Leaflet stresses during crimping simulations of a CoreValve Evolut Pro model using a compression loading system

Oguz C. Eren , Neil W. Bressloff
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Abstract

Background: Transcatheter aortic valve implantation is experiencing continued growth as an option for the treatment of aortic stenosis. With larger numbers of procedures being performed on lower risk and younger patients, there is increased scrutiny on valve durability. Leaflet stresses and potential damage have a significant role to play in this regard. Predictions of leaflet stresses have so far focused on either fluid-structure interaction simulations of blood flow through the prosthesis or, crimping simulations using a cylindrical surface. However, in reality, when a compression loading system (CLS) is used in the crimping of self-expanding valves, this could result in different stresses in the valve leaflets relative to those that might occur in crimping with a cylindrical surface.

Method: A full model of a CoreValve Evolut Pro (Medtronic, Minneapolis, MN, USA) device was developed, comprising the frame, skirt and leaflets along with a representative model for the CLS as used in clinical practice. The full device was crimped to a final diameter of 18 Fr using the CLS model and the distribution and intensity of leaflet stresses was assessed. A similar assessment of leaflet stresses was also performed for crimping using radial displacement of a cylindrical surface. Comparison of the predicted leaflet stresses between the two models was undertaken, alongside a comparison of the stresses produced when dynamically loading the leaflets after deployment of the valve.

Results: Both the CLS and cylinder crimping methods produced higher average and peak stresses on the leaflets compared to those produced during leaflet loading. The peak von Mises stresses for CLS crimping, cylinder crimping, and leaflet loading were 3.42 MPa, 3.92 MPa, and 1.77 MPa respectively. The leaflet folding pattern between the CLS crimping and cylinder crimping methods were different, resulting in different high stress locations on the leaflets. However, the average stress magnitude at the final crimped stage between the two crimping methods were similar.

Conclusions: High fidelity simulations of crimping and expansion of a complete CoreValve Evolut Pro model using a compression loading system model have been performed, wherein the results showed that peak leaflet stresses in the crimped valve were approximately twice as high as the maximum leaflet stresses under dynamic loading. This finding has significant implications for device durability due to the high stresses and possible damage they might inflict on the leaflets. It was also found that crimping using a compression loading system versus a simpler cylindrical surface produced different folding patterns and stress distributions. However, for future studies that are not concerned with accurately capturing the leaflet folding patterns and stresses throughout the crimping process, crimping via a cylindrical surface can be used instead of simulating the full CLS model.

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使用压缩加载系统模拟 CoreValve Evolut Pro 模型卷曲过程中的瓣叶应力
背景:作为治疗主动脉瓣狭窄的一种选择,经导管主动脉瓣植入术正在经历持续增长。随着越来越多的低风险和年轻患者接受手术,对瓣膜耐久性的审查也越来越严格。瓣叶应力和潜在损伤在这方面起着重要作用。迄今为止,对瓣叶应力的预测主要集中在对流经假体的血流进行流体-结构相互作用模拟,或使用圆柱表面进行卷曲模拟。然而,在现实中,当压缩加载系统(CLS)用于自扩张瓣膜的卷曲时,可能会导致瓣叶应力不同于圆柱表面卷曲时的应力:开发了 CoreValve Evolut Pro(美敦力,美国明尼苏达州明尼阿波利斯市)装置的完整模型,包括框架、裙边和瓣叶,以及临床实践中使用的 CLS 代表模型。使用 CLS 模型将整个装置卷曲到 18 Fr 的最终直径,并评估瓣叶应力的分布和强度。在使用圆柱表面径向位移进行卷曲时,也对瓣叶应力进行了类似的评估。对两种模型预测的瓣叶应力进行了比较,同时还对瓣膜展开后对瓣叶进行动态加载时产生的应力进行了比较:与瓣叶加载时产生的应力相比,CLS 和气缸压接法产生的瓣叶平均应力和峰值应力都更高。CLS 卷边、气缸卷边和瓣叶加载的峰值 von Mises 应力分别为 3.42 兆帕、3.92 兆帕和 1.77 兆帕。CLS 压边法和圆柱压边法的小叶折叠模式不同,导致小叶上的高应力位置也不同。然而,两种卷边方法在最后卷边阶段的平均应力大小相似:使用压缩加载系统模型对完整的 CoreValve Evolut Pro 模型的卷曲和扩张进行了高保真模拟,结果显示卷曲瓣膜的瓣叶应力峰值大约是动态加载下最大瓣叶应力的两倍。由于高应力及其可能对瓣叶造成的损坏,这一发现对设备的耐用性有重大影响。研究还发现,使用压缩加载系统卷曲与使用简单的圆柱表面卷曲会产生不同的折叠模式和应力分布。不过,在未来的研究中,如果不需要准确捕捉整个卷曲过程中的小叶折叠模式和应力,则可以使用圆柱面卷曲,而不是模拟完整的 CLS 模型。
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来源期刊
Biomedical engineering advances
Biomedical engineering advances Bioengineering, Biomedical Engineering
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