Purpose

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.

Methods

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.

Results

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.

Conclusions

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.

中文翻译：

---

血管内动脉瘤封闭 (EVAS) 系统故障的流体动力学

目的

这项工作的主要目的是研究 EVAS（血管内动脉瘤封闭术）中发生的血流动力学现象，以了解它们是否以及如何导致 1a 型内漏和重新干预。为此，基于计算流体力学的方法被实施为检查特定 EVAS 配置行为的工具，从术后条件开始。对于 Nellix 的两种配置，压力和速度场进行了详细和比较，一种是在正确植入后获得的，另一种是在病理条件下，由于内袋的迁移或错位。

方法

计算流体动力学 (CFD) 方法用于模拟腹部分叉前后主动脉段内的血液行为。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结构，并生成网格，在该网格上离散化和求解流体力学方程，以推导出心跳期间的压力和速度场。

结果

主要结果是根据局部速度场和壁压力获得的。在内袋中，对于植入后的情况，在整个心动周期中的速度通常是相当有规律的，而对于迁移的情况，它们的速度则更加不规则。两种情况之间最大的差异在于主动脉后部再循环区域和内袋之间区域的形状和位置，由于两者之一或两者的迁移而形成间隙。在这个间隙中，两种条件之间的压力场差异很大，与植入后条件相比，迁移情况下的压力峰值和压力梯度至少大四倍。

结论

在本文中，一个或两个内袋的迁移被认为与作用在两者之间形成的间隙中的现有压差有关，这可能会继续推动两个分支一个远离另一个，从而导致动脉瘤重新激活和内漏。仅在内袋迁移和存在动脉瘤的情况下才会显示流动再循环和低压降区域。这些区域应该会导致可能的斑块形成和动脉粥样硬化。