The remarkably high patency rate of the internal mammary artery (internal thoracic artery) when used as a bypass conduit was first demonstrated in patients who had undergone the Vineberg operation. Implantation of the left internal mammary artery into the left anterior descending (LAD) coronary artery was not performed until the late 1960s and, because of the relative ease and success of using saphenous veins as bypass conduits to the coronary arteries, use of the internal mammary artery initially remained quite limited.

Fortunately, however, a few centers chose to use the internal mammary artery as a bypass conduit in many patients. This later led to the 1986 publication of Loop et al. detailing the results of the Cleveland Clinic experience and showing exceptionally high patency rates and improved long-term outcome in patients receiving internal mammary arteries as bypass grafts (1). In their landmark paper, it was shown convincingly that the internal mammary artery, when used as a conduit and placed to the LAD coronary artery, reduced the risk of late myocardial infarction (MI), and decreased the risk of late cardiac events and need for cardiac reoperation. Most important, the 10-year survival was superior in patients who had a mammary artery graft placed to their LAD coronary artery versus those in whom only saphenous vein grafts (SVG) were used. Since then, the internal mammary artery graft has become the graft of choice for patients undergoing coronary artery bypass surgery whenever it is technically feasible. Indeed, the importance of total arterial surgical myocardial revascularization now is well recognized, and many patients with multivessel disease will have both the right and left internal mammary arteries used as conduits. The improved survival among diabetic patients who underwent surgical revascularization compared to balloon angioplasty (BA) in the Bypass Angioplasty Revascularization Intervention (BARI) trial is attributed to the use and patency of the left internal mammary artery (2).

The explanation for improved long-term patency of internal mammary artery grafts compared with SVG may lie in their apparent resistance to atherosclerosis. Detailed autopsy studies confirm that the incidence of atherosclerosis in the internal mammary arteries is extremely low, even in the presence of significant coronary artery disease (3,4). Accelerated atherosclerosis does not appear to occur in internal mammary artery grafts (4,5), whereas it is common in SVG (6).

Obstructive lesions, however, can occur in internal mammary artery grafts, although this is recognized to be uncommon. “Atherosclerotic” lesions in the body of the internal mammary artery are seen only rarely, and this probably relates to technical issues at the time of coronary artery bypass surgery, such as traumatic handling or injury. In these cases, the artery, and in particular the luminal endothelium, may be damaged during the mobilization of the artery and handling of the artery when performing the arterial anastomosis. This is more likely to occur during difficult dissections in patients who have undergone prior surgery or had external irradiation, or if complications occur intraoperatively. More commonly, obstructions will be seen at the distal anastomotic site, and these lesions probably relate more to the suturing technique, size of the distal vessel, and progression of disease or smooth muscle proliferation in the native vessel at the site of the anastomosis. Finally, some patients will present with recurrent symptoms and ischemia secondary to progressive disease in the distal native vessel without obstructive lesions in the internal mammary artery.