Effect of systemic vasodilators on internal mammary flow during coronary bypass grafting

Background. The effect of vasodilators on acute flow in the internal mammary (IMA) is unclear. Topical vasodilators show no effect on acute flow when the distal segment of the IMA is resected. The purpose of this study was to evaluate the effect of systemic vasodilators when this segment is resected. Methods. We studied 60 patients with proximal anterior descending coronary artery lesions in whom the left IMA was harvested for grafting to the left anterior descending coronary artery. The patients were divided into six groups (n = 10), based on which of the following agents were studied: normal saline solution, nitroglycerin, nitroprusside, dobutamine, dopexamine, and amrinone. After harvesting, the IMA was trimmed as proximally as possible (and at least 3 cm proximal to the bifurcation), and free flow was measured before any pharmacologic intervention (flow 1). Systemic infusion of one of the six agents commenced. A mean of 17 ± 3.4 minutes after infusion began, with a comparable cardiac index, a second measurement of IMA flow was taken (flow 2). Hemodynamic measurements for each flow, including blood pressure, heart rate, and cardiac output, were taken. Results. A significant increase in IMA flow was noted for those patients receiving nitroglycerin (93.5 versus 106.8 mL/min; p = 0.025), and a significant decrease in flow was noted for those receiving nitroprusside (91.0 versus 78.2 mL/min; p = 0.042). The effects remained significant when corrected for cardiac index and compared with the normal saline solution group. No other systemic agents tested significantly affected the IMA flow (dobutamine, 83.8 versus 85.0 mL/min; dopexamine, 101.8 versus 91.4 mL/min; amrinone, 75.4 versus 79 mL/min; normal saline solution, 85.8 versus 84.6 mL/min). Conclusions. Resection of the distal segment of the IMA and the use of intravenous nitroglycerin optimizes the flow in IMA grafts.