Study supports the use of the internal mammary artery in coronary artery bypass grafting

Long-term follow up with heart bypass patients treated in Veterans Affairs hospitals shows that 85 percent of left internal mammary artery grafts and 61 percent of vein grafts remain open (patent) after 10 years, and that these grafts are more likely to offer long-term success when they are attached to larger arteries on the heart, according to a new study in the Dec. 7, 2004 issue of the Journal of the American College of Cardiology.

“Clinicians can use our data to tell patients what their long-term chances are of having a patent internal mammary artery or vein graft. Ten-year vein graft patency is better than most people thought, especially when the graft is placed to a larger recipient coronary artery, that is, one with a diameter greater than two millimeters. Also, internal mammary artery patency is not as good as most people thought,” said Steven Goldman, M.D., F.A.C.C., of the Southern Arizona VA Health Care System and the University of Arizona Sarver Heart Center in Tucson.

The researchers studied patients who underwent heart bypass surgery at one of 13 VA Health System hospitals in the mid- to late-1980s. Grafts of leg veins were used in 1,074 patients, while 457 patients received grafts using their internal mammary arteries. The mammary arteries are located in the chest. The patients were not randomized, and the blood vessels used for the grafts were selected by the surgeons who performed the procedure.

While earlier studies and clinical experience have provided substantial evidence that internal mammary arteries generally remain open longer than vein grafts, this study provides a unique look at the long-term relative benefits of the two types of grafts that are used to bypass blood flow around blockages in arteries that feed the muscle of the heart.

“Most studies of vein graft and internal mammary artery patency are not prospective studies; ours is a prospective study,” Dr. Goldman said. “The major difference between our study and others is that we obtained serial angiograms at one week, one year, three years and 10 years prospectively. The first three angiograms were planned ahead of time and the 10-year angiogram was done as part of our final study design,” he added.

The study pointed to certain factors that appear to influence the long term success of the grafts. The researchers found that if the grafts were open a week after surgery, the 10-year success rates for both types of blood vessels rose slightly, to 88 percent for internal mammary artery grafts and 68 percent for vein grafts. Also, vein grafts onto the left anterior descending coronary artery were more likely to remain open than vein grafts to the right coronary artery. And size mattered; if the coronary artery that the graft was connected to was larger than two millimeters in diameter, 88 percent of vein grafts were still open a decade later. However, when the recipient blood vessel was two millimeters across or smaller, the 10-year success rate dropped to 55 percent.

“I would stress that the size of the recipient vessel is a key factor that has not been well appreciated,” Dr. Goldman said.

This study tracked the long-term outcomes of vein and artery grafts as they were typically used during the study period. It was not a direct comparison of the different types of grafts.

“The major limitation of our study is that the number of patients declines out to 10 years. This is inevitable in any study of middle aged men with heart disease. Many of these patients die, if not from their heart disease, then from other causes. This limitation is present for all studies of this nature,” Dr. Goldman said.

Eugene H. Blackstone, M.D., F.A.C.C., at the Cleveland Clinic Foundation in Cleveland, who was not connected with this research effort, said that although this study found that artery grafts did not perform as well as some earlier studies indicated, the overall results support the usual preference for internal mammary arteries over leg veins.

“This study provides powerful, new and important information that supports use, whenever possible, of the internal mammary artery in coronary artery bypass grafting. It is one decision in the hands of the surgeon that can make an important difference 10, 20 and more years down the line,” Dr. Blackstone said.

Dr. Blackstone also noted that the researchers used sophisticated statistical techniques to help draw a clearer picture of the long-term experiences of heart bypass patients.

“Beside the important clinical information, the study has a special strength ‘beneath its skin.’ Statistical techniques not widely available until the last decade have been used to properly account for the fact that a given patient has multiple grafts, such as a mix of internal mammary artery and saphenous vein grafts, assessed by coronary angiography. The authors are to be congratulated for using modern methods of analysis that take this fact into account,” Dr. Blackstone said.