The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Ali N. Azadani - One of the best experts on this subject based on the ideXlab platform.
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Blood Stasis on Transcatheter Valve Leaflets and Implications for Valve-in-Valve Leaflet Thrombosis.
The Annals of thoracic surgery, 2017Co-Authors: Koohyar Vahidkhah, Danny Dvir, Shahnaz Javani, Mostafa Abbasi, Peyman N. Azadani, Anwar Tandar, Ali N. AzadaniAbstract:Leaflet thrombosis after valve-in-valve (ViV) procedure has been increasingly recognized. This study aimed to investigate the flow dynamics aspect of Leaflet thrombosis by quantifying the blood stasis on the noncoronary and coronary Leaflets of a surgical aortic valve (SAV) and a transcatheter aortic valve (TAV) in a ViV setting. Two computational models, representing a SAV and a TAV in ViV setting, were developed in a patient-specific geometry. Three-dimensional flow fields were obtained through a fluid-solid interaction modeling approach to study the difference in blood residence time (BRT) on the coronary and noncoronary Leaflets. Longer BRT was observed on the TAV Leaflets compared with the SAV, specifically near the Leaflet fixed boundary. Particularly, at the end of diastole, the areas of high BRT (≥1.2 seconds) on the surface of the TAV model Leaflets were four times larger than those of the SAV model. The distribution of BRT on the three Leaflets exhibited a similar pattern in the model for the TAV in ViV setting. That was in contrast to the SAV model where large areas of high BRT were observed on the noncoronary Leaflet. Geometric confinement of the TAV by the Leaflets and the frame of the degenerated bioprosthesis that circumferentially surround the TAV stent increases the BRT on the Leaflets, which may act as a permissive factor in the TAV Leaflet thrombosis after ViV procedure. A similar distribution pattern of BRT observed on the TAV Leaflets may explain the similar rate of occurrence of thrombosis on the three Leaflets. Copyright © 2017 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.
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Leaflet stress and strain distributions following incomplete transcatheter aortic valve expansion
Journal of Biomechanics, 2015Co-Authors: Mostafa Abbasi, Ali N. AzadaniAbstract:Transcatheter aortic valve replacement (TAVR) is an established treatment alternative to surgical valve replacement in high-risk patients with severe symptomatic aortic stenosis. The current guidelines for TAVR are to upsize transcatheter aortic valve (TAV) relative to the native annulus to secure the device and minimize paravalvular leakage. Unlike surgical stented bioprosthetic valves where Leaflets are attached to a rigid frame, TAVs must expand to fit within the native annulus. Fully-expanded circular TAVs have consistent Leaflet kinematics; however, subtle variations in the degree of stent expansion may affect Leaflet coaptation. The objective of this study was to determine the impact of incomplete TAV expansion on Leaflet stress and strain distributions. In this study, we developed finite element models of a 23 mm homemade TAV expanded to diameters ranging from 18 to 23 mm in 1mm increments. Through dynamic finite element simulations, we found that Leaflet stress and strain distributions were dependent on the diameter of the inflated TAV. After complete expansion of the TAV to 23 mm, high stress and strain regions were observed primarily in the commissures during diastole. However, 2-3mm incomplete TAV stent expansion induced localized high stress regions within the TAV commissures, while 4-5mm incomplete stent expansion induced localized high stress regions within the belly of the TAV Leaflets during the diastolic phase of the cardiac cycle. Increased mechanical stress and flexural deformation on TAV Leaflets due to incomplete stent expansion may lead to accelerated tissue degeneration and diminished long-term valve durability.
Robert A Levine - One of the best experts on this subject based on the ideXlab platform.
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saddle shaped mitral valve annuloplasty rings improve Leaflet coaptation geometry
The Journal of Thoracic and Cardiovascular Surgery, 2011Co-Authors: Morten O Jensen, Henrik Jensen, Robert A Levine, Ajit P Yoganathan, Niels Trolle Andersen, Hans Nygaard, Michael J Hasenkam, Sten Lyager NielsenAbstract:Objectives The mitral valve annulus naturally conforms to a saddle shape in systole. This configuration is believed to put the Leaflets into a lower-energy equilibrium with the annulus and subvalvular apparatus. Conventional flat annuloplasty rings restrict posterior Leaflet motion, which may result in a "monocusp" valve, affecting valvular stress distribution. It is hypothesized that saddle-shaped annuloplasty rings cause less distortion of the physiologic Leaflet geometry than do flat rings. Methods Twelve pigs were studied in an acute setting with 3-dimensional echocardiography and sonomicrometry before and after implantation of rigid flat (n = 5) and saddle-shaped (n = 7) annuloplasty rings. The rings were true sized to the annulus with equal anterior–posterior and commissure–commissure circumferential dimensions. The saddle-shaped rings had an annular height to commissural width ratio of 15%. Results Saddle-shaped rings maintained both Leaflets operational ( P P Conclusions Saddle-shaped annuloplasty rings provide better Leaflet coaptation geometry than do flat rings by not hoisting the papillary muscles toward the posterior annulus through the commissural chordae, allowing greater Leaflet mobility. This entails a potentially beneficial impact on valvular stress distribution that could affect durability of the repaired valve.
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mitral Leaflet adaptation to ventricular remodeling prospective changes in a model of ischemic mitral regurgitation
Circulation, 2009Co-Authors: Miguel Chaput, Mark D Handschumacher, Luis J Guerrero, Godtfred Holmvang, Jacob P Dalbianco, Suzanne Sullivan, Gus J Vlahakes, Judy Hung, Robert A LevineAbstract:Background— Functional mitral regurgitation (MR) is caused by systolic traction on the mitral Leaflets related to ventricular distortion. Little is known about whether chronic tethering causes the mitral Leaflet area to adapt to the geometric needs imposed by tethering, in part because of inability to reconstruct Leaflet area in vivo. Our aim was to explore whether adaptive increases in Leaflet area occur in patients with functional MR compared with normal subjects and to test the hypothesis that Leaflet area influences MR severity. Methods and Results— A new method for 3-dimensional echocardiographic measurement of mitral Leaflet area was developed and validated in vivo against 15 sheep heart valves, later excised. This method was then applied in 80 consecutive patients from 3 groups: patients with normal hearts by echocardiography (n=20), patients with functional MR caused by isolated inferior wall-motion abnormality or dilated cardiomyopathy (n=29), and patients with inferior wall-motion abnormality or...
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integrated mechanism for functional mitral regurgitation Leaflet restriction versus coapting force in vitro studies
Circulation, 1996Co-Authors: Arnold A Fontaine, Ajit P Yoganathan, Ehud Schwammenthal, Robert A LevineAbstract:Background Functional mitral regurgitation in patients with ischemic or dilated ventricles has been related to competing factors: altered tension on the Leaflets due to displacement of their papillary muscle and annular attachments, which restricts Leaflet closure, versus global ventricular dysfunction with reduced transmitral pressure to close the Leaflets. In vivo, however, geometric changes accompany dysfunction, making it difficult to study these factors independently. Functional mitral regurgitation also paradoxically decreases in midsystole, despite peak transmitral driving pressure, suggesting a change in the force balance acting to create a regurgitant orifice, with rising transmitral pressure counteracting forces that restrict Leaflet closure. In vivo, this mechanism cannot be tested independently of annular contraction that could also reduce midsystolic regurgitation. Methods and Results An in vitro model was developed that allows independent variation of papillary muscle position, annular size,...
John E Mayer - One of the best experts on this subject based on the ideXlab platform.
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tissue engineered heart valves autologous valve Leaflet replacement study in a lamb model
Circulation, 1996Co-Authors: Toshiharu Shinoka, Peter X, Dominique Shumtim, Christopher K Breuer, Robert A Cusick, Gregor Zund, Robert Langer, Joseph P Vacanti, John E MayerAbstract:Background We have previously reported the successful creation of tissue-engineered valve Leaflets and the implantation of these autologous tissue Leaflets in the pulmonary valve position. This study was designed to trace cultured cells that were seeded onto a biodegradable polymer with the use of a 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (Di-I) cell-labeling method. We also examined the time-related biochemical, biomechanical, and histological characteristics and evolution of these tissue constructs. Methods and Results Mixed cell populations of endothelial cells and fibroblasts were isolated from explanted ovine arteries. Endothelial cells were selectively labeled with an acetylated low-density lipoprotein marker and separated from fibroblasts with the use of a fluorescence-activated cell sorter. A synthetic biodegradable scaffold consisting of polyglycolic acid fibers was seeded first with fibroblasts, then coated with endothelial cells. Using these methods, we implanted autologous cell/polymer constructs in six animals. In two additional control animals, a Leaflet of polymer was implanted without prior cell seeding. In each animal, cardiopulmonary bypass was used to completely resect the right posterior Leaflet of the pulmonary valve and replace it with an engineered valve Leaflet with (n=6) or without (n=2) prior cultured cell seeding. The animals were killed either after 6 hours or after 1, 6, 7, 9, or 11 weeks, and the implanted valve Leaflets were examined histologically, biochemically, and biomechanically. 4-Hydroxyproline assays were performed to determine collagen content. Leaflet strength was evaluated in vitro with a mechanical tester. Factor VIII and elastin stains were done to verify histologically that endothelial cells and elastin, respectively, were present. Animals receiving Leaflets made from polymers without cell seeding were killed and examined in a similar fashion after 8 weeks. In the control animals, the acellular polymer Leaflets were completely degraded, with no residual Leaflet tissue at 8 weeks. The tissue-engineered valve Leaflet persisted in each animal in the experimental group. 4-Hydroxyproline analysis of the constructs showed a progressive increase in collagen content. Immunohistochemical staining demonstrated elastin fibers in the matrix and factor VIII on the surface of the Leaflet. The cell-labeling experiments demonstrated that the cells on the Leaflets had persisted from the in vitro seeding of the Leaflets. Conclusions In the tissue-engineered heart valve Leaflet, transplanted autologous cells generated a proper matrix on the polymer scaffold in a physiological environment at a period of 8 weeks after implantation.
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tissue engineering heart valves valve Leaflet replacement study in a lamb model
The Annals of Thoracic Surgery, 1995Co-Authors: Toshiharu Shinoka, Peter X, Christopher K Breuer, Gregor Zund, Robert Langer, Joseph P Vacanti, Ronn E Tanel, Takuya Miura, John E MayerAbstract:Background Valve replacements using either bioprosthetic or mechanical valves have the disadvantage that these structures are unable to grow, repair, or remodel and are both thrombogenic and susceptible to infection. These characteristics have significantly limited their durability and longevity. In an attempt to begin to overcome these shortcomings, we have tested the feasibility of constructing heart valve Leaflets in lambs by seeding a synthetic polyglycolic acid fiber matrix in vitro with fibroblasts and endothelial cells. Methods Mixed cell populations of endothelial cells and fibroblasts were isolated from explanted ovine arteries. Endothelial cells were selectively labeled with an acetylated low-density lipoprotein marker and separated from the fibroblasts using a fluorescent activated cell sorter. A synthetic biodegradable scaffold constructed from polyglycolic acid fibers was seeded with fibroblasts, which grew to form a tissue-like sheet. This tissue was subsequently seeded with endothelial cells, which formed a cellular monolayer coating around the Leaflet. Using these constructs, autologous (n = 3) and allogenic (n = 4) tissue engineered Leaflets were implanted in 7 animals. In each animal the right posterior Leaflet of the pulmonary valve was resected and replaced with an engineered valve Leaflet. Results All animals survived the procedure. Postoperative echocardiography demonstrated no evidence of stenosis and trivial pulmonary regurgitation in the autografts and moderate regurgitation in the allogenic valves. Collagen analysis of the constructs showed development of an extracellular matrix. Histologic evaluation of the constructs demonstrated appropriate cellular architecture. Conclusions This preliminary experiment showed that a tissue engineered valve Leaflet constructed from its cellular components can function in the pulmonary valve position. Tissue engineering of a heart valve Leaflet is feasible, and these preliminary studies suggest that autograft tissue will probably be superior to allogenic tissue.
Kok Meng John Chan - One of the best experts on this subject based on the ideXlab platform.
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tricuspid Leaflet augmentation to address severe tethering in functional tricuspid regurgitation
European Journal of Cardio-Thoracic Surgery, 2008Co-Authors: Gilles D Dreyfus, Shahzad G Raja, Kok Meng John ChanAbstract:This paper describes a technique for treating severe tricuspid regurgitation due to severe tethering of the tricuspid valve Leaflets. The anterior tricuspid Leaflet is augmented by use of an autologous pericardial patch, which increases its size, and hence its surface area of coaptation, allowing increased Leaflet coaptation to occur with reduced tension within the right ventricle. A Carpentier-Edwards annuloplasty ring is then implanted. We have successfully performed this operation in 15 patients with severe tricuspid regurgitation due to severe Leaflet tethering and have achieved complete elimination of tricuspid regurgitation with good coaptation of the tricuspid Leaflets. We describe this simple and easily reproducible technique to treat severe tricuspid regurgitation due to tethering of the tricuspid valve Leaflets.
D Craig Miller - One of the best experts on this subject based on the ideXlab platform.
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Evidence of adaptive mitral Leaflet growth
Journal of the mechanical behavior of biomedical materials, 2012Co-Authors: Manuel K. Rausch, D Craig Miller, Frederick A. Tibayan, Ellen KuhlAbstract:Ischemic mitral regurgitation is mitral insufficiency caused by myocardial infarction. Recent studies suggest that mitral Leaflets have the potential to grow and reduce the degree of regurgitation. Leaflet growth has been associated with papillary muscle displacement, but role of annular dilation in Leaflet growth is unclear. We tested the hypothesis that chronic Leaflet stretch, induced by papillary muscle tethering and annular dilation, triggers chronic Leaflet growth. To decipher the mechanisms that drive the growth process, we further quantified regional and directional variations of growth. Five adult sheep underwent coronary snare and marker placement on the left ventricle, papillary muscles, mitral annulus, and mitral Leaflet. After eight days, we tightened the snares to create inferior myocardial infarction. We recorded marker coordinates at baseline, acutely (immediately post-infarction), and chronically (five weeks post-infarction). From these coordinates, we calculated acute and chronic changes in ventricular, papillary muscle, and annular geometry along with acute and chronic Leaflet strains. Chronic left ventricular dilation of 17.15% (p
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Mitral Leaflet remodeling in dilated cardiomyopathy.
Circulation, 2006Co-Authors: Tomasz A. Timek, David T Lai, Paul Dagum, David Liang, George T Daughters, Neil B Ingels, D Craig MillerAbstract: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.
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Mitral Leaflet Remodeling in Dilated Cardiomyopathy
Circulation, 2006Co-Authors: Tomasz A. Timek, David T Lai, Paul Dagum, David Liang, George T Daughters, Neil B Ingels, D Craig MillerAbstract:Background— 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. Methods and Results— 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 S 1 to S 4 and 2 on the posterior Leaflet (PML) forming 2 distinct segments S 5 and S 6 . 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 4 lengthened by 23±17% and S 5 by 24±18%; P Conclusion— 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.
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Influence of anterior mitral Leaflet second-order chordae on Leaflet dynamics and valve competence
The Annals of thoracic surgery, 2001Co-Authors: Tomasz A. Timek, Paul Dagum, George T Daughters, Neil B Ingels, Sten Lyager Nielsen, G.randall Green, Ann F. Bolger, J. Michael Hasenkam, D Craig MillerAbstract:Chordal transposition is used in mitral valve repair, yet the effects of second-order chord transection on valve function have not been extensively studied. We evaluated Leaflet coaptation, three-dimensional anterior mitral valve Leaflet shape, and valve competence after cutting anterior second-order chordae. In 8 sheep radiopaque markers were affixed to the left ventricle, mitral annulus, and Leaflets. Animals were studied immediately with biplane videofluoroscopy and echocardiography before (Control) and after (Cut2) severing two anterior second-order "strut" chordae. Leaflet coaptation was assessed as separation between Leaflet edge markers in the midLeaflet and near each commissure (anterior commissure, posterior commissure). Anterior Leaflet geometry was determined 100 milliseconds after end-diastole from three-dimensional coordinates of 13 markers. Anterior Leaflet geometry changed only slightly after chordal transection without inducing mitral regurgitation. Leaflet coaptation times were 79+/-17 and 87+/-22 milliseconds at the anterior commissure; 72+/-21, 72+/-19 milliseconds at midLeaflet, and 71+/-12 and 75+/-8 milliseconds at the posterior commissure (p = NS) for Control and Cut2, respectively. Cutting anterior second-order chordae did not cause delayed Leaflet coaptation, alter Leaflet shape, or create mitral regurgitation. These data indicate that transposition of second-order anterior chordae ("strut" chordae) is not deleterious to anterior Leaflet motion per se.
