EFFECT OF SYSTEMIC VASODILATORS ON INTERNAL MAMMARY FLOW DURING CORONARY-BYPASS GRAFTING

Background. The effect of vasodilators on acute flow in the internal m ammary (IMA) is unclear. Topical vasodilators show no effect on acute now when the distal segment of the IMA is resected, The purpose of thi s study was to evaluate the effect of systemic vasodilators when this segment is resected. Methods. We studied 60 patients with proximal ant erior descending coronary artery lesions in whom the left IMA was harv ested for grafting to the left anterior descending coronary artery. Th e patients were divided into six groups (n = 10), based on which of th e following agents were studied: normal saline solution, nitroglycerin , nitroprusside, dobutamine, dopexamine, and amrinone. After harvestin g, the IMA was trimmed as proximally as possible (and at least 3 cm pr oximal to the bifurcation), and free flow was measured before any phar macologic intervention (flow I). Systemic infusion of one of the six a gents commenced. A mean of 17 +/- 3.4 minutes after infusion began, wi th a comparable cardiac index, a second measurement of LMA flow was ta ken (flow 2). Hemodynamic measurements for each flow including blood p ressure, heart rate, and cardiac output, were taken. Results. A signif icant increase in IMA flow was noted for those patients receiving nitr oglycerin (93.5 versus 106.8 mL/min; p = 0.025), and a significant dec rease in flow was noted for those receiving nitroprusside (91.0 versus 78.2 mL/min; p = 0.042). The effects remained significant when correc ted for cardiac index and compared with the normal saline solution gro up. No other systemic agents tested significantly affected the IMA dow (dobutamine, 83.8 versus 85.0 mL/min; dopexamine, 101.8 versus 91.4 m L/min; amrinone, 75.4 versus 79 mL/min; normal saline solution, 85.8 v ersus 84.6 mL/min). Conclusions. Resection of the distal segment of th e IMA and the use of intravenous nitroglycerin optimizes the now in IM A grafts.