Relationship between preoperative hemoglobin A1c levels and long-term mortality after coronary artery bypass grafting in patients with type 2 diabetes mellitus

BackgroundPatients with type 2 diabetes mellitus (T2DM) have an increased risk of coronary heart disease and death. We aimed to investigate the association between preoperative hemoglobin A1c (HbA1c) levels and long-term mortality after coronary artery bypass grafting (CABG) among patients with T2DM.MethodsAll patients with T2DM who underwent CABG in Sweden from 2003 to 2013 were included from the SWEDEHEART register. Information about diabetes was retrieved from the Swedish National Diabetes Register. We used Cox regression to calculate hazard ratios (HR) with 95% confidence intervals (CI) for all-cause mortality and also a combination of death or a major cardiovascular event (MACE).ResultsIn total, 6313 patients were included. During a mean follow-up time of 5.5 (± 3.8) years, (34,482 person-years), 1630 (26%) patients died. After multivariable adjustment, HbA1c was associated with an increased risk of death in patients with HbA1c levels 9.1-10%, and > 10% (HR (95% CI): 1.26 (1.04-1.53), and 1.33 (1.05-1.69), respectively). There was an increased risk for death or MACE at HbA1c levels 8.1-9%, 9.1-10%, and > 10% (HR (95% CI): 1.17 (1.04-1.33), 1.44 (1.22-1.70), and 1.50 (1.22-1.84), respectively). In patients with insulin-treatment there was no association between HbA1c levels and death.ConclusionsIn patients with T2DM who underwent CABG we found an increased risk of death at HbA1c levels above 9.0%, and also for the combination of death or MACE at HbA1c levels above 8.1%. There was no association between HbA1c levels and death in T2DM patients who were insulin-treated.