Does chronic metformin therapy offer cardiomyoprotection in coronary artery bypass grafting surgery patients? A case-control study

Introduction

Metformin, widely used as an antidiabetic drug, activates the AMP activated protein kinase, a key regulator of the metabolism providing protection under fuel deficiency. Chronic metformin therapy has been shown in long-term follow-up clinical studies to reduce cardiovascular mortality [1]. In animal experiments, acute metformin pretreatment has been shown to reduce ischemia-reperfusion injury on cardiomyocytes [2]. We want to evaluate whether outcomes are affected in coronary artery bypass grafting (CABG) surgery.

Methods

We performed a retrospective case-control study on 341 patients admitted exclusively for CABG surgery with cardiopulmonary bypass between January 2006 and April 2012. Eighty-one patients chronically on metformin were matched 1:3 with nonmetformin-treated ones using gender, age, body mass index and number of arterial bypass grafts. Global mortality, ICU-free 28 postoperative days and creatinine kinase MB (CKMB) at postoperative baseline, 8 and 18 hours post baseline were compared.

Results

Metformin-treated patient mortality was not significantly lower than in nonmetformin (1.2% vs. 3.1%, P = 0.24, Fischer exact test). ICU-free 28 postoperative days were higher in the metformin group (median 23.4 days; 95% CI = 22.5 to 24.3) than in the nonmetformin group (median 22.9 days; 95% CI 22.3 to 23.5, P 0.04, Wilcoxon test). Median CKMB levels at postoperative baseline were 21 versus 26 ng/ml (P 0.003), at 8 hours were 22 versus 53 ng/ml (P 0.004) and 18 hours post baseline were 21.5 versus 27.5 ng/ml (P 0.012). See Table 1.

Table 1 Case-control analysis

Conclusion

These data suggest that chronic preoperative treatment with metformin is associated with lower CKMB levels at postsurgery baseline, 8 and 18 hours post baseline with a shorter ICU stay in patients receiving CABG surgery under extracorporeal circulation.