Numerical Analysis of the Hemodynamics in Optimized Coronary Artery Bypass

Coronary artery bypass grafting is a widely used revascularization procedure for restoring blood supply downstream of obstructed coronary arteries. However, the hemodynamic performance of a bypass graft depends not only on the severity of the native coronary stenosis, but also on the geometry of the graft and the resulting flow interaction at the distal anastomosis. This thesis investigates the combined and separate effects of native stenosis severity and topology-optimized bypass geometry on the hemodynamics of idealized aorto-coronary bypass configurations. Three-dimensional computational domains were reconstructed from two-dimensional topology-optimized bypass layouts. Two groups of cases were analyzed: matched $S_XOB_X$ configurations, in which native stenosis severity and the corresponding optimized bypass geometry varied together, and $S90OB_X$ configurations, in which the stenosis was fixed at a severe $S90$ condition while the bypass geometry was varied. Pulsatile computational fluid dynamics simulations were performed assuming incompressible Newtonian blood flow, laminar conditions, and rigid vessel walls. The assessment focused on flow redistribution, pressure losses, velocity and streamline organization, vorticity, TAWSS, OSI, and RRT. The numerical study shows a transition from a mixed native--graft flow regime to a graft-dominated regime as stenosis severity increases. When residual native flow remains significant, the stenosed native artery contributes to flow acceleration, pressure loss, and local disturbance. As the system becomes graft-dominated, the main disturbance shifts toward the distal anastomosis, where bypass flow enters the native artery, and reorganizes the downstream flow field. Unfavorable near-wall conditions are localized mainly along the coronary floor and, in some configurations, near the toe. Under fixed severe stenosis, bypass geometry strongly affected the quality of the anastomotic flow field. Smaller bypass geometries produced more concentrated graft inflow and larger disturbed-flow regions near the anastomosis, whereas more open geometries promoted smoother flow redirection and more favorable near-wall conditions. Among the analyzed configurations, $S90OB90$ showed the most favorable overall behavior, combining graft-dominated downstream perfusion with smoother flow organization, a more uniform pressure distribution, improved TAWSS near the toe, and a more favorable RRT distribution near the graft--native junction. Overall, the thesis shows that CABG hemodynamics should be evaluated by considering the coupled interaction between native vessel resistance, graft geometry, and anastomotic flow quality.