Patients undergoing coronary artery bypass grafting (CABG) who have more than 8% preoperative hemoglobin A1c (HbA1c) are at a higher risk for mortality and adverse cardiac events, such as myocardial infarction and percutaneous intervention upon follow-up, according to study results published in the European Journal of Cardio-Thoracic Surgery.

Among patients with diabetes mellitus who have multivessel coronary artery disease, coronary artery bypass grafting is the preferred intervention; however, both diabetes mellitus and increased preoperative HbA1c levels are predictors of poor survival. Despite this knowledge, the range of HbA1c, its changes during postoperative follow-up, and its interaction with other risk factors are not well understood.

A team of investigators conducted an observational retrospective cohort study using data from the Veterans Affairs national database to assess the relationship of preoperative HbA1c levels and midterm survival in patients with diabetes mellitus after coronary artery bypass grafting, as well as the rates of all-cause mortality and adverse cardiovascular events in this patient population.


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Data from 16,190 patients (mean age, 64.9 years; 98% men; 53% insulin-dependent) with diabetes mellitus who underwent isolated coronary artery bypass grafting were included. Patients were categorized into 1 of 4 groups based on their HbA1c levels; 19.4% of patients had HbA1c levels less than 6.5% (group 1), 45.4% of patients had HbA1c levels from 6.5% to 8% (group 2), 27% of patients had HbA1c levels from 8% to 10% (group 3) and 8.2% of patients had HbA1c levels greater than 10% (group 4).

Patients in group 4 were the youngest (mean age, 60.9 years) and had the highest rates of insulin dependence (78%), previous myocardial infarction (52.8%), and left ventricular systolic dysfunction (19.6%).

Of the cohort, 30-day mortality, acute kidney injury, and stroke were noted in 1.5%, 1.4%, and 1.2% of patients, respectively. Postoperative stroke rates were highest among patients in group 3 (P =.003) and other reported adverse events were comparable across all 4 groups.

The median follow-up was 5.87 years, and 5781 deaths were reported during the follow-up period. The 5-year morality rates for groups 1, 2, 3, and 4 were 22%, 20%, 21%, and 24%, respectively, and the 10-year mortality rates were 47%, 44%, 50%, and 55%, respectively. Following adjustment for preoperative HbA1c levels, increased mortality was affected by increased age (hazard ratio [HR], 1.4), left ventricular systolic dysfunction (HR, 1.65), previous myocardial infarction (HR, 1.30), and insulin dependence (HR, 1.34).

The relation between HbA1c levels and mortality was nonlinear and increased with HbA1c values greater than 8%, especially in levels greater than 9%. Using the study mean HbA1c level of 7.3% (HR, 1), patients with HbA1c levels greater than 10% had a 30% increased mortality risk. Compared with patients who had HbA1c levels less than 8%, patients in groups 3 and 4 had an increased risk of myocardial infarction (HRs, 1.24 and 1.39, respectively) and the need for reintervention (HRs, 1.20 and 1.24, respectively).

“Rather than categorization, modelling HbA1c as a continuous spline provides a clearer understanding of the incremental risk per unit increase in its value,” the researchers stated.

“In patients with elevated pre-operative HbA1c levels, we observed significant rates of improvement. Yet, more can be done to improve long-term well-being in these patients,” they concluded.

Reference

Deo S, Sundaram V, Sheikh MA, et al. Pre-operative glycaemic control and long-term survival in diabetic patients after coronary artery bypass grafting. Eur J Cardiothorac Surg. Published online May 10, 2021. doi:10.1093/ejcts/ezab180