Computational Analysis of EndoAnchor Effectiveness in Dilating Abdominal Aortic Aneurysm Neck

Abstract

Endovascular surgery is standard of care for nearly all aortic aneurysm repairs. A paradigm shift is under way concerning endoleaks, especially in the population of patients with persistent sac pressurization or growth. Focus is shifting from type II endoleaks to the most vulnerable part of the aorta-endograft interface leading to stable or expanding sacs—the proximal seal zone (type IA). Clinically, fixation and seal are often thought of as a single entity and considered in selecting an appropriately sized endograft based on patient-specific parameters, such as neck diameter and geometry. However, mechanistically, seal and fixation are two different problems. Active graft fixation with EndoAnchors (EAs; Medtronic, Santa Rosa, Calif) is showing improved rates of sac regression and seal zone stabilization. Whereas there is growing clinical understanding of the effectiveness of EAs in endovascular surgery, a biophysical understanding of the role of EAs under different mechanisms of seal zone failure is lacking. We build on our prior work using finite element analysis with cohesive zone modeling of the seal zone to study the role of EAs on interfacial stability under hypertensive conditions. In the current work, we study the role of EAs in preventing seal zone failure as a function of continued aortic neck dilation. Aortic dilation is modeled by a morphoelasticity approach (Fig). We study radial, circumferential, longitudinal, and isotropic dilation. Our simulations show that seal zone loss is sensitive to neck dilation. As the neck dilates, the seal zone is lost, similar to cases in which the supra-device aorta is overpressurized. EA placement prevents seal zone failure with neck dilation. The pattern of seal zone failure is sensitive to the mode and degree of aortic neck dilation. Isotropic dilation leads to the fastest failure because mode 1, 2, and 3 fracture is activated. Circumferential and radial dilation lead to different modes of interfacial fracture dominating. Our work provides the first biophysical mechanism for the effectiveness of EA fixation in a dilating aortic neck (disease progression). We show that EAs do stabilize the seal zone under these conditions. However, this effectiveness is sensitive to the mode of dilation.