COLORADO SPRINGS – The survival advantage of bilateral internal over left internal mammary artery grafts persists even among multivessel CABG patients perceived to be at high surgical risk, Nishant Saran, MD, reported at the annual meeting of the Western Thoracic Surgical Association.
Many surgeons hesitate to perform bilateral internal mammary artery (BIMA) grafting in high-risk patients on the presumption that BIMA might not benefit them. It’s a concern that appears to be without merit, however, based on a retrospective analysis of the 6,468 multivessel CABG procedures performed at the Mayo Clinic during 2000-2015, said Dr. Saran of the Mayo Clinic in Rochester, Minn.
The BIMA patients were as a whole significantly younger, primarily men, and less likely to have diabetes or to be obese than the LIMA patients. Also, LIMA patients were fourfold more likely to have baseline heart failure, twice as likely to have a history of stroke, and had a twofold greater prevalence of chronic lung disease.
“The unmatched comparison shows the clear treatment selection bias we have: BIMA goes to the healthier patients,” Dr. Saran observed.
But is that bias justified? To find out, he and his coinvestigators performed extensive propensity score matching using several dozen baseline variables in order to identify 1,011 closely matched patient pairs. In this propensity score-matched analysis, 5- and 10-year survival rates were significantly better in the BIMA group. The gap between the two survival curves widened after about 7 years and continued to expand steadily through year 10. Incision time averaged 298 minutes in the BIMA group and 254 minutes in the propensity-matched LIMA group.
Discussant Eric J. Lehr, MD, a cardiac surgeon at Swedish Medical Center in Seattle, noted that the impressive survival benefit for BIMA in the retrospective Mayo Clinic study came at what he termed “a modest cost”: a doubled incidence of sternal site infections, from 1.4% in the LIMA group to 3% with BIMA. Importantly, though, there was no significant difference in the more serious deep sternal wound infections.
He agreed with Dr. Saran that BIMA is seriously underutilized, noting that only one cardiothoracic surgery program in the state of Washington uses BIMA more than 10% of the time in multivessel CABG.
Dr. Lehr then posed a provocative question: “Should BIMA grafting be considered a quality metric in coronary revascularization surgery, despite the small increase in sternal site infections, even though sternal wound infections have been declared a ‘never’ event and are tied to reimbursement?”
“I think BIMA should be a gold standard,” Dr. Saran replied. “The first thing that a cardiac surgeon should always think of when a patient is going to have CABG is ‘BIMA first,’ and only then look into reasons for not doing it. But I guess in current real-world practice, things are different.”
Howard K. Song, MD, commented, “I think a study like this doesn’t necessarily show that every surgeon should be using BIMA liberally, it shows that surgeons in your practice who do that have excellent outcomes.”
Dr. Song, professor of surgery and chief of the division of cardiothoracic surgery at Oregon Health and Science University, Portland, added that he believes extensive use of BIMA is actually a surrogate marker for a highly skilled subspecialist who would be expected to have very good outcomes as a matter of course.
“That may be one way of looking at it; however, I do think that even very skilled surgeons still have an inherent resistance to doing BIMA,” Dr. Saran responded.
“In the current era, the surgeon is pressured to achieve improved short-term outcomes and improved OR turnover times. An extra half hour for BIMA tends to push the surgeon away,” he added.
Dr. Saran reported having no financial conflicts of interest.