Influence of aorto-left coronary bypass graft geometry on wall shear stress distribution.

Idealized geometries of bypass grafts have been constructed to analyze the blood flow in an aorto-coronary bypass graft system. In this paper we discuss the influence of the realistic bypass graft geometry for the in-plane and out-of-plane aorto-left bypass graft models on the wall shear stress distribution. In the in-plane aorto-left coronary bypass graft model we have the centerlines of the aorta, the left coronary vessel and the bypass graft to lie in the same plane (planar geometry) where as in the out-of-plane model the centerlines of the vessels no longer lie in a constant plane (non-planar geometry). Computational fluid dynamic (CFD) studies are carried out using the commercial software FLUENT. It is known that the coronaries are well perfused during the diastole and hence even though simulations are performed at different instances (both the systole and diastole phase) of the cardiac cycle, we have demonstrated the wall shear stress distribution in the distal anastomotic section for both the models at two specific instances of the diastolic phase, namely, early diastole (t=0.45 s) and mid-diastole (t=0.7 s). Our results reveal that in comparison to the in-plane model, the wall shear stress magnitude in the out-of-plane model is greatly reduced at the bed of the anastomosis. Thus a subtle change in the geometry can affect the flow field significantly that may promote graft patency.