Exploring in-stent hemodynamics after abdominal aortic endovascular interventions: a computational study.

Endovascular Aneurysm Repair (EVAR) is an innovative technique for the treatment of abdominal aortic aneurysm (AAA). However, complex anatomies characterized by localized aneurysms close to the renal arteries and vessel tortuosity lead to post-operative complications. To help prevent them, a computational study explores hemodynamics within the stents. The aim of this work is to compare the hemodynamic impact of different endoprosthesis in a male 68 years old patient having a short aortic neck and a fenestrated stent (f-EVAR) implant, which was affected to a iliac arteries rotation after surgery. Patient-specific CAD models of the aorta before the intervention (preOP) and after the f-EVAR implant are built using a manual segmentation by the CT-scans. Computational fluid dynamics (CFD) simulations are performed using the finite-element code CRISMON setting the patient-specific inflow and the 3-elements Windkessel model at each outlet as boundary condition. The chimneys stent (Ch-EVAR) model, instead is built by simulating the stent-graft model deployment inside the tortuous arterial model generated from patient pre-operative scan using Abaqus software. CFD, in fact, requires an input from the finite element (FE) simulation to obtain a reliable and precise fluid domain (the stent-graft implant surface). A second f-EVAR model is built without evaluate the iliacs rotation for a better hemodynamic comparison. On the stent main-body of the Ch-EVAR, the chimneys have been replaced by the fenestrated arteries. The technique used to build the Ch-EVAR model simulating the deployment of the stent from the pre-operative scan cannot, indeed, predict the rotation of the iliac arteries. CFD simulation of the Preoperative, f-EVAR and Ch-EVAR models is performed to analysed and compared hemodynamic aspects. Looking at the blood flow, blood pressure and Wall Shear Stress (WSS) for the EVAR models, the postoperative hemodynamic changes that affect the preoperative hemodynamic are analyzed, focus on the renal arteries. The stent protrusions inside the aorta lead to an increase in maximum velocity and pressure in the EVAR models compared to the preoperative one. It is observed a new higher recirculation zone in the middle of the stent in the fenestrated models. In fact, areas with WSS close to the upper physiological limit (7 Pascal) decreased after the stent implant. Despite the findings, all procedures must be evaluated individually, based on the severity of the injury, on the patient anatomy and evaluating the risk / benefit ratio of the intervention.