Gao Ran, Liang Fuyou
School of Naval Architecture, Ocean & Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, P.R.China.
Sheng Wu Yi Xue Gong Cheng Xue Za Zhi. 2020 Dec 25;37(6):983-989. doi: 10.7507/1001-5515.202009070.
External support stent is a potential means for restricting the deformation and reducing wall stress of the vein graft, thereby improving the long-term patency of the graft in coronary artery bypass surgery. However, there still lacks a theoretical reference for choosing the size of stent based on the diameter of graft. Taking the VEST (venous external support) stent currently used in the clinical practice as the object of study, we constructed three models of VEST stents with different diameters and coupled them respectively to a model of the great saphenous vein graft, and numerically simulated the expansion-contraction process of the vein graft under the constraint of the stents to quantitatively evaluate the influence of stent size on the radial deformation and wall stress of the vein graft. The results showed that while the stent with a small diameter had a high restrictive effect in comparison with larger stents, it led to more severe concentration of wall stress and sharper changes in radial deformation along the axis of the graft, which may have adverse influence on the graft. In order to solve the aforementioned problems, we ameliorated the design of the stent by means of changing the cross-sectional shape of the thick and thin alloy wires from circle into rectangle and square, respectively, while keeping the cross-sectional areas of alloy wires and stent topology unchanged. Further numerical simulations demonstrated that the ameliorated stent evidently reduced the degrees of wall stress concentration and abrupt changes in radial deformation, which may help improve the biomechanical environment of the graft while maintaining the restrictive role of the stent.
体外支撑支架是限制静脉移植物变形和降低血管壁应力的一种潜在手段，从而可提高冠状动脉旁路移植术中移植物的长期通畅率。然而，目前仍缺乏基于移植物直径选择支架尺寸的理论参考。以目前临床实践中使用的VEST（静脉体外支撑）支架为研究对象，构建了三种不同直径的VEST支架模型，并分别将它们与大隐静脉移植物模型耦合，对支架约束下静脉移植物的扩张-收缩过程进行数值模拟，以定量评估支架尺寸对静脉移植物径向变形和血管壁应力的影响。结果表明，与较大直径的支架相比，小直径支架虽然具有较高的限制作用，但会导致血管壁应力更严重的集中以及沿移植物轴线的径向变形更急剧的变化，这可能会对移植物产生不利影响。为了解决上述问题，我们在保持合金丝横截面积和支架拓扑结构不变的情况下，通过将粗细合金丝的横截面形状分别从圆形改为矩形和正方形的方式对支架设计进行了改进。进一步的数值模拟表明，改进后的支架明显降低了血管壁应力集中程度和径向变形的突变，这在保持支架限制作用的同时可能有助于改善移植物的生物力学环境。
