Impact of type 2 diabetes mellitus on short- and long-term mortality after coronary artery bypass surgery

BACKGROUND: Type 2 diabetes mellitus (DM) is a frequent co-morbidity among patients undergoing coronary artery bypass grafting (CABG) surgery. The aim of this study was to evaluate the impact of DM on the early- and long-term outcomes of patients who underwent isolated CABG. METHODS: We performed an observational cohort study in a large tertiary medical center over a period of 11 years. All data from patients who had undergone isolated CABG surgery between 2004 and 2014 were obtained from our departmental database. The study population included 2766 patients who were divided into two groups: Group I (1553 non-diabetic patients), and Group II (1213 patients suffering from type 2 DM). Group II patients were then divided into two subgroups: subgroup IIA (981 patients treated with oral antihyperglycemic medications) and subgroup IIB (232 insulin-treated patients with or without additional oral antihyperglycemic drugs). In-hospital, 1-, 3-, 5- and 10-year mortality outcome variables were evaluated. Mean follow-up was 97 ± 41 months. RESULTS: In-hospital mortality was similar between Group I and Group II patients (1.87% vs. 2.31%, p = 0.422) and between the subgroups IIA and IIB (2.14% vs. 3.02%, p = 0.464). Long-term mortality (1, 3, 5 and 10 years) was higher in Group II (DM type 2) compared with Group I (non-diabetic patients) (5.3% vs. 3.6%, p = 0.038; 9.3% vs. 5.6%, p < 0.001; 15.3% vs. 9.3%, p < 0.001 and 47.3% vs. 29.6% p < 0.001). Kaplan-Meier analysis demonstrated that all-cause mortality was higher in Group II compared with Group I (p < 0.001) and in subgroup IIB compared with subgroup IIA (p = 0.001). Multivariable analysis showed that DM increased the mortality hazard by twofold, and among diabetic patients, insulin treatment increased the mortality hazard by twofold. CONCLUSIONS: Diabetic and non-diabetic patients have similar in-hospital mortality rates. Survival rates of diabetic patients start to deteriorate 3 year after surgery. Type 2 DM is an independent predictor for long-term mortality after isolated CABG surgery. Mortality is even higher when the diabetes treatment strategy included insulin.