INFLUENCE OF MILRINONE AND NOREPINEPHRINE ON BLOOD-FLOW IN CANINE INTERNAL MAMMARY ARTERY GRAFTS

Background. Vasoactive agents are frequently needed in patients underg oing myocardial revascularization. The purpose of this study was to ex amine blood flow in the internal mammary artery (IMA) during infusion of drugs that are commonly used after myocardial revascularization. Me thods. A canine right heart bypass preparation allowed precise control of cardiac output and blood pressure, which were maintained constant during drug infusion to isolate the effect of the drug on the IMA cond uit. The IMA was anastomosed to a ligated left anterior descending cor onary artery. Electromagnetic flow probes measured IMA graft flow. Res ults. Norepinephrine (0.1 mu g . kg . min(-1)) alone and when combined with phentolamine (8:5 ratio) did not alter IMA flow. Milrinone incre ased IMA flow 33% +/- 9%, from 37 +/- 7 to 49 +/- 10 ml/min. All hemod ynamic variables were unchanged. Conclusions. The results suggest that : (1) norepinephrine did not have a deleterious effect on IMA flow and (2) milrinone may be a useful drug in patients undergoing myocardial revascularization by increasing IMA blood flow.