Low-Dose Magnesium for Atrial Fibrillation With Rapid Ventricular Response in the Emergency Department

Atrial fibrillation with rapid ventricular response is a common emergency department presentation. Prior studies suggest that intravenous magnesium may improve rate control when used with atrioventricular nodal blockers, however these studies primarily used digoxin and variable magnesium dosing strategies. Lower doses commonly used in the emergency department remain unexplored. This study evaluated whether commonly used emergency department doses of intravenous magnesium, added to diltiazem or metoprolol, improve rate control compared with AV nodal blocker therapy alone, with subgroup analysis by baseline magnesium level.

This retrospective cohort study included adults with atrial fibrillation with rapid ventricular response who received intravenous diltiazem or metoprolol in the emergency department. Patients received magnesium and atrioventricular nodal blocker or atrioventricular nodal blocker alone. Exclusions included hypotension at presentation, pregnancy, age < 18, prisoner status, and initial cardioversion. A subgroup analysis evaluated the effects of serum magnesium on magnesium efficacy. The primary outcome was sustained rate control, defined as > 50% of heart rate measurements < 110 within four hours. Secondary outcomes included time to rate control, need for additional rate or rhythm control agents, hospital admission, and incidence of bradycardia or hypotension.

A total of 162 patients were included, with 37 receiving magnesium. Baseline characteristics were similar. Most patients in the magnesium group received two grams, with similar proportions receiving metoprolol and diltiazem. Sustained rate control occurred more often with magnesium (73% v 48.3%, p = 0.011). Time to rate control was significantly shorter in the group that did not receive magnesium. The need for additional rate or rhythm control agents, hospital admission, and safety outcomes did not differ between groups.

Intravenous magnesium administered with diltiazem or metoprolol was associated with higher achievement of sustained rate control in atrial fibrillation with rapid ventricular response without increasing adverse events.