CHICAGO — The long-term clinical benefits associated with multiple internal mammary artery bypass grafting in patients with multivessel coronary disease, compared with single internal mammary artery grafting, were confirmed in a 20-year follow-up study presented at the annual meeting of the Society of Thoracic Surgeons.

“Long-term rates of all adverse events are reduced with multiple internal mammary artery bypass, compared with single internal mammary artery bypass, as long as the grafts are placed to the two largest coronary systems,” said Dr. J. Scott Rankin, who said the procedure should be considered the “therapeutic standard.”

Investigators used the Duke University Cardiovascular Databank to assess 20-year outcomes and benefits of multiple internal mammary artery (MIMA) versus single internal mammary artery (SIMA) grafting and to evaluate possible differences in results between two multiple IMA configurations: left anterior descending (LAD) plus left circumflex grafts versus LAD plus right coronary grafts.

The series represents consecutive coronary bypass procedures by two surgeons working in the same practice at Duke University Medical Center, Durham, N.C., over a 3-year period beginning July 1, 1984.

One surgeon emphasized MIMA grafting for multivessel disease, and performed 654 procedures over the 3-year period. The other emphasized SIMA grafting, performing 413 procedures. “Both used primarily saphenous veins for adjunctive grafts,” said Dr. Rankin, who is now with Vanderbilt University in Nashville, Tenn.

In the final analysis, there were 490 patients in the SIMA cohort and 377 in the MIMA group. Two-thirds of the latter group underwent the LAD/left circumflex combination.

“In general, the philosophy was to use the IMAs for the two largest vessels. The LAD/circumflex patients had primarily pedicled right IMA grafts to the LAD and left IMAs to the circumflex,” he said.

End points for the data analysis were all-cause death, nonfatal MI, percutaneous coronary intervention, and redo coronary bypass; all four were combined as a composite end point. There were no statistically significant differences between the mostly male groups with respect to median ejection fractions, sternal infections, hospital mortality, or the 4-year requirement for redo bypass. There were small, statistically significant differences in rates of prior smoking, diabetes, and hypertension.

At 20-year follow-up, the MIMA group had a statistically significant mean reduction in nonfatal myocardial infarction of 37%, and what Dr. Rankin called a “striking” 63% reduced incidence of redo coronary bypass—from 12.6% in the SIMA group to 4.6% in the MIMA group, which was highly significant. There were statistical trends toward fewer percutaneous coronary interventions (PCIs) and all-cause mortality in the MIMA group.

In the adjusted Cox model composite end point for SIMA versus MIMA, advanced age and a higher number of comorbidities were the most important determinants of long-term positive outcome, “but multiple IMA versus single IMA also was significant, with a 17% risk reduction over the 20 years,” said Dr. Rankin. “In further analyses, the average life expectancy was extended by almost 1 year in the multiple IMA patients, with a P value of .001.” There was no significant difference between the LAD configurations.

“Multiple IMA grafting can be performed in over 70% of patients with multivessel coronary artery disease. Operative mortality and sternal infections in our series were not increased, and the configuration is not critical as long as the two largest vessels are grafted,” he said.

In addition, multiple IMA grafting is applicable to the entire spectrum of coronary patients—including the elderly [and] diabetics—and in emergencies; results were just as good in these high-risk groups. The long-term incidence of all adverse cardiac outcomes—including nonfatal MI, PCI, redo coronary bypass, and all-cause death—are reduced, and overall composite outcome is significantly improved, statistically and clinically, over a full 20 years of follow-up,” Dr. Rankin said.

These findings should affect clinical practice, Dr. Rankin said in an interview. “From our viewpoint, with the exception of the extremely elderly, we probably ought to be doing MIMA grafts in most ages and in diabetics,” he said.

Furthermore, “even though women tend to have smaller vessels, as long as you really check out the [mammary arteries] so that you don't end up with one that's too small or doesn't have good enough flow, it's fine to use double [IMA grafts] in females,” he added.

The road to these conclusions has been a long one, beginning with the proposition and observation 2 decades ago that MIMA grafting had superior patency.

“When we originally presented our series from 1984 and showed no increase in infection rate, nobody believed it,” said Dr. Rankin, explaining that the Duke data did not turn positive until the second decade of follow-up.

“But there are all kinds of papers out now showing the advantages of MIMA grafting in patients” with severe coronary artery disease, he said.

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'We probably ought to be doing MIMA grafts in most ages and in diabetics.' DR. RANKIN

20-Year Study Confirms Benefits of MIMA Bypass : The long-term rates of adverse events are decreased, provided the grafts are placed on the two largest vessels.