Pharmacologic dilatation of the internal mammary artery during coronary bypass grafting.

Spasm of the internal mammary artery during coronary bypass grafting is a widely recognized problem during and after mobilization of the IMA. On the basis of previous laboratory studies, we have developed a buffered vasodilator solution containing glyceryl trinitrate and verapamil (pH 7.4). When tested in human internal mammary artery segments in the organ bath, this solution caused full relaxation of the segments with a 1- to 2-minute onset and a duration of action of more than 2 hours. In 31 patients undergoing internal mammary artery grafting, flow through the internal mammary artery was measured immediately after mobilization and 20 minutes later. In 10 untreated patients, flow increased by 13% from 41.8 +/- 7.1 to 47.3 +/- 7.5 ml/min (p < 0.025). In 11 patients, intraluminal injection of glyceryl trinitrate-verapamil solution into the internal mammary artery on one side caused an increase in flow of 55 +/- 10 ml/min (95%), which was greater than that caused by Ringer's solution, 22 +/- 8 ml/min (53%), in the opposite internal mammary artery (p < 0.025). In another 10 patients intraluminal injection of glyceryl trinitrate-verapamil solution in one internal mammary artery caused an increase in flow of 57.9 +/- 8.7 ml/min (107%), which was similar to that caused by papaverine solution (pH 5.2) in the opposite internal mammary artery of 45.0 +/- 12.3 ml/min (80%). We conclude that intraluminal injection of vasodilator solution is effective in dilating the IMA graft and that because of its rapid onset, long action, and neutral pH, glyceryl trinitrate-verapamil solution may be preferable to papaverine.