Science ID 000268457100002

  View details for PubMedID 19558521

• Multiplanar Reconstruction of Three-Dimensional Transthoracic Echocardiography Improves the Presurgical Assessment of Mitral Prolapse JOURNAL OF THE AMERICAN SOCIETY OF ECHOCARDIOGRAPHY Beraud, A., Schnittger, I., Miller, D. C., Liang, D. H. 2009; 22 (8): 907-913

  Abstract

  The aim of this study was to evaluate the value and accuracy of multiplanar reconstruction (MPR) of three-dimensional (3D) transthoracic echocardiographic data sets in assessing mitral valve pathology in patients with surgical mitral valve prolapse (MVP).Sixty-four patients with surgical MVP and preoperative two-dimensional (2D) and 3D transthoracic echocardiography were analyzed. The descriptions obtained by 3D MPR and 2D were compared in the context of the surgical findings.Two-dimensional echocardiography correctly identified the prolapsing leaflets in 32 of 64 patients and 3D MPR in 46 of 64 patients (P=.016). Among the 27 patients with complex pathology (ie, more than isolated middle scallop of the posterior leaflet prolapse), 3D MPR identified 20 correctly, as opposed to 6 with 2D imaging (P<.001).Interpretation of 3D transthoracic echocardiographic images with MPR improved the accuracy of the description of the MVP compared with 2D interpretation. This added value of 3D MPR was most important in extensive and/or commissural prolapse.

  View details for DOI 10.1016/j.echo.2009.05.007

  View details for PubMedID 19553082

• Reduced Systolic Torsion in Chronic "Pure" Mitral Regurgitation CIRCULATION-CARDIOVASCULAR IMAGING Ennis, D. B., Nguyen, T. C., Itoh, A., Bothe, W., Liang, D. H., Ingels, N. B., Miller, D. C. 2009; 2 (2): 85-92

  Abstract

  Global left ventricular (LV) torsion declines with chronic ischemic mitral regurgitation (MR), which may accelerate the LV remodeling spiral toward global cardiomyopathy; however, it has not been definitively established whether this torsional decline is attributable to the infarct, the MR, or their combined effect. We tested the hypothesis that chronic "pure" MR alone reduces global LV torsion.Chronic "pure" MR was created in 13 sheep by surgically punching a 3.5- to 4.8-mm hole (HOLE) in the mitral valve posterior leaflet. Nine control (CNTL) sheep were operated on concurrently. At 1 (WK-01) and 12 weeks (WK-12) postoperatively, the 4D motion of implanted radiopaque markers was used to calculate global LV torsion. MR-grade in HOLE was greater than CNTL at WK-01 and WK-12 (2.5+/-1.1 versus 0.6+/-0.5, P<0.001 at WK-12). HOLE LV mass index was larger at WK-12 compared with CNTL (195+/-14 versus 170+/-17 g/m(2), P<0.01), indicating LV remodeling. Global LV systolic torsion decreased in HOLE from WK-01 to WK-12 (4.1+/-2.8 degrees versus 1.7+/-1.7 degrees , P<0.01), but did not change in CNTL (5.5+/-1.8 degrees versus 4.2+/-2.7 degrees , P=NS). Global LV torsion was lower in HOLE relative to CNTL at WK-12 (P<0.05) but not at WK-01 (P=NS).Twelve weeks of chronic "pure" MR resulting in mild global LV remodeling is associated with significantly increased LV mass index and reduced global LV systolic torsion, but no other significant changes in hemodynamics. MR alone is a major component of torsional deterioration in "pure" MR and may be an important factor in chronic ischemic mitral regurgitation.

  View details for DOI 10.1161/CIRCIMAGING.108.785923

  View details for PubMedID 19808573

• Catheter Localization in the Left Atrium using an Outdated Anatomic Reference for Guidance Annual International Conference of the IEEE-Engineering-in-Medicine-and-Biology-Society Koolwal, A. B., Barbagli, F., Carlson, C. R., Liang, D. H. IEEE. 2009: 5567–5570

  Abstract

  We present a method for registering real-time ultrasound of the left atrium to an outdated, anatomic surface mesh model, whose shape differs from that of the anatomy. Using an intracardiac echo (ICE) catheter with mounted 6DOF electromagnetic position/orientation sensor (EPS), we acquire images of the left atrium and determine where the ICE catheter must be positioned relative to the surface mesh to generate similar, "virtual" ICE images. Further, we use an affine warping model to infer how the shape of the surface mesh differs from that of the atrium. Our registration and warping algorithm allows us to display EPS-sensorized catheters inside the surface mesh, facilitating guidance for left atrial procedures. By solving for the atrium-to-mesh warping parameters, we ensure that tissue contact in the anatomy is properly displayed as tissue contact in the mesh. After considering less than thirty seconds worth of ICE data, we are able to accurately localize EPS measurements within the surface mesh, despite surface mesh warpings of up to +/-20% along and about the principal axes of the left atrium. Further, because our estimation framework is iterative and continuous, our accuracy improves as new data is acquired.

  View details for Web of Science ID 000280543604119

  View details for PubMedID 19964395

• An Image-Based Localization Algorithm for Catheter Navigation in the Left Atrium 11th International Symposium on Experimental Robotics (ISER) Koolwal, A. B., Barbagli, F., Carlson, C. R., Liang, D. H., Prinz, F. B. SPRINGER-VERLAG BERLIN. 2009: 251–260

  View details for Web of Science ID 000268803300024

• Alterations in transmural myocardial strain - An early marker of left ventricular dysfunction in mitral regurgitation? 80th Annual Scientific Session of the American-Heart-Association (AHA) Carlhaell, C. J., Nguyen, T. C., Itoh, A., Ennis, D. B., Bothe, W., Liang, D., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2008: S256–S262

  Abstract

  In asymptomatic patients with severe isolated mitral regurgitation (MR), identifying the onset of early left ventricular (LV) dysfunction can guide the timing of surgical intervention. We hypothesized that changes in LV transmural myocardial strain represent an early marker of LV dysfunction in an ovine chronic MR model.Sheep were randomized to control (CTRL, n=8) or experimental (EXP, n=12) groups. In EXP, a 3.5- or 4.8-mm hole was created in the posterior mitral leaflet to generate "pure" MR. Transmural beadsets were inserted into the lateral and anterior LV wall to radiographically measure 3-dimensional transmural strains during systole and diastolic filling, at 1 and 12 weeks postoperatively. MR grade was higher in EXP than CTRL at 1 and 12 weeks (3.0 [2-4] versus 0.5 [0-2]; 3.0 [1-4] versus 0.5 [0-1], respectively, both P<0.001). At 12 weeks, LV mass index was greater in EXP than CTRL (201+/-18 versus 173+/-17 g/m(2); P<0.01). LVEDVI increased in EXP from 1 to 12 weeks (P=0.015). Between the 1 and 12 week values, the change in BNP (-4.5+/-4.4 versus -3.0+/-3.6 pmol/L), PRSW (9+/-13 versus 23+/-18 mm Hg), tau (-3+/-11 versus -4+/-7 ms), and systolic strains was similar between EXP and CTRL. The changes in longitudinal diastolic filling strains between 1 and 12 weeks, however, were greater in EXP versus CTRL in the subendocardium (lateral: -0.08+/-0.05 versus 0.02+/-0.14; anterior: -0.10+/-0.05 versus -0.02+/-0.07, both P<0.01).Twelve weeks of ovine "pure" MR caused LV remodeling with early changes in LV function detected by alterations in transmural myocardial strain, but not by changes in BNP, PRSW, or tau.

  View details for DOI 10.1161/CIRCULATIONAHA.107.753525

  View details for PubMedID 18824764

• Laser-machined shape memory alloy sensors for position feedback in active catheters SENSORS AND ACTUATORS A-PHYSICAL Tung, A. T., Park, B., Liang, D. H., Niemeyer, G. 2008; 147 (1): 83-92

  Abstract

  Catheter-based interventions are a form of minimally invasive surgery that can decrease hospitalization time and greatly lower patient morbidity compared to traditional methods. However, percutaneous catheter procedures are hindered by a lack of precise tip manipulation when actuation forces are transmitted over the length of the catheter. Active catheters with local shape-memory-alloy (SMA) actuation can potentially provide the desired manipulation of a catheter tip, but hysteresis makes it difficult to control the actuators. A method to integrate small-volume, compliant sensors on an active catheter to provide position feedback for control would greatly improve the viability of SMA-based active catheters. In this work, we describe the design, fabrication, and performance of resistance-based position sensors that are laser-machined from superelastic SMA tubing. Combining simple material models and rapid prototyping, we can develop sensors of appropriate stiffness and sensitivity with simple modifications in sensor geometry. The sensors exhibit excellent linearity over the operating range and are designed to be easily integrated onto an active catheter substrate.

  View details for DOI 10.1016/j.sna.2008.03.024

  View details for Web of Science ID 000259017500012

  View details for PubMedCentralID PMC2598764

• The effect of pure mitral regurgitation on mitral annular geometry and three-dimensional saddle shape 87th Annual Meeting of the American-Association-for-Thoracic-Surgery Nguyen, T. C., Itoh, A., Carlhall, C. J., Bothe, W., Timek, T. A., Ennis, D. B., Oakes, R. A., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. MOSBY-ELSEVIER. 2008: 557–65

  Abstract

  Chronic ischemic mitral regurgitation is associated with mitral annular dilatation in the septal-lateral dimension and flattening of the annular 3-dimensional saddle shape. To examine whether these perturbations are caused by the ischemic insult, mitral regurgitation, or both, we investigated the effects of pure mitral regurgitation (low pressure volume overload) on annular geometry and shape.Eight radiopaque markers were sutured evenly around the mitral annulus in sheep randomized to control (CTRL, n = 8) or experimental (HOLE, n = 12) groups. In HOLE, a 3.5- to 4.8-mm hole was punched in the posterior leaflet to generate pure mitral regurgitation. Four-dimensional marker coordinates were obtained radiographically 1 and 12 weeks postoperatively. Mitral annular area, annular septal-lateral and commissure-commissure dimensions, and annular height were calculated every 16.7 ms.Mitral regurgitation grade was 0.4 +/- 0.4 in CTRL and 3.0 +/- 0.8 in HOLE (P < .001) at 12 weeks. End-diastolic left ventricular volume index was greater in HOLE at both 1 and 12 weeks; end-systolic volume index was larger in HOLE at 12 weeks. Mitral annular area increased in HOLE predominantly in the commissure-commissure dimension, with no difference in annular height between HOLE versus CTRL at 1 or 12 weeks, respectively.In contrast with annular septal-lateral dilatation and flattening of the annular saddle shape observed with chronic ischemic mitral regurgitation, pure mitral regurgitation was associated with commissure-commissure dimension annular dilatation and no change in annular shape. Thus, infarction is a more important determinant of septal-lateral dilatation and annular shape than mitral regurgitation, which reinforces the need for disease-specific designs of annuloplasty rings.

  View details for DOI 10.1016/j.jtcvs.2007.12.087

  View details for PubMedID 18805251

• Effect of local annular interventions on annular and left ventricular geometry 21st Annual Meeting of the European-Association-for-Cardio-Thoracic-Surgery (EACTS) Timek, T. A., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. OXFORD UNIV PRESS INC. 2008: 1049–54

  Abstract

  Etiology-specific annular interventions and annuloplasty rings are now commercially available for the treatment of different types of mitral regurgitation; however, knowledge concerning the effects of local annular alterations on annular and left ventricular (LV) geometry is limited.Seven adult sheep underwent implantation of eight radiopaque markers around the mitral annulus (MA) and eight markers on the LV (four each on two levels: basal and apical), and one on each papillary muscle tip. Trans-annular septal-lateral (SL) sutures were placed between the corresponding markers on the septal and lateral annulus at valve center (CENT) and near anterior (ACOM) and posterior (PCOM) commissures and externalized. Hemodynamic parameters and 4D marker coordinates were measured before and during SL annular cinching ('SLAC'; suture tightening 3-5 mm for 20s) at each suture location. Mitral annular SL diameter, annular area (MAA), and distance from the mid-septal annulus to the LV markers and papillary muscle tips were determined from marker coordinates every 17ms.End-systolic MAA decreased from 5.93+/-1.27 to 5.23+/-1.29(*)cm(2), 5.98+/-1.16 to 5.33+/-1.31(*)cm(2), and 6.30+/-1.65 to 5.61+/-1.37(*)cm(2) for SLAC(ACOM), SLAC(CENT), and SLAC(PCOM), respectively ((*)p<0.05 vs pre-cinching). Each SLAC intervention reduced the SL diameter at all three locations, while both SLAC(ACOM) and SLAC(CENT) affected ventricular geometry, and SLAC(PCOM) only slightly altered valvular-subvalvular distance. Only SLAC(CENT) altered papillary muscle position.Local annular SL reduction influences remote annular SL dimensions and affects LV geometry. The effect of local annular interventions on global annular geometry and LV remodeling should be considered in surgical or interventional approaches to mitral regurgitation and the design of new annular prostheses as well as supra-annular and sub-annular catheter interventions.

  View details for DOI 10.1016/j.ejcts.2008.03.040

  View details for PubMedID 18442919

• The aortopathy of bicuspid aortic valve disease has distinctive patterns and usually involves the transverse aortic arch 33rd Annual Meeting of the Western-Thoracic-Surgical-Association Fazel, S. S., Mallidi, H. R., Lee, R. S., Sheehan, M. P., Liang, D., Fleischman, D., Herfkens, R., Mitchell, S., Miller, D. C. MOSBY-ELSEVIER. 2008: 901–U54

  Abstract

  Bicuspid aortic valves are associated with a poorly characterized connective tissue disorder that predisposes to aortic catastrophes. Because no criterion exists dictating the appropriate extent of aortic resection in aneurysmal disease of the bicuspid aortic valve, we studied the patterns of aortic dilation in this population.Sixty-four patients with bicuspid aortic valves who underwent computed tomographic or magnetic resonance angiography and echocardiography were retrospectively identified between January 2002 and March 2006. Orthonormal 2-dimensional or 3-dimensional aortic diameters were measured at 10 levels. Agglomerative hierarchic clustering with centered correlation distance measurements and complete linkage analysis was used to detect distinct patterns of aortic dilatation.Mean aortic diameter was 28.1 +/- 0.7 mm at the annulus and 21.7 +/- 0.4 mm at the diaphragmatic hiatus. The aorta was largest in the tubular ascending aorta (45.9 +/- 1.0 mm). Compared with the descending aorta, the transverse aortic arch was also dilated (P < .01). Cluster analysis showed 4 patterns of aortic dilatation: cluster I, aortic root alone (n = 8, 13%); cluster II, tubular ascending aorta alone (n = 9, 14%); cluster III, tubular portion and transverse arch (n = 18, 28%); and, cluster IV, aortic root and tubular portion with tapering across the transverse arch (n = 29, 45%).Distinct patterns of aortic dilatation in patients with bicuspid aortic valves call for an individualized degree of aortic replacement to minimize late aortic complications and reoperation. Patients in clusters III and IV should have transverse arch replacement (plus concomitant root replacement in cluster IV). Patients in cluster I should undergo complete aortic root replacement, whereas in patients in cluster II supracommissural ascending aortic grafting is adequate.

  View details for DOI 10.1016/j.jtcvs.2008.01.022

  View details for PubMedID 18374778

• Effect of semi-rigid or flexible mitral ring annuloplasty on anterior leaflet three-dimensional geometry 4th Biennial Meeting of the Society-for-Heart-Valve-Disease Timek, T. A., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2008: 149–54

  Abstract

  A saddle-shaped mitral annulus may optimize anterior leaflet shape and, in theory, reduce leaflet and chordal stress. Although annuloplasty rings alter native annular height and immobilize the posterior mitral leaflet, their effects on anterior leaflet geometry are unknown.Four radiopaque markers were placed on the central meridian of the anterior mitral leaflet (AML), and eight on the mitral annulus, of 20 sheep. Six animals were then implanted with a Carpentier-Edwards Physio ring, and six a Medtronic Duran flexible ring. Eight animals served as controls. All animals were then studied with biplane 60 Hz videofluoroscopy at 7-10 days after surgery. The angle Theta was calculated as the angle between each AML leaflet marker and the annular septal-lateral diameter, while AML marker excursion was expressed as the difference between maximum and minimum angle Theta during the cardiac cycle. The intrinsic AML shape was described by three angles, each between three consecutive leaflet markers from the mid-septal annular marker to the leaflet edge (Phi1-3, from annulus to leaflet edge).Hemodynamic parameters differed only in left ventricular pressure, which was higher in control animals. Anterior leaflet excursion during the cardiac cycle for all four leaflet markers did not change with ring annuloplasty. The intrinsic leaflet angles (Phi1-3) were also unaffected by annular fixation, and thus leaflet shape remained unaltered.Neither semi-rigid nor flexible annuloplasty rings affected anterior leaflet excursion or the intrinsic geometry of the AML at end-systole or end-diastole. These data suggest that, in normal sheep hearts, annuloplasty rings do not alter anterior leaflet shape and hence do not perturb leaflet stress distribution.

  View details for PubMedID 18512484

• Functional uncoupling of the mitral annulus and left ventricle with mitral regurgitation and dopamine 4th Biennial Meeting of the Society-for-Heart-Valve-Disease Nguyen, T. C., Itoh, A., Carlhall, C. J., Oakes, R. A., Liang, D., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2008: 168–77

  Abstract

  The mitral annulus and left ventricle are generally thought to be functionally coupled, in the sense that increases in left ventricular (LV) size, as seen in ischemic mitral regurgitation (MR), or decreases in LV size, as seen with inotropic stimulation, are thought to increase or decrease annular dimensions in similar manner. The study aim was to elucidate the functional relationship between the mitral annulus and left ventricle during acute MR and inotrope-induced MR reduction.Radiopaque markers were implanted on the left ventricle and mitral annulus of five adult sheep. A suture was placed on the central scallop of the posterior mitral leaflet and exteriorized through the atrial-ventricular groove. Open-chest animals were studied at baseline (CTRL), at seconds after pulling on the suture to create moderate-severe 'pure' MR (PULL), and after titration of dopamine until the MR grade was maximally reduced (PULL+DOPA). This process was repeated two to three times for each animal.The MR grade was increased with PULL (from 0.5 +/- 0.01 to 3.4 +/- 0.4, p < 0.01) and decreased after PULL+DOPA (from 3.4 +/- 0.4 to 1.5 +/- 0.9, p < 0.001). PULL resulted in an increase in mitral annular (MA) area, predominantly by an increase in the muscular mitral annulus. PULL+DOPA caused a decrease in MA area, but the LV volume and dimensions were not altered with either PULL or PULL+DOPA.The acute geometric response to 'pure' MR and inotrope-induced MR reduction was limited to the mitral annulus. Surprisingly, the LV volume and dimensions did not change with acute MR or with inotrope-induced MR reduction. This suggests that, under these two conditions in an ovine model, the mitral annulus and left ventricle are functionally uncoupled.

  View details for PubMedID 18512487

• Pre- and postoperative imaging of the aortic root for valve-sparing aortic root repair (V-SARR). Seminars in thoracic and cardiovascular surgery Fleischmann, D., Liang, D. H., Mitchell, R. S., Miller, D. C. 2008; 20 (4): 365-373

  Abstract

  Valve-sparing aortic root repair (V-SARR) using the David reimplantation method is an increasingly popular alternative to composite valve graft aortic root replacement in patients with aortic root aneurysms or dissections who wish to avoid anticoagulation. Computed tomography (CT) with retrospective electrocardiograph (ECG)-gating has become routine before and following V-SARR at Stanford. CT allows accurate measurement of aortic dimensions and provides unprecedented three-dimensional (3D) images of the sinuses, the aortic valve cusps, and coronary arteries in patients with the Marfan syndrome (MFS), with a bicuspid aortic valve (BAV), or other aortic diseases. This helps the surgeon to conceptualize the size of the aortic grafts required and how much reduction is necessary proximally (aortic annulus) and distally. These maneuvers are used to reduce the aortic annular diameter (when necessary) and replace the sinuses and ascending aorta (T. David-V, Stanford modification V-SARR). Postoperative ECG-gated CT confirms the reconstructed geometry and reliably detects coronary or other anastomotic problems.

  View details for DOI 10.1053/j.semtcvs.2008.11.009

  View details for PubMedID 19251178

• Developing an Arterial Bleed Detection Algorithm for Diagnostic Ultrasound IEEE Ultrasonics Symposium Wang, A. S., Bech, F., Lee, J., Taylor, C. A., Liang, D. H. IEEE. 2008: 1627–1630

  View details for Web of Science ID 000268845800397

• Advances in echocardiography. Seminars in thoracic and cardiovascular surgery Liang, D. H. 2008; 20 (4): 374-379

  Abstract

  Echocardiography remains the main tool for noninvasive cardiac evaluation. Advances in echo technology and techniques offer new information, which will impact both the timing and method of surgical intervention. Three-dimensional echocardiography, in particular, provides improved tools for quantification both of volumes and of flows. Geometrical relations necessary for understanding functional abnormalities are also preserved with three-dimensional (3D) echocardiography. Finally 3D echocardiography also provides a unique tool for guiding minimally invasive interventions.

  View details for DOI 10.1053/j.semtcvs.2008.11.010

  View details for PubMedID 19251179

• Technical advances in cardiovascular imaging. Seminars in thoracic and cardiovascular surgery Fleischmann, D., Liang, D. H., Herfkens, R. J. 2008; 20 (4): 333-339

  Abstract

  Cardiovascular imaging technology is continuously evolving and provides an increasing array of tests to evaluate cardiovascular morphology and function. A basic understanding of imaging technology is helpful to select the best modality to answer a specific clinical question. This article provides a brief overview of recent technical developments in computed tomography (CT), magnetic resonance (MR), and echocardiography, which have increased our diagnostic understanding and may modulate treatment planning of patients with cardiovascular diseases: electrocardiographically (ECG)-gated CT, 4D-flow magnetic resonance imaging (MRI), and three-dimensional (3D) echocardiography.

  View details for DOI 10.1053/j.semtcvs.2008.11.015

  View details for PubMedID 19251174

• An Incremental Method for Registering Electroanatomic Mapping Data to Surface Mesh Models of the Left Atrium 11th International Conference on Medical Image Computing and Computer-Assisted Intervention (MICCAI2008) Koolwal, A. B., Barbagli, F., Carlson, C. R., Liang, D. H. SPRINGER-VERLAG BERLIN. 2008: 847–854

  View details for Web of Science ID 000261373800102

• An incremental method for registering electroanatomic mapping data to surface mesh models of the left atrium. Medical image computing and computer-assisted intervention : MICCAI ... International Conference on Medical Image Computing and Computer-Assisted Intervention Koolwal, A. B., Barbagli, F., Carlson, C. R., Liang, D. H. 2008; 11: 847-854

  Abstract

  We present a method for registering position and orientation data collected from an electroanatomic mapping system (EMS) to a surface mesh based on segmented Computed Tomography (CT) or Magnetic Resonance (MR) images of the left atrium. Our algorithm is based on the Unscented Particle Filter (UPF) for stochastic state estimation. Using an intracardiac echo (ICE) ultrasound catheter with mounted mapping sensor, we acquire ultrasound images of the atrium from multiple configurations and iteratively determine the catheter's pose with respect to anatomy. After considering less than a minute's worth of ICE data, the algorithm converges to an accurate pose estimate which, in turn, yields the registration parameters transforming EMS coordinates to mesh coordinates. The iterative framework of the UPF allows us to be robust to unmodeled EMS noise and drift, problems which complicate traditional registration methods assuming regularity in image data structure.

  View details for PubMedID 18982684

• Multiplanar visualization in 3D transthoracic echocardiography for precise delineation of mitral valve pathology ECHOCARDIOGRAPHY-A JOURNAL OF CARDIOVASCULAR ULTRASOUND AND ALLIED TECHNIQUES Liang, D., Paloma, A., Kuppahally, S. S., Miller, D. C., Schnittger, I. 2008; 25 (1): 84-87

  Abstract

  A novel multiplanar reformatting (MPR) technique in three-dimensional transthoracic echocardiography (3D TTE) was used to precisely localize the prolapsed lateral segment of posterior mitral valve leaflet in a patient symptomatic with mitral valve prolapse (MVP) and moderate mitral regurgitation (MR) before undergoing mitral valve repair surgery. Transesophageal echocardiography was avoided based on the findings of this new technique by 3D TTE. It was noninvasive, quick, reproducible and reliable. Also, it did not need the time-consuming reconstruction of multiple cardiac images. Mitral valve repair surgery was subsequently performed based on the MPR findings and corroborated the findings from the MPR examination.

  View details for DOI 10.1111/j.1540-8175.2007.00566.x

  View details for PubMedID 18186784

• Effect of chronotropy and inotropy on stitch tension in the edge-to-edge mitral repair 79th Annual Scientific Session of the American-Heart-Association Timek, T. A., Nielsen, S. L., Lai, D. T., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2007: I276–I281

  Abstract

  Our prior studies suggest that mitral annular septal-lateral (SL) diameter is the chief determinant of "Alfieri stitch" tension, but hemodynamic parameters may also play a role. We approximated the central edge of the mitral leaflets with a miniature force transducer to measure tension (T) at the leaflet approximation point during inotropic and chronotropic stimulation.Eight sheep were studied under open-chest conditions immediately after surgical placement of a miniature force transducer to approximate the leaflets and implantation of radiopaque markers on the LV and mitral annulus (MA). Chronotropic stimulation was induced with atrial pacing at 130 minutes(-1) (n=5) whereas inotropic state was increased with i.v. CaCl2 bolus (n=8). Hemodynamic data, stitch tension, and 3-D marker coordinates were obtained throughout the cardiac cycle before and during each intervention. Peak stitch tension (T(MAX)) under all conditions was observed in diastole and temporally correlated with peak annular SL (SL(MAX)) size. Atrial pacing did not change peak transducer tension or annular size. Calcium infusion also did not alter peak transducer tension (0.29+/-0.11 versus 0.32+/-0.10 N; P=NS) and only slightly reduced SL dimension (29.9+/-3.3 versus 29.3+/-3.5 mm; P<0.05).Isolated increase in heart rate or inotropic state did not alter peak stitch tension whereas enhanced contractile state decreased SL diameter minimally. These data, combined with those from our previous study, suggest that geometric (SL diameter) rather than hemodynamic parameters are the main determinants of "Alfieri stitch" tension. This implies that any interventional or surgical edge-to-edge repair performed without concomitant annular reduction to limit the SL dimension could expose the leaflet junction to forces which could limit repair durability.

  View details for DOI 10.1161/CIRCULATIONAHA.106.680801

  View details for PubMedID 17846317

• Laser-machined shape memory, alloy actuators for active catheters 1st IEEE RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob 2006) Tung, A. T., Park, B., Niemeyer, G., Liang, D. H. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. 2007: 439–46

  View details for DOI 10.1109/TMECH.2007.901926

  View details for Web of Science ID 000248878200006

• Rapid aneurysmal degeneration of a Stanford type B aortic dissection in a patient with Loeys-Dietz syndrome JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Lee, R. S., Fazel, S., Schwarze, U., Fleischmann, D., Berry, G. J., Liang, D., Miller, D. C., Mitchell, R. S. 2007; 134 (1): 242-U32

  View details for DOI 10.1016/j.jtcvs.2007.03.004

  View details for PubMedID 17599521

• Undersized mitral annuloplasty inhibits left ventricular basal wall thickening but does not affect equatorial wall cardiac strains 3rd Biennial Meeting of Society-for-Heart-Valve-Disease Cheng, A., Nguyen, T. C., Malinowski, M., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2007: 349–58

  Abstract

  Undersized mitral annuloplasty has been widely employed for patients with ischemic mitral regurgitation. Beyond correction of mitral regurgitation, ring annuloplasty is postulated to normalize global left ventricular (LV) shape, thereby decreasing LV wall stress and promoting reverse LV remodeling. The effect of undersized annuloplasty on regional transmural LV wall thickening and strain patterns, however, has not been examined.In nine sheep, transmural radiopaque beadsets were inserted into the anterobasal and equatorial lateral LV walls, with additional markers silhouetting the left ventricle and mitral annulus. Four-dimensional marker dynamics were studied with biplane videofluoroscopy (open-chest) before and after tightening a Paneth-type mitral annuloplasty suture. LV volumes, mitral dimensions, transmural circumferential, longitudinal, and radial systolic strains, and end-diastolic (ED) and end-systolic (ES) remodeling strains in the two LV regions were computed.In the anterobasal LV wall close to the mitral annulus, annuloplasty increased ED wall thickness and surprisingly reduced systolic radial strain (wall thickening) at all transmural depths. Radial subepicardial, midwall, and subendocardial wall-thickening strains at ES in the anterobasal LV site were 0.25 +/- 0.15, 0.33 +/- 0.16, and 0.47 +/- 0.29, respectively, before tightening the suture annuloplasty, compared to 0.13 +/- 0.12, 0.15 +/- 0.18, and 0.20 +/- 0.26 after tightening. In the equatorial lateral LV wall further away from the annulus, most LV transmural systolic and remodeling strains did not change.Simulated undersized annuloplasty acutely decreased transmural systolic LV wall thickening in the anterobasal region, without substantially affecting transmural deformations in the lateral LV wall. These acute effects of undersized annuloplasty require a better understanding as they may potentially be deleterious, and a direct ventricular approach may be needed as an adjunct to promote reverse LV remodeling.

  View details for PubMedID 17702358

• Interventional three-dimensional echocardiography: Using real-time three-dimensional echocardiography to guide and evaluate intracardiac therapies CARDIOLOGY CLINICS Gill, E. A., Liang, D. H. 2007; 25 (2): 335-?

  Abstract

  Real-time three-dimensional echocardiography (RT3DE) already has demonstrated its utility in guiding intracardiac procedures. This article discusses the advantages RT3DE has over the previous standard of 2D echocardiography.

  View details for DOI 10.1016/j.ccl.2007.06.004

  View details for Web of Science ID 000249732100016

  View details for PubMedID 17765114

• Comparison of three-dimensional echocardiography to two-dimensional echocardiography and fluoroscopy for monitoring of endomyocardial biopsy AMERICAN JOURNAL OF CARDIOLOGY Amitai, M. E., Schnittger, I., Popp, R. L., Chow, J., Brown, P., Liang, D. H. 2007; 99 (6): 864-866

  Abstract

  Real-time 3-dimensional echocardiography (RT3DE) offers the rapid acquisition of quantitative and qualitative anatomic data without the use of geometric assumptions. This study was designed to test the feasibility and potential superiority of RT3DE versus 2-dimensional echocardiography (2DE) and standard fluoroscopy for monitoring endomyocardial biopsies (EMBs). Thirty-eight consecutive EMBs performed under fluoroscopic guidance in 26 patients were monitored using 2DE and RT3DE alternately. Two reviewers scored each biopsy pass for visualization of the tip of the bioptome and location of the actual biopsy. Overall image quality was noted as good or poor, and the effect of image quality on tip localization was analyzed. A total of 243 biopsy attempts were made during 38 EMBs. The location of the biopsy was determined in 74% of the biopsies monitored with RT3DE, whereas 2DE demonstrated the location with certainty in only 43% of the biopsies (p <0.0001). On a procedure-by-procedure comparison, RT3DE was found to show the bioptome tip better in 23 of 38 biopsies, compared with 1 of 38 for 2DE (p = 0.001). In 14 of 38 EMBs, neither method was clearly better. In conclusion, RT3DE improves the ability to see the location of the bioptome during EMB compared with 2DE and fluoroscopy.

  View details for DOI 10.1016/j.amjcard.2006.10.050

  View details for Web of Science ID 000245289200027

  View details for PubMedID 17350384

• Septal-lateral annnular cinching perturbs basal left ventricular transmural strains 20th Annual Meeting of the European-Association-for-Cardio-Thoracic-Surgery/14th Annual Meeting of the European-Society-of-Thoracic-Surgeons Nguyen, T. C., Cheng, A., Tibayan, F. A., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. OXFORD UNIV PRESS INC. 2007: 423–29

  Abstract

  Septal-lateral annular cinching ('SLAC') corrects both acute and chronic ischemic mitral regurgitation in animal experiments, which has led to the development of therapeutic surgical and interventional strategies incorporating this concept (e.g., Edwards GeoForm ring, Myocor Coapsys, Ample Medical PS3). Changes in left ventricular (LV) transmural cardiac and fiber-sheet strains after SLAC, however, remain unknown.Eight normal sheep hearts had two triads of transmural radiopaque bead columns inserted adjacent to (anterobasal) and remote from (midlateral equatorial) the mitral annulus. Under acute, open chest conditions, 4D bead coordinates were obtained using videofluoroscopy before and after SLAC. Transmural systolic strains were calculated from bead displacements relative to local circumferential, longitudinal, and radial cardiac axes. Transmural cardiac strains were transformed into fiber-sheet coordinates (X(f), X(s), X(n)) oriented along the fiber (f), sheet (s), and sheet-normal (n) axes using fiber (alpha) and sheet (beta) angle measurements. Results: SLAC markedly reduced (approximately 60%) septal-lateral annular diameter at both end-diastole (ED) (2.5+/-0.3 to 1.0+/-0.3 cm, p=0.001) and end-systole (ES) (2.4+/-0.4 to 1.0+/-0.3 cm, p=0.001). In the LV wall remote from the mitral annulus, transmural systolic strains did not change. In the anterobasal region adjacent to the mitral annulus, ED wall thickness increased (p=0.01) and systolic wall thickening was less in the epicardial (0.28+/-0.12 vs 0.20+/-0.06, p=0.05) and midwall (0.36+/-0.24 vs 0.19+/-0.11, p=0.04) LV layers. This impaired wall thickening was due to decreased systolic sheet thickening (0.20+/-0.8 to 0.12+/-0.07, p=0.01) and sheet shear (-0.15+/-0.07 to -0.11+/-0.04, p=0.02) in the epicardium and sheet extension (0.21+/-0.11 to 0.10+/-0.04, p=0.03) in the midwall. Transmural systolic and remodeling strains in the lateral midwall (remote from the annulus) were unaffected.Although SLAC is an alluring concept to correct ischemic mitral regurgitation, these data suggest that extreme SLAC adversely effects systolic wall thickening adjacent to the mitral annulus by inhibiting systolic sheet thickening, sheet shear, and sheet extension. Such alterations in LV strains could result in unanticipated deleterious remodeling and warrant further investigation.

  View details for DOI 10.1016/j.ejcts.2006.12.019

  View details for PubMedID 17223567

• Transesophageal echocardiography assessment of severe aortic regurgitation in type a aortic dissection caused by a prolapsed circumferential intimal flap JOURNAL OF CARDIOTHORACIC AND VASCULAR ANESTHESIA Chow, J. L., Mariano, E. R., Liang, D. 2007; 21 (1): 85-87

  View details for DOI 10.1053/j.jvca.2005.09.005

  View details for Web of Science ID 000244804600016

  View details for PubMedID 17289486

• Tenting volume: Three-dimensional assessment of geometric perturbations in functional mitral regurgitation and implications for surgical repair 75th Annual Scientific Session of the American-Heart-Association Tibayan, F. A., Wilson, A., Lai, D. T., Timek, T. A., Dagum, P., Rodriguez, F., Zasio, M. K., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2007: 1–7

  Abstract

  Functional mitral regurgitation (FMR) often complicates dilated cardiomyopathy (DCM), and portends a poor prognosis. Debate over the optimal treatment continues, underscoring the present incomplete understanding of the patho-anatomic mechanisms of this disease. Studies of mitral tenting volume and tenting area, and echocardiographic measures of abnormal apical systolic leaflet geometry have linked mitral leaflet deformation with subvalvular left ventricular (LV) remodeling in chronic ischemic MR. The relative contributions of annular versus subvalvular remodeling in FMR due to DCM are less clear. Here, the validity of 3-D measurement of mitral deformation, tenting volume, as a correlate of MR in DCM, was tested. The ability of annular and subvalvular remodeling to predict mitral deformation was then determined.Eight sheep underwent placement of radiopaque markers on the mitral annulus and leaflets. Global LV, annular and subvalvular geometry, as well as mitral tenting height, area and volume were calculated before (Control) and after the development of pacing-induced cardiomyopathy and MR (DCM). Multivariable regression determined which measure of mitral deformation was the best predictor of MR. Regression analysis was also used to find geometric predictors of mitral tenting volume.In a multivariable analysis, mitral tenting volume was the only independent predictor of severity of MR (r(2) = 0.79, standard error of estimate (SEE) = 0.58). Increased tenting volume correlated best with increased mitral annular septal-lateral diameter (r(2) = 0.67, SEE = 0.72).The 3-D tenting volume correlates best with severity of FMR. Mitral deformation (increased tenting volume) observed in DCM is predicted by annular dilation, but not by subvalvular LV remodeling. These data support the use of an undersized annuloplasty in DCM complicated by FMR, and may guide the rational design of new therapies for this vexing disease.

  View details for PubMedID 17315376

• Altered myocardial shear strains are associated with chronic ischemic mitral regurgitation 42nd Annual Meeting of the Society-of-Thoracic-Surgeons Nguyen, T. C., Cheng, A., Langer, F., Rodriguez, F., Oakes, R. A., Itoh, A., Ennis, D. B., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. ELSEVIER SCIENCE INC. 2007: 47–54

  Abstract

  Ischemic mitral regurgitation (IMR) limits life expectancy and can lead to postinfarction global left ventricular (LV) dilatation and remodeling, the pathogenesis of which is not completely known. We tested the hypothesis that IMR perturbs adjacent myocardial LV systolic strains.Thirteen sheep had three columns of miniature beads inserted across the lateral LV wall, with additional epicardial markers silhouetting the ventricle. One week later posterolateral infarction was created. Seven weeks thereafter, the animals were divided into two groups according to severity of IMR (< or = 1+, n = 7, IMR[-] vs > or = 2+, n = 6, IMR[+]). Four dimensional marker coordinates and quantitative histology were used to calculate ventricular volumes, transmural myocardial systolic strains, and systolic fiber shortening.Seven weeks after infarction, end-diastolic (ED) volume increased similarly in both groups, end-systolic (ES) E13 (circumferential-radial) shear increased in both groups, but more so in IMR(+) than IMR(-) (+0.12 vs 0.04, p < 0.005), and E12 (circumferential-longitudinal) shear increased in IMR(-) but not IMR(+) (+0.04 vs -0.01, p < 0.005). There were no significant differences in ED or ES remodeling strains or systolic fiber shortening between IMR(-) and IMR(+).An equivalent increase in LV end-diastolic (ED) volume in both groups, coupled with unchanged ED and end-systolic remodeling strains as well as systolic circumferential, longitudinal, and radial strains, argue against a global LV or regional myocardial geometric basis for the cardiomyopathy associated with IMR. Further, similar systolic fiber shortening in both groups militates against an intracellular (cardiomyocyte) mechanism. The differences in subepicardial E12 and E13 shears, however, suggest a causal role of altered interfiber (cytoskeleton and extracellular-matrix) interactions.

  View details for DOI 10.1016/j.athoracsur.2006.08.039

  View details for PubMedID 17184629

• Feasibility of noncontact intracardiac ultrasound ablation and Imaging catheter for treatment of atrial fibrillation IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL Wong, S. H., Scott, G. C., Conolly, S. M., Narayan, G., Liang, D. H. 2006; 53 (12): 2394-2405

  Abstract

  Atrial fibrillation (AF) affects 1% of the population and results in a cost of 2.8 billion dollars from hospitalizations alone. Treatments that electrically isolate portions of the atria are clinically effective in curing AF. However, such minimally invasive catheter treatments face difficulties in mechanically positioning the catheter tip and visualizing the anatomy of the region. We propose a noncontact, intracardiac transducer that can ablate tissue and provide rudimentary imaging to guide therapy. Our design consists of a high-power, 20 mm by 2 mm, 128-element, transducer array placed on the side of 7-French catheter. The transducer will be used in imaging mode to locate the atrial wall; then, by focusing at that location, a lesion can be formed. Imaging of previously formed lesions could potentially guide placement of subsequent lesions. Successive rotations of the catheter will potentially enable a contiguous circular lesion to be created around the pulmonary vein. The challenge of intracardiac-sized transducers is achieving high intensities (300-5000 W/cm2) needed to raise the temperature of the tissue above 43 degrees C. In this paper, we demonstrate the feasibility of an intracardiac-sized transducer for treatment of atrial fibrillation. In simulations and proof-of-concept experiments, we show a 37 degrees C temperature rise in the lesion location and demonstrate the possibility of lesion imaging.

  View details for DOI 10.1109/TUFFC.2006.188

  View details for Web of Science ID 000242390900022

  View details for PubMedID 17186922

• Mitral leaflet remodeling in dilated cardiomyopathy 78th Annual Scientific Session of the American-Heart-Association Timek, T. A., Lai, D. T., Dagum, P., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2006: I518–I523

  Abstract

  Normal mammalian mitral leaflets have regional heterogeneity of biochemical composition, collagen fiber orientation, and geometric deformation. How leaflet shape and regional geometry are affected in dilated cardiomyopathy is unknown.Nine sheep had 8 radio-opaque markers affixed to the mitral annulus (MA), 4 markers sewn on the central meridian of the anterior mitral leaflet (AML) forming 4 distinct segments S1 to S4 and 2 on the posterior leaflet (PML) forming 2 distinct segments S5 and S6. Biplane videofluoroscopy and echocardiography were performed before and after rapid pacing (180 to 230 bpm for 15+/-6 days) sufficient to develop tachycardia-induced cardiomyopathy (TIC) and functional mitral regurgitation (FMR). Leaflet tethering was defined as change of displacement of AML and PML edge markers from the MA plane from baseline values while leaflet length was obtained by summing the segments between respective leaflet markers. With TIC, total AML and PML length increased significantly (2.11+/-0.16 versus 2.43+/-0.23 cm and 1.14+/-0.27 versus 1.33+/-0.25 cm before and after pacing for AML and PML, respectively; P<0.05 for both), but only segments near the edge of each leaflet (S4 lengthened by 23+/-17% and S5 by 24+/-18%; P<0.05 for both) had significant regional remodeling. AML shape did not change and no leaflet tethering was observed.TIC was not associated with leaflet tethering or shape change, but both anterior and posterior leaflets lengthened because of significant remodeling localized near the leaflet edge. Leaflet remodeling accompanies mitral regurgitation in cardiomyopathy and casts doubt on FMR being purely "functional" in etiology.

  View details for PubMedID 16820630

• Passive ventricular constraint prevents transmural shear strain progression in left ventricle remodeling 78th Annual Scientific Session of the American-Heart-Association Cheng, A., Nguyen, T. C., Malinowski, M., Langer, F., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2006: I79–I86

  Abstract

  Passive ventricular constraint provides external cardiac support to reduce left ventricular (LV) wall stress and myocardial stretch, which are primary determinants of LV remodeling. Altered wall strain results in cytokine and reactive oxygen species production, which, in turn, stimulates apoptosis and extracellular matrix disruption and could be an important trigger for adverse global LV dilatation and remodeling. The effects of the Acorn cardiac support device (CSD) on regional transmural LV wall strains, however, remain unknown.Thirty-three sheep had transmural radiopaque beadsets surgically inserted into the anterior basal and lateral equatorial LV walls, with additional markers silhouetting the left ventricle. Eight animals had CSD implanted (myocardial infarction [MI]+CSD). One week thereafter, the MI+CSD group and 10 animals without CSD (MI) underwent posterior LV infarction by snaring obtuse marginal coronary arteries. Fifteen animals (Sham) had no infarction or CSD. 4D marker dynamics were measured with biplane videofluoroscopy 1 and 8 weeks postoperatively. LV volumes, sphericity index, and transmural circumferential, longitudinal, and radial systolic strains were analyzed. Compared with Sham, infarction (MI) dilated the heart, reduced sphericity index (LV length/width), and increased longitudinal-radial shear strains in the inner half of both the anterior and lateral LV walls. CSD prevented this shear strain perturbation, minimized LV end diastolic volume increase, and augmented the LV sphericity index.Prophylactic CSD prevented infarct-induced shear strain progression not only in myocardium adjacent to, but also remote from, the infarct. CSD also prevented LV dilatation and sphericalization. By attenuating shear strain abnormalities, CSD could prevent the heart from entering into a positive feedback loop of further LV dilatation and exaggeration of LV wall stress and may reduce biochemical triggers portending adverse LV remodeling.

  View details for PubMedID 16820650

• Effects of undersized mitral annuloplasty on regional transmural left ventricular wall strains and wall thickening mechanisms 78th Annual Scientific Session of the American-Heart-Association Cheng, A., Nguyen, T. C., Malinowski, M., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2006: I600–I609

  Abstract

  Undersized mitral annuloplasty, widely used for ischemic and functional mitral regurgitation (MR), has been proposed as an "annular solution to a ventricular problem." Beyond relief of MR, it is thought to improve global left ventricular (LV) shape, hence potentially reducing myocardial stress and promoting beneficial reverse LV remodeling. We previously observed that undersized annuloplasty inhibited systolic wall thickening at the LV base near the mitral annulus. In this study, we measured the effects of undersized annuloplasty on regional transmural LV wall fiber and sheet strains and wall thickening mechanisms.Nine sheep had transmural radiopaque beadsets surgically inserted into anterobasal and lateral equatorial LV regions, with additional markers silhouetting the LV and mitral annulus. 4-Dimensional marker dynamics were studied with biplane videofluoroscopy before and after tightening an adjustable Paneth-type mitral annuloplasty suture. Transmural circumferential, longitudinal, and radial systolic and remodeling strains in the subepicardium (20% depth), midwall (50%), and subendocardium (80%) in both regions were computed. Fiber and sheet angles from quantitative regional histology allowed transformation of these strains into local fiber (f), sheet (s), and sheet-normal (n) coordinates. Further analysis calculated the transmural contributions of sheet extension (E(ssc)), sheet thickening (E(nnc)), and sheet shear (E(snc)) to systolic wall thickening (E(33)). In the anterobasal region, undersized annuloplasty reduced systolic wall thickening (E33) by &50% at all transmural depths by inhibiting: (1) subendocardial systolic fiber shortening (-0.10+/-0.05 versus -0.04+/-0.05; P<0.05); (2) subepicardial (0.16+/-0.15 versus 0.09+/-0.08; P<0.05) and subendocardial (0.45+/-0.40 versus 0.19+/-0.18; P<0.05) systolic sheet thickening; (3) midwall sheet extension (0.22+/-0.12 versus 0.11+/-0.06; P<0.05); and (4) transmural sheet shear (subepicardium, -0.14+/-0.07 versus -0.08+/-0.07; midwall, 0.21+/-0.12 versus 0.10+/-0.11; subendocardium, -0.19+/-0.23 versus -0.11+/-0.16; P<0.05). In the remote lateral equatorial region, fiber-sheet strains and E33 were unchanged.In this acute animal study, undersized annuloplasty inhibited systolic wall thickening in the anterobasal region by reducing subendocardial systolic fiber shortening and laminar sheet wall thickening, but had no effects in a more distant LV region. This suggests that undersized mitral annuloplasty may have potentially deleterious effects on local myocardial mechanics.

  View details for PubMedID 16820645

• Posterior mitral leaflet extension: An adjunctive repair option for ischemic mitral regurgitation? JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Langer, F., Rodriguez, F., Cheng, A., Ortiz, S., Nguyen, T. C., Zasio, M. K., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2006; 131 (4): 868-875

  Abstract

  Residual or recurrent mitral regurgitation frequently occurs after mitral valve repair for ischemic mitral regurgitation with an annuloplasty ring. Because annuloplasty primarily addresses annular dilatation, we studied an adjunctive technique that might correct restricted leaflet (Carpentier type IIIb) systolic closing motion, which often accompanies annular dilatation in patients with ischemic mitral regurgitation.Six sheep had radiopaque markers placed on the left ventricle, mitral leaflets and annulus, and mitral subvalvular apparatus. A pericardial patch was sutured into the middle scallop of the posterior mitral valve leaflet and furled in with a reefing stitch placed in the radial axis. Posterolateral left ventricular myocardial ischemia was created by using proximal circumflex occlusion to induce acute ischemic mitral regurgitation. Under open-chest conditions, 3-dimensional marker coordinates were measured by using biplane videofluoroscopy at baseline and during acute ischemia both before and after release of the reefing stitch (leaflet extension); transesophageal echocardiography was used to grade ischemic mitral regurgitation.Leaflet apical systolic tethering was not improved by leaflet extension, but ischemic mitral regurgitation decreased (control, 0.9 +/- 0.3*; ischemia, 2.4 +/- 0.3; leaflet extension, 1.5 +/- 0.3; *P < 0.002). Posterior mitral valve leaflet midline length (control, 1.45 +/- 0.09*; ischemia, 1.53 +/- 0.10; leaflet extension, 1.83 +/- 0.13*; *P < 0.001) and posterior mitral valve leaflet middle scallop area (control, 1.66 +/- 0.20 cm2*; ischemia, 1.91 +/- 0.22 cm2; leaflet extension, 2.36 +/- 0.22 cm2*; *P < 0.006) increased with leaflet extension because of patch unfurling (mean +/- 1 standard error of the mean; repeated-measures analysis of variance, Dunnet post-hoc test vs ischemia).Posterior mitral valve leaflet extension ameliorated acute ischemic mitral regurgitation but did not correct the abnormal apically restricted systolic posterior mitral valve leaflet closing motion. This technique might be a useful adjunct repair in combination with ring annuloplasty for ischemic mitral regurgitation, but the clinical role of this adjunct remains to be defined in patients.

  View details for DOI 10.1016/j.jtcvs.2005.11.027

  View details for PubMedID 16580446

• Amplitude-modulating switching feedback for position control of shape memory alloy actuators 1st IEEE RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob 2006) Koolwal, A. B., Park, B. H., Nelson, B., Niemeyer, G., Liang, D. H. IEEE. 2006: 429–434

  View details for Web of Science ID 000244445100073

• Design and fabrication of tubular shape memory alloy actuators for active catheters 1st IEEE RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics (BioRob 2006) Tung, A. T., Park, B., Koolwal, A., Nelson, B., Niemeyer, G., Liang, D. IEEE. 2006: 885–890

  View details for Web of Science ID 000244445100152

• Effect of cutting second-order chordae on in-vivo anterior mitral leaflet compound curvature 3rd Biennial Meeting of Society-for-Heart-Valve-Disease Rodriguez, F., Langer, F., Harrington, K. B., Tibayan, F. A., Zasio, M. K., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2005: 592–601

  Abstract

  Leaflet curvature determines leaflet stress. In order to assess the influence of second-order chordae (2 degrees CT) on anterior mitral valve leaflet (AMVL) geometry, AMVL curvature was measured before (Baseline) and after (CUT) cutting the 2 degrees CT.Miniature radiopaque markers were sutured onto the AMVL in eight sheep: four along the central-meridian from mid-septal annulus to the free-margin; and one each at the 2 degrees CT insertion. Biplane videofluoroscopic data were acquired (open-chest) before and after CUT. Marker-triplet 3-D coordinates were used to calculate radii-of-curvature at LVPmax along the central-meridian (ROCm) and across the AMVL belly (commissure-commissure axis, ROCc-c).CUT did not change LVPmax (111 +/- 12 versus 106 +/- 11 mmHg; p = 0.19). At baseline, the AMVL central-meridian had compound curvature: Convex to the left ventricle near the annulus (-ROCm) and concave near the free-margin (+ROCm). After CUT, the AMVL flattened: ROCm increased near the annulus (from -1.37 +/- 0.52 to -12.58 +/- 29.04 cm; p = 0.02), but did not change near the edge. In the commissure-commissure axis, ROCc-c was concave to the left ventricle at baseline and increased after CUT in all eight animals. In five sheep, ROCc-c was increased (from 1.93 +/- 1.01 to 2.80 +/- 1.36 cm; p = 0.03), but in three sheep ROCc-c was increased and inverted (from 3.65 +/- 2.17 to -1.72 +/- 0.53 cm; p = 0.03), becoming convex to the left ventricle.Compound curvature along the AMVL central-meridian appears to be an intrinsic leaflet property that persists even without support from second-order chordae, whereas concave curvature in the commissure-commissure axis is more dependent on intact second-order chordae. Leaflet compound curvature must be incorporated into future finite element models to characterize leaflet stresses accurately. The importance of second-order chordae in maintaining leaflet shape must be considered during mitral repair. A larger ROC increases leaflet stresses, while reversal of ROC changes tensile stress to compressive stress; this might trigger deleterious leaflet remodeling after chordal cutting.

  View details for PubMedID 16245497

• Subvalvular repair - The key to repairing ischemic mitral regurgitation? 77th Scientific Meeting of the American-Heart-Association Langer, F., Rodriguez, F., Ortiz, S., Cheng, A., Nguyen, T. C., Zasio, M. K., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2005: I383–I389

  Abstract

  Residual or recurrent mitral regurgitation frequently occurs after mitral ring annuloplasty repair for ischemic mitral regurgitation (IMR), because annuloplasty primarily addresses annular dilatation. We describe a subvalvular repair technique addressing posterior papillary muscle (PPM) displacement.Ten sheep had radiopaque markers placed on the left ventricle (LV) and mitral apparatus. A suture was anchored at the right fibrous trigone, passed through the PPM tip and LV wall, and exteriorized through a tourniquet (STRING-1). A second suture was anchored transmurally in the high septum (anterobasal LV wall) and passed through the PPM and LV wall (STRING-2). Reversible posterolateral ischemia was induced by temporarily occluding the proximal circumflex artery. Under open chest conditions, 3D marker coordinates were obtained with biplane videofluoroscopy at baseline and during acute ischemia before and after tightening of each STRING using transesophageal echocardiography to grade IMR. IMR decreased (mean+/-SEM, 2.0+/-0.1 to 1.2+/-0.1; P<0.05) when STRING-1 was tightened, did not change after tightening STRING-2 (2.3+/-0.1 to 2.3+/-0.1), and decreased after tightening both sutures (STRING-1+2, 2.3+/-0.2 to 1.3+/-0.2; P<0.05). STRING-1 and STRING-1+2 (STRING-1, 1.7+/-0.4 mm; STRING-2, 0.7+/-0.5 mm; STRING-1+2, 1.5+/-0.3 mm; P<0.05) resulted in significant PPM basal repositioning. Tightening of any STRING sutures did not affect anterior mitral leaflet excursion.Basal repositioning of the PPM with STRING-1 reduced acute IMR without concomitant annular reduction. This technique may be a useful adjunct if residual IMR is likely after undersized ring annuloplasty.

  View details for DOI 10.1161/CIRCULATIONAHA.104.523464

  View details for PubMedID 16159851

• Annular height-to-commissural width ratio of annulolasty rings in vivo 77th Scientific Meeting of the American-Heart-Association Timek, T. A., Glasson, J. R., Lai, D. T., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2005: I423–I428

  Abstract

  A "saddle-shaped" mitral annulus with an optimal ratio between annular height and commissural diameter may reduce leaflet and chordal stress and is purported to be conserved across mammalian species. Whether annuloplasty rings maintain this relationship is unknown.Twenty-three adult sheep underwent implantation of radiopaque markers on the left ventricle and mitral annulus. Eight animals underwent implantation of a Carpentier-Edwards Physio ring, 7 underwent a Medtronic Duran flexible ring, and 8 served as controls. Animals were studied with biplane videofluoroscopy 7 to 10 days postoperatively. Annular height and commissural width (CW) were determined from 3D marker coordinates, and annular height:CW ratio (AHWCR) was calculated. Annular height was similar in Control and Duran animals but significantly lower in the Physio group at end diastole (8.4+/-3.8, 6.7+/-2.3, and 3.4+/-0.6 mm, respectively, for Control, Duran, and Physio; ANOVA=0.005) and at end systole (14.5+/-6.2, 10.5+/-5.5, and 5.8+/-2.5 mm, respectively, for Control, Duran, and Physio; ANOVA=0.004). Both ring groups reduced CW significantly relative to Control. AHCWR did not differ between Control and Duran but was lower in Physio (23+/-11%, 24+/-7%, and 12+/-2% at end diastole and 42+/-17%, 37+/-17%, and 21+/-10% at end systole, respectively, for Control, Duran, and Physio, respectively; ANOVA <0.05 for both).Mitral annular height and AHWCR of the native valve were unchanged by a Duran ring, whereas the Physio ring led to a lower AHWCR. Theoretically, such a flexible annuloplasty ring may provide better leaflet stress distribution by maintaining normal AHWCR.

  View details for DOI 10.1161/CIRCULATIONAHA.104.525485

  View details for PubMedID 16159857

• Time-resolved three-dimensional magnetic resonance velocity mapping of aortic flow in healthy volunteers and patients after valve-sparing aortic root replacement 30th Annual Meeting of the Western-Thoracic-Surgical-Association Markl, M., Draney, M. T., Miller, D. C., Levin, J. M., Williamson, E. E., Pelc, N. J., Liang, D. H., Herfkens, R. J. MOSBY-ELSEVIER. 2005: 456–63

  Abstract

  To provide more complete characterization of ascending aortic blood flow, including vortex formation behind the valve cusps, in healthy subjects and patients after valve-sparing aortic root replacement (David reimplantation).Time-resolved 3-dimensional magnetic resonance imaging velocity mapping was performed to analyze pulsatile blood flow by using encoded 3-directional vector fields in the thoracic aortas of 10 volunteers and 12 patients after David reimplantation using a cylindrical tube graft (T. David I) and two versions of neosinus recreation (T. David-V and T. David-V-S mod ). Aortic flow was evaluated by using 3-dimensional time-resolved particle traces and velocity vector fields reformatted onto 2-dimensional planes. Semiquantitative data were derived by using a blinded grading system (0-3: 0, none; 1, minimal; 2, medium; 3, prominent) to analyze the systolic vortex formation behind the cusps, as well as retrograde and helical flow in the ascending aorta.Systolic vortices were seen in both coronary sinuses of all volunteers (greater in the left sinus [2.5 +/- 0.5] than the right [1.8 +/- 0.8]) but in only 4 of 10 noncoronary sinuses (0.7 +/- 0.9). Comparable coronary vortices were detected in all operated patients. Vorticity was minimal in the noncoronary cusp in T. David-I repairs (0.7 +/- 0.7) but was prominent in T. David-V noncoronary graft pseudosinuses (1.5 +/- 0.6; P = .035). Retrograde flow (P = .001) and helicity (P = .028) were found in all patients but were not distinguishable from normal values in the T. David-V-S mod patients.Coronary cusp vorticity was preserved after David reimplantation, regardless of neosinus creation. Increased retrograde flow and helicity were more prominent in T. David-V patients. These novel magnetic resonance imaging methods can assess the clinical implications of altered aortic flow dynamics in patients undergoing various types of valve-sparing aortic root replacement.

  View details for DOI 10.1016/j.jtcvs.2004.08.056

  View details for PubMedID 16077413

• Annular or subvalvular approach to chronic ischemic mitral regurgitation? 30th Annual Meeting of the Western-Thoracic-Surgical-Association Tibayan, F. A., Rodriguez, F., Langer, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. MOSBY-ELSEVIER. 2005: 1266–75

  Abstract

  We sought to investigate whether annular or subvalvular interventions corrected chronic ischemic mitral regurgitation differently.Sheep underwent placement of markers on the left ventricle, mitral annulus, papillary muscles (anterior and posterior), and both leaflet edges. A transannular suture (septal-lateral annular cinching) was anchored to the midseptal mitral annulus and externalized through the midlateral mitral annulus. Another suture (papillary muscle repositioning) from the posterior papillary muscle was passed through the mitral annulus near the posterior commissure and externalized. After 7 days, 3-dimensional marker data were obtained before inducing posterolateral myocardial infarction. After 7 weeks, animals in whom chronic ischemic mitral regurgitation developed (n = 10) were restudied before and after pulling septal-lateral annular cinching or papillary muscle repositioning sutures. End-systolic septal-lateral annular diameter and 3-dimensional displacement of the papillary muscles and leaflet edges were computed.Infarction increased mitral regurgitation (0.6 +/- 0.5 to 2.3 +/- 1.1); mitral annular septal-lateral dilation (4 +/- 1 mm); posterior papillary muscle displacement laterally (4 +/- 2 mm), posteriorly (9 +/- 3 mm), and toward the annulus (2 +/- 1 mm); posterior mitral leaflet apical tethering (3 +/- 1 mm); and interleaflet separation (+3 +/- 1 mm, P < .05 baseline vs chronic ischemic mitral regurgitation). Septal-lateral annular cinching reduced septal-lateral dimension (-9 +/- 3 mm), corrected lateral posterior papillary muscle displacement (4 +/- 1 mm) and septal-lateral interleaflet separation (-4 +/- 2 mm), and decreased mitral regurgitation (0.6 +/- 0.6, P < .05 septal-lateral annular cinching vs chronic ischemic mitral regurgitation) without affecting posterior leaflet restriction. Papillary muscle repositioning reduced septal-lateral diameter (-4 +/- 1 mm), moved the anterior papillary muscle closer to the annulus (2 +/- 1 mm), and relieved posterior leaflet apical restriction (2 +/- 1 mm, P < .05 papillary muscle repositioning vs chronic ischemic mitral regurgitation) but did not change lateral posterior papillary muscle displacement or decrease mitral regurgitation (1.9 +/- 1.2).Septal-lateral annular cinching moved the lateral annulus and the posterior papillary muscle closer to the septum and reduced mitral regurgitation unlike posterior papillary muscle repositioning, and thus the key mitral subvalvular repair component must correct posterior papillary muscle lateral displacement.

  View details for DOI 10.1016/j.jtcvs.2005.01.021

  View details for PubMedID 15942566

• Altered mitral valve kinematics with atrioventricular and ventricular pacing 2nd Biennial Meeting of the Society-for-Heart-Valve-Disease Langer, F., Tibayan, F. A., Rodriguez, F., Timek, T., Zasio, M. K., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2005: 286–94

  Abstract

  Pacing-induced mitral regurgitation contributes to the 'pacemaker syndrome', which usually is observed with ventricular (V) pacing, but has also been reported with atrioventricular (AV) sequential pacing. Effects of different pacing modes on 3-D kinematics of the mitral apparatus are incompletely understood.Radio-opaque markers were placed on the left ventricular (LV) and mitral apparatus including the annulus, leaflets and papillary muscles of eight sheep. Hemodynamic and 3-D dynamic marker geometry were obtained one week later with biplane videofluoroscopy (60 Hz) during atrial (pacing site = left atrium), AV-sequential (140 ms interval) and (anterolateral LV epicardial) ventricular pacing.Compared with A-pacing (*p <0.05): 1) The regurgitant fraction increased with both AV- and V-pacing (A: 6 +/- 3%, AV: 13 +/- 3%*, V: 15 +/- 2%*); 2) AV and V-pacing delayed closure at the leaflet center (A: 21 +/- 10 ms, AV: 52 + 5 ms*, V: 92 +/- 6 ms*) and posterior commissure (A: 17 +/- 10 ms, AV: 46 +/- 8 ms*, V: 94 +/- 6 ms*). V-pacing delayed valve closure at the anterior commissure (A: 27 +/- 9 ms, V: 94 +/- 6 ms*); 3) The end-diastolic leaflet opening angle was greater with AV- and V-pacing (anterior mitral leaflet (AML): A: 32 +/- 2 degrees, AV: 41 +/- 4 degrees*, V: 46 +/- 4 degrees*; posterior mitral leaflet (PML): A: 56 +/- 4 degrees, AV: 62 +/- 3 degrees*, V: 68 +/- 3 degrees*); 4) 'Effective' end-diastolic PML midline length was reduced with AV- and V-pacing (A: 11.2 +/- 0.7 mm, AV: 10.0 +/- 0.4 mm*, V: 10.2 +/- 0.3 mm*), as was the distance from each papillary muscle (PM) tip to the AML edge ('effective' chordal length) close to the commissures (anterior PM-AML: A: 31.5 +/-1.8 mm, AV: 30.5 +/- 1.9 mm*, V: 29.7 +/- 1.8 mm*; posterior PM-AML: A: 33.7 +/- 1.8 mm, AV: 33.1 +/- 1.9 mm*, V: 32.8 +/- 1.9 mm*).Both ventricular and AV-sequential-pacing resulted in a more widely opened valve at end-diastole and leaflet dyssynchrony with delayed mitral valve closure and early systolic mitral regurgitation. These alterations which result in pacing-induced mitral regurgitation may be clinically important in patients with impaired LV function.

  View details for PubMedID 15974520

• A microfabricated intravascular ultrasound scanner for intravascular interventions Conference on MOEMS Display and Imaging Systems III Liang, D. H., Park, B. H., Koolwal, A., Prinz, F. SPIE-INT SOC OPTICAL ENGINEERING. 2005: 115–118

  View details for DOI 10.1117/12.597160

  View details for Web of Science ID 000228764100015

• An evaluation of using real-time volumetric display of 3D ultrasound data for intracardiac catheter manipulation tasks 4th International Workshop on Volume Graphics Wang, A. S., Narayan, G., Kao, D., Liang, D. EUROGRAPHICS ASSOC. 2005: 41–45

  View details for Web of Science ID 000231146600004

• Feasibility of intravascular ultrasound ablation and imaging catheter for treatment of atrial fibrillation IEEE International Ultrasonics Symposium Wong, S. H., Scott, G. C., Conolly, S. M., Narayan, G., Liang, D. H. IEEE. 2005: 1751–1754

  View details for Web of Science ID 000236090702083

• Importance of mitral valve second-order chordae for left ventricular geometry, wall thickening mechanics, and global systolic function 40th Annual Meeting of the Society-of-Thoracic-Surgeons Rodriguez, F., Langer, F., Harrington, K. B., Tibayan, F. A., Zasio, M. K., Cheng, A., Liang, D., Daughters, G. T., Covell, J. W., Criscione, J. C., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2004: II115–II122

  Abstract

  Mitral valvular-ventricular continuity is important for left ventricular (LV) systolic function, but the specific contributions of the anterior leaflet second-order "strut" chordae are unknown.Eight sheep had radiopaque markers implanted to silhouette the LV, annulus, and papillary muscles (PMs); 3 transmural bead columns were inserted into the mid-lateral wall between the PMs. The strut chordae were encircled with exteriorized wire snares. Three-dimensional marker images and hemodynamic data were acquired before and after chordal cutting. Preload recruitable stroke work (PRSW) and end-systolic elastance (E(es)) were calculated to assess global LV systolic function (n=7). Transmural strains were measured from bead displacements (n=4). Chordal cutting caused global LV dysfunction: E(es) (1.48+/-1.12 versus 0.98+/-1.30 mm Hg/mL, P=0.04) and PRSW (69+/-16 versus 60+/-15 mm Hg, P=0.03) decreased. Although heart rate and time from ED to ES were unchanged, time of mid-ejection was delayed (125+/-18 versus 136+/-19 ms, P=0.01). Globally, the LV apex and posterior PM tip were displaced away from the fibrous annulus and LV base-apex length increased at end-diastole and end-systole (all +1 mm, P<0.05). Locally, subendocardial end-diastolic strains occurred: Longitudinal strain (E22) 0.030+/-0.013 and radial thickening (E33) 0.081+/-0.041 (both P<0.05 versus zero). Subendocardial systolic shear strains were also perturbed: Circumferential-longitudinal "micro-torsion" (E12) (0.099+/-0.035 versus 0.075+/-0.025) and circumferential radial shear (E13) (0.084+/-0.023 versus 0.039+/-0.008, both P<0.05).Cutting second-order chords altered LV geometry, remodeled the myocardium between the PMs, perturbed local systolic strain patterns affecting micro-torsion and wall-thickening, and caused global systolic dysfunction, demonstrating the importance of these chordae for LV structure and function.

  View details for DOI 10.1161/01.CIR.0000138580.57971.b4

  View details for PubMedID 15364849

• Undersized mitral annuloplasty alters left ventricular shape during acute ischemic mitral regurgitation CIRCULATION Tibayan, F. A., Rodriguez, F., Langer, F., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2004; 110 (11): II98-II102

  Abstract

  Underlying left ventricular (LV) dysfunction contributes to poor survival after operation to correct ischemic mitral regurgitation (IMR). Many surgeons do not appreciate that a key component of the Bolling undersized mitral ring annuloplasty concept is to decrease LV wall stress by altering LV shape, but precise 3-dimensional (3-D) geometric data do not exist substantiating this effect. We tested the hypothesis that annular reduction decreases regional circumferential LV radius of curvature (ROC) in a model of acute IMR.Eight adult sheep underwent insertion of an adjustable Paneth-type annuloplasty suture and radiopaque markers on the LV and mitral annulus. The animals were studied with biplane videofluoroscopy during baseline conditions, then before and after tightening the annuloplasty suture during proximal left circumflex occlusion. End-systolic circumferential regional LV ROC and mitral annular area were computed.Acute IMR was eliminated (MR grade 2.1+/-0.4 to 0.4+/-0.4, mean+/-SD, P<0.05) by tightening the Paneth annuloplasty suture. Paneth suture tightening during circumflex occlusion also decreased end-systolic regional circumferential radii of curvature at the basal (anterior, 3.40+/-0.16 to 3.34+/-0.14 cm; posterior, 3.31+/-0.23 to 3.24+/-0.26 cm; P<0.05) and equatorial levels (anterior, 2.99+/-0.21 to 2.89+/-0.29 cm; posterior, 2.86+/-0.38 to 2.81+/-0.41 cm; P<0.05).Acute proximal circumflex occlusion caused IMR and increased end-systolic LV radii of curvature in this experimental preparation. Annular reduction sufficient to abolish IMR also decreased end-systolic anterior and posterior LV ROC, which would be expected to reduce LV wall stress and oxygen consumption in these regions, both potentially beneficial effects. The long-term effects of undersized annuloplasty on LV remodeling and function, however, will require further study in chronic animal preparations or patients with chronic IMR.

  View details for DOI 10.1161/01.CIR.0000128395.45145.45

  View details for PubMedID 15364846

• Cutting second-order chords does not prevent acute ischemic mitral regurgitation 76th Annual Scientific Session of the American-Heart-Association Rodriguez, F., Langer, F., Harrington, K. B., Tibayan, F. A., Zasio, M. K., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2004: II91–II97

  Abstract

  Cutting anterior mitral leaflet second-order chordae has been proposed for repair in ischemic mitral regurgitation (IMR). We examined the efficacy of such chordal cutting in preventing acute IMR.Six sheep underwent radiopaque marker placement (left ventricle, mitral annulus, papillary muscles [PMs], and leaflets). The largest second-order chord from each PM was encircled with exteriorized wire snares. Three-dimensional marker coordinates were obtained with biplane videofluoroscopy before and during acute ischemia (80 seconds of mid-circumflex occlusion). Color Doppler transesophageal echocardiography was used to grade MR on a 0 to 4+ scale. Data were acquired immediately before and after dividing second-order chordae. Slope of the end-diastolic volume-stroke work relationship (PRSW) was calculated to assess systolic function. Chordal cutting increased anterior leaflet inflection angle (155+/-12 versus 162+/-9 degrees; P=0.03), resulting in a flatter leaflet, but did not increase effective leaflet length (1.97+/-0.24 versus 2.08+/-0.23 cm; P=0.15); PRSW decreased (63+/-15 versus 56+/-12 mm Hg; P=0.008). Both before and after chordal cutting, ischemia caused: Septal-lateral annular dilation (P=0.005), posterior PM displacement away from the mid-septal annulus (P=0.06), increased leaflet tenting area (P=0.001), and increased leaflet tenting volume (P=0.002). Before chordal cutting, MR increased significantly during ischemia (0.5+/-0.3 versus 1.7+/-0.4; P<0.001), and IMR increased similarly even after the second-order chords were cut (0.7+/-0.4 versus 1.9+/-0.9; P<0.001).Cutting second-order chordae resulted in LV systolic dysfunction and neither prevented nor decreased the severity of acute IMR, septal-lateral annular dilation, leaflet tenting area, or leaflet tenting volume.

  View details for DOI 10.1161/01.CIR.0000138396.24335.6a

  View details for PubMedID 15364845

• Effects of paracommissural septal-lateral annular cinching on acute ischemic mitral regurgitation 76th Annual Scientific Session of the American-Heart-Association Timek, T. A., Liang, D., Tibayan, F., Langer, F., Rodriguez, F., Daughters, G. T., Ingels, N. B., Miller, D. C. LIPPINCOTT WILLIAMS & WILKINS. 2004: II79–II84

  Abstract

  Previous experimental studies demonstrated that central septal-lateral (SL) annular cinching (SLAC) abolishes acute ischemic mitral regurgitation (IMR), but whether localized cinching near the anterior (ACOM) or posterior (PCOM) commissure is equally effective is unknown.Six adult sheep underwent implantation of 9 radiopaque markers on the left ventricle, 8 around the mitral annulus (MA) and 1 on each papillary muscle (PM) tip. Transannular SL sutures were placed at the valve center (CENT) and near ACOM and PCOM and externalized. Acute IMR was induced by proximal circumflex coronary snare occlusion. Biplane videofluoroscopy and transesophageal echocardiography were performed before and continuously during 3 episodes of myocardial ischemia including 20 seconds of SLAC at each different location. End-systolic MA SL dimension at each suture location and distances between the anterior and posterior PM tips and mid-septal annulus ("saddle horn") were calculated from the 3-dimensional (3D) marker coordinates.SLAC interventions in all 3 locations reduced the degree of IMR, but cinching at the center, SLAC(CENT), had a significantly greater effect on reducing the magnitude of IMR than SLAC(PCOM) or SLAC(ACOM) (mean grade of IMR reduction=1.0+/-0.5, 1.8+/-0.5, and 0.9+/-0.2 for SLAC(ACOM), SLAC(CENT), and SLAC(PCOM), respectively; P=0.044). Although ACOM and PCOM cinching reduced SL(CENT) somewhat, only SLAC(CENT) simultaneously reduced both SL(ACOM) and SL(PCOM) and also repositioned both PM tips closer to the annular saddle horn.SLAC in all 3 positions reduced acute IMR, but central SLAC cinching was most effective, reduced all mitral annular SL dimensions, and relocated both PM tips closer to the mid-septal annulus. Central SLAC is most capable of correcting the annular and subvalvular perturbations accompanying acute left ventricular ischemia that lead to IMR.

  View details for DOI 10.1161/01.CIR.0000138975.05902.a5

  View details for PubMedID 15364843

• Alterations in left ventricular torsion and diastolic recoil after myocardial infarction with and without chronic ischemic mitral regurgitation CIRCULATION Tibayan, F. A., Rodriguez, F., Langer, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2004; 110 (11): II109-II114

  Abstract

  Chronic ischemic mitral regurgitation (CIMR) is associated with heart failure that continues unabated whether the valve is repaired, replaced, or ignored. Altered left ventricular (LV) torsion dynamics, with deleterious effects on transmural gradients of oxygen consumption and diastolic filling, may play a role in the cycle of the failing myocardium. We hypothesized that LV dilatation and perturbations in torsion would be greater in animals in which CIMR developed after inferior myocardial infarction (MI) than in those that it did not.8+/-2 days after marker placement in sheep, 3-dimensional fluoroscopic marker data (baseline) were obtained before creating inferior MI by snare occlusion. After 7+/-1 weeks, the animals were restudied (chronic). Inferior MI resulted in CIMR in 11 animals but not in 9 (non-CIMR). End-diastolic septal-lateral and anterior-posterior LV diameters, maximal torsional deformation (phi(max), rotation of the LV apex with respect to the base), and torsional recoil in early diastole (phi(5%), first 5% of filling) for each LV free wall region (anterior, lateral, posterior) were measured.Both CIMR and non-CIMR animals demonstrated derangement of LV torsion after inferior MI. In contrast to non-CIMR, CIMR animals exhibited greater LV dilation and significant reductions in posterior maximal torsion (6.1+/-4.3 degrees to 3.9+/-1.9 degrees * versus 4.4+/-2.5 degrees to 2.8+/-2.0 degrees; mean+/-SD, baseline to chronic, *P<0.05) and anterior torsional recoil (-1.4+/-1.1 degrees to -0.2+/-1.0 degrees versus -1.2+/-1.0 degrees to -1.3+/-1.6 degrees ).MI associated with CIMR resulted in greater perturbations in torsion and recoil than inferior MI without CIMR. These perturbations may be linked to more LV dilation in CIMR, which possibly reduced the effectiveness of fiber shortening on torsion generation. Altered torsion and recoil may contribute to the "ventricular disease" component of CIMR, with increased gradients of myocardial oxygen consumption and impaired diastolic filling. These abnormalities in regional torsion and recoil may, in part, underlie the "ventricular disease" of CIMR, which may persist despite restoration of mitral competence.

  View details for DOI 10.1161/01.CIR.0000138385.05471.41

  View details for PubMedID 15364848

• Increases in mitral leaflet radii of curvature with chronic ischemic mitral regurgitation 2nd Biennial Meeting of the Society-for-Heart-Valve-Disease Tibayan, F. A., Rodriguez, F., Langer, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Karlsson, M., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2004: 772–78

  Abstract

  Leaflet curvature is a primary determinant of leaflet stress, but no quantitative in-vivo leaflet curvature data exist. Chronic ischemic mitral regurgitation (CIMR) is associated with remodeling of the valvular-ventricular complex. It was hypothesized that leaflet radii of curvature (ROC) would change with such remodeling.Twelve sheep had placement of radiopaque markers on the anterior (APM) and posterior (PPM) papillary muscles, mitral annulus, and anterior (AL) and posterior leaflet (PL) midlines. After 8 +/- 2 days, videofluoroscopy provided baseline 3-D marker data prior to creating inferior myocardial infarction (MI) by snare occlusion of the obtuse marginal coronary arteries. After 7 +/- 1 weeks, the animals were re-studied; 3-D marker coordinates were used to determine end-systolic leaflet ROC, leaflet length, annular septal-lateral diameter, and the distance of each papillary muscle to the mid-septal annulus and each commissure.Before and after CIMR, the AL had compound curvature, and CIMR increased ROC of both curves (proximal ROC 1.27 +/- 0.59 to 1.38 +/- 0.60 cm (p <0.05); distal ROC 1.41 +/- 0.61 to 2.60 +/- 1.52 cm (p < 0.05)). The PL ROC also increased with CIMR (from 2.01 +/- 1.40 to 3.46 +/- 3.93) (p <0.05). Multiple regression analysis determined that annular septal-lateral diameter (proximal AL and distal AL), distance from the APM to anterior commissure (distal AL), and PPM to mid-septal annulus (PL) were independent predictors of leaflet ROC.CIMR increased ROC of both the AL and PL. Leaflet extension may be a compensatory mechanism to minimize the regurgitant orifice, but the attendant increase in ROC will tend to augment leaflet stress. Annular and subvalvular geometry both affect leaflet curvature, and should be considered during mitral repair. These novel quantitative in-vivo data are now available for modification of finite element models, and for comparison to finite element model output.

  View details for PubMedID 15473478

• Mitral suture annuloplasty corrects both annular and subvalvular geometry in acute ischemic mitral regurgitation JOURNAL OF HEART VALVE DISEASE Tibayan, F. A., Rodriguez, F., Langer, F., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2004; 13 (3): 414-420

  Abstract

  Papillary muscle displacement is an important element in the pathogenesis of ischemic mitral regurgitation (IMR). The effects of standard ring annuloplasty on subvalvular geometry are incompletely understood. The hypothesis was tested that annular reduction with a Panethtype suture annuloplasty would correct both annular and papillary muscle geometric abnormalities during acute left ventricular (LV) ischemia.Eight adult sheep underwent insertion of an adjustable, double-suture Paneth-type mitral annuloplasty and radiopaque markers on the left ventricle, mitral annulus, leaflet edges, and anterior (APM) and posterior (PPM) papillary muscle tips. Immediately after surgey, 3-D marker coordinates were determined during Control conditions and during proximal left circumflex occlusion before and after tightening the annuloplasty suture.Acute IMR (MR grade 0.3 +/- 0.3 to 2.1 +/- 0.4, Control versus Ischemia) was associated with end-systolic LV dilatation (+27 +/- 16 ml, change relative to Control), greater septal-lateral (+4.6 +/- 3.1 cm) and commissure-commissure (+3.3 +/- 1.6 cm) mitral annular diameters, longer anterior (+1.5 +/- 0.9 cm) and posterior (+0.6 +/- 0.9 cm) papillary muscle tethering distances, greater distance from the APM to the anterior commissure (+0.9 +/- 0.8 cm), and shorter distance from the PPM to the poslerior commissure (-1.3 +/- 1.5 cm). Suture annuloplasty corrected the annular and subvalvular changes, and IMR returned to Control levels (0.5 +/- 0.5); only LV end-systolic volume (ESV) was different from Control (+25 +/- 18 ml) (mean +/- SD, p < 0.05 versus Control by RMANOVA and Dunnett's test).Suture annuloplasty corrected ischemia-induced end-systolic distortions of the entire valvular-ventricular complex (i.e. inter-leaflet separation, mitral annular dilatation in both axes, and papillary muscle displacements), and abolished acute IMR, independent of any change in ESV. A better understanding of the effects of annular reduction on papillary muscle geometry may lead to improved subvalvular mitral repair techniques.

  View details for PubMedID 15222288

• Does septal-lateral annular cinching work for chronic ischemic mitral regurgitation? 29th Annual Meeting of the Western-Thoracic-Surgical-Association Tibayan, F. A., Rodriguez, F., Langer, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. MOSBY-ELSEVIER. 2004: 654–63

  Abstract

  Ring annuloplasty, the current treatment of choice for chronic ischemic mitral regurgitation, abolishes dynamic annular motion and immobilizes the posterior leaflet. In a model of chronic ischemic mitral regurgitation, we tested septal-lateral annular cinching aimed at maintaining normal annular and leaflet dynamics.Twenty-five sheep had radiopaque markers placed on the mitral annulus and anterior and posterior mitral leaflets. A transannular suture was anchored to the midseptal mitral annulus and externalized through the midlateral mitral annulus. After 7 days, biplane cinefluoroscopy provided 3-dimensional marker data (baseline) prior to creating inferior myocardial infarction by snare occlusion of obtuse marginal branches. After 7 weeks, the 9 animals that developed chronic ischemic mitral regurgitation were restudied before and after septal-lateral annular cinching. Anterior and posterior mitral leaflet angular excursion and annular septal-lateral and commissure-commissure dimensions and percent shortening were computed.Septal-lateral annular cinching reduced septal-lateral dimension (baseline: 3.0 +/- 0.2; chronic ischemic mitral regurgitation: 3.5 +/- 0.4 [P <.05 vs baseline by repeated measures analysis of variance and Dunnett's test]; septal-lateral annular cinching: 2.4 +/- 0.3 cm; maximum dimension) and eliminated chronic ischemic mitral regurgitation (baseline: 0.6 +/- 0.5; chronic ischemic mitral regurgitation: 2.3 +/- 1.0 [P <.05 vs baseline by repeated measures analysis of variance and Dunnett's test]; septal-lateral annular cinching: 0.6 +/- 0.6; mitral regurgitation grade [0 to 4+]) but did not alter dynamic annular shortening (baseline: 7 +/- 3; chronic ischemic mitral regurgitation: 10 +/- 5; septal-lateral annular cinching: 6 +/- 2, percent septal-lateral shortening) or posterior mitral leaflet excursion (baseline: 46 degrees +/- 8 degrees; chronic ischemic mitral regurgitation: 41 degrees +/- 13 degrees; septal-lateral annular cinching: 46 degrees +/- 8 degrees ).In this model, septal-lateral annular cinching decreased chronic ischemic mitral regurgitation, reduced annular septal-lateral diameter (but not commissure-commissure diameter), and maintained normal annular and leaflet dynamics. These findings provide additional insight into the treatment of chronic ischemic mitral regurgitation.

  View details for DOI 10.1016/j.jtcvs.2003.09.036

  View details for PubMedID 15001893

• Mitral annular size predicts Alfieri stitch tension in mitral edge-to-edge repalir JOURNAL OF HEART VALVE DISEASE Timek, T. A., Nielsen, S. L., Lai, D. T., Tibayan, F., Liang, D., Daughters, G. T., Beineke, P., Hastie, T., Ingels, N. B., Miller, D. C. 2004; 13 (2): 165-173

  Abstract

  Whilst increased 'Alfieri stitch' tension may reduce the durability of 'edge-to-edge' mitral repair, the factors affecting suture tension are unknown. In order to study hemodynamics and left ventricular (LV) and annular dynamics that determine suture tension, the central edge of the mitral leaflets was approximated with a miniature force transducer to measure leaflet tension (T) at the leaflet approximation point.Eight sheep were studied under open-chest conditions immediately after surgical placement of a force transducer and implantation of radiopaque markers on the left ventricle and mitral annulus (MA). Hemodynamic variables were altered by two caval occlusion steps (deltaV1 and deltaV2) and dobutamine infusion. Three-dimensional marker coordinates were obtained by simultaneous biplane videofluoroscopy to measure LV volume, MA area (MAA) and septal-lateral (SL) annular dimension throughout the cardiac cycle.At baseline, peak Alfieri stitch tension (0.30 +/- 0.18 N) was observed 96 +/- 61 ms prior to end-diastole coincident with peak annular SL diameter (98 +/- 58 ms before end-diastole). Dobutamine infusion decreased suture tension (from 0.30 +/- 0.18 N to 0.20 +/- 0.12 N, p = 0.01), although peak systolic pressure increased significantly (138 +/- 19 versus 115 +/- 14 mmHg; p = 0.03). A regression model was fitted with the goal of interpreting the hemodynamic and geometric predictors of tension as their influence varied with time: Tt (N) = 0.1916 + 0.2115 x SL (cm) - 0.1996 x MAA/SL (cm2/cm) + ft x LVP (mmHg), where Tt is tension at any time during the cardiac cycle and ft is the time-varying coefficient of LVP.Tension on the leaflets in the edge-to-edge repair is determined primarily by MA SL size, and paradoxically is lower when the contractile state is enhanced. This indicates that annular and/or LV dilatation increase stitch tension and may adversely affect durability of the repair if concomitant ring annuloplasty is not performed.

  View details for PubMedID 15086253

• Fixed-apex mitral annular descent correlates better with left ventricular systolic function than does free-apex left ventricular long-axis shortening 75th Annual Scientific Session of the American-Heart-Association Rodriguez, F., Tibayan, F. A., Glasson, J. R., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. MOSBY-ELSEVIER. 2004: 101–7

  Abstract

  Echocardiographic measures of mitral annular descent (MAD) assume a fixed left ventricular (LV) apex throughout the cardiac cycle, ignoring the apical component of LV long-axis shortening (LAS). We tested whether apical motion contributes significantly to LAS, making LAS a better surrogate of LV systolic function than MAD. Three-dimensional LV systolic MAD, LAS, and apical motion were measured in sheep using implanted radiopaque markers and biplane videofluoroscopy. End-diastolic volume-stroke work relationship (preload recruitable stroke work) was computed as a load-independent index of LV systolic function. Apical motion was 1.4 +/- 0.8 mm, representing 22% of LAS (P <.05). Linear regression demonstrated that MAD correlated slightly better with preload recruitable stroke work (r = 0.808) than LAS (r = 0.792, both P <.001). Receiver operating characteristic curves demonstrated MAD was more accurate in predicting depressed LV function than LAS (93% vs 84%, respectively). Although LV apical motion contributed significantly to LAS, MAD measured with a fixed-apex assumption, as currently done echocardiographically, correlated more closely with LV preload recruitable stroke work.

  View details for DOI 10.1067/j.echo.2003.11.007

  View details for PubMedID 14752482

• Intravascular ultrasound ablation and imaging catheter for treatment of Atrial Fibrillation IEEE Ultrasonics Symposium Wong, S. H., Scott, G. C., Conolly, S. M., Narayan, G., Liang, D. H. IEEE. 2004: 1785–1787

  View details for Web of Science ID 000228557202054

• Aorto-mitral annular dynamics 39th Annual Meeting of the Society-of-Thoracic-Surgeons Timek, T. A., Green, G. R., Tibayan, F. A., Lai, D. T., Rodriguez, F., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. ELSEVIER SCIENCE INC. 2003: 1944–50

  Abstract

  The aortic and mitral valves are coupled through fibrous aorto-mitral continuity, but their synchronous dynamic physiology has not been completely characterized.Seven sheep underwent implantation of five radiopaque markers on the left ventricle, 10 on the mitral annulus, and 3 on the aortic annulus. One of the mitral annulus markers was placed at the center of aorto-mitral continuity (mitral annulus "saddle horn"). Animals were studied with bi-plane videofluoroscopy 7 to 10 days postoperatively. Total circumference and lengths of mitral fibrous annulus, mitral muscular annulus, aortic fibrous annulus, and aortic muscular annulus were calculated throughout the cardiac cycle from three dimensional marker coordinates as was mitral annular area and aortic annular area. Aorto-mitral angle was determined as the angle between the centroid of the aortic annulus markers, the saddle horn, and the centroid of the mitral annulus markers. Aortic annulus and mitral annulus flexion was expressed as the difference between maximum and minimum values of the aortic and mitral annulus angles during the cardiac cycle.Mitral and aortic annular areas changed in roughly a reciprocal fashion during late diastole and early systole with an overall 32 +/- 8% change in aortic annular area and a 13 +/- 13% change in mitral annular area. Aortic fibrous annulus changed much less than aortic muscular annulus (6 +/- 2% vs 18 +/- 4%; p = 0.0003) as did mitral fibrous annulus relative to mitral muscular annulus (4 +/- 1% vs 8 +/- 2%; p = 0.004). Aortic annulus and mitral annulus flexion was 8 +/- 2 degrees and increased to 11 +/- 2 degrees (p = 0.009) with inotropic stimulation.Dynamic aortic and mitral annular area changes were not mediated through the anatomic fibrous continuity. Aorto-mitral flexion, which increased with enhanced contractility, may facilitate left ventricle ejection. The effect of valvular surgical interventions on aorto-mitral flexion needs further investigation.

  View details for DOI 10.1016/S0003-4975(03)01078-6

  View details for Web of Science ID 000186986500037

  View details for PubMedID 14667619

• Annular remodeling in chronic ischemic mitral regurgitation: Ring selection implications 39th Annual Meeting of the Society-of-Thoracic-Surgeons Tibayan, F. A., Rodriguez, F., Langer, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. ELSEVIER SCIENCE INC. 2003: 1549–54

  Abstract

  More precise understanding of annular remodeling in the evolution of chronic ischemic mitral regurgitation is needed to provide a more rational basis for optimal annuloplasty ring sizing and selection as well as the design of new reparative techniques. Three-dimensional in vivo data describing these geometric perturbations however are lacking. Using an ovine model of chronic myocardial infarction we determined the three-dimensional distortions of the mitral annulus associated with the development of chronic ischemic mitral regurgitation.Ten sheep underwent placement of radiopaque markers on the left ventricle and mitral annulus as well as placement of snares around the second and third obtuse marginal coronary arteries. After 8 days biplane cinefluoroscopy provided three-dimensional marker data and snare occlusion created an inferior infarction. After 7 more weeks the animals were studied again.Severity of mitral regurgitation increased (0.6 +/- 0.5 to 2.5 +/- 0.7). Septal-lateral (2.99 +/- 0.20 cm to 3.64 +/- 0.35 cm, maximum dimension) and commissure-commissure (3.71 +/- 0.32 cm to 4.40 +/- 0.30 cm) mitral annular diameters and the lengths of the muscular (7.77 +/- 0.39 cm to 9.51 +/- 0.72 cm) and fibrous annular perimeters (3.36 +/- 0.37 cm to 3.85 +/- 0.39 cm, p < 0.0001 for all) increased while the height of the annular "saddle horn" above a best-fit plane fell (0.73 +/- 0.52 cm to 0.57 +/- 0.42 cm, minimum dimension, p = 0.01).These three-dimensional in vivo data reflect annular remodeling in chronic ischemic mitral regurgitation and suggest that mitral repair in this context should be aimed at preventing further lengthening of the intertrigonal distance, reducing the septal-lateral annular diameter to reestablish adequate leaflet coaptation, and restoring the saddle shape of the annulus.

  View details for DOI 10.1016/S0003-4975(03)00880-4

  View details for PubMedID 14602284

• Images in cardiovascular medicine. Simultaneous "Tirone David-V" valve-sparing aortic root replacement and radical mitral valve repair for the Marfan syndrome with Barlow syndrome. Circulation Demers, P., Liang, D., Miller, D. C. 2003; 108 (16): e116-7

  View details for PubMedID 14568889

• Simultaneous "Tirone David-V" valve-sparing aortic root replacement and radical mitral valve repair for the Marfan syndrome with Barlow syndrome CIRCULATION Demers, P., Liang, D., Miller, D. C. 2003; 108 (16): E116-E117

  View details for DOI 10.1161/01.CIR.0000092236.67713.04

  View details for Web of Science ID 000186055600021

• Ablation of mitral annular and leaflet muscle: effects on annular and leaflet dynamics AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY Timek, T. A., Lai, D. T., Dagum, P., Tibayan, F., Daughters, G. T., Liang, D., Berry, G. J., Miller, D. C., Ingels, N. B. 2003; 285 (4): H1668-H1674

  Abstract

  Mitral annular (MA) and leaflet three-dimensional (3-D) dynamics were examined after circumferential phenol ablation of the MA and anterior mitral leaflet (AML) muscle. Radiopaque markers were sutured to the left ventricle, MA, and both mitral leaflets in 18 sheep. In 10 sheep, phenol was applied circumferentially to the atrial surface of the mitral annulus and the hinge region of the AML, whereas 8 sheep served as controls. Animals were studied with biplane video fluoroscopy for computation of 3-D mitral annular area (MAA) and leaflet shape. MAA contraction (MAACont) was determined from maximum to minimum value. Presystolic MAA (PS-MAACont) reduction was calculated as the percentage of total reduction occurring before end diastole. Phenol ablation decreased PS-MAACont (72 +/- 6 vs. 47 +/- 31%, P = 0.04) and delayed valve closure (31 +/- 11 vs. 57 +/- 25 ms, P = 0.017). In control, the AML had a compound sigmoid shape; after phenol, this shape was entirely concave to the atrium during valve closure. These data indicate that myocardial fibers on the atrial side of the valve influence the 3-D dynamic geometry and shape of the MA and AML.

  View details for DOI 10.1152/ajpheart.00179.2003

  View details for PubMedID 12969884

• Paneth suture annuloplasty abolishes acute ischemic mitral regurgitation but preserves annular and leaflet dynamics. Circulation Tibayan, F. A., Rodriguez, F., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2003; 108: II128-33

  Abstract

  Ring annuloplasty, the standard treatment for ischemic mitral regurgitation (IMR), abolishes normal annular dynamics and freezes the posterior leaflet. We examined the impact of Paneth suture annuloplasty during acute IMR on motion of the mitral annulus and leaflets in an ovine model.Eight sheep had radiopaque markers placed on the left ventricle, anterior mitral leaflet, posterior mitral leaflet, and mitral annulus. A Paneth suture annuloplasty that could be reversibly tightened was anchored to each fibrous trigone and externalized through the mid-lateral mitral annulus. Acute IMR was induced by proximal circumflex artery occlusion. Transesophageal echocardiography assessed the degree of IMR, and biplane cinefluoroscopy measured 3-dimensional marker coordinates before and during circumflex ischemia, and tightening of the Paneth suture. Paneth suture annuloplasty eliminated acute IMR, and reduced septal-lateral and commissure-commissure mitral annular dimensions. Tightening of the annuloplasty sutures, even beyond the degree necessary to eliminate mitral regurgitation (MR), did not reduce septal-lateral or commissure-commissure annular shortening, shortening of the muscular annular perimeter, annular flexion, or angular excursion of the anterior or posterior leaflets relative to ischemic conditions.In contrast to ring annuloplasty, annular reduction sufficient to restore mitral competence during acute IMR can be achieved with a Paneth suture annuloplasty while simultaneously maintaining normal annular and leaflet dynamic motion. These findings should prompt additional investigation and design of repair methods that preserve the mobility of the mitral apparatus.

  View details for PubMedID 12970221

• Edge-to-edge mitral valve repair without ring annuloplasty for acute ischemic mitral regurgitation CIRCULATION Timek, T. A., Nielsen, S. L., Lai, D. T., Tibayan, F. A., Liang, D., Rodriguez, F., Daughters, G. T., Ingels, N. B., Miller, D. C. 2003; 108 (10): 122-127

  View details for DOI 10.1161/01.cir.0000087943.76135.fd

  View details for Web of Science ID 000185265000022

• Edge-to-edge mitral valve repair without ring annuloplasty for acute ischemic mitral regurgitation. Circulation Timek, T. A., Nielsen, S. L., Lai, D. T., Tibayan, F. A., Liang, D., Rodriguez, F., Daughters, G. T., Ingels, N. B., Miller, D. C. 2003; 108: II122-7

  Abstract

  Alfieri edge-to-edge mitral repair has been used clinically with ring annuloplasty to correct ischemic mitral regurgitation (IMR), but its efficacy without concomitant ring annuloplasty has not been described in this setting.Seventeen sheep underwent implantation of 9 radiopaque markers on the left ventricle, 8 on the mitral annulus (MA), 1 on each papillary muscle (PM) tip, and 1 on the anterior and posterior leaflet edges near the anterior and posterior commissures. Alfieri repair was performed in 7 animals, and 10 were controls. Biplane videofluoroscopy and transesophageal echocardiography (TEE) were performed (open chest) before and continuously during left circumflex coronary artery occlusion to induce acute IMR. MA area (MAA), anterior (APM), and posterior (PPM) papillary muscle tip distances to midseptal MA ("saddle horn"), and distance of each leaflet marker to the mitral annular plane were calculated from 3-dimensional marker coordinates at end-systole (ES).Severity of IMR was not different between groups (+1.9+/-0.7 versus +1.4+/-0.5 for Control and Alfieri, respectively; P=not significant [NS]). Mitral annular area (MAA; 21+/-15 versus 19+/-9%; P =NS) and septal-lateral (SL) annular diameter (12+/-6 versus 12+/-11%; P =NS) increased similarly during ischemia. While PPM-saddle horn distance increased in both groups (1.5+/-1.3 and 1.6+/-1.4 mm for Control and Alfieri, respectively; P<0.05 versus preischemia), APM-saddle horn distance increased in Control (1.0+/-1.2 mm; P=0.03) but not in the Alfieri animals (0.8+/-08 mm; P=0.07). Leaflet edge displacements from the annular plane during ischemia were similar in both groups.Alfieri repair did not prevent acute IMR nor alter ischemic valvular or subvalvular geometric perturbations. Adjunct surgical procedures, such as ring annuloplasty, are also necessary.

  View details for PubMedID 12970220

• Paneth suture annuloplasty abolishes acute ischemic mitral regurgitation but preserves annular and leaflet dynamics CIRCULATION Tibayan, F. A., Rodriguez, F., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2003; 108 (10): 128-133

  View details for DOI 10.1161/01.cir.0000087942.09226.b2

  View details for Web of Science ID 000185265000023

• Geometric distortions of the mitral valvular-ventricular complex in chronic ischemic mitral regurgitation. Circulation Tibayan, F. A., Rodriguez, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Langer, F., Ingels, N. B., Miller, D. C. 2003; 108: II116-21

  Abstract

  Better understanding of the precise 3-dimensional geometric changes of the mitral valvular-ventricular complex in chronic ischemic mitral regurgitation (CIMR) is needed in order to devise better surgical repair techniques. We hypothesized that changes after inferior myocardial infarction would be different in hearts that developed CIMR compared with those that did not.Twenty-four sheep underwent coronary snare and marker placement (annulus, papillary muscles, and anterior and posterior leaflets). After 8 days, cinefluoroscopy provided 3-dimensional marker data, and snare occlusion of obtuse marginal branches created inferior myocardial infarction, including the posterior papillary muscle. After 7 weeks, the 16 surviving animals were studied again and grouped by mitral regurgitation grade (>or= 2+, n=10 versus

  View details for PubMedID 12970219

• Geometric distortions of the mitral valvular-ventricular complex in chronic ischemic mitral regurgitation CIRCULATION Tibayan, F. A., Rodriguez, F., Zasio, M. K., Bailey, L., Liang, D., Daughters, G. T., Langer, F., Ingels, N. B., Miller, D. C. 2003; 108 (10): 116-121

  View details for DOI 10.1161/01.cir.0000087940.17524.8a

  View details for Web of Science ID 000185265000021

• A visual approach for the accurate determination of echocardiographic left ventricular ejection fraction by medical students JOURNAL OF THE AMERICAN SOCIETY OF ECHOCARDIOGRAPHY Hope, M. D., de la Pena, E., Yang, P. C., Liang, D. H., McConnell, M. V., Rosenthal, D. N. 2003; 16 (8): 824-831

  Abstract

  Previously published reports show that there is significant intraobserver, interobserver, and interinstitutional variability in the determination of left ventricular (LV) ejection fraction (EF) by echocardiography. With the increased deployment of echocardiography (eg, handheld devices), there exists a need for developing a simple, intuitive approach for evaluating LVEF that allows a wider range of physicians to accurately and rapidly determine LVEF.We sought to create a system for assessing LVEF that relies on recognition and matching of patterns, rather than on mathematic calculations and geometric assumptions.A library of videoclips of cardiac function was compiled from 54 patients who spanned the spectrum of LVEF. LVEFs were calculated for these patients using standard echocardiographic methods, with further validation of a subsample using cardiac magnetic resonance imaging measurement of LVEF. The library of images was used to create a software tool for assessing LVEF on the basis of a "template-matching" approach. The software tool was then tested on medical students (N=13) to determine whether it enabled relatively untrained individuals to make accurate LVEF estimates.Using a template-matching approach for interpretation of echocardiograms, medical students were able to accurately estimate LVEF after only a limited introduction to echocardiography. Their LVEF estimates showed good correlation and agreement with gold standard (r = 0.88, standard square of the estimate = 6.0, limits of agreement = +12.0%, -15.6%).A new visual approach for assessing cardiac function using template matching can accurately estimate LVEF. With minimal training, medical students can make LVEF estimates that correlate well with gold standard. The application of this new approach includes allowing for the interpretation of LVEF from echocardiograms to be performed by a broader spectrum of physicians.

  View details for DOI 10.1067/S0894-7317(03)00400-0

  View details for Web of Science ID 000184604400007

  View details for PubMedID 12878991

• Accuracy of hand-carried ultrasound ECHOCARDIOGRAPHY-A JOURNAL OF CARDIOVASCULAR ULTRASOUND AND ALLIED TECHNIQUES Liang, D., Schnittger, I. 2003; 20 (5): 487-490

  Abstract

  Hand-carried ultrasound introduces a new group of devices, operators and usage patterns to echocardiography. This may have significant impact on the accuracy of the findings obtained with hand-carried ultrasound. Although reasonable agreement can be obtained with standard echocardiography in certain circumstances, limitations in imaging modes, device image quality, operator experience, and study completeness may significantly limit the diagnostic accuracy of hand carried ultrasound. Despite this, hand-carried ultrasound has the potential to improve significantly upon the data obtained by physical examination.

  View details for Web of Science ID 000183844800015

  View details for PubMedID 12848872

• Alterations in left ventricular curvature and principal strains in dilated cardiomyopathy with functional mitral regurgitation ACC Annual Scientific Meeting Tibayan, F. A., Lai, D. T., Timek, T. A., Dagum, P., Liang, D., Zasio, M. K., Daughters, G. T., Miller, D. C., Ingels, N. B. I C R PUBLISHERS. 2003: 292–99

  Abstract

  Functional mitral regurgitation (FMR) is increasingly recognized as a left ventricular (LV) disease. Dilated cardiomyopathy (DCM) is commonly accompanied by FMR and reduction of LV torsion. Therapeutic targets for DCM include LV size reduction, altered LV shape, elimination of MR, and increasing LV torsion. It was hypothesized that, in addition to increasing LV size, DCM with FMR would alter normal LV shape and reduce and alter the direction of principal strains across the LV wall. This hypothesis was tested by measuring changes in epicardial and endocardial 2-D principal strains and regional radii of curvature accompanying tachycardia-induced cardiomyopathy in ovine hearts.Radio-opaque marker arrays were implanted into the left ventricle of eight sheep, including one subepicardial triangle and one subendocardial triangle in the anterior wall of the left ventricle. At one week postoperatively, biplane videofluoroscopy was used to determine marker dynamics. Rapid ventricular pacing was then instituted until FMR and signs of heart failure developed, and fluoroscopy was repeated. Circumferential LV radii of curvature were determined from marker triplets.DCM changed the normal epicardial oval LV cross-section to a more circular configuration. The endocardium maintained its normal circular shape as the left ventricle dilated. Deformations of the triangles from end-diastole to end-systole were determined, and the magnitude and direction of 2-D principal strains calculated. DCM was associated with decreased magnitude of both epicardial (-0.095 +/- 0.055 versus -0.040 +/- 0.032, p = 0.006) and endocardial (-0.117 +/- 0.047 versus -0.073 +/- 0.037, p = 0.023) principal strains. DCM reduced the angle of epicardial but not endocardial principal strain.DCM with FMR is associated with LV dilation, circularization of the normally oval equatorial circumferential LV epicardium, transmural reduction in principal strain, and decrease in angle of principal epicardial strain. These changes contribute to a reduction in the net torsional moment and may guide the development of reverse remodeling procedures for the dilated, failing ventricle with FMR.

  View details for PubMedID 12803327

• Ischemia in three left ventricular regions: Insights into the pathogenesis of acute ischemic mitral regurgitation 82nd Annual Meeting of the American-Association-for-Thoracic-Surgery Timek, T. A., Lai, D. T., Tibayan, F., Liang, D., Daughters, G. T., Dagum, P., Zasio, M. K., Lo, S., Hastie, T., Ingels, N. B., Miller, D. C. MOSBY-ELSEVIER. 2003: 559–69

  Abstract

  Acute posterolateral left ventricular ischemia in sheep results in ischemic mitral regurgitation, but the effects of ischemia in other left ventricular regions on ischemic mitral regurgitation is unknown.Six adult sheep had radiopaque markers placed on the left ventricle, mitral annulus, and anterior and posterior mitral leaflets at the valve center and near the anterior and posterior commissures. After 6 to 8 days, animals were studied with biplane videofluoroscopy and transesophageal echocardiography before and during sequential balloon occlusion of the left anterior descending, distal left circumflex, and proximal left circumflex coronary arteries. Time of valve closure was defined as the time when the distance between leaflet edge markers reached its minimum plateau, and systolic leaflet edge separation distance was calculated on the basis of left ventricular ejection.Only proximal left circumflex coronary artery occlusion resulted in ischemic mitral regurgitation, which was central and holosystolic. Delayed valve closure (anterior commissure, 58 +/- 29 vs 92 +/- 24 ms; valve center, 52 +/- 26 vs 92 +/- 23 ms; posterior commissure, 60 +/- 30 vs 94 +/- 14 ms; all P <.05) and increased leaflet edge separation distance during ejection (mean increase, 2.2 +/- 1.5 mm, 2.1 +/- 1.9 mm, and 2.1 +/- 1.5 mm at the anterior commissure, valve center, and posterior commissure, respectively; P <.05 for all) was seen during proximal left circumflex coronary artery occlusion but not during left anterior descending or distal left circumflex coronary artery occlusion. Ischemic mitral regurgitation was associated with a 19% +/- 10% increase in mitral annular area, and displacement of both papillary muscle tips away from the septal annulus at end systole.Acute ischemic mitral regurgitation in sheep occurred only after proximal left circumflex coronary artery occlusion along with delayed valve closure in early systole and increased leaflet edge separation throughout ejection in all 3 leaflet coaptation sites. The degree of left ventricular systolic dysfunction induced did not correlate with ischemic mitral regurgitation, but both altered valvular and subvalvular 3-dimensional geometry were necessary to produce ischemic mitral regurgitation during acute left ventricular ischemia.

  View details for DOI 10.1067/mtc.2003.43

  View details for PubMedID 12658198

• Tachycardia-induced cardiomyopathy in the ovine heart: Mitral annular dynamic three-dimensional geometry JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Timek, T. A., Dagum, P., Lai, D. T., Liang, D., Daughters, G. T., Tibayan, F., Ingels, N. B., Miller, D. C. 2003; 125 (2): 315-324

  Abstract

  Ring annuloplasty has been used to correct annular dilatation and mitral regurgitation in dilated cardiomyopathy, but little is known about the dynamic precise 3-dimensional geometry of the mitral annulus in this condition.Nine sheep had radiopaque markers sewn to the mitral annulus, creating 8 distinct segments beginning at the posterior commissure (segments 1-4, septal mitral annulus; segments 5-8, lateral mitral annulus). Biplane videofluoroscopy and transesophageal echocardiography were performed before and after rapid pacing (180-230 min(-1) for 15 +/- 6 days) sufficient to develop tachycardia-induced cardiomyopathy and mitral regurgitation. Mitral annular segment contraction was defined as the percentage difference between maximum and minimum lengths. Mitral annular area and mitral annular septal-lateral and commissure-commissure diameters and 3-dimensional shape were determined from marker coordinates.With tachycardia-induced cardiomyopathy, end-diastolic mitral annular area, septal-lateral diameter, and commissure-commissure diameter increased by 36% +/- 14%, 25% +/- 12%, and 9% +/- 5%, respectively (P <.01), whereas mitral regurgitation increased from 0.3 +/- 0.2 to 2.2 +/- 0.9 (P <.0001). All annular segments dilated at end-diastole with tachycardia-induced cardiomyopathy, except the segment between the midseptal annulus and the left fibrous trigone. Annular segment contraction was significantly decreased with tachycardia-induced cardiomyopathy in the lateral, but not in the septal, regions. Three-dimensional reconstruction of annular shape revealed a saddle shape of the annulus at baseline; this shape was also measured with tachycardia-induced cardiomyopathy, but there was some flattening of the septal annulus.With tachycardia-induced cardiomyopathy, the mitral annulus dilated substantially, being more in the septal-lateral than in the commissure-commissure dimension. Greater annular segmental dilatation and decreased contraction occurred in the lateral annulus. The saddle shape of the annulus was retained but flattened.

  View details for DOI 10.1067/mtc.2003.80

  View details for PubMedID 12579100

• Clinical use of cardiac ultrasound performed with a hand-carried device in patients admitted for acute cardiac care AMERICAN JOURNAL OF CARDIOLOGY Rugolotto, M., CHANG, C. P., Hu, B., Schnittger, I., Liang, D. H. 2002; 90 (9): 1040-?

  View details for Web of Science ID 000178991100033

  View details for PubMedID 12398985

• Atrial contraction and mitral annular dynamics during acute left atrial and ventricular ischemia in sheep AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY Timek, T. A., Lai, D. T., Tibayan, F., Daughters, G. T., Liang, D., Dagum, P., Lo, S., Miller, D. C., Ingels, N. B. 2002; 283 (5): H1929-H1935

  Abstract

  In six sheep, radiopaque markers were placed on the left ventricle (LV), the mitral annulus, the left atrium (LA), and the central edge of both mitral leaflets to investigate the effects of acute LV ischemia on atrial contraction, mitral annular area (MAA), and mitral regurgitation (MR). Animals were studied with biplane videofluoroscopy and transesophageal echocardiography before and during balloon occlusion of the left anterior descending (LAD), distal circumflex (dLCX), and proximal circumflex (pLCX) coronary arteries. MAA and LA area were calculated from the corresponding markers. LAD occlusion did not alter LA area reduction or presystolic MAA reduction, whereas dLCX occlusion resulted in a mild decrease in the former with no change in the latter. Neither occlusion resulted in MR. pLCX occlusion, however, significantly decreased LA area and presystolic MAA reduction and resulted in increased end-diastolic MAA, delayed valve closure from end diastole, and MR. Decreased atrial contractile function, as observed during acute posterolateral ischemia, is linked to diminished presystolic mitral annular reduction, a larger mitral annular size at end diastole, and MR.

  View details for DOI 10.1152/ajpheart.00149.2002

  View details for PubMedID 12384471

• The effects of mitral annuloplasty rings on mitral valve complex 3-D geometry during acute left ventricular ischemia 37th Annual Meeting of the Society-of-Thoracic-Surgeons Lai, D. T., Timek, T. A., Tibayan, F. A., Green, G. R., Daughters, G. T., Liang, D., Ingels, N. B., Miller, D. C. ELSEVIER SCIENCE BV. 2002: 808–16

  Abstract

  Annuloplasty rings are used to treat ischemic mitral regurgitation (IMR), but their exact effects on 3-D geometry of the overall mitral valve complex during acute left ventricular (LV) ischemia remain unknown.Radiopaque markers were sutured to the mitral leaflet edges, annulus, papillary muscle tips, and ventricle in three groups of sheep. One group served as control (n = 5), and the others underwent Duran (n = 6) or Physio (n = 5) ring annuloplasty. One week later, 3-D marker coordinates at end-systole were obtained before and during balloon occlusion of the circumflex artery.In all control animals, acute LV ischemia was associated with: (i) septal-lateral separation of the leaflet edges, which was predicted by lateral displacement of the lateral annulus during septal-lateral mitral annular dilatation; (ii) apical restriction of the posterior leaflet edge, which was predicted by displacement of the lateral annulus away from the non-ischemic anterior papillary muscle; (iii) displacement of the posterior papillary muscle, which was not predictive of either septal-lateral leaflet separation or leaflet restriction; and (iv) mitral regurgitation. In the Duran group during ischemia, the posterior leaflet edge shifted posteriorly due to posterior movement of the lateral annulus, but no IMR occurred. In the Physio group during ischemia, neither the posterior leaflet edge nor the lateral annulus changed positions, and there was no IMR. In both the Duran and Physio groups, displacement of the posterior papillary muscle did not lead to IMR.Either annuloplasty ring prevented the perturbations of mitral leaflet and annular--but not papillary muscle tip--3-D geometry during acute LV ischemia. By fixing the septal-lateral annular dimension and preventing lateral displacement of the lateral annulus, annuloplasty rings prevented systolic septal-lateral leaflet separation and posterior leaflet restriction, and no acute IMR occurred. The flexible ring allowed posterior displacement of the posterior leaflet edge and the lateral annulus, which was not observed with a semi-rigid ring.

  View details for PubMedID 12414050

• Ischemia-induced malcoaptation of scallops within the posterior mitral leaflet JOURNAL OF HEART VALVE DISEASE Myrmel, T., Lai, D. T., Lo, S., Timek, T. A., Liang, D., Miller, D. C., Ingels, N. B., Daughters, G. T. 2002; 11 (6): 823-829

  Abstract

  The posterior mitral leaflet is divided into a variable number of scallops, and little is known about the role of scallopmalcoaptation in ischemic mitral regurgitation. The study aim was to assess whether acute ischemia in the posterolateral wall of the left ventricle would induce scallop separation that would contribute to mitral regurgitation.Radio-opaque markers were surgically placed in the left ventricle, around the mitral annulus, and at three sites along the posterior mitral leaflet edge in eight sheep. Three-dimensional marker coordinates were obtained by biplane videofluoroscopy at 60 Hz and 0.1 mm resolution before and during echocardiographically verified acute ischemic mitral regurgitation produced by balloon occlusion of the circumflex coronary artery.During systole, the mean (+/-SD) distance between the central and anterolateral markers, both placed on the central scallop of the posterior mitral leaflet, was unaffected by ischemia (7.4+/-2.4 versus 7.4+/-2.5 mm; n = 8; p = NS). In contrast, the systolic distance between the central scallop marker and the posteromedial marker increased by 2.3+/-0.2 mm (p = 0.008) in three hearts with the posteromedial marker on the posteromedial scallop, compared with no separation (0.2+/-0.5 mm; p = NS) in five hearts with both the central and posteromedial markers on the central scallop itself. This result shows systolic separation of the central and posteromedial scallops during acute ischemic mitral regurgitation.During acute left ventricular ischemia, the central and posteromedial scallops of the posterior mitral leaflet can fail to coapt during systole, potentially contributing to the mitral regurgitation observed.

  View details for PubMedID 12479283

• Will a partial posterior annuloplasty ring prevent acute ischemic mitral regurgitation? Circulation Timek, T. A., Dagum, P., Lai, D. T., Tibayan, F., Liang, D., Daughters, G. T., Hayase, M., Ingels, N. B., Miller, D. C. 2002; 106 (12): I33-I39

  Abstract

  Acute posterolateral ischemia in sheep results in ischemic mitral regurgitation (IMR). While complete ring annuloplasty prevents acute IMR, partial annuloplasty rings may offer a more physiologic repair, but are untested in animal models of IMR.Radiopaque markers were placed on the LV, mitral annulus (MA), and leaflets in 13 sheep. Seven sheep served as controls, and 6 had a St. Jude Tailor partial flexible ring implanted (29 mm in 5, 31 mm in 1). After 8+/-1 day, the animals were studied with biplane videofluoroscopy and echocardiography before and during acute posterolateral LV ischemia (balloon occlusion of circumflex artery). Mitral annular area (MAA), septal-lateral annular diameter (SL), annular perimeters, and leaflet edge separation were calculated from 3-D marker coordinates.The average degree of mitral regurgitation increased from 0.0+/-0.0 to 2.1+/-0.7 (P=0.0006) in the control group during acute ischemia but remained unchanged in the Tailor group (0.1+/-0.2 for both conditions). The change in MAA throughout the cardiac cycle before ischemia was 17+/-4% in control animals, but only 5+/-2% (P=0.0002) in the Tailor ring group. Unlike the control animals, there was no increase in MAA (5.4+/-0.8 and 5.5+/-0.7 cm(2), respectively; p=NS) nor dilatation of the muscular annulus (6.2+/-0.3 and 6.2+/-0.4, respectively; p=NS) during ischemia with the Tailor ring. Mitral SL dimension increased slightly with ischemia (2.3+/-0.2 versus 2.2+/-0.2 cm, P=0.03). Although posterior leaflet motion was limited, as observed with complete rings, normal annular flexion was maintained with the Tailor ring before and during acute ischemia.The Tailor partial annuloplasty ring prevented acute IMR probably by limiting SL diameter dilatation during acute ischemia. In this animal model of acute IMR, a partial, flexible posterior annuloplasty ring is as effective as a complete ring.

  View details for PubMedID 12354706

• Annular versus subvalvular approaches to acute ischemic mitral regurgitation. Circulation Timek, T. A., Lai, D. T., Tibayan, F., Liang, D., Rodriguez, F., Daughters, G. T., Dagum, P., Ingels, N. B., Miller, C. 2002; 106 (12): I27-I32

  Abstract

  Ischemic mitral regurgitation (IMR) has been attributed to annular dilatation, papillary muscle (PM) displacement ("apical leaflet tenting"), or both. We compared the efficacy of reducing annular or subvalvular dimensions to gain more mechanistic insight into acute IMR.Eight adult sheep underwent implantation of radiopaque markers on the LV, mitral annulus (MA), each leaflet edge, and each PM tip. Trans-annular septal-lateral (SL) and inter-PM tip sutures were placed and externalized. Biplane videofluoroscopy and transesophageal echocardiography were performed before and continuously during LCx occlusion-induced IMR with SL annular (SLAC) or inter-PM (PAPS) suture tightening (4 to 5 mm of cinching for 5 seconds during ischemia). MA SL dimension, inter-papillary distance (APM-PPM), and the distances between the anterior (APM) and posterior (PPM) PM tips and the mid-septal annulus ("saddle horn") were calculated from 3-D marker coordinates at end-systole.SLAC reduced IMR (grade=2.1+/-0.6 versus 0.7+/-0.5, P.001), SL annular diameter (4.9+/-2.5 mm smaller versus pre-cinching; P.001), and PM-"saddle horn" distances (0.9+/-0.7 and 1.0+/-0.8 mm reduction for APM and PPM, respectively; P.005). PAPS reduced APM-PPM distance (3.7+/-1.8 mm reduction versus precinching; P.001), only slightly decreased the PPM-"saddle horn" distance (0.3+/-0.3 mm reduction; P.03), and had no effect on IMR.Acute IMR was abolished by annular SL reduction, which also repositioned both PM tips closer to the mid-septal annulus and paradoxically increased leaflet "apical tenting"; reducing inter-papillary dimension was not effective, even though it displaced the leaflets toward the annular plane (less "apical tenting").

  View details for PubMedID 12354705

• Mechanistic insights into posterior mitral leaflet inter-scallop malcoaptation during acute ischemic mitral regurgitation. Circulation Lai, D. T., Tibayan, F. A., Myrmel, T., Timek, T. A., Dagum, P., Daughters, G. T., Liang, D., Ingels, N. B., Miller, D. C. 2002; 106 (12): I40-I45

  Abstract

  Three-dimensional dynamics of the 3 individual scallops within the posterior mitral leaflet during acute ischemic mitral regurgitations have not been previously measured.Radiopaque markers were sutured to the mitral annulus, papillary muscle tips, and leaflet edges in 13 sheep. Immediately postoperatively, under open-chest conditions, 3-D marker coordinates were obtained using high-speed biplane videofluoroscopy before and during echocardiographically verified acute ischemic mitral regurgitation produced by occlusion of the left circumflex coronary artery.During acute ischemic mitral regurgitation, at end systole, the anterolateral edge of the central scallop was displaced 0.8+/-0.9 mm laterally and 0.9+/-0.6 mm apically away from the anterolateral scallop; such displacement correlated with lateral displacement of the lateral annulus (R(2)=0.7, SEE=0.7 mm, P<0.001) and movement of the right lateral annulus away from the nonischemic anterior papillary tip (R(2)=0.6, SEE=0.8 mm, P=0.002), respectively. End-systolic displacement of the posteromedial edge of the central scallop was 1.4+/-0.9 mm anteriorly and 0.9+/-0.6 mm laterally away from the posteromedial scallop, corresponding to anterior displacement of the mid-lateral annulus (R(2)=0.5, SEE=1.0 mm, P<0.001).Malcoaptation of the scallops within the posterior leaflet during acute left ventricular ischemia is a novel observation. The primary geometric mechanism underlying scallop malcoaptation in acute ischemic mitral regurgitation was annular dilatation, which hindered leaflet coaptation by drawing the individual scallops apart. These findings support the use of annular reduction in the repair of ischemic mitral regurgitation and also suture closure of prominent subcommissures between posterior leaflet scallops.

  View details for PubMedID 12354707

• Hemodynamic performance of an unstented xenograft mitral valve substitute JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Timek, T. A., Lai, D. T., Tibayan, F. A., Dagum, P., Daughters, T., Liang, D., Ingels, N. B., Miller, D. C. 2002; 124 (3): 541-552

  Abstract

  Stentless mitral xenografts offer potential clinical benefits because they mimic the normal bileaflet mitral valve. How best to implant them and their hemodynamic performance and durability, however, remain unknown.A stentless porcine mitral xenograft valve (Medtronic physiologic mitral valve) was implanted in 7 sheep with papillary muscle sewing tubes attached with transmural left ventricular sutures. Radiopaque markers were inserted on the leaflets, annular cuff, papillary tips, and left ventricle. After 10 +/- 5 days, the animals were studied with biplane videofluoroscopy to determine 3-dimensional marker coordinates at baseline and during dobutamine infusion. Transesophageal echocardiography assessed mitral regurgitation and valvular gradients. Mitral annular area was calculated from the annular markers. Physiologic mitral valve leaflet and annular dynamics were compared with 8 native sheep valves.Average mitral regurgitation grade at baseline was 1.2 +/- 1.0 (range, 0-4), and the mean transvalvular pressure gradients were 3.6 +/- 1.3 and 6.2 +/- 2.2 mm Hg during baseline and dobutamine infusion, respectively. Xenograft mitral annular area contraction throughout the cardiac cycle was reduced (6% +/- 6% vs 13% +/- 4% for physiologic mitral valve and control valve, respectively; P =.03). Physiologic mitral valve leaflet geometry during closure differed from the native valve, with the anterior leaflet being convex to the atrium and with little motion of the posterior leaflet. Three animals survived more than 3 months; good healing of the annular cuff and papillary muscle tubes was demonstrated.This stentless xenograft mitral valve substitute had low gradients at baseline and during stress conditions early postoperatively, with mild mitral regurgitation. Preliminary analysis of healing characteristics appeared favorable at 3 months. Additional studies are needed to determine long-term xenograft mitral valve performance and resistance to calcification.

  View details for DOI 10.1067/mtc.2002.124390

  View details for PubMedID 12202871

• Alterations in left ventricular torsion in tachycardia-induced dilated cardiomyopathy JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Tibayan, F. A., Lai, D. T., Timek, T. A., Dagum, P., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2002; 124 (1): 43-49

  Abstract

  Left ventricular torsion reduces transmural systolic gradients of fiber strain, and torsional recoil in early diastole is thought to enhance left ventricular filling. Left ventricular remodeling in dilated cardiomyopathy may result in changes in torsion dynamics, but these effects are not yet characterized. Tachycardia-induced cardiomyopathy is accompanied by systolic and diastolic heart failure and left ventricular remodeling. We hypothesized that cardiomyopathy would alter systolic and diastolic left ventricular torsion mechanics, and this hypothesis was tested by studying sheep before and after the development of tachycardia-induced cardiomyopathy.Implanted miniature radiopaque markers were used in 8 sheep to measure left ventricular geometry and function, maximal torsional deformation, and early diastolic recoil before and after rapid ventricular pacing was used to create tachycardia-induced cardiomyopathy.All animals had significant heart failure with ventricular dilatation and remodeling. With tachycardia-induced cardiomyopathy, maximum torsion relative to control conditions decreased (1.69 degrees +/- 0.61 degrees vs 4.25 degrees +/- 2.33 degrees ), and early diastolic recoil was completely abolished (0.53 degrees +/- 1.19 degrees vs -1.17 degrees +/- 0.94 degrees ).Cardiomyopathy is accompanied by decreased and delayed systolic left ventricular torsional deformation and loss of early diastolic recoil, which may contribute to left ventricular dysfunction by increasing systolic transmural strain gradients and impairing diastolic filling. Analysis of left ventricular torsion with radiofrequency-tagging magnetic resonance imaging should be explored to elucidate the role of torsion in patients with cardiomyopathy.

  View details for DOI 10.1067/mtc.2002.121299

  View details for PubMedID 12091807

• Reversal of phen-fen associated valvular regurgitation documented by serial echocardiography JOURNAL OF THE AMERICAN SOCIETY OF ECHOCARDIOGRAPHY Vagelos, R., Jacobs, M., Popp, R. L., Liang, D. 2002; 15 (6): 653-657

  Abstract

  We report a case of anorexigen-associated moderate to severe aortic and mitral regurgitation in which the regression of lesions was marked and well documented over more than 2 years. The stability of our patient, as well as the degree of regression of regurgitation documented in our patient, and others, suggests it is prudent both to observe such patients and to avoid operation until such observation has been carried out.

  View details for DOI 10.1067/mje.2002.117864

  View details for Web of Science ID 000176263900010

  View details for PubMedID 12050608

• Septal-lateral annular cinching abolishes acute ischemic mitral regurgitation JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Timek, T. A., Lai, D. T., Tibayan, F., Liang, D., Daughters, G. T., Dagum, P., Ingels, N. B., Miller, D. C. 2002; 123 (5): 881-888

  Abstract

  Ring annuloplasty prevents acute ischemic mitral regurgitation in sheep, but it also abolishes normal mitral annular and posterior leaflet dynamics. We investigated a novel surgical approach of simple septal-lateral annular cinching with sutures to treat acute ischemic mitral regurgitation.Nine adult sheep underwent implantation of multiple radiopaque markers on the left ventricle, mitral anulus, and mitral leaflets. A septal-lateral transannular suture was anchored to the midseptal mitral anulus and externalized to a tourniquet through the midlateral mitral anulus and left ventricular wall. Open-chest animals were studied immediately postoperatively. Acute ischemic mitral regurgitation was induced by means of proximal left circumflex artery snare occlusion, and 3 progressive steps of septal-lateral annular cinching (each 2-3 mm suture tightening for 5 seconds) were performed with the transannular suture. Biplane videofluoroscopy for 3-dimensional marker coordinates and transesophageal echocardiography were performed continuously before and during left circumflex ischemia and septal-lateral annular cinching.Acute left circumflex ischemia caused ischemic mitral regurgitation (+0.5 +/- 0.4 [baseline] vs +2.0 +/- 0.7 [ischemia]; P =.005; scale, +0-4), which decreased progressively with each step of septal-lateral annular cinching and was eliminated during the third step (ischemic mitral regurgitation, +0.6 +/- 0.5; P = not significant vs baseline). The third step of septal-lateral annular cinching decreased the septal-lateral diameter by 6.0 +/- 2.6 mm (P =.005); however, mitral anulus area reduction (8.5% +/- 1.0% and 6.9% +/- 1.9% for ischemic mitral regurgitation and septal-lateral annular cinching step 3, respectively; P =.006) and posterior leaflet excursion (50 degrees +/- 9 degrees and 44 degrees +/- 11 degrees for regurgitation and annular cinching step 3, respectively; P =.002) throughout the cardiac cycle were affected only mildly. Normal mitral annular 3-dimensional shape was maintained with septal-lateral annular cinching.Isolated 22% +/- 10% reduction in mitral annular septal-lateral dimension abolished acute ischemic mitral regurgitation in normal sheep hearts while allowing near-normal mitral annular and posterior leaflet dynamic motion. Septal-lateral annular cinching may represent a simple method for the surgical treatment of ischemic mitral regurgitation, either as an adjunctive technique or alone, which helps preserve physiologic annular and leaflet function.

  View details for DOI 10.1067/mtc.2002.122296

  View details for PubMedID 12019372

• Septal-lateral annular cinching ('SLAC') reduces mitral annular size without perturbing normal annular dynamics 1st Biennial Meeting of the Society-for-Heart-Valve-Disease Timek, T. A., Lai, D. T., Tibayan, F. A., Daughters, G. T., Liang, D., Dagum, P., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2002: 2–9

  Abstract

  Septal-lateral (S-L) mitral annular diameter reduction is thought to be central to the efficacy of ring annuloplasty in correcting functional mitral regurgitation (MR), but rings perturb mitral annulus (MA) dynamic motion and limit posterior leaflet excursion. The effects of S-L annular cinching ('SLAC'), a novel method for mitral annular reduction, were investigated.Eight adult sheep had multiple radioopaque markers placed on the left ventricle, leaflet edges, and around the MA. The S-L trans-annular suture was anchored to the mid-septal MA and externalized through the mid-lateral MA and left ventricular wall. Animals were studied immediately postoperatively with biplane videofluoroscopy before and after suture cinching to reduce annular size. MA area (MAA) and S-L dimension were calculated throughout the cardiac cycle from the annular marker coordinates. MAA contraction (AMAA) was expressed as percentage decrease from maximum to minimum MAA. Anterior (AML) and posterior (PML) leaflet angular excursion were calculated as the change in angle between each leaflet edge marker and the S-L annular dimension during the cardiac cycle. MA folding was calculated as the change in distance during systole of the mid-septal annular marker from a plane fitted to the lateral MA markers.SLAC reduced end-diastolic (ED) S-L diameter (21.6+/-2.8 versus 17.1+/-2.6 mm; p = 0.0005) and ED MAA (618+/-126 versus 525+/-114 mm2; p = 0.0004), but did not perturb normal AMAA (15.8+/-4.1 versus 15.1+/-4.8%; p = 0.4), annular flexion (2.0+/-0.7 versus 1.8+/-0.7 mm; p = 0.3) or AML excursion (55+/-7 versus 53+/-7 degrees; p = 0.1). PML excursion was decreased only slightly (52+/-11 versus 44+/-12 degrees; p = 0.002).SLAC substantially reduced S-L annular size, but without perturbing normal MA contraction dynamics, MA flexion, or anterior leaflet excursion. This novel surgical method might represent an alternative to mitral annuloplasty for patients with certain types of mitral pathology.

  View details for PubMedID 11843501

• Rapid assessment of cardiac anatomy and function with a new hand-carried ultrasound device (OptiGo): a comparison with standard echocardiography. European journal of echocardiography Rugolotto, M., Hu, B. S., Liang, D. H., Schnittger, I. 2001; 2 (4): 262-269

  Abstract

  The aim of this study was to evaluate image quality and accuracy of a new hand-carried ultrasound device, OptiGo (Agilent Technologies) when compared to standard echocardiography in the setting of a focused examination in the assessment of cardiac anatomy and function.One-hundred and twenty-one patients were prospectively enrolled. Image quality and accuracy in assessment of chamber sizes, left ventricular (LV) wall thickness and contractility, right ventricular (RV) function, mitral and aortic leaflet thickening, mitral annular calcification, pericardial effusion and valvular regurgitation were assessed. Two-dimensional (2D) findings were graded on a four-point scale, except for LV function (six-point) and valvular leaflet opening (two-point). Colour Doppler assessment of valvular regurgitation was graded on a seven-point scale. A one-point difference was considered minor; a two or more point difference was considered major. There was no statistically significant difference in image quality between the two devices. For 2D data, the number of total (minor and major) differences between the hand-carried and standard echocardiograph examinations was significantly greater than the inter-observer variability (14.3% vs 10.7%, P< 0.05), however, major differences alone were not statistically different. For the colour Doppler assessment of regurgitation there was a significant difference between the devices for total (minor and major) differences, (40.0% vs 31.8%,P < 0.007) however, the number of major differences is explained by inter-observer variability.Image quality and diagnostic accuracy of the hand-carried device, OptiGo, was adequate for the purpose of performing a focused assessment of a limited number of 2D and Doppler parameters for the evaluation of cardiac anatomy and function.

  View details for PubMedID 11888820

• Three-dimensional in-vivo dimensions of 'He's triangle' during acute left ventricular ischemia 1st Biennial Meeting of the Society-for-Heart-Valve-Disease Lai, D. T., Tibayan, F. A., Timek, T. A., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. I C R PUBLISHERS. 2001: 767–73

  Abstract

  Changes in the dimensions of 'He's triangle' (formed by mitral leaflet segments subtending two associated chordae tendineae) derived from data obtained in in-vitro mitral valve models have been proposed to provide a mechanistic explanation for mitral leaflet malcoaptation. The in-vivo dynamics of He's triangle, however, have not been hitherto determined.Radio-opaque markers were placed in 13 sheep to delineate the mitral annulus and four (of an infinite number of possible) He's triangles formed by: (i) the anterior mitral leaflet (AML), first- (CT1) and second-order (CT2) chordae tendineae emanating from the anterior papillary tip (APT1) as well as from the posterior papillary tip (PPT1), respectively; and (ii) the posterior mitral leaflet (PML), CT1 and CT2 emanating from other loci on the anterior as well as the posterior papillary tips (APT2 and PPT2), respectively. Immediately postoperatively (anesthetized, open-chest), three-dimensional end-systolic marker positions were measured before and during circumflex coronary artery occlusion sufficient to produce mitral regurgitation, as verified by echocardiography.During ischemia, three leaflet segments constituting one side of three He's triangles elongated: The AML attached to APT1 and to PPT1 by 1.5+/-1.2 mm (p <0.001) and 1.3+/-0.8 mm (p <0.001), respectively, and the posterior leaflet attached to APT2 by 1.4+/-1.9 mm (p = 0.02). Apart from a 0.9+/-1.1 mm (p = 0.02) increase in the length of CT2 attached to APT2, the length of the seven other CT1 and CT2 remained relatively unchanged during acute left ventricular ischemia.With acute posterolateral ischemia, the lengths of CT1 and CT2 remained relatively constant, but the AML and PML lengths were not constant as the AML and PML 'unfurled' during acute left ventricular ischemia. These geometric changes may provide further insight into the mechanisms of acute ischemic mitral regurgitation, though it is not clear how they will be clinically helpful.

  View details for PubMedID 11767184

• Three-dimensional geometric comparison of partial and complete flexible mitral annuloplasty rings JOURNAL OF THORACIC AND CARDIOVASCULAR SURGERY Dagum, P., Timek, T., Green, G. R., Daughters, G. T., Liang, D., Ingels, N. B., Miller, D. C. 2001; 122 (4): 665-673

  Abstract

  It has previously been shown in sheep that mitral annular physiologic dynamics during the cardiac cycle are abolished by complete ring annuloplasty, but recent clinical studies suggest that flexible partial ring annuloplasty preserves normal mitral annular dynamics.Eight radiopaque markers were sutured equidistantly around the mitral anulus in 3 groups of sheep: no-ring control animals (n = 16); animals with a flexible Tailor partial ring annuloplasty (n = 6; St Jude Medical, Inc, St Paul, Minn); and animals with a flexible Duran ring annuloplasty (n = 7; Medtronic, Inc, Minneapolis, Minn). After 7 to 10 days' recovery, 3-dimensional marker coordinates were measured by biplane cinefluoroscopy. Mitral annular area and folding (defined as displacement of the mitral anulus from a least-squares plane) and mitral annular septal-lateral and commissure-commissure dimensions were calculated from the 3-dimensional marker coordinates throughout the cardiac cycle every 17 ms.In the no-ring control group mitral annular area varied from 8.0 +/- 0.2 to 7.2 +/- 0.2 cm(2) (10% +/- 2%), and the septal-lateral and commissure-commissure dimensions varied from 27.7 +/- 0.4 to 25.9 +/- 0.4 mm (7% +/- 1%) and from 38.2 +/- 0.8 to 36.4 +/- 0.8 mm (5% +/- 1%), respectively (mean +/- standard error of the mean, P <.001 for all comparisons). In the Duran ring annuloplasty and Tailor partial ring annuloplasty groups, the anulus was fixed in size throughout the cardiac cycle (area = 4.8 +/- 0.1 and 5.3 +/- 0.3 cm(2), septal-lateral = 21.8 +/- 0.7 and 22.0 +/- 0.8 mm, and commissure-commissure = 27.7 +/- 0.7 and 31.2 +/- 1.7 mm). Mitral annular folding did not differ significantly between the control and Tailor partial ring annuloplasty groups but was dampened in the Duran ring annuloplasty group.Partial Tailor flexible ring annuloplasty fixed mitral annular area and dimensions throughout the cardiac cycle in sheep; however, it preserved physiologic mitral annular folding dynamics, which might be important in terms of long-term valve function and prevention of left ventricular outflow tract obstruction.

  View details for PubMedID 11581596

• Edge-to-edge mitral repair - Tension on the approximating suture and leaflet deformation during acute ischemic mitral regurgitation in the ovine heart CIRCULATION Nielsen, S. L., Timek, T. A., Lai, D. T., Daughters, G. T., Liang, D., Hasenkam, J. M., Ingels, N. B., Miller, D. C. 2001; 104 (12): I29-I35

  Abstract

  Edge-to-edge approximation of the mitral valve leaflets (Alfieri procedure) is a novel surgical treatment for patients with ischemic mitral regurgitation (IMR). Long-term durability may be limited if abnormal mitral leaflet stresses result from this procedure. The aim of the current study was to measure Alfieri stitch tension (F(A)) and to explore its geometric determinants in an ovine model of acute IMR as a reflection of the mitral leaflet stresses imposed by the procedure.Eight sheep were studied immediately after surgical placement of (1) a force transducer interposed between sutures approximating the central leaflet edges and (2) radiopaque markers around the mitral annulus and leaflet edges. Computer-aided analysis of videofluorograms was used to obtained 3D marker coordinates. Simultaneous measurements of F(A), septal-lateral annular dimension (L(S-L)), leaflet edge separation (L(SEP)), anterior (L(AL)) and posterior (L(PL)) leaflet length, and hemodynamic variables were obtained at baseline (CTL) and during acute IMR (circumflex artery occlusion). F(A) was significantly elevated throughout the cardiac cycle during IMR compared with CTL, with maximum F(A) in diastole (0.26+/-0.05 versus 0.46+/-0.08 N, CTL versus IMR; P<0.05). Multivariable analysis revealed L(S-L) as the single independent predictor of maximum F(A) (P<0.001). Positive linear correlations were shown between values of F(A) and L(AL) and L(PL) (dependent variables).These experimental data demonstrate higher F(A) during IMR and cyclic changes in F(A) closely paralleling changes in L(S-L), eg, being greatest in diastole when the annulus is largest. Increased F(A) during IMR is probably indicative of successful therapeutic intent, but higher diastolic leaflet stresses resulting from persistent or progressive mitral annular dilatation may adversely affect repair durability. This indirectly implies that concomitant mitral ring annuloplasty should be added to the Alfieri repair.

  View details for Web of Science ID 000171201500007

  View details for PubMedID 11568026

• Pathogenesis of mitral regurgitation in tachycardia-induced cardiomyopathy CIRCULATION Timek, T. A., Dagum, P., Lai, D. T., Liang, D., Daughters, G. T., Ingels, N. B., Miller, D. C. 2001; 104 (12): I47-I53

  Abstract

  Dilated cardiomyopathy is often associated with mitral regurgitation (MR), or so-called functional MR, the mechanism of which continues to be debated. We studied the valvular and ventricular 3D geometric perturbations associated with MR in an ovine model of tachycardia-induced cardiomyopathy (TIC).Nine sheep underwent myocardial marker implantation in the left ventricle (LV), mitral annulus, and mitral leaflets. After 5 to 8 days, the animals were studied with biplane videofluoroscopy (baseline), and mitral competence was assessed by transesophageal echocardiography. Rapid ventricular pacing (180 to 230 bpm) was subsequently initiated for 15+/-6 days until the development of TIC and MR, whereupon biplane videofluoroscopy and transesophageal echocardiography studies were repeated. LV volume was calculated from the epicardial marker array. Valve closure time was defined as the time after end diastole when the distance between leaflet edge markers reached its minimal plateau. TIC resulted in increased LV end-diastolic volume (P=0.001) and LV end-systolic volume (P=0.0001) and greater LV sphericity (P=0.02). MR increased significantly (grade 0.2+/-0.3 versus 2.2+/-0.9, P=0.0001), as did mitral annulus area (817+/-146 versus 1100+/-161 mm(2), P=0.0001) and mitral annulus septal-lateral diameter (28.2+/-3.5 versus 35.1+/-2.6 mm, P=0.0001). Time of valve closure (70+/-18 versus 87+/-14 ms, P=0.23) and angular displacement of both the anterior (29+/-5 degrees versus 27+/-3 degrees, P=0.3) and posterior (55+/-15 degrees versus 44+/-11 degrees, P=0.13) leaflet edges relative to the mitral annulus after valve closure did not change, but leaflet edge separation after closure increased (5.2+/-0.9 versus 6.8+/-1.2 mm, P=0.019).MR in TIC resulted from decreased leaflet coaptation secondary to annular dilatation in the septal-lateral direction. These data support the use of annular reduction procedures, such as rigid, complete ring annuloplasty, to address functional MR in patients with dilated cardiomyopathy.

  View details for PubMedID 11568029

• Edge-to-edge mitral repair: gradients and three-dimensional annular dynamics in vivo during inotropic stimulation 14th Annual Meeting of the European-Association-for-Cardio-Thoracic-Surgery Timek, T. A., Nielsen, S. L., Liang, D., Lai, D. T., Dagum, P., Daughters, G. T., Ingels, N. B., Miller, D. C. ELSEVIER SCIENCE BV. 2001: 431–37

  Abstract

  The edge-to-edge (Alfieri) mitral repair technique appears to be clinically promising, but the potential for functional mitral stenosis, especially with exercise, remains a concern. We used the myocardial marker method combined with Doppler echocardiography to evaluate mitral annular (MA) three-dimensional (3-D) dynamics and transvalvular gradients after leaflet approximation before and during dobutamine infusion.Eight adult sheep underwent implantation of eight myocardial markers around the MA and nine in the left ventricle. Mitral leaflet edges were approximated at the valve center and micromanometers were placed in the left ventricle and atrium. The animals were studied with biplane videofluoroscopy to determine 3-D marker coordinates for computation of precise 3-D MA area and left ventricular (LV) volume. Epicardial Doppler echocardiography measured peak and mean diastolic mitral valve gradients at baseline and during dobutamine infusion (10 microg/kg per min).During dobutamine stimulation, left ventricular dP/dt increased from 1776+/-712 to 3390+/-618 mmHg/s (P=0.002), and cardiac output (CO) increased from 2.7+/-1.1 to 5.1+/-1.2 l/min (P=0.009). Mitral annular area (MAA) at end-diastole (ED) fell from 8.6+/-1.4 to 7.0+/-1.8 cm(2) (P=0.001) with inotropic stimulation, but only a modest increase was observed in mean (1.4+/-0.4 vs. 2.4+/-1.0 mmHg, P=0.046) and peak (2.7+/-0.8 vs. 4.9+/-2.5 mmHg, P=0.03) diastolic mitral valve gradients. MAA changed dynamically throughout the cardiac cycle, reflecting normal physiology, but the magnitude of MAA change was augmented during inotropic stimulation (18+/-5% and 27+/-4% for control and dobutamine, respectively; P=0.004).Dobutamine increased CO by 89% and decreased ED annular area by 19% after edge-to-edge repair, yet only a small increase in valve gradient occurred. Marker analysis showed enhanced dynamic motion of the mitral annulus. Thus, the edge-to-edge mitral valve repair was not associated with substantial transvalvular obstruction during high flow conditions and did not perturb normal MA 3-D dynamics in normal ovine hearts.

  View details for PubMedID 11306308

• Coordinate-free analysis of mitral valve dynamics in normal and ischemic hearts. Circulation Dagum, P., Timek, T. A., Green, G. R., Lai, D., Daughters, G. T., Liang, D. H., Hayase, M., Ingels, N. B., Miller, D. C. 2000; 102 (19): III62-9

  Abstract

  The purpose of this investigation was to study mitral valve 3D geometry and dynamics by using a coordinate-free system in normal and ischemic hearts to gain mechanistic insight into normal valve function, valve dysfunction during ischemic mitral regurgitation (IMR), and the treatment effects of ring annuloplasty.Radiopaque markers were implanted in sheep: 9 in the ventricle, 1 on each papillary tip, 8 around the mitral annulus, and 1 on each leaflet edge midpoint. One group served as a control (n=7); all others underwent flexible Tailor partial (n=5) or Duran complete (n=6) ring annuloplasty. After an 8+/-2-day recovery, 3D marker coordinates were measured with biplane videofluoroscopy before and during posterolateral left ventricular ischemia, and MR was assessed by color Doppler echocardiography. Papillary to annular distances remained constant throughout the cardiac cycle in normal hearts, during ischemia, and after ring annuloplasty with either type of ring. Papillary to leaflet edge distances similarly remained constant throughout ejection. During ischemia, however, the absolute distances from the papillary tips to the annulus changed in a manner consistent with leaflet tethering, and IMR was observed. In contrast, during ischemia in either ring group, those distances did not change from preischemia, and no IMR was observed.This analysis uncovered a simple pattern of relatively constant intracardiac distances that describes the 3D geometry and dynamics of the papillary tips and leaflet edges from the dynamic mitral annulus. Ischemia perturbed the papillary-annular distances, and IMR occurred. Either type of ring annuloplasty prevented such changes, preserved papillary-annular distances, and prevented IMR.

  View details for PubMedID 11082364

• Coordinate-free analysis of mitral valve dynamics in normal and ischemic hearts CIRCULATION Dagum, P., Timek, T. A., Green, G. R., Lai, D., Daughters, G. T., Liang, D. H., Hayase, M., Ingels, N. B., Miller, D. C. 2000; 102 (19): 62-69

  View details for Web of Science ID 000165177300012

• The effects of ring annuloplasty on mitral leaflet geometry during acute left ventricular ischemia 80th Annual Meeting of the American-Association-for-Thoracic-Surgery Lai, D. T., Timek, T. A., Dagum, P., Green, G. R., Glasson, J. R., Daughters, G. T., Liang, D., Ingels, N. B., Miller, D. C. MOSBY-ELSEVIER. 2000: 966–75

  Abstract

  The perturbed mitral leaflet geometry that leads to acute ischemic mitral regurgitation during acute left ventricular ischemia has not been quantified, nor is it known whether annuloplasty rings affect these detrimental changes in leaflet geometry.Radiopaque markers were implanted on both mitral leaflets and around the anulus in 3 groups of sheep: one group without rings served as the control group (n = 7); the others underwent Duran (n = 6; Medtronic Heart Valve Division, Minneapolis, Minn) or Carpentier-Edwards Physio (n = 5; Baxter Cardiovascular Division, Santa Ana, Calif) ring annuloplasty. After recovery, 3-dimensional marker coordinates were obtained by means of biplane videofluoroscopy before and during acute posterolateral left ventricular ischemia. Leaflet geometry was defined by measuring distances between annular and leaflet markers and perpendicular distances to the leaflet markers from a best-fit annular plane.In all control animals, left ventricular ischemia was associated with acute ischemic mitral regurgitation and apical displacement (away from the annular plane) of the posterior leaflet edge and base markers by 0.6 +/- 0.4 mm (P =.01) and 0.7 +/- 0.2 mm (P <.001), respectively. The distance between the posterior leaflet markers and the mid-posterior anulus did not change significantly during ischemia. The anterior leaflet edge marker extended 1.0 +/- 0. 5 mm (P =.01) away from the mid-anterior anulus during ischemia, but compared with its nonischemic position, the anterior leaflet was not displaced apically away from the annular plane. In all animals in the Duran and Physio groups, leaflet geometry was unchanged during ischemia, and acute ischemic mitral regurgitation was not detected.Acute ischemic mitral regurgitation was associated with restricted motion of the posterior leaflet and extension of the anterior leaflet. Annuloplasty rings prevented these geometric perturbations of the mitral leaflets during acute left ventricular ischemia and preserved valvular competence.

  View details for PubMedID 11044323

• Contrast echocardiography is superior to tissue harmonics for assessment of left ventricular function in mechanically ventilated patients AMERICAN HEART JOURNAL Kornbluth, M., Liang, D. H., BROWN, P., Gessford, E., Schnittger, I. 2000; 140 (2): 291-296

  Abstract

  Assessment of left ventricular function by echocardiography is frequently challenging in mechanically ventilated patients. We evaluated the potential value of contrast-enhanced imaging and tissue harmonic imaging over standard fundamental imaging for endocardial border detection (EBD) in these patients.Fifty patients underwent standard transthoracic 2D echocardiography and were imaged in fundamental and tissue harmonic modes and subsequently with intravenous contrast (Optison). Two echocardiographers reviewed all studies for ease of visualization of endocardial border segments and scoring of wall motion. EBD for each wall segment was graded from 1 to 4 (1 = excellent EBD). Wall motion was scored by a standard 16-segment model and 1 to 5 scale. Studies were categorized as nondiagnostic if 4 of 6 segments in the apical 4-chamber view were either poorly seen or not seen (EBD score 3 or 4). Quantification of ejection fraction was independently performed offline. Visualization of 68% of all segments improved with contrast echocardiography versus 17% improvement with tissue harmonics compared with fundamental mode. Significant improvement (poor/not seen to good/excellent) occurred in 60% of segments with contrast echocardiography versus 18% with tissue harmonics. A total of 850 segments were deemed poor/not seen, 78% of which improved to good/excellent with contrast echocardiography versus 23% with tissue harmonics. Interobserver agreement on EBD was 64% to 70%. Conversion of nondiagnostic to diagnostic studies occurred in 85% of patients with contrast echocardiography versus 15% of patients with tissue harmonics. Scoring of wall motion with fundamental mode, tissue harmonics, and contrast echocardiography was possible in 61%, 74%, and 95% of individual segments, respectively (P <.001). Wall motion scoring was altered in 17% of segments with contrast echocardiography and in 8% with tissue harmonics. Interobserver agreement on wall motion scoring was 84% to 88%. Contrast echocardiography permitted measurement of ejection fraction 45% (P =.003) more often over fundamental mode versus a 27% (P =.09) increase with tissue harmonics.Contrast echocardiography is superior to tissue harmonic imaging for EBD, wall motion scoring, and quantification of ejection fraction in mechanically ventilated patients.

  View details for Web of Science ID 000088739900018

  View details for PubMedID 10925345

• Clinical outcome in the Marfan syndrome with ascending aortic dilatation followed annually by echocardiography AMERICAN JOURNAL OF CARDIOLOGY Kornbluth, M., Schnittger, I., Eyngorina, I., Gasner, C., Liang, D. H. 1999; 84 (6): 753-?

  Abstract

  This study reviewed the utility of echocardiography in following patients with the Marfan syndrome for whom cardiovascular complications, especially aortic root dilatation, dissection and rupture, are the major causes of morbidity and mortality. We conclude that echocardiography can be used to follow asymptomatic patients with the Marfan syndrome.

  View details for Web of Science ID 000082536100027

  View details for PubMedID 10498154

• The nerve-electrode interface of the cochlear implant: Current spread IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Liang, D. H., Lusted, H. S., White, R. L. 1999; 46 (1): 35-43

  Abstract

  One of the fundamental facets of the cochlear implant that must be understood to predict accurately the effect of an electrical stimulus on the auditory nerve is the nerve-electrode interface. One aspect of this interface is the degree to which current delivered by an electrode spreads to neurons distant from it. This paper reports a direct mapping of this current spread using recordings from single units from the cat auditory nerve. Large variations were seen in the degree to which the different units are selective in responding to electrodes at different positions within the scala tympani. Three types of units could be identified based on the selectiveness of their response to the different electrodes in a linear array. The first type of unit exhibited a gradual increase in threshold as the stimulating site was moved from more apical to more basal locations within the scala tympani. The second type of unit exhibited a sharp local minimum, with rapid increases in threshold in excess of 6 dB/mm in the vicinity of the minimum. At electrode sites distant from the local minima the rate of change of the threshold approached that of the first type of units. The final type of unit also demonstrated a gradual change in threshold with changing electrode position, however, two local minima, one apical and one basal, could be identified. These three types are hypothesized to correspond to units which originate apical to the electrode array, along the electrode array and basal to the electrode array.

  View details for Web of Science ID 000077782600005

  View details for PubMedID 9919824

• New real-time interactive cardiac magnetic resonance imaging system complements echocardiography JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY Yang, P. C., Kerr, A. B., Liu, A. C., Liang, D. H., Hardy, C., Meyer, C. H., Macovski, A., Pauly, J. M., Hu, B. S. 1998; 32 (7): 2049-2056

  Abstract

  We conducted an initial clinical trial of a newly developed cardiac magnetic resonance imaging (CMRI) system. We evaluated left ventricular (LV) function in 85 patients to compare the clinical utility of the CMRI system with echocardiography, the current noninvasive gold standard.Conventional CMRI systems require cardiac-gating and respiratory compensation to synthesize a single image from data acquired over multiple cardiac cycles. In contrast, the new CMRI system allows continuous real-time dynamic acquisition and display of any scan plane at 16 images/s without the need for cardiac gating or breath-holding.A conventional 1.5T Signa MRI Scanner (GE, Milwaukee, Wisconsin) was modified by the addition of an interactive workstation and a bus adapter. The new CMRI system underwent clinical trial by testing its ability to evaluate global and regional LV function. The first group (A) consisted of 31 patients with acceptable echocardiography image quality. The second group (B) consisted of 31 patients with suboptimal echocardiography image quality. The third group (C) consisted of 29 patients with severe lung disease or congenital cardiac malformation who frequently have suboptimal echo study. Two independent observers scored wall motion and image quality using the standard 16-segment model and rank-order analysis.CMRI evaluation was complete in less than 15 min. In group A, no significant difference was found between ECHO and CMRI studies (p = NS). In group B, adequate visualization of wall segments was obtained 38% of the time using ECHO and 97% of the time using CMRI (p < 0.0001). When grouped into coronary segments, adequate visualization of at least one segment occurred in 18 of 30 patients (60%) with ECHO and in all 30 patients (100%) with CMRI (p < 0.0001). In group C, adequate visualization of the wall segments was obtained in 58% (CI 0.53-0.62) of the time using echocardiography and 99.7% (CI 0.99-1.0) of the time using CMRI (p < 0.0001).The new CMRI system provides clinically reliable evaluation of LV function and complements suboptimal echocardiography. In comparison with the conventional CMRI, the new CMRI system significantly reduces scan time, patient discomfort and associated cost.

  View details for Web of Science ID 000077396200039

  View details for PubMedID 9857892

• Paradoxical embolism of a shotgun pellet ANNALS OF THORACIC SURGERY Ikonomidis, J. S., Nisco, S. J., Liang, D. H., Robbins, R. C. 1998; 66 (2): 562-564

  Abstract

  Paradoxical embolism of a projectile from the venous to arterial system is a rare occurrence, which can cause diagnostic confusion. We present a case of venous embolism of a shotgun pellet from the left upper extremity to the noncoronary sinus of the aortic valve across a secundum-type atrial septal defect. Prevention of distal embolism of the pellet was presumably a result of its containment by flow vortices created within the sinuses of Valsalva.

  View details for Web of Science ID 000075554900054

  View details for PubMedID 9725410

• Native tissue harmonic imaging improves endocardial border definition and visualization of cardiac structures JOURNAL OF THE AMERICAN SOCIETY OF ECHOCARDIOGRAPHY Kornbluth, M., Liang, D. H., Paloma, A., Schnittger, I. 1998; 11 (7): 693-701

  Abstract

  The purpose of this study was to examine the impact of native tissue harmonic imaging on endocardial border definition, wall motion scoring, and visualization of intracardiac structures.For wall motion analysis, 60 consecutive patients underwent standard transthoracic echocardiograms in both harmonic and fundamental modes. Three experienced echocardiographers reviewed each echocardiogram. Endocardial border definition for each wall segment was graded from 1 to 4 (1 = excellent endocardial definition). Wall motion was scored by using a standard 16-segment model and 1 to 5 scale. For visualization of cardiac structures, 50 consecutive patients were studied. Two experienced interpreters reviewed each echocardiogram for both normal and abnormal structures by using the following scoring scale: (1) harmonic is much better than fundamental, (2) harmonic is slightly better than fundamental, (3) harmonic and fundamental are equivalent, (4) fundamental is slightly better than harmonic, and (5) fundamental is much better than harmonic. Visualization of 64% (95% confidence interval [CI] 0.61 to 0.66) of all segments improved in harmonic mode, with 26% (95% CI 0.24 to 0.29) improving from poor/not seen to good/excellent. Of 444 segments deemed poor/not seen, visualization of 312 (70%) (95% CI 0.66 to 0.75) improved to good/excellent with harmonic mode. Of these 312 segments, 55% comprised the lateral and anterior walls on apical views. Interobserver agreement on endocardial border definition was 82% to 86%. Scoring of wall motion was altered in 171 of 1075 (16%) of segments by harmonic mode. This was significantly greater than the interobserver disagreement, which was only 10% (p<0.002). Mitral valve chordae and papillary muscles were visualized slightly/much better with harmonic mode in 40 of 50 echocardiograms. Left atrial boundaries were seen slightly/much better in harmonic mode in 29 of 50 studies. Abnormal structures were seen slightly/much better in harmonic mode in 12 of 14 cases.Native tissue harmonic imaging has significant impact on endocardial border definition and wall motion scoring and improves the visualization of both normal and abnormal cardiac structures.

  View details for Web of Science ID 000074885200003

  View details for PubMedID 9692526

• Relation of donor age and preexisting coronary artery disease on angiography and intracoronary ultrasound to later development of accelerated allograft coronary artery disease JOURNAL OF THE AMERICAN COLLEGE OF CARDIOLOGY Gao, S. Z., Hunt, S. A., Alderman, E. L., Liang, D., Yeung, A. C., Schroeder, J. S. 1997; 29 (3): 623-629

  Abstract

  This study assessed the influence of donor age and preexisting donor coronary disease on the later development of allograft coronary artery disease, ischemic events and overall survival.The increasing demand for heart donors has led to a tendency to liberalize age criteria for donor acceptability.A total of 233 consecutive heart transplant recipients who had baseline, early postoperative and follow-up coronary angiograms, as well as a subset of 47 patients with baseline intracoronary ultrasound imaging recordings, were analyzed (mean 3.8 years of follow-up). Patients were subclassified according to the presence of donor coronary artery disease on the baseline angiogram and stratified at age 40 years.patients without evidence of preexisting coronary artery disease on a baseline angiogram (n = 219) were significantly less likely to develop new disease than the 14 patients with preexisting coronary artery disease (p = 0.002). Although older donors exhibited earlier coronary artery disease than younger donors at 3 years of follow-up, there was no difference by 5 years (p = 0.25). There was no difference in survival or probability of developing ischemic events between the groups. Baseline ultrasound imaging revealed substantial disease in 7 of 9 older donated hearts, and in only 7 of 38 younger donated hearts (p = 0.002). Preexisting coronary artery disease, nonuse of calcium channel blocking agents, older donor age, posttransplantation cytomegalovirus infection, elevated very low density lipoprotein levels and previous ischemic heart disease in the recipient were significant predictors of allograft coronary artery disease.Heart donors with angiographic evidence of preexisting coronary artery disease and older donors are more likely to develop new allograft coronary artery disease by 3 years. However, there is no difference in survival or freedom from ischemic events between younger and older donors at a mean follow-up of 3.8 years.

  View details for Web of Science ID A1997WL49000023

  View details for PubMedID 9060902

• Forward-looking catheters. Seminars in interventional cardiology : SIIC Liang, D. H., Hu, B. S. 1997; 2 (1): 75-81

  Abstract

  Current intravascular ultrasound catheters provide a cross-sectional view of the blood vessel that limits their ability to visualize severely stenosed or occluded vessels. Forward-looking ultrasound catheters can overcome these limitations. Development of a practical forward-looking ultrasound catheter requires solutions to address the need for improved lateral resolution and depth of penetration presented by the forward-looking format. Methods are also needed to generate the forward-looking scan within the space constraints of a catheter. New developments using mechanical scanning methods suggest that a practical device appears achievable. Two-dimensional, as well as three-dimensional imaging, may be possible. Early efforts towards a phased array scanner have also begun.

  View details for PubMedID 9546988

• Role of compensatory enlargement and shrinkage in transplant coronary artery disease - Serial intravascular ultrasound study CIRCULATION Lim, T. T., Liang, D. H., Botas, J., Schroeder, J. S., Oesterle, S. N., Yeung, A. C. 1997; 95 (4): 855-859

  Abstract

  Compensatory enlargement of the vessel wall has been described in the early stages of native atherosclerosis. Whether compensatory enlargement plays a role in transplant coronary artery disease is not known. The objective of this study was to determine, by use of serial intravascular ultrasound (IVUS), whether compensatory dilation occurs in transplant coronary artery disease over time.Seventy-five heart transplant recipients with 151 matched coronary segments were selected for the presence of intimal disease progression as detected by serial IVUS examinations 1 to 3 years apart. Intimal disease progression was defined as a > 10% increase in intimal area (IA). IVUS catheter location in follow-up studies was verified angiographically in relation to branch vessels. Luminal area (LA) and total vessel area (TA) were measured at each site. Intimal area (IA = TA-LA) was calculated. Changes in IA (delta IA) and TA (delta TA) between baseline and follow-up IVUS were compared: delta IA, 2.9 +/- 0.2 mm2: delta TA, 2.7 +/- 0.4 mm2. A remodeling index (RI) was defined as RI = delta TA/delta IA. Three subgroups could be distinguished: over compensation (RI > I), partial compensation (RI 0 to 1), and no compensation or shrinkage (RI < or = 0). Seventy-four segments (49%) showed overcompensation, 44 (29%) showed partial compensation, and 33 (22%) showed no compensation or shrinkage.In this study, serial IVUS shows that early after cardiac transplantation, a large proportion of the coronary segments with progression of intimal thickening have compensatory dilation of the vessel wall. However, a substantial number of coronary segments (22%) show no compensatory dilation or shrinkage. The progressive luminal narrowing in transplant patients may be due in part to vessel shrinkage or the lack of compensatory dilation over time.

  View details for Web of Science ID A1997WJ28200021

  View details for PubMedID 9054742

• A forward-viewing intravascular ultrasound catheter suitable for intracoronary use. Biomedical instrumentation & technology Liang, D. H., Hu, B. S. 1997; 31 (1): 45-53

  Abstract

  Current intravascular ultrasound (IVUS) catheters provide a transverse cross-sectional view of the blood vessel, thus limiting their ability to visualize severely stenosed or occluded vessels. Forward-viewing IVUS devices can overcome these limitations. Previously described forward-viewing IVUS catheters are mechanically complex, making them too bulky for use in coronary arteries. A new design for small-forward viewing IVUS catheters was developed. Using this design, flexible 5-Fr (1.6 mm diameter) and 8-Fr (2.6 mm diameter) prototype catheters up to 110 cm long, suitable for intravascular work, were constructed. Imaging of cadaver arterial segments was performed using these prototype catheters. Structures such as branches and plaque and features such as calcium were well seen with these catheters. Correlation of lumen dimensions measured with the IVUS catheters and by histology (HIST) was excellent: IVUS = 1.06 x HIST - 1.45 mm, r2 = 0.98. This new technology holds promise as a tool for guiding intravascular interventions.

  View details for PubMedID 9051225

• Are heart-lung transplant recipients protected from developing transplant coronary artery disease? A case-matched intracoronary ultrasound study CIRCULATION Lim, T. T., Botas, J., Ross, H., Liang, D. H., Theodore, J., Hunt, S. A., Oesterle, S. N., Yeung, A. C. 1996; 94 (7): 1573-1577

  Abstract

  Accelerated coronary artery disease is a major cause of mortality in heart transplant recipients; however, it does not appear to play a major role in the clinical outcome of heart-lung transplant recipients. The purpose of this study was to determine whether the incidence and severity of transplant coronary artery disease as detected by intracoronary ultrasound in heart-lung transplant recipients are less than those encountered in heart transplant recipients.We studied the left anterior descending coronary artery with the use of intracoronary ultrasound imaging in 22 heart-lung transplant recipients at the time of their routine annual coronary angiogram. Twenty-two heart transplant recipients were case matched for number of years after transplant at ultrasound study, recipient age, donor age, and diagnosis of nonischemic cardiomyopathy. Mean intimal area, intimal index, Stanford class, and incidence of at least moderate disease (Stanford class > or = 3) were measured and calculated in each group and then compared between the two groups. Mean intimal area (1.6 +/- 2.5 versus 3.8 +/- 2.8 mm2), mean intimal index (0.07 +/- 0.10 versus 0.22 +/- 0.14), mean Stanford class (1.7 +/- 1.0 versus 2.7 +/- 1.2), and incidence of Stanford class > or = 3 (14% versus 45%) were significantly lower in the heart-lung transplant recipient group.The incidence and severity of transplant coronary artery disease are much less in patients receiving heart-lung transplants than in those receiving heart transplants alone.

  View details for PubMedID 8840846

• Prediction of angiographic disease by intracoronary ultrasonographic findings in heart transplant recipients JOURNAL OF HEART AND LUNG TRANSPLANTATION Liang, D. H., Gao, S. Z., Botas, J., Pinto, F. J., Schroeder, J. S., Alderman, E. L., Yeung, A. C. 1996; 15 (10): 980-987

  Abstract

  Intracoronary ultrasonography has proven to be a more sensitive test than angiography for the detection of intimal thickening in transplant recipients. However, the prognostic significance of the intimal thickening detected by intracoronary ultrasonography has not been proven.During a 1-year period, 70 transplant recipients without angiographically apparent coronary artery disease underwent intracoronary ultrasonography examination. For each intracoronary ultrasonography study an intimal index, defined as the ratio of the plaque area to the area within the media, was measured for the most diseased segment imaged. The subsequent annual follow-up angiograms of these 70 patients were reviewed for the development of visually apparent coronary artery disease. The time since transplantation for the 70 patients without angiographically apparent coronary artery disease ranged from 1 to 15 years, with a mean of 4.2 years an median of 3.9 years. Mean duration of angiographic follow-up was 2.0 years (range 1 to 3 years).Angiographically apparent coronary artery disease developed on follow-up angiograms in 13 of the 70 patients, with a mean time to development of 1.5 years. Four of 46 patients (9%) with an intimal index < 0.3 subsequently had angiographically apparent coronary artery disease, whereas of 25 patients (36%) with an intimal index > or = 0.3 subsequently had angiographically apparent coronary artery disease. Odds ratio for future angiographically apparent coronary artery disease between patients with an intimal index > or = and intimal index < 0.3 was 5.9 (p < 0.01 by Fisher's Exact test). In a subgroup of 22 patients more than 5 years after transplantation at the time of intracoronary ultrasonography, 12 had an intimal index < 0.3 and 10 had an intimal index > or = 0.3. In this subgroup none of the 12 patients with an intimal index < 0.3 had angiographically apparent coronary artery disease and only 1 of the 10 with an intimal index > or = 0.3 had angiographically apparent coronary artery disease (difference not significant).The presence of moderate to severe intimal thickening by intracoronary ultrasonography is predictive of the future development of angiographically apparent coronary artery disease among patients more than 1 year and less than 5 years after transplantation. This same degree of intimal thickening may not carry the same prognostic significance among patients greater than 5 years after transplantation without the development of angiographically apparent coronary artery disease.

  View details for Web of Science ID A1996VT54800003

  View details for PubMedID 8913914

• INFLUENCE OF PREEXISTENT DONOR CORONARY-ARTERY DISEASE ON THE PROGRESSION OF TRANSPLANT VASCULOPATHY - AN INTRAVASCULAR ULTRASOUND STUDY CIRCULATION Botas, J., Pinto, F. J., Chenzbraun, A., Liang, D., SCHRODER, J. S., Oesterle, S. N., Alderman, E. L., Popp, R. L., Yeung, A. C. 1995; 92 (5): 1126-1132

  Abstract

  Transplant vasculopathy (TxCAD) limits longterm survival of allograft recipients. The possibility that preexistent donor coronary disease (PEDD) might accelerate this process is of concern. The serial progression of sites with and without PEDD as assessed by intravascular ultrasonic imaging is explored in this study.Thirty patients with baseline intravascular imaging within 3 weeks of cardiac transplantation who had at least one annual follow-up study were included in this study. Vessel luminal area (LA), total area (TA), intimal index (II = TA - LA/TA), mean intimal thickness (MIT), and Stanford classification were expressed for each image site and for each patient at each study. Progression of sites and of patients with and without PEDD on the baseline study was compared. Patients with PEDD (n = 9) still had significantly more intimal disease than those without PEDD (n = 21) at the first follow-up study (MIT = 0.35 +/- 0.13 versus 0.13 +/- 0.11 mm; II = 0.29 +/- 0.11 versus 0.11 +/- 0.1; class = 3.7 +/- 0.5 versus 2.2 +/- 0.94; P < .001 for all comparisons). However, the increase in intimal thickness during the 1- year interval was not significantly different between the two groups. In 4 patients in whom both types of sites were present, no difference in progression was found. Data were similar for patients and sites studied over > 1 year.PEDD does not accelerate the progression of TxCAD within the first few years after cardiac transplantation. The pathophysiology of TxCAD is most likely immune mediated and does not seem to be accelerated by native coronary artery disease.

  View details for Web of Science ID A1995RR27600012

  View details for PubMedID 7648656

• DOES COMPENSATORY DILATION OCCUR IN HEART-TRANSPLANT RECIPIENTS WITH PROGRESSIVE CORONARY-ARTERY DISEASE - SERIAL STUDIES USING INTRAVASCULAR ULTRASOUND Lim, T. T., Botas, J., Liang, D. H., Schroeder, J. S., Oesterle, S. N., Popp, R. L., Yeung, A. C. LIPPINCOTT WILLIAMS & WILKINS. 1994: 639–39

  View details for Web of Science ID A1994PN41703467

• A METHOD FOR EVALUATING THE SELECTIVITY OF ELECTRODES IMPLANTED FOR NERVE SIMULATION IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING Liang, D. H., Kovacs, G. T., Storment, C. W., White, R. L. 1991; 38 (5): 443-449

  Abstract

  The scale of stimulating electrodes possible for use in functional electrical stimulation to restore motor and sensory function is rapidly approaching that of individual neurons. Although the electrodes may approach the dimensions of single nerve cells, it is unclear if the region of excitation elicited by each electrode will be correspondingly small. Previous techniques for evaluating this have either been tedious or have lacked the resolution necessary. This paper describes a method that uses the refractory interaction of the compound action potentials elicited by a stimulus pulse pair, along with high-resolution recording of those potentials, to achieve measurements of the selectivity of stimulation down to the scale of a few axon diameters. The feasibility of this technique is demonstrated in sciatic nerves of frogs (Rana Catesbiana) acutely implanted with a sapphire electrode array.

  View details for Web of Science ID A1991FP65500007

  View details for PubMedID 1874526

• STANFORD-UNIVERSITY GENERAL-PURPOSE MICROELECTRODE FABRICATION PROCESS 1989 ANNUAL INTERNATIONAL CONF OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOC Kovacs, G. T., Storment, C. W., Liang, D. H., White, R. L., Rosen, J. M. I E E E. 1988: 1651–1652

  View details for Web of Science ID A1988BP88P00850