Computational analysis of biomechanical contributors to possible endovascular graft failure

Abstract

This paper evaluates numerically coupled blood flow and wall structure interactions in a representative stented abdominal aortic aneurysm (AAA) model, leading potentially to endovascular graft (EVG) failure. A total of 12 biomechanical contributors to possible EVG migration were considered. The results show that after EVG insertion for the given model, the peak AAA sac-pressure was reduced to 14.2 mmHg (11.8% of p(lumen)), and hence the maximum von Mises wall stress and wall deformation dropped by factors of 20 and 10, respectively. Thus, an EVG can significantly reduce sac pressure, mechanical stress, pulsatile wall motion, and the maximum diameter in AAAs and hence prevent AAA rupture effectively. In the absence of endoleaks, elevated sac-pressure can still be caused by fluid-structure interactions between the EVG, stagnant blood, and AAA wall. EVG migration forces vary from 1.4 to 7 N for different EVG geometries, material properties, and hemodynamic conditions. AAA-neck angle, iliac bifurcation angle, neck aorta-to-iliac diameter ratio, EVG size, aorto-uni-iliac EVG, and hypertension play important roles in generating forces potentially leading to EVG migration.

Effect of Curvature on Displacement Forces Acting on Aortic Endografts: A 3-Dimensional Computational Analysis

“…7 A number of factors hypothesized to affect device migration have been clinically investigated, including aortic neck diameter, length, and angulation; neck calcification and thrombus; neck enlargement; inadequate proximal and distal fixation length; and neck enlargement. [8][9][10] In-vitro 11 and in-vivo experimental studies, 12 as well as theoretical 13 and computational studies, [14][15][16][17][18][19] have been conducted to investigate the magnitude of the loads acting on endografts. These loads have been referred to as migration forces, displacement forces, or drag forces.…”

Computational Analysis of Blood Flow Characteristics in an Aortic System with Abdominal and Left Common Iliac Aneurysm Pre- and Post-Stent Grafting

“…Also, drag forces depend on the anatomically curved configuration of the stent graft, anterior/posterior angle and inlet crosssectional area. Drag forces analysis may help determine stent graft migration [11] that will be focus of our future studies.…”

“…We did not have the measured blood flow for this specific patient, so we took the average values. Also, we did not consider wall properties and fluidstructure interaction [5], [9], [11] which have important role in mechanisms of aneurysmal growth and rupture, as well as in the stent graft migration and durability. …”

Studying the Flow Dynamics Within Endografts in Abdominal Aortic Aneurysms

“…A validated Finite Volume analysis software ANSYS v 12.1 (Ansys Inc., Canonsburg, PA, USA) was used for Computational Fluid Dynamics (CFD). The velocity and pressure waveforms during a period of 1.2 s as previously described in a one-dimensional fluid-dynamics model for the abdominal aorta (Olufsen et al, 2000 andLi et al, 2005) were used for both models as inlet and outlet boundary conditions. Blood was assumed to be non-Newtonian fluid, according to the Carreau-Yasuda model, with a density of 1050 kg/m 3 .…”