Abstract: Objective:To study the effects of competitive blood flow from differently stenotic coronary artery on internal mammary artery graft flow. Methods: Coronary artery bypass grafting (CABG) was conducted in 15 Chinese miniswines using left internal mammary artery(LIMA) anastomosed to left anterior descending artery (LAD). The proximal LAD was mad differently stenotic (0%,30%,50%,75%,90% and 100%) through a flow occlusion and the mean flow of LIMA and LAD proximal and distal to the anastomosis were respectively measured through the transit time flow measurement (TTFM). Results:The mean flow of LIMA was (9.75±1.45), (11.63±1.69), (15.63±2.26), (19.75±2.37), (23.50±2.34) and (26.75±2.11)ml/min, respectively. The mean pulsatility index (PI) value was respectively 4.4±1.7, 4.1±1.6, 4.2±1.9, 3.7±1.8, 3.3±1.6 and 2.5±1.4. Themean flow of LIMA when the stenosis of the proximal LAD was 90% or 100% was significant higher than that of LIMA when the stenosis of the proximal LAD was 0%, 30% or 50%（P<0.01）. When the proximal LAD was not fully occluded, there were dual flow in LIMA. There were no difference in LAD flow distal to the anastomosis. Conclusion: The competitive flow from patent LAD does exist and has important effects on IMA graft flow and may be an important cause of IMA graft failure.

Key words: Coronary artery bypass grafting, Competitive flow, Blood volume determination, Internal mammary artery, Swine