ENDOTHELIUM-DEPENDENT AND ENDOTHELIUM-INDEPENDENT FLOW REGULATION IN CORONARY VASCULAR REGIONS SUPPLIED BY ARTERIAL AND VENOUS BYPASS GRAFTS

The endothelium-dependent and endothelium-independent vasodilation of arterial and venous coronary bypass grafts and of epicardial conduit v essels and microcirculatory coronary vessels supplied by these grafts was investigated. Vasodilatory response and flow regulation were teste d with cumulative intracoronary doses of acetylcholine (25 and 50 mu g i.c.), nitroglycerin (0.3 mg i.c.), and papaverine (10 mg i.c.) in 10 patients (age 60 +/- 2.3 years) with arterial grafts and in 16 patien ts (age 57.7 +/- 1.5 years) with venous grafts. The effect of acetylch oline on arterial and venous bypass grafts and on large conduit arteri es was evaluated by quantitative coronary angiography. Coronary blood flow velocity changes as a parameter of microcirculatory function were measured by intraluminal Doppler ultrasound. Indices for coronary flo w and coronary resistance were calculated from the mean Doppler flow v elocity and the computed cross-sectional vascular area. The coronary r esistance decreased endothelium dependent after 25 and 50 mu g of acet ylcholine by 16 +/- 30% (p < 0.05 vs. control) and 22 +/- 25% (p < 0.0 5 vs. control), respectively, in regions supplied by venous grafts and by 48 +/- 20% (p < 0.05 vs. control and vs. venous graft) and 41 +/- 32% (p < 0.05 vs. control), respectively, in regions supplied by arter ial grafts. The coronary resistance decreased endothelium independent after 0.3 mg nitroglycerin and 10 mg papaverine by 18 +/- 56% (p < 0.0 5 vs. control) and 39 +/- 29% (p < 0.05 vs. control), respectively in regions supplied by venous grafts and by 45 +/- 45% (p < 0.05 vs. cont rol) and 70 +/- 12% (p < 0.05 vs. control and vs. venous graft), respe ctively in regions supplied by arterial grafts. In conclusion, during the long-term course after coronary artery bypass grafting, vascular r egions supplied by arterial grafts have a better preserved endothelium -dependent and endothelium-independent flow reserve as compared with v ascular regions supplied by venous grafts.