Preoperative hemoglobin A1c predicts atrial fibrillation after off-pump coronary bypass surgery

OBJECTIVE: Diabetes mellitus has been recognized as a risk factor for mortality and morbidity after coronary bypass grafting, but a significant association between diabetes mellitus and postoperative atrial fibrillation (AF) has not been found. Although a recent study demonstrated a potential link between preoperative hemoglobin A1c level and risk of postoperative AF, there has not been sufficient examination of this relationship. We aimed to investigate the association between preoperative hemoglobin A1c and AF after isolated off-pump coronary bypass grafting. METHODS: Of 912 consecutive patients undergoing isolated coronary bypass surgery, 805 were retrospectively analyzed for AF after excluding the following 107 cases: emergency (n = 81), chronic AF (n = 18), and pacemaker rhythm (n = 8). We performed a group analysis with hemoglobin A1c levels categorized into tertiles of the baseline distribution and a continuous analysis based on 1% increments in hemoglobin A1c levels. The cutoff points for the tertiles were as follows: lower, 3.8-5.6% (n = 283); middle, 5.7-6.7% (n = 282); upper, 6.8-11.4% (n = 240). RESULTS: AF occurred in 159 patients (19.8%) after surgery. The median value (25th-75th percentile) of preoperative hemoglobin A1c was significantly lower in patients who developed AF than in those who did not (5.8 (5.4-6.3) vs 6.1 (5.5-7.2), p = 0.01). The incidence of postoperative AF was 28.3% (80/283) in the lower tertile, 17.4% (49/282) in the middle tertile, and 12.5% (30/240) in the upper tertile (p for trend = 0.01). The unadjusted odds ratio (95% confidence interval) for the association between hemoglobin A1c and postoperative AF was 0.70 (0.61-0.83) per 1% increase and 0.42 (0.29-0.70) for the upper versus the lower tertile. This association persisted after adjustment for the univariate predictors (0.74 (0.60-0.92) per 1% increase; 0.54 (0.31-0.90) for upper vs lower tertile) and the known risk factors (0.78 (0.63-0.95) per 1% increase; 0.55 (0.35-0.88) for upper vs lower tertile). The area under the receiver operator characteristic curve (95% confidence interval) for preoperative hemoglobin A1c as a predictor of postoperative AF was 0.70 (0.65-0.75) (p = 0.01). CONCLUSIONS: Preoperative hemoglobin A1c independently predicts the occurrence of AF after isolated off-pump coronary bypass grafting.