Department of Mechanical and Aerospace Engineering, Sapienza University of Roma, Roma, Italy.
Department of Clinical and Molecular Medicine, Sapienza University of Roma, Roma, Italy.
Cardiovasc Eng Technol. 2021 Jun;12(3):300-310. doi: 10.1007/s13239-021-00520-3. Epub 2021 Feb 9.
The main objective of this work is to investigate hemodynamics phenomena occurring in EVAS (Endo Vascular Aneurysm Sealing), to understand if and how they could lead to type 1a endoleaks and following re-intervention. To this aim, methods based on computational fluid mechanics are implemented as a tool for checking the behavior of a specific EVAS configuration, starting from the post-operative conditions. Pressure and velocity fields are detailed and compared, for two configurations of the Nellix, one as attained after correct implantation and the other in pathological conditions, as a consequence of migration or dislocation of endobags.
The computational fluid dynamics (CFD) approach is used to simulate the behavior of blood within a segment of the aorta, before and after the abdominal bifurcation. The adopted procedure allows reconstructing the detailed vascular geometry from high-resolution computerized tomography (CT scan) and generating the mesh on which the equations of fluid mechanics are discretized and solved, in order to derive pressure and velocity field during heartbeats.
The main results are obtained in terms of local velocity fields and wall pressures. Within the endobags, velocities are usually quite regular during the whole cardiac cycle for the post-implanted condition, whereas they are more irregular for the migrated case. The largest differences among the two cases are observed in the shape and location of the recirculation region in the rear part of the aorta and the region between the endobags, with the formation of a gap due to the migration of one or both of the two. In this gap, the pressure fields are highly different among the two conditions, showing pressure peaks and pressure gradients at least four times larger for the migrated case in comparison to the post-implanted condition.
In this paper, the migration of one or both endobags is supposed to be related to the existing differential pressures acting in the gap formed between the two, which could go on pushing the two branches one away from the other, thus causing aneurysm re-activation and endoleaks. Regions of flow recirculation and low-pressure drops are revealed only in case of endobag migration and in presence of an aneurysm. These regions are supposed to lead to possible plaque formation and atherosclerosis.
本工作的主要目的是研究 EVAS（血管内动脉瘤密封）中发生的血液动力学现象，以了解它们是否以及如何导致 1a 型内漏，并随之需要再次介入。为此，基于计算流体力学的方法被用作检查特定 EVAS 配置行为的工具，该配置从术后条件开始。详细比较和对比了两种 Nellix 配置的压力和速度场，一种是正确植入后的状态，另一种是由于内套囊迁移或脱位而处于病理状态。
采用计算流体动力学（CFD）方法模拟腹主动脉分叉前后一段血管内的血液行为。所采用的程序允许从高分辨率计算机断层扫描（CT 扫描）重建详细的血管几何形状，并生成网格，在网格上离散和求解流体力学方程，以得出心跳过程中的压力和速度场。
主要结果以局部速度场和壁压表示。在内套囊中，对于植入后的情况，整个心动周期内的速度通常相当规则，而对于迁移的情况则更不规则。两种情况下最大的差异发生在后主动脉和内套囊之间的回流区域的形状和位置，由于一个或两个内套囊的迁移，形成了一个间隙。在这个间隙中，两种情况下的压力场有很大的不同，迁移情况下的压力峰值和压力梯度至少比植入后情况下大四倍。
在本文中，一个或两个内套囊的迁移被认为与在两个之间形成的间隙中作用的现有压差有关，这可能会继续将两个分支彼此推开，从而导致动脉瘤重新激活和内漏。仅在内套囊迁移和存在动脉瘤的情况下才会出现流动再循环和低压降区域。这些区域可能导致斑块形成和动脉粥样硬化。
