BACKGROUND: The mortality risk is high in patients with diabetes who sustain myocardial infarction. Recent evidence1 suggests that coronary artery bypass grafting (CABG) reduces long-term mortality better than percutaneous transluminal coronary angioplasty (PTCA), but the protective effect of CABG for patients with diabetes who have a future acute myocardial infarction is not known. This substudy of the Bypass Angioplasty Revascularization Investigation addresses this question.
POPULATION STUDIED: A total of 3603 patients who were severely symptomatic and who had angiographic evidence of multivessel coronary artery disease were identified at 18 sites in North America. Of this group, 1829 were randomized; the remainder underwent the revascularization procedure selected by their physician, usually CABG. At the beginning of the study, the mean age was 61.5 years, 73% were men, 64% had unstable angina, 41% had 3-vessel disease, 9% had congestive heart failure, and 19% had diabetes mellitus.
STUDY DESIGN AND VALIDITY: Patients were randomized to PTCA or CABG. Patients were re-evaluated with clinic visits and electrocardiograms between 4 and 14 weeks and then annually either in person (odd years) or by telephone (even years) for up to 5 years. After 5 years, annual follow-up was by telephone only. Only spontaneous Q-wave myocardial infarctions that occurred after revascularization were analyzed. Cumulative mortality data were collected for a mean of 5.5 years from the time of randomization. Kaplan-Meier analysis of cumulative mortality risk and Cox regression analysis of relative mortality risks were appropriately employed.
OUTCOMES MEASURED: The primary outcomes were death from all causes and death from Q-wave infarction. A secondary outcome was an estimate of relative mortality risk in those who underwent PTCA or CABG.
RESULTS: All-cause mortality at 5 years was higher in patients with diabetes than in those who did not have diabetes (20% vs 8%, P <.001; number needed to treat [NNT]=8). The corresponding mortality rates for those patients who underwent CABG were 18% and 7%, respectively, compared with rates of 25% and 8% in the PTCA group. Q-wave myocardial infarction occurred in 4.8% of patients during the 5-year follow-up; this rate was similar between CABG and PTCA groups. There was no significant difference in the estimated 5-year mortality risk after a spontaneous Q-wave infarction in patients who did not have diabetes who underwent either PTCA or CABG (30% vs 27%, P=ns). Among patients who had Q-wave infarction, there was no significant difference in mortality risk between patients who did and did not have diabetes who underwent CABG (17% vs 27%, P=ns). However, mortality after a Q-wave infarction was much higher in patients with diabetes who underwent PTCA instead of CABG (80% vs 17%, NNT=1.6). Compared with PTCA, CABG protected patients with diabetes who had a subsequent Q-wave infarction (relative risk of death=0.09; 95% confidence interval [CI], 0.03-0.29; P <.001). CABG also protected patients with diabetes who did not have an infarction (relative risk=0.65; 95% CI, 0.45-0.94; P=.02). The study was well designed, particularly considering the relatively rare occurrence of Q-wave infarction after revascularization. The randomization was not concealed and could have introduced selection bias in the results. The severity, duration, and control of diabetes were also not analyzed in this study.
Myocardial infarction after revascularization is a relatively rare event. Nevertheless, the evidence is strong that CABG protects the ability of patients with diabetes to survive future Q-wave infarction, especially when compared with PTCA. Given this result, patients with diabetes with symptomatic multivessel heart disease should undergo CABG instead of PTCA. Although some may argue that stenting could improve the outcomes for patients with diabetes treated with PTCA, there is no convincing patient-oriented evidence to support this claim.