Internal mammary artery--coronary artery anastomosis. Influence of the side branches on surgical result.

Five of 20 (25%) symptomatic patients with internal mammary artery (IMA) grafts were found to have unusually enlarged side branches on arteriographic studies. One had a large lateral costal branch and four had large pericardial branches with collaterals draining into the pulmonary circulation. In these patients there was significant reduction (mean 44% +/- 3%) in the lumen of the distal IMA compared to its proximal part, with poor filling of the grafted coronary artery. This appeared to be the only cause of anginal symptoms in three of these five patients. The other 15 patients (75%) with small or no side branches had little or no reduction (mean 10% +/- 2%) of the distal IMA lumen. There was good coronary filling in these cases. The enlargement of the side branches indicates large flow in these branches with consequent reduction of flow in the grafted coronary artery. The marked reduction of the distal IMA lumen is a useful sign of reduced graft flow. This phenomenon may be one of the causes of poor results following IMA grafting.