Magnesium Sulfate to Prevent Perioperative Atrial Fibrillation in Cardiac Surgery: A Randomized Clinical Trial

OBJECTIVES: To determine whether perioperative IV magnesium sulfate infusion, targeting serum magnesium concentrations of 1.5-2.0 mmol/L, reduces the incidence of postoperative atrial fibrillation (POAF) in patients undergoing cardiac surgery. DESIGN: Double-blind, randomized, placebo-controlled, single-center clinical trial with interim analysis for futility. SETTING: HagaZiekenhuis, The Hague, The Netherlands (February 2022-November 2023). PATIENTS: Adult patients undergoing coronary artery bypass grafting and/or valvular surgery without prior atrial arrhythmias or severe renal dysfunction. INTERVENTIONS: Continuous IV infusion of magnesium sulfate (3 mmol/hr, with bolus if [baseline] magnesium < 1.0 mmol/L) or placebo (Ringer's lactate), initiated after induction of anesthesia and continued until ICU discharge. MEASUREMENTS AND MAIN RESULTS: A total of 265 patients underwent randomization before the trial was stopped at interim analysis for futility. Magnesium supplementation achieved clear separation in serum magnesium concentrations between groups. POAF occurred in 50 of 132 patients (37.9%) in the magnesium group and 38 of 133 patients (28.6%) in the placebo group (relative risk, 1.29; 95% CI, 0.92-1.80). No subgroup demonstrated benefit. Time-to-event and day-by-day analyses showed no early reduction in POAF with magnesium. Vasopressor use was more frequent in the magnesium group, although differences were not statistically significant. No safety signal was identified. CONCLUSIONS: In this randomized trial, perioperative magnesium infusion targeting serum concentrations of 1.5-2.0 mmol/L did not reduce POAF after cardiac surgery. These findings do not support routine prophylactic magnesium supplementation for prevention of POAF.