Thirty-year follow-up defines survival benefit for second internal mammary artery in propensity-matched groups

Background: The value of the left internal mammary artery (LIMA) graft is well established. However, the incremental value of a second IMA graft is controversial. Despite reports of improved survival with bilateral IMA (BIMA) grafting, the Society of Thoracic Surgeons reports its use in 4% of coronary artery bypass graft operations. We report the influence of BIMA vs SIMA grafting on hospital and late mortality in comparable groups.

Methods: Retrospective review was conducted of 4584 consecutive isolated coronary artery bypass graft operations (2369 SIMA and 2215 BIMA) performed from 1972 to 1994. The influence of the second IMA was assessed by multivariate analyses of risk factors associated with hospital and late mortality and by propensity score analysis that compares patients with similar baseline characteristics for receiving a second IMA graft. All patients were monitored clinically to assess outcomes.

Results: Hospital mortality was 4.5% for SIMA vs 2.6% for BIMA patients (p = 0.001). When stratified by propensity score to undergo BIMA grafting, no difference in hospital mortality was found. Multivariate analyses showed SIMA grafting was significantly associated with late but not hospital mortality. Survival curves after 52,572 patient-years of follow-up (mean, 11.5 years; range, 6 weeks to 32 years) demonstrated improved long-term survival for BIMA vs SIMA patients in all quintiles except those with the greatest propensity for SIMA, wherein late survival was comparable between groups. In matched groups, survival favored BIMA patients (p = 0.001).

Conclusions: BIMA grafting offers a long-term survival advantage over SIMA grafting in propensity-matched groups.