S.S. Dhara1, M.A. Varsanik1, K. Cao1, J.A. Pugar1, L. Pocivavsek1 1University of Chicago, Department Of Surgery, Chicago, ILLINOIS, USA
Introduction: Endovascular aortic repair, in the form of EVAR/TEVAR, has become increasingly common. Mechanistically, EVAR/TEVAR depressurizes the aneurysm sac by blood flow exclusion via apposition between a stent and segment of non-diseased aorta, creating the seal zone. The seal zone is conceptualized as two cylindrical bodies (the aorta and the stent) interacting through adhesive forces. In reality, the stent never perfectly opposes the inner aortic wall. Thus, there exists a potential space within the seal zone for fluid, causing endoleak. We created a model system with adequate imaging resolution in order to capture this space and performed computational fluid dynamic (CFD) analysis to understand the mechanics of endoleak, a major failure mode for EVAR/TEVAR.
Methods: A model seal zone was constructed by placing a small stent (30 mm x 10 mm) within an 8 mm quartz tube (Figure 1A), filled with fluid, and imaged with microCT (~20 μ m resolution). Our model incorporates a 25% oversizing of the stent. Images were reconstructed and segmented to highlight the quartz tube, metal stent, and stent fabric (Figure 1B). Geometry was imported into XFLOW, a CFD solver, to run simulations. Initial data were generated using constant velocity (inlet, 0.6 m/s) and pressure (outlet, 13333 Pa) boundary conditions while blood was simulated as a Newtonian fluid.
Results: The endoleak potential space can be clearly seen in light green caused by infolding of the oversized fabric (Figure 1B), demonstrating the imperfect apposition inherent to any seal zone. The velocity profiles in Figure 1C show that the bulk lumen flow is consistent with the inlet boundary condition but complex flow patterns exist in the endoleak region. An added consequence of the non-uniform geometry experienced by fluid in this space is development of high regions of static pressure specific to the endoleak (Figure 1D).
Conclusion: Our model seal zone CFD simulation demonstrates a varied endoleak velocity distribution and regions of elevated pressure isolated to the endoleak. We hope our work can advance understanding regarding the relationship between stent oversizing and positioning on endoleak formation. Future directions include varying the degree of oversizing to examine how this clinically tunable parameter impacts endoleak mechanics.