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

Randomized controlled trial in adults undergoing elective isolated coronary artery bypass grafting at a midwestern university medical center over a 5-year period. Eligible patients had preserved left ventricular function, normal renal function, and no prior chronic arrhythmia; patients with liver dysfunction, hypotension, elevated postoperative creatinine, or need for cardiac assist were excluded. The experimental magnesium group included 105 participants.

Magnesium sulfate 80 mg/kg ideal body weight was infused in 100 mL D5W over 30 minutes before cardiopulmonary bypass, followed by a continuous intravenous infusion of 8.0 mg/kg ideal body weight per hour for 48 hours in 100 mL D5W. The comparator was placebo infusion.

Overall prophylactic magnesium did not significantly reduce postoperative atrial or ventricular arrhythmias after CABG. Total atrial fibrillation occurred in 32 of 105 patients (30.5%) in the magnesium group versus 41 of 97 (42.3%) in control, p=0.08. A benefit was seen only for atrial fibrillation on postoperative day 1, which was lower with magnesium (3/105, 2.9%) than with control (9/97, 9.3%), p=0.05. Urine magnesium and calcium excretion were higher in the magnesium group, but serum magnesium levels were not significantly different after postoperative day 4.

The main arrhythmia endpoint was not statistically significant, and the apparent benefit was limited to one early postoperative day. Interpretation is constrained by a single-center design, a moderate sample size, and short-term postoperative follow-up focused on early arrhythmias rather than longer-term clinical outcomes.