Hemoglobin A1c Level in Patients with Diabetes Mellitus Predicts Adverse Outcomes Following Coronary Artery Bypass Surgery

Introduction: Hemoglobin A1c (HbA1c) is the recommended method of monitoring long term glycemic control in patients with diabetes mellitus (DM). The American Diabetes Association suggests HbA1c levels less than 7% as a therapeutic goal in DM population. Our aim was to estimate the association between HbA1c levels below and above 7% and the rate of Major Cardio and Cerebrovascular Events (MACCE) defined as death, stroke, percutaneous coronary intervention (PCI) or acute MI in patients with DM undergoing Coronary Artery Bypass Grafting (CABG) during ten years follow-up.

Methods: DM patients undergoing CABG in Soroka University Medical Center (SUMC) in were assessed (2002-2013). HbA1c within three months prior to the surgery was recorded. The primary outcome was MACCE.

Results: Pre-surgical HbA1c levels were available in 579 DM patients (30.0%) out of 1910 DM patients who underwent CABG during the follow-up period. Mean HbA1c was 8.0±1.7%, 206 (35.6%) patients had HbA1c ≤7% and 373 (64.4%) had HbA1c >7%. during study follow up (median=5.9 years) MACCE rates were 34.5% vs 41.6% in HbA1c ≤ 7% and HbA1c > 7%, respectively (Kaplan-Meier estimates, log rank p=0.049). Multivariable Cox proportional hazards regression analysis showed that patients in HbA1c > 7% group had MACCE hazard ratio of 1.45 (p=0.01) and in patients older than 75 hazard ratio of 2.14 (p=0.02). Moreover, HbA1c> 7% was associated with a mortality hazard ratio 2.32 (p<0.001). All models were adjusted for age, gender, smoking, previous ischemic heart disease, hypertension, chronic renal failure and acute coronary syndrome as an indication for CABG.

Conclusions: Our findings showed that in a CABG population of patients with diabetes, HbA1c remains an independent predictor of the macrovascular events.