Influence of milrinone and norepinephrine on blood flow in canine internal mammary artery grafts.

Abstract

Vasoactive agents are frequently needed in patients undergoing myocardial revascularization. The purpose of this study was to examine blood flow in the internal mammary artery (IMA) during infusion of drugs that are commonly used after myocardial revascularization. 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 conduit. The IMA was anastomosed to a ligated left anterior descending coronary artery. Electromagnetic flow probes measured IMA graft flow. Norepinephrine (0.1 microgram.kg-1.min-1) alone and when combined with phentolamine (8:5 ratio) did not alter IMA flow. Milrinone increased IMA flow 33% +/- 9%, from 37 +/- 7 to 49 +/- 10 mL/min. All hemodynamic variables were unchanged. 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.