Pathology of internal mammary arteries used as bypass grafts.

We describe four patients in whom internal mammary arteries used as coronary artery bypass grafts demonstrated pathologic changes that could affect long-term patency. Two grafts showed evidence of arteritis, and two showed degenerative changes as seen in so-called cystic medial necrosis. In one of these two cases intraoperative dissection of the internal mammary artery and aorta occurred. Aside from the rare occurrence of atherosclerosis, we have found no previous reports of systemic vascular disease affecting this artery.