Does the use of bilateral mammary artery grafts compared with the use of a single mammary artery graft offer a long-term survival benefit in patients undergoing coronary artery bypass surgery?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was: 'Does the use of bilateral mammary artery grafts compared with the use of a single mammary artery graft offer a long-term survival benefit in patients undergoing coronary artery bypass surgery?' Altogether 214 papers were found using the reported search, of which 13 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. All the included studies were follow-up studies; eight studies used prospective data collection, and five studies collected the study data retrospectively. No randomized controlled trials were found. Nine of the 13 included papers used a propensity-score-matched comparison of the survival of bilateral mammary artery graft [or, bilateral internal thoracic artery (BITA) graft] patients vs single mammary artery graft [or, single internal thoracic artery (SITA) graft] patients. These studies consistently showed an enhanced survival of BITA patients compared with propensity-score-matched SITA patients. Three of the 13 included papers used Cox proportional hazards regression analysis to compare survival of BITA vs SITA patients; one larger study showed better crude survival of BITA patients, but did not identify BITA grafts as independent predictor of enhanced survival. The remaining two studies also did not identify BITA grafts as independent predictor of enhanced survival. One study only presented crude survival estimates of BITA vs SITA patients and therefore was of limited informative value. We conclude that the use of BITA grafts seems to offer a long-term survival benefit compared with a SITA graft for patients undergoing coronary artery bypass grafting surgery. Although randomized evidence is lacking, observational evidence supporting this hypothesis is mounting.