Influence of diabetes and mammary artery grafting on survival after coronary bypass.

The effect of diabetes on survival after coronary bypass surgery is uncertain. Also, although the overall clinical benefits of internal mammary artery (IMA) grafting are well established, the survival benefit attributable to IMA grafting in diabetics is not well characterized. To determine the influence of diabetes and IMA grafting on survival after bypass surgery in the current surgical era, characteristics related to subsequent outcome were analyzed in 5,654 consecutive patients undergoing surgery in the decade of the 1980s. The 1,132 diabetic patients (20%) had more extensive coronary disease, had more left ventricular dysfunction, were older, were more frequently female, received a greater number of grafts (mean, 3.5 versus 3.1), and received more IMA grafts (67% versus 58%) than the 4,522 nondiabetic patients (all p less than 0.001). Overall 5-year survival probability was 0.91 in nondiabetic and 0.80 in diabetic patients (p less than 0.0001). Nondiabetic survival exceeded diabetic survival even in high-risk subgroups such as ejection fraction less than or equal to 0.40 (0.80 versus 0.66, p less than 0.02), age greater than or equal to 65 years (0.85 versus 0.73, p less than 0.0003), and, urgent surgery (0.89 versus 0.76, p less than 0.0001). By multivariate analysis, impairment of left ventricular function, advanced age, failure to use an IMA graft, diabetes, female sex, urgent surgery, number of diseased vessels, and mitral insufficiency were incremental risk factors for cardiac mortality (all p less than 0.006). Failure to use an IMA graft and diabetes were equally strong predictors of outcome. Use of an IMA graft conveyed an independent survival benefit to both nondiabetic (p less than 0.0001) and diabetic (p less than 0.02) patients. The magnitude of the survival benefit attributable to IMA grafting in the two groups did not differ (p = 0.4). Diabetes is an important risk factor for late cardiac mortality after bypass surgery and should be included in analyses of the efficacy of therapies for coronary artery disease. IMA grafting conveys a similar benefit to diabetic and nondiabetic patients but does not negate the adverse effect of diabetes on survival.