Functional evaluation of internal mammary artery bypass grafts in the early and late postoperative periods

Objectives.We sought to determine whether internal mammary artery grafts adapt to an increase in myocardial flow demand and whether they restore maximal flow reserve.Background.Although mammary grafts are now considered the graft of choice for coronary artery bypass surgery, there is still controversy about whether they can provide adequate flow at periods of peak myocardial demand.Methods.Of 28 patients with a mammary graft anastomosed to the left anterior descending coronary artery, 15 were studied early (mean [±SD] 8 ± 2 days) and 13 late (19 ± 15 months) after operation by quantitative angiography and selective intravascular Doppler analysis at baseline, during pacing and after injection of papaverine and isosorbide dinitrate into the graft. Eleven patients with a normal left anterior descending artery served as control subjects.Results.At baseline, mean graft diameter (2.39 ± 0.41 vs. 2.42 ± 0.45 mm) and bypass flow (38 ± 22 vs. 30 ± 12 ml/min) were similar in the early and late postoperative periods. Significant and similar vasodilation was observed in mammary grafts after administration of papaverine (+6 ± 5% vs. +9 ± 6%) and nitrates (+14 ± 7% vs. +16 ± 9%) both early and late after bypass surgery. Graft diameter increased during pacing late (+6 ± 3%, p < 0.05) but not early after operation. Bypass flow increased similarly during pacing in both groups, but maximal flow reserve induced by papaverine was significantly lower in mammary grafts studied early (2.70 ± 0.62) than those studied late (3.66 ± 0.81, p < 0.01) and in normal coronary arteries (4.05 ± 0.96, p < 0.001).Conclusions.An increase in myocardial blood flow induced by pacing resulted in vasodilation of mammary grafts in the late but not in the early postoperative period. Significant vasodilation of mammary grafts after papaverine and isosorbide dinitrate administration was observed both early and late after operation. However, bypass flow reserve after papaverine injection was significantly lower in the early postoperative period but normalized over time. This finding seems unrelated to the conduit; rather, it appears to be related to the periphery and could be the result of injury to the microvasculature during operation