Cardiovascular Mechanics Laboratory, Department of Mechanical Engineering, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
Division of Applied Mechanics (DAM), Office of Science and Engineering Laboratories (OSEL), Center for Devices and Radiological Health (CDRH), Food and Drug Administration (FDA), Silver Spring, MD 20993.
J Biomech Eng. 2020 Jan 1;142(1). doi: 10.1115/1.4044235.
Transcatheter aortic valves (TAV) are symmetrically designed, but they are often not deployed inside cylindrical conduits with circular cross-sectional areas. Many TAV patients have heavily calcified aortic valves, which often result in deformed prosthesis geometries after deployment. We investigated the effects of deformed valve annulus configurations on a surgical bioprosthetic valve as a model for TAV. We studied valve leaflet motions, stresses and strains, and analog hydrodynamic measures (using geometric methods), via finite element (FE) modeling. Two categories of annular deformations were created to approximate clinical observations: (1) noncircular annulus with valve area conserved, and (2) under-expansion (reduced area) compared to circular annulus. We found that under-expansion had more impact on increasing stenosis (with geometric orifice area metrics) than noncircularity, and that noncircularity had more impact on increasing regurgitation (with regurgitation orifice area metrics) than under-expansion. We found durability predictors (stress/strain) to be the highest in the commissure regions of noncircular configurations such as EllipMajor (noncircular and under-expansion areas). Other clinically relevant performance aspects such as leaflet kinematics and coaptation were also investigated with the noncircular configurations. This study provides a framework for choosing the most challenging TAV deformations for acute and long-term valve performance in the design and testing phase of device development.
经导管主动脉瓣（TAV）为对称设计，但在具有圆形横截面积的圆柱形导管内通常无法展开。许多 TAV 患者的主动脉瓣严重钙化，这常常导致在展开后假体几何形状变形。我们研究了变形瓣环构型对手术生物瓣的影响，将其作为 TAV 的模型。我们通过有限元（FE）建模研究了瓣叶运动、应力和应变以及模拟的流体动力措施（使用几何方法）。创建了两类环形变形来近似临床观察结果：（1）瓣口面积保持不变的非圆形环，以及（2）与圆形环相比扩张不足（面积减小）。我们发现，与非圆形相比，扩张不足对增加狭窄（使用几何瓣口面积度量）的影响更大，而非圆形对增加反流（使用反流瓣口面积度量）的影响大于扩张不足。我们发现，在非圆形构型（如 EllipMajor，非圆形和扩张不足区域）的交界处区域，耐用性预测因子（应力/应变）最高。还研究了其他与临床相关的性能方面，如瓣叶运动学和对合。这项研究为在器械开发的设计和测试阶段选择最具挑战性的 TAV 变形以用于急性和长期瓣膜性能提供了框架。
