Bailey Jonathon, Curzen Nick, Bressloff Neil W
Computational Engineering and Design Group, Faculty of Engineering and the Environment, University of Southampton, Southampton, UK.
Southampton University Hospitals NHS Trust, Southampton, UK; Faculty of Medicine, University of Southampton, Southampton, UK.
J Biomech. 2017 Feb 28;53:22-28. doi: 10.1016/j.jbiomech.2016.12.031. Epub 2016 Dec 29.
TAVI devices are manufactured with cylindrical frames. However, the frames are rarely cylindrical post-deployment since deformation due to localised under expansion can be induced by calcified material on the native valve leaflets exerting irregular forces upon the frame. Consequently, the leaflets within a deformed TAVI device may undergo elevated stress during operation, which may lead to premature device failure. Using computational analysis a complete TAVI device model was simulated undergoing deployment into an aortic root model derived from CT data for a patient with severe calcific aortic stenosis, followed by a pressure simulated cardiac cycle. The complete analysis was performed eight times, each with the device at a different rotational orientation relative to the native valve, with an increment spacing of 15°. The TAVI device frames consistently featured significant distortions associated with bulky calcified material at the base of the non-coronary sinus. It was found that the average von Mises stress in the prosthetic valves was only increased in one of the cases relative to an idealised device. However, the maximum von Mises stress in the prosthetic valves was elevated in the majority of the cases. Furthermore, it was found that there were preferable orientations to deploy the prosthetic device, in this case, when the prosthetic leaflets were aligned with the native leaflets. As device orientation deviated from this orientation, the stresses in the valve increased because the distance between the prosthetic commissures decreased. This potentially could represent a sufficient increase in stress to induce variation in device lifespan.
经导管主动脉瓣植入术（TAVI）设备是采用圆柱形框架制造的。然而，由于天然瓣膜小叶上的钙化物质会对框架施加不规则力，从而导致局部扩张不足引起变形，这些框架在植入后很少是圆柱形的。因此，变形的TAVI设备内的小叶在手术过程中可能会承受更高的应力，这可能会导致设备过早失效。利用计算分析，对一个完整的TAVI设备模型进行了模拟，该模型被植入到一个从患有严重钙化性主动脉瓣狭窄患者的CT数据中导出的主动脉根部模型中，随后进行了模拟心脏周期的压力测试。完整的分析进行了八次，每次设备相对于天然瓣膜处于不同的旋转方向，增量间距为15°。TAVI设备框架始终呈现出与无冠状动脉窦底部大量钙化物质相关的明显变形。结果发现，与理想化设备相比，只有一种情况下人工瓣膜中的平均冯·米塞斯应力有所增加。然而，在大多数情况下，人工瓣膜中的最大冯·米塞斯应力有所升高。此外，还发现存在植入人工设备的优选方向，在这种情况下，当人工小叶与天然小叶对齐时。随着设备方向偏离该方向，瓣膜中的应力会增加，因为人工瓣叶连合之间的距离减小。这可能意味着应力的充分增加，从而导致设备寿命的变化。
