The efficacy of supplemental magnesium in reducing atrial fibrillation after coronary artery bypass grafting.

Randomized, double-blind, placebo-controlled trial of elective isolated CABG in 202 adults ( Mg group n=105; control n=97 ). Inclusion: age ≥18; no history of chronic arrhythmia; ejection fraction >25%; creatinine <1.5 mg/dL.

80 mg/kg ideal body weight of magnesium sulfate in 100 mL 5% dextrose water (D5W) given over 30 minutes before cardiopulmonary bypass, followed by 8 mg/kg ideal body weight per hour intravenous magnesium sulfate infusion for 48 hours postoperatively.

Serum magnesium rose after the first bolus (4.75 mg/dL in Mg vs 1.91 mg/dL in control, p<0.001) and remained higher through postoperative day 4 (3.24/3.05 mg/dL, p=0.24 for POD 2–5). Urinary magnesium excretion was markedly higher in the Mg group (324.5 mg/24 h vs 45.1 mg/24 h, p=0.01). Atrial fibrillation occurred in 30.5% of the Mg group vs 42.3% of controls (p=0.08); on postoperative day 1 AF was lower with Mg (2.9% vs 9.3%, p=0.05). No differences in tissue Mg levels. Overall, prophylactic magnesium did not significantly reduce atrial or ventricular arrhythmias; the only notable benefit was reduced AF on the first postoperative day.

Single-center trial; 202 participants; not powered to detect small differences in arrhythmias; tissue Mg analyzed in a subset of 80 patients; preoperative medications were not standardized beyond routine practice.