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 operation 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 bilateral IMA grafts were compared. We included studies in which at least 100 patients in each group had been followed up for at least 4 years. We assessed study quality on the basis of patient selection, comparability of intervention groups (especially for age, sex, ventricular function, and diabetes status), outcome assessment, and completeness of follow-up. Our primary outcome was survival. Estimates of treatment effect (single versus bilateral) expressed as hazard ratios were pooled across studies. Findings: None of the studies was a randomised trial, but nine cohort studies met our inclusion criteria. Seven studies yielded survival data for meta-analysis, and included 15 962 patients: 11 269 single and 4693 bilateral IMA grafts. The bilateral group had significantly better survival than the single group (hazard ratio for death 0.81; 95% CI 0.70-0.94). Exclusion of methodologically weak studies improved survival rates with bilateral IMA grafts. Interpretation: Because no study was a randomised trial, our results are more uncertain than is indicated by the 95% CI. Nevertheless, bilateral IMA grafts seem to give better survival rates than single grafts.