**Survival benefits of BIMA versus Single Internal Mammary Artery (SIMA)**

Several observational, retrospective studies have found that there are significantly greater long-term survival benefits in patients who received BIMA grafting compared to SIMA grafting. Lytle *et al.* studied 10,124 elective CABG patients receiving either SIMA or BIMA grafts with or without any additional vein grafts in a retrospective, non-randomized study with a mean follow-up of 10 post-operative years. Hospital mortality rates were identical for the SIMA and BIMA groups (0.7%). However, over 12 years of post-operative follow up, survival rates for BIMA patients were significantly better than for SIMA patients (79.1% versus 71.6% respectively, p < 0.001) [9]. In a follow-up to the original study, which extended the mean post-operative follow up to 16.5 years, survival rates for BIMA and SIMA patients at 20 years were 50% versus 37% respectively (p < 0.0001), demonstrating a significant long-term survival advantage for patients receiving two internal mammary grafts compared to just one [10].

Nasso *et al.* aimed to determine whether or not there were significant benefits to using two arterial conduits rather than just a single arterial conduit. 815 patients were randomized to one of four revascularization strategies: *in situ* LIMA to LAD plus isolated RIMA Y graft, *in situ* RIMA to LAD plus *in situ* LIMA, *in situ* LIMA to LAD plus free radial artery, and *in situ* LIMA to LAD with saphenous vein grafts as a control. All revascularization groups received saphenous vein grafts to bypass the remaining coronary occlusions, if needed. Although the authors found no significant overall survival advantage between any of their revascularization groups over a follow-up period of two years, there was a significant difference in survival when considering cardiac event-free survival. Patients in groups receiving two arterial grafts had significantly better cardiac event-free survival rates when compared to patients who only received a single internal mammary artery (LIMA) grafted to the LAD with saphenous vein grafts. These arterial revascularization strategies were also seen to convey significantly better cardiac event-free survival rates to elderly (> 75 years) patients as well. The study did not find any significant differences in survival based on the choice of either the RIMA or the radial artery as the second arterial conduit [11].

In the longest reported retrospective analysis of CABG procedures, ranging from 6 weeks to 32 years of follow up, Kurlansky *et al.* conducted a review of 4,584 isolated CABG procedures between 1972 and 1994. When patient differences were accounted for and comparisons made between 2,197 matched patients, survival was 16.5% for SIMA patients and 28.5% for BIMA patients after 25 years (p = 0.001). The median survival for SIMA patients was 11.8 years compared to 15.9 years for BIMA patients. There were no significant differences between the two groups in the rates of non-fatal myocardial infarction, reoperation, percutaneous coronary intervention, permanent stroke, or composite freedom from late adverse cardiac events. [12

The location of the distal anastomosis of the RIMA graft also does not appear to significantly affect clinical outcomes of patients undergoing BIMA grafting. Kurlansky *et al.* performed a propensity-matched study of 2,215 patients undergoing BIMA CABG procedures having the RIMA grafted to either the right coronary system or to the left coronary system. In both the matched and unmatched analyses, there was no significant difference in operative or late mortality between the two groups. The median survival for propensity-matched patients in both groups was 16.1 years (p = 0.671) [13]. In another study by Rankin *et al.* there were no significant differences in long-term outcomes based on grafting territory of BIMA grafts as long as they are anastomosed to the two largest coronary systems [14].

Not all studies have found significantly increased survival rates for BIMA use over SIMA use. In a study performed by Dewar *et al.*, there was not a significant difference in the 5 or 7-year survival rates for patients undergoing either unilateral or bilateral IMA grafting with supple‐ mental vein grafts. 5-year survival rates for SIMA and BIMA revascularization for patients less than 60 years of age were 94.4% and 94.8%, respectively (p = not significant). There was also no significant difference in 5-year survival rates for patients over 60 years of age. However, the authors did note that there was a trend in lower rates of angina in the patient group receiving BIMA grafts less than 60 years of age [15].
