Boyd April J, Kuhn David C S, Lozowy Richard J, Kulbisky Gordon P
Department of Vascular Surgery, University of Manitoba, Winnipeg, Manitoba, Canada.
Department of Mechanical Engineering, University of Manitoba, Winnipeg, Manitoba, Canada.
J Vasc Surg. 2016 Jun;63(6):1613-9. doi: 10.1016/j.jvs.2015.01.040. Epub 2015 Mar 7.
Aortic diameter as the primary criterion in the decision to repair abdominal aortic aneurysms (AAAs) has drawbacks as some rupture below size thresholds, whereas others reach extreme size without rupture. Predictions of static aortic wall stress have also failed to reliably predict rupture potential. The objective of this study was to computationally assess blood flow characteristics at the site of infrarenal AAA rupture. On the basis of the finite element literature correlating rupture location with high static local wall stress, we hypothesized that a computational fluid dynamics approach would also demonstrate rupture at regions of high pressure and wall shear stress (WSS).
Three-dimensional AAA geometry was generated from computed tomography angiography images of seven ruptured AAAs. Aortic blood flow velocity, pressure, and WSS were computationally determined. Flow characteristics at the site of rupture were determined and compared across all cases.
AAA size at the time of rupture was 8.3 ± 0.9 cm. Only three of the seven AAAs ruptured at the site of maximal diameter. Blood flow velocity in the aneurysmal aorta showed dominant flow channels with zones of recirculation, where low WSS predominated. Regardless of aneurysm size or configuration, rupture occurred in or near these flow recirculation zones in all cases. WSS was significantly lower and thrombus deposition was more abundant at the site of rupture.
This computational study was the first to assess blood flow characteristics at the site of infrarenal AAA rupture in realistic aortic geometries. In contradiction to our initial hypothesis, rupture occurred not at sites of high pressure and WSS but rather at regions of predicted flow recirculation, where low WSS and thrombus deposition predominated. These findings raise the possibility that this flow pattern may lead to thrombus deposition, which may elaborate adventitial degeneration and eventual AAA rupture.
将主动脉直径作为决定修复腹主动脉瘤（AAA）的主要标准存在缺陷，因为一些AAA在尺寸阈值以下破裂，而另一些则在达到极大尺寸时仍未破裂。对主动脉壁静态应力的预测也未能可靠地预测破裂可能性。本研究的目的是通过计算评估肾下腹主动脉瘤破裂部位的血流特征。基于有限元文献中关于破裂位置与高静态局部壁应力的相关性，我们假设计算流体动力学方法也将显示在高压和壁面切应力（WSS）区域会发生破裂。
从7例破裂性腹主动脉瘤的计算机断层血管造影图像生成三维腹主动脉瘤几何模型。通过计算确定主动脉血流速度、压力和WSS。确定并比较所有病例中破裂部位的血流特征。
破裂时腹主动脉瘤大小为8.3±0.9cm。7例腹主动脉瘤中只有3例在最大直径部位破裂。动脉瘤主动脉内的血流速度显示出主导流道以及再循环区域，其中低WSS占主导。无论动脉瘤大小或形态如何，所有病例的破裂均发生在这些血流再循环区域内或其附近。破裂部位的WSS显著更低，血栓沉积更丰富。
这项计算研究首次在逼真的主动脉几何模型中评估肾下腹主动脉瘤破裂部位的血流特征。与我们最初的假设相反，破裂并非发生在高压和WSS部位，而是发生在预测的血流再循环区域，这些区域以低WSS和血栓沉积为主。这些发现增加了这种血流模式可能导致血栓沉积的可能性，而血栓沉积可能会引发外膜退变并最终导致腹主动脉瘤破裂。
