FACTORS AFFECTING INTERNAL MAMMARY ARTERY GRAFT-SURVIVAL - HOW IS COMPETITIVE FLOW FROM A PATENT NATIVE CORONARY VESSEL A RISK FACTOR

Recent studies have suggested that competitive flow is an important fa ctor in early internal mammary artery (IMA) graft failure. Flow compet ition from minimally diseased native coronary vessels has been implica ted in the failure of IMA grafts, but does not seem to affect saphenou s vein grafts (SVG). The objective of this study was to determine the effects of competitive flow on SVG and TMA grafts and to compare the p atterns of flow dynamics and pressure on proximal and distal grafts to the left anterior descending (LAD) artery; factors that may be involv ed in graft failure. Twelve mongrel dogs underwent coronary artery byp ass grafting using IMAs and a SVG to an open LAD artery. The right IMA (PIMA) and the SVG were anastomosed in the proximal LAD and the left IMA (DIMA) was anastomosed at a more distal location. The procedure wa s performed through a left thoracotomy, using an ''off pump'' techniqu e. Graft flows were measured isolated and in competition. The IMAs and SVG provided flow levels similar to the native LAD when each one was the sole inflow to the LAD. During competitive flow conditions, total and diastolic SVG flows were reduced 54.4 and 50.5%, respectively (P<0 .05). Total and diastolic PIMA and DIMA flows were reduced more drasti cally (68.6-73.3 and 69.5-68.1%, respectively; P <0.05). The DIMA had better preservation of diastolic flow compared to PIMA. A delay in the pressure wave was noted in the isolated IMAs, but not in the SVG. Thi s pattern of flow disappeared during competition due to the large, sys tolic retrograde flow up the IMA grafts. In conclusion, IMAs compared to the SVG are longer and narrower conduits with lower levels of flow during competition. Low levels of flow and oscillating flow (retrograd e/antegrade) may be poorly tolerated by the IMA endothelium and may be factorial to graft failure. These data suggest that a more distal pla cement of the IMA graft may be protective to the arterial graft under competitive flow conditions. (C) 1997 Academic Press.