Abstract 709: Computational Seal Zone Mechanics - Predicting EVAR Failures

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Introduction: Endovascular aortic stent-graft technology (EVAR) radically altered aortic aneurysm repair from a maximally invasive procedure to a minimally invasive approach. While the overall principle of the repair remained the same, the surgeon ceded control of graft/aorta coupling with EVAR from the time-honored surgical approach of suturing, which creates a mechanical kinematic coupling constraint at the graft/aorta interface. In EVAR, the coupling condition is replaced by contact mechanics between the outer graft surface and the aorta. We hypothesize that proximal endograft failure is linked to the complex contact mechanics occurring at the graft/aorta interface. Methods: We performed a detailed geometric/finite element analysis (FEA) of an abdominal aortic aneurysm in a patient who presented with a ruptured juxta-renal AAA. We used the pre and post-operative CTA imaging to perform FEA and defined the stent graft (SG)/aortic wall interactions using a fully integrated cohesive zone model (CZM) (see figure 1). Results: Three degrees of adhesion strength were studied, corresponding to F~0.1, 10, and 1000 Newton. In the case of the two weaker adhesion strengths, the SG and neck separated at local points along the interface. These areas of separation (interfacial failure) corresponded to zones of high stress (~ 10MPa) within the aortic wall. This points to a new physical model of aortic/SG stability, where local elastic deformation energy in the neck (G) competes with aortic/SG adhesion energy (gamma~Gc) giving rise to the criterion for seal failure: G>Gc . Conclusions: The energy balance of deformation of the aortic neck with stent graft adhesion strength provides a key new parameter in evaluating future EVAR repairs. Non-linear neck geometries give rise to complex non-linear stress distributions that can greatly impact the stability of a repair. We provide a computational methodology in which this can be systematically studied for any given patient anatomy.