Background: Magnesium supplementation may reduce the incidence of arrhythmias, which often occur after cardiac surgery; however, recent findings of the effectiveness of magnesium prophylaxis have yielded discrepant results.
Methods: We searched electronic databases for randomized controlled trials of magnesium for the prevention of arrhythmias after cardiac surgery. The primary outcomes comprised the incidence of supraventricular and ventricular arrhythmias, and the secondary outcomes comprised serum magnesium concentration, length of hospital stay, myocardial infarction, and mortality. Effect sizes were estimated using a random-effects model.
Results: Seventeen trials (n=2069 patients) met the inclusion criteria. Pooled serum magnesium concentration at 24 hours after surgery in the treatment group was significantly higher than that in the control group (weighted mean difference=0.45 mmol/L [1.1 mg/dL]; 95% confidence interval [CI]: 0.30 to 0.59 mmol/L [0.7 to 1.4 mg/dL]; P <0.001). Magnesium supplementation reduced the risk of supraventricular arrhythmias (relative risk [RR]=0.77; 95% CI: 0.63 to 0.93; P=0.002) and ventricular arrhythmias (RR = 0.52; 95% CI: 0.31 to 0.87; P <0.0001), but had no effect on the length of hospital stay (weighted mean difference=-0.28 days; 95% CI: -0.70 to 1.27 days; P=0.48), the incidence of perioperative myocardial infarction (RR=1.03; 95% CI: 0.52 to 2.05; P = 0.99), or mortality (RR=0.97; 95% CI: 0.43 to 2.20; P=0.94).
Conclusion: Administration of prophylactic magnesium reduced the risk of supraventricular arrhythmias after cardiac surgery by 23% (atrial fibrillation by 29%) and of ventricular arrhythmias by 48%. Supplementation had no notable benefit with respect to length of hospitalization, incidence of myocardial infarction, or mortality.