Magnesium Sulfate versus Placebo for Paroxysmal Atrial Fibrillation: A Randomized Clinical Trial

The objective was to investigate the efficacy of magnesium sulfate (MgSO4) in decreasing the ventricular rate in emergency department (ED) patients presenting with new-onset, rapid atrial fibrillation (AF). A double-blinded, placebo-controlled randomized clinical trial was conducted in an adult university hospital. Patients aged >= 18 years with AF onset of less than 48 hours and a sustained ventricular rate of > 100 beats/min were randomized to either intravenous (IV) MgSO4 10 mmol or normal saline (NSal). Rhythm and instantaneous heart rate as measured by the monitor were recorded at baseline and every 15 minutes for 2 hours after starting the trial drug. Heart rate and rhythm were compared at 2 hours. A multilevel modeling analysis was performed to adjust for differences in baseline heart rate and any additional treatment and to examine changes in heart rate over time. Twenty-four patients were randomized to MgSO4 and 24 to NSal. Baseline heart rate was lower in the MgSO4 group (mean +/- standard deviation [+/- SD] = 125 +/- 24 vs. 140 +/- 21 beats/min]. One and 3 patients in the MgSO4 and NSal groups, respectively, were given another antiarrhythmic or were electrically cardioverted within 2 hours after starting the trial drug. Heart rate (mean +/- SD) at 2 hours in both MgSO4 (116 +/- 30 beats/min) and NSal groups (114 +/- 31 beats/min) decreased below their respective baseline levels. However, the rate of heart rate decrease across time did not differ between groups (p = 0.124). The proportion of patients who converted to sinus rhythm 2 hours post-trial drug did not differ (MgSO4 8.7% vs. NSal 25.0%, p = 0.25). This study was unable to demonstrate a difference between IV MgSO4 10 mmol and saline placebo for reducing heart rate or conversion to sinus rhythm at 2 hours posttreatment in ED patients with AF of less than 48 hours duration.