The geometric confinement of TAV by the failed bioprosthesis or the calcified native valve increases the BRT on the TAV leaflets. This may act as a permissive factor in valve thrombosis.
Mechanical properties of the cardiac tissue play an important role in normal heart function. The goal of this study was to determine the passive mechanical properties of all heart chambers through a paired comparison study in an ovine model. Ovine heart was used due its physiological and anatomical similarities to human heart. A total of 189 specimens from anterior and posterior portions of the left and right ventricles, atria, and appendages underwent biaxial mechanical testing. A Fung-type strain energy function was used to fit the experimental data. Tissue behavior was quantified based on the magnitude of strain energy, as indicator of tissue stiffness, at equibiaxial strains of 0.10, 0.15, and 0.20. Statistical analysis revealed no significant difference in strain energy storage between anterior and posterior portions of each chamber, except for the right ventricle where strain energy storage in the posterior specimens were higher than the anterior specimens. Additionally, all chambers from the left side of the heart had significantly higher strain energy storage than the corresponding chambers on the right side. Furthermore, the highest to lowest stored strain energy were associated with ventricles, appendages, and atria, respectively. Microstructure of tissue specimens from different chambers was also compared using histology.
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.
BACKGROUND Formation of leaflet thrombosis following transcatheter aortic valve replacement (TAVR) has been increasingly recognized. However, the underlying mechanisms have remained unclear. This study aimed to shed light on such mechanisms from a fluid mechanics standpoint via quantification of blood residence time (BRT) on the transcatheter aortic valve (TAV) leaflets.METHODS Unlike surgical bioprostheses, the aortic portion of the TAV frame is circumferentially surrounded by calcified leaflets in TAVR, or by degenerated bioprostheses in valve-in-valve setting ( Figure 1). Two computational models representing a surgical bioprosthesis and a TAV were developed. 3D flow fields were obtained via a one-way fluidsolid interaction modeling approach validated by experimental testing. Subsequently, a particle tracking procedure was applied to calculate BRT on the valve leaflets. Finally, statistical analysis was performed to compare the BRT values in the two models.
RESULTSSignificantly larger values of BRT on the leaflets were obtained for the TAV than the surgical bioprosthesis ( Figure 1). During forward flow, the mean value of BRT was 35% higher in the TAV compared to the surgical bioprosthesis (p<0.0001). During diastole, from end of closing to mid-diastole and mid-diastole to systole, BRT was longer for the TAVR model by 139% and 24%, respectively (p<0.0005).CONCLUSION TAVR, as opposed to surgical valve replacement, may alter the natural flow field around the leaflets. The geometric confinement of the TAV increases the BRT on the TAV leaflets. The increased BRT may act as a permissive factor for thrombogenesis.BACKGROUND Valve-in-valve (ViV) transcatheter aortic implantation (TAVI) is an alternative to repeat open heart surgery for patients with a failing aortic bioprosthesis. Unlike degenerate stented aortic bioprostheses, failing stentless bioprostheses lack anatomic markers which may complicate ViV-TAVI. We sought to compare clinical outcomes after ViV-TAVI in stentless versus stented bioprostheses using a large global registry.
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