COLORADO SPRINGS – Using bilateral internal mammary artery grafts provided a significant long-term survival advantage over single mammary artery grafts for coronary artery bypass surgery patients with normal or moderately impaired left ventricular function, according to a large retrospective study with lengthy follow-up.
But when preoperative left ventricular ejection fraction (EF) was less than 30%, the procedure choice made no difference from a survival standpoint.
Dr. David Galbut
"BIMA grafting is the operation of choice in patients with a life expectancy beyond 1-2 decades," Dr. David Galbut declared at the annual meeting of the Western Thoracic Surgical Association.
He reported on 4,537 consecutive patients who underwent CABG with internal mammary artery grafting during 1972-1994 at three Florida hospitals. BIMA grafts were performed in 48% of the patients, an exceptionally high BIMA rate. In contrast, the Society of Thoracic Surgeons database shows that, nationally, 4% of patients undergoing CABG receive BIMA grafts. The reason for the 12-fold higher BIMA rate in the Florida study is that Dr. Galbut and his coinvestigators have a decades-long conviction that BIMA offers major clinical advantages.
In the Florida study, 233 patients had an EF below 30%, another 1,256 had an EF of 30%-50%, and 3,048 had a normal EF. In the low EF group, 87 BIMA patients were matched to an equal number of SIMA patients on the basis of 14 preoperative variables. In like manner, propensity scores were used to match 448 BIMA patients in the moderately impaired EF group and 1,137 BIMA patients with a normal EF to similar SIMA patients.
One of the reasons many surgeons are reluctant to use BIMA grafting is a concern that it will result in increased in-hospital complications. This wasn’t the case in the Florida series. Indeed, operative morbidity – including sternal wound infection rates – were similar in matched groups receiving BIMA or SIMA, according to Dr. Galbut of the Aventura (Fla.) Medical Center.
The 20-year survival rate in BIMA patients with moderately impaired EF was 33.1%, significantly better than the 19% survival in matched SIMA patients. In the normal EF group, the 20-year survival rate was 38.1% with BIMA and 35.8% with SIMA.
The general strategy the surgeons followed in BIMA grafting was to run the left internal mammary artery (LIMA) graft to the left anterior descending coronary artery. The LIMA is the dominant vessel in most patients and would therefore be the most durable conduit, Dr. Galbut explained. The right internal mammary artery graft was placed wherever it fit best.
Discussant Dr. Anthony P. Furnary was quick to observe that retrospective studies can’t prove causality, not even when they’re large, painstakingly performed, and feature more than 2 decades of follow-up, as did this one.
He suspects that limitations in the propensity score matching may account for much or all of the long-term survival advantage observed with BIMA grafting in this study. Although patients were extensively matched in terms of 14 preoperative variables, the year of surgery wasn’t among them.
The 22-year study period beginning in 1972 saw the introduction of many modern myocardial protection techniques. If more SIMA patients were operated on in the earlier years of the study, they might well have missed out on the salutary effects of these adjunctive therapies, said Dr. Furnary of the Providence Heart and Vascular Institute in Portland, Ore.
Dr. Galbut declared having no financial conflicts.