Analysis of flow patterns on branched endografts for aortic arch aneurysms

Rupture of aneurysm on the aortic arch leads to significant rates of mortality. Traditional surgical repair is traumatic and may be inappropriate for some patients. Deployment of internally directed side branches provides a feasible alternative, but the hemodynamic implications have not been fully investigated and will be addressed in this study. Both patient specific pre- and post-operative conditions are treated here with computational fluid dynamics. Quantitative indicators like volume flow rate, wall shear stress and helicity index are employed. Changes in volume flow are generally mild unless an antegrade branch is utilized. Wall shear stress reveals a fluctuating and complex flow pattern between the brachiocephalic and left subclavian artery after graft implantation. Circumferentially averaged oscillatory shear indices at the left common carotid artery are in the range of (0.18, 0.26). Helical flows are observed both before and after surgical repairs, and are measured by spatially integrated helicity and a ‘helicity flow index’. Before surgical implant of grafts, blood flows frequently display a predominant direction of rotation. This feature is typically diminished after the implantation. In general, aortic blood flow displayed a higher degree of oscillatory and helical features after internal side branches were deployed. Clinically, oscillatory flows may promote blood clot formation. Furthermore, flow separation points near the outer wall of internal side branches induce fluctuations in pressure and force which might threaten the integrity of the stent graft. To achieve the goal of side branch patency, proper stent orientation is thus critical.