School of Engineering Sciences, University of Southampton, Southampton SO17 1BJ, UK.
Ann Biomed Eng. 2010 May;38(5):1893-907. doi: 10.1007/s10439-010-9962-0. Epub 2010 Feb 23.
The design of coronary stents has evolved significantly over the past two decades. However, they still face the problem of in-stent restenosis, formation of neointima within 12 months of the implant. The biological response after stent implantation depends on various factors including the stent geometry which alters the hemodynamics. This study takes five different coronary stent designs, used in clinical practice, and explores the hemodynamic differences arising due to the difference in their design. Of particular interest is the design of the segments (connectors) that connect two struts. Pulsatile blood flow analysis is performed for each stent, using 3-D computational fluid dynamics (CFD), and various flow features viz. recirculation zones, velocity profiles, wall shear stress (WSS) patterns, and oscillatory shear indices are extracted for comparison. Vessel wall regions with abnormal flow features, particularly low, reverse, and oscillating WSS, are usually more susceptible to restenosis. Unlike previous studies, which have tried to study the effect of design parameters such as strut thickness and strut spacing on hemodynamics, this work investigates the differences in the flow arising purely due to differences in stent-shape, other parameters being similar. Two factors, the length of the connectors in the cross-flow direction and their alignment with the main flow, are found to affect the hemodynamic performance. This study also formulates a design index (varying from 18.81% to 24.91% for stents used in this study) that quantifies the flow features that could affect restenosis rates and which, in future, could be used for optimization studies.
在过去的二十年中，冠状动脉支架的设计有了显著的发展。然而，它们仍然面临着支架内再狭窄的问题，即在植入后 12 个月内形成新生内膜。支架植入后的生物反应取决于各种因素，包括改变血液动力学的支架几何形状。本研究采用了五种不同的临床应用的冠状动脉支架设计，探讨了由于设计差异而产生的血液动力学差异。特别感兴趣的是连接两个支柱的段（连接）的设计。使用三维计算流体动力学（CFD）对每个支架进行脉动血流分析，并提取各种流动特征，如再循环区、速度剖面、壁切应力（WSS）模式和振荡剪切指数进行比较。具有异常流动特征的血管壁区域，特别是低、反向和振荡 WSS，通常更容易发生再狭窄。与之前试图研究支架厚度和支架间距等设计参数对血液动力学影响的研究不同，这项工作纯粹是由于支架形状的差异而研究了流动的差异，其他参数相似。两个因素，即横流方向上连接器的长度及其与主流的对准，被发现会影响血液动力学性能。本研究还提出了一个设计指数（本研究中使用的支架从 18.81%到 24.91%不等），该指数量化了可能影响再狭窄率的流动特征，未来可用于优化研究。
