Effect of topically-applied milrinone or nitroglycerin on internal mammary artery free flow

Surgical mobilization of the internal mammary artery (IMA) can induce graft vasospasm, which is commonly managed by wrapping the IMA in a vasodilator-soaked swab before grafting. However, the choice of the most effective topical vasodilator remains the subject of continued investigation. We carried out a prospective randomized controlled trial to compare the effect of topically-applied milrinone, nitroglycerin and normal saline on IMA free flow.<b><i>Methods </i></b>Forty-six consecutive patients undergoing elective primary coronary artery bypass grafting were enrolled. After the left IMA was harvested, free flow was measured under controlled hemodynamic conditions before any intervention (flow 1) and at a mean of 12.5 minutes after the topical application of one of three agents (milrinone, nitroglycerin or normal saline) on the IMA (flow 2).<b><i>Results </i></b>All agents induced a significant increase in IMA flow, and flow 2 was significantly higher in the nitroglycerin and milrinone groups compared to the normal saline group, even while controlling for flow 1 as a centered continuous variable. Nevertheless, there was no statistically significant difference in flow 2 between the nitroglycerin and milrinone groups.<b><i>Conclusions</i></b>Topically-applied milrinone and nitroglycerin can increase blood flow of the IMA significantly in the early period after surgical mobilization. IMA blood flow was greater after the topical application of milrinone compared to nitroglycerin, but this has failed to reach statistical significance in the present study setting.