Diabetic patients undergoing coronary artery bypass grafting: effects of haemoglobin A1c and peri-operative glucose levels

Abstract

Background: Nearly half of patients undergoing coronary artery bypass grafting (CABG) have diabetes. There is mixed data as to whether pre-operative (haemoglobin A1c=HbA1c) and/or peri-operative diabetes management is associated with mortality and morbidity after CABG. We reviewed the characteristics and outcomes of diabetic patients undergoing CABG with a focus on HbA1c, peri-operative glucose levels and diabetic treatments. Methods: Diabetic patients undergoing CABG during July 2010-June 2010 were studied (n=306). Last pre-operative HbA1c levels, and peri-operative glucose levels (mean) and variability (standard deviation and coefficient of variation (CV)) from the day before operation to 3 days after were retrospectively recorded, as well as the pre-existing and peri-operative diabetes treatment modalities for analyses. Results: Mean HbA1c was 7.7+/-1.6%, and 11.1% (34), 56.2% (172), and 32.7% (100) of patients were managed pre-operatively with diet, oral diabetic medications and insulin respectively. For operative mortality, C-statistics (95% confidence interval) was only significant for HbA1c 0.855 (0.757-0.975) and glucose CV on the day of surgery 0.722 (0.567-0.877). HbA1c also detected post-operative renal failure c-statistic 0.617 (0.504-0.730), but not other complications or mortality during follow-up. In multivariate analysis, HbA1c was the only diabetes-related independent predictor of operative mortality hazards ratio 4.13 (1.04-16.4), and none of the diabetes-related variables predicted mortality during follow-up or other post-operative complications. Conclusion: Pre-operative HbA1c was the only diabetic variable to independently predict after operative mortality after CABG, suggesting medium-term pre-operative diabetes control being more important and prognostic of operative outcomes than peri-operative diabetes control.