A computational fluid dynamics simulation study of coronary blood flow affected by graft placement†.

OBJECTIVES: To determine the effect of graft placement and orientation on flow rates through a partially obstructed coronary artery. METHODS: A numerical, parametric study of blood flow in the human coronary artery was conducted using computational fluid dynamics simulation. A cylindrical approximation of the coronary artery with varying degrees of stenosis, with and without a bypass graft, was modelled to determine trends in volumetric flow rates. Steady and transient simulations were conducted for geometric variations of percentage of blockage, length and shape of stenosis, graft position relative to the coronary blockage and graft orientation. Accurate simulations were performed using a non-Newtonian fluid model and pressure-driven viscous flow. RESULTS: Simulations demonstrate, as expected, that total outlet flow rates of grafted arteries are consistently improved for upstream stenosis varying between 0 and 90% blockage. Grafts angled towards the artery provided increased total outflow. However, flow rates in the coronary artery upstream of the graft are substantially reduced in comparison with the non-grafted configuration due to competing flows. For some configurations (reduced blockage, graft placed close to long grafts), flow rates in the graft are below that of the flow rate through the stenosis. In general, a graft angled more towards the artery increased flow rates upstream of the graft. CONCLUSIONS: Placement and orientation of a graft may adversely affect upstream flow, with the degree of effect dependent on geometric factors of downstream position and graft angle.

A prospective randomized trial of endoscopic versus conventional harvesting of the saphenous vein in coronary artery bypass surgery.

OBJECTIVES: Our objectives were (1) to determine whether minimally invasive endoscopic harvesting of the saphenous vein reduces morbidity due to postoperative wound infection and pain with improved cosmetic results and mobilization as compared with the conventional technique and (2) to compare the histologic properties of the saphenous veins harvested conventionally and endoscopically. METHODS: One hundred forty-four patients undergoing coronary artery bypass grafting were randomized to have vein harvesting performed by either the conventional (n = 72) or an endoscopic (n = 72) minimally invasive technique. RESULTS: Vein harvest time (open leg wound time) was significantly reduced in the endoscopic group (27.6 vs 64.4 minutes; P <.0001). The rate of leg wound infection was significantly reduced in the endoscopic group (4.3%) as compared with the conventional group (24.6%), a relative risk reduction of 83% (95% confidence interval: 36%-129%; P =.0006). The majority of infections (84.2%) occurred after hospital discharge. Postoperative leg pain, mobilization, and overall patient satisfaction were also significantly improved in the endoscopic group. Double blinded histologic assessment of harvested vein (n = 28) showed no evidence of any clinically important significant damage to the specimens in either group. CONCLUSIONS: In this prospective randomized trial, endoscopic harvesting of the saphenous vein significantly reduced postoperative leg wound complications, including infection, and improved patient satisfaction as compared with the conventional harvesting technique. There were no significant histologic differences between the conventional and endoscopically harvested saphenous veins.