Effect of arterial revascularisation on survival: a systematic review of studies comparing bilateral and single internal mammary arteries

Background Coronary artery bypass grafting (CABG) is the commonest major op eration in most developed countries. A single internal mammary artery (IMA) graft has proven survival benefits, but the additional survival advantage of a second graft is unknown. We systematically reviewed published studies of bilateral versus single IMA grafts in CABG to assess any differences in survival. Methods We identified from Medline all studies in which single and bilatera l IMA grafts were compared. We included studies in which at least 100 patie nts in each group had been followed up for at least 4 years. We assessed st udy quality on the basis of patient selection, comparability of interventio n groups (especially for age, sex, ventricular function, and diabetes statu s), outcome assessment, and completeness of follow-up. Our primary outcome was survival. Estimates of treatment effect (single versus bilateral) expre ssed as hazard ratios were pooled across studies. Findings None of the studies was a randomised trial, but nine cohort studie s met our inclusion criteria. Seven studies yielded survival data for meta- analysis, and included 15 962 patients: 11269 single and 4693 bilateral IMA grafts. The bilateral group had significantly better survival than the sin gle group (hazard ratio for death 0.81; 95% Cl 0.70-0.94). Exclusion of met hodologically weak studies improved survival rates with bilateral IMA graft s. Interpretation Because no study was a randomised trial, our results are mor e uncertain than is indicated by the 95% CI. Nevertheless, bilateral IMA gr afts seem to give better survival rates than single grafts.