Department of Information Engineering and Mathematical Methods, University of Bergamo, Italy.
Artif Organs. 2012 Apr;36(4):368-78. doi: 10.1111/j.1525-1594.2011.01356.x. Epub 2011 Oct 14.
Bicuspid aortic valve (BAV) predisposes to aortic aneurysms with a high prevalence. A first hypothesis for this phenomenon is related to fibrillin deficiency (genetic hypothesis). The present article focused on a complementary, hemodynamic hypothesis stating that it is the peculiar fluid dynamics of blood in the ascending aorta of patients with BAV configurations that leads to aneurysm formation. To corroborate this hypothesis, a parametric study was performed based on numerical simulations of ascending aorta hemodynamics with different configurations of orifice area and valve orientation. The resulting wall shear stress (WSS) distributions and degree of asymmetry of the blood jet were investigated, and surrogate indices introduced. The results showed that WSS was more pronounced in subjects with BAV morphologies, also in the nonstenotic case. In particular, a maximum WSS of 3Pa was found (vs. 1.5Pa in subjects with a tricuspid configuration). It is localized at the mid-ascending aorta, the segment more prone to dilate as shown by the index related to maximum WSS (0.869 in BAV vs. 0.322 in tricuspid). Moreover, the asymmetry of the blood flow was found larger for decreasing valve area, the related index at mid-ascending aorta being more than three times higher than that found for tricuspid configuration (0.70 vs. 0.20). Further, WSS and flow asymmetry were higher also at the sinus of Valsalva and sinotubolar junction for a latero-lateral (LL) BAV configuration in keeping with the clinical observation on association between BAV configurations and different aortic aneurysm morphology. These findings may help explain the higher risk of aneurysm formation in BAV patients. The proposed indices will require validation prior to application in clinical settings.
二叶式主动脉瓣（BAV）易患主动脉瘤，患病率较高。这种现象的第一个假设与纤维蛋白原缺乏有关（遗传假设）。本文侧重于一个补充的血流动力学假设，即正是 BAV 构型患者升主动脉中血液的特殊流动动力学导致了动脉瘤的形成。为了证实这一假设，我们基于不同瓣口面积和瓣膜方位的升主动脉血流动力学的数值模拟进行了参数研究。研究了由此产生的壁面切应力（WSS）分布和血流喷射的不对称程度，并引入了替代指标。结果表明，BAV 形态的受试者的 WSS 更为明显，即使在非狭窄的情况下也是如此。特别是，在 BAV 形态的受试者中发现了 3Pa 的最大 WSS（而三叶形态的受试者为 1.5Pa）。它位于升主动脉的中段，这是一段更容易扩张的部位，最大 WSS 相关指数（BAV 为 0.869，三叶为 0.322）表明了这一点。此外，随着瓣膜面积的减小，血流的不对称性也会增大，升主动脉中部的相关指数比三叶形态的高 3 倍以上（0.70 比 0.20）。此外，对于侧向（LL）BAV 构型，在瓦氏窦和窦管交界处的 WSS 和血流不对称性也更高，这与 BAV 构型与不同主动脉瘤形态之间的临床观察一致。这些发现可能有助于解释 BAV 患者形成动脉瘤的风险较高的原因。在应用于临床环境之前，需要对所提出的指数进行验证。
