Introduction:
We analyzed the national Veteran Affairs (VA) data to evaluate the association of preoperative glycated Hemoglobin (HbA1c) and long-term outcome after isolated coronary artery bypass grafting (CABG).
Methods:
Between January 2007 - December 2014, Veterans with diabetes mellitus (DM) that underwent isolated CABG were divided on into three groups (I: HbA1c < 8%, II: HbA1c 8 - 10% and III: HbA1c > 10%). Demographic and clinical differences between groups were evaluated with the t-test or chi-square test. The relationship of preoperative HbA1c and long-term survival was evaluated with a multivariable proportional hazards model; restricted cubic splines were used to model non-linear effects. The cumulative incidence of secondary end-points (myocardial infarction, urgent revascularization) for each group was modeled as a competing-risk analysis.
Results:
Overall, 3,210 patients (mean age 64.6 years, male 98.8%; insulin dependent - 53%) with DM underwent isolated CABG. Group III patients were younger (61 vs 65 years in group I). Median HbA1c levels were similar between races (white - 7.3% and blacks - 7.35%). Insulin dependence was higher in group III (79.3%) vs groups I (43.5%) and II (69.9%). In groups I,II and III, 5 and 10 year survival was 76.2%, 74.4%, 75.4% and 38.9%, 36.9% and 30.2% respectively. HbA1c was observed to have a J-shaped association with mortality with values < 6% and > 9% at higher risk of death. Left ventricular systolic dysfunction [HR 1.5 (1.3 - 1.7)], prior myocardial infarction [HR 1.3 (1.2 - 1.5)] and insulin dependence [HR 1.4 (1.2 - 1.5)] were also associated with lower survival. Myocardial infarction was observed in 9.8% , 13.4% and 12.8% patients in groups I, II and III respectively.
Conclusions:
Pre-operative HbA1c impacts long-term survival among diabetic patients undergoing CABG. We observed a J-shaped relationship between HbA1c and survival with values < 6% and > 9% associated with increased mortality.
