Efficacy of Intravenous Magnesium in Facilitating Cardioversion of Atrial Fibrillation

Background - Low serum magnesium (Mg) levels are associated with an increased risk of atrial fibrillation. Some studies have shown a benefit of Mg in facilitating pharmacological cardioversion. The role of an intravenous infusion of Mg alone in facilitating electric cardioversion is not clear. Methods and Results - In a prospective, randomized, double-blind, placebo-controlled trial, we enrolled patients with atrial fibrillation who were scheduled for electric cardioversion. Patients were randomized to receive Mg or placebo before cardioversion using a step-up protocol with 75, 100, 150, and 200 J biphasic shocks. Patients with hypokalemia, hypermagnesemia, or postcardiac surgery atrial fibrillation were excluded. Patients on antiarrhythmic drugs were included as long as they were at steady state. All patients were monitored for 1 hour post procedure for the maintenance of sinus rhythm. A total of 261 patients (69% male, mean age 65.5±11.1 years) were randomized (132 and 129 patients receiving Mg and placebo, respectively). Baseline characteristics were similar between both the groups. There was no statistically significant difference in the success rate of cardioversion between the 2 groups (86.4% versus 86.0%; P=0.94), cumulative amount of energy required for successful cardioversion (123.3±55.5 versus 129.5±52.6 J; P=0.40), or the number of shocks required to convert to sinus rhythm (2.25±1.24 versus 2.41±1.22, P=0.31). No adverse events were noted in either group. Conclusions - In patients undergoing electric cardioversion for persistent atrial fibrillation, Mg infusion does not increase the rate of successful cardioversion. Clinical Trial Information - URL: https://clinicaltrials.gov. Unique identifier: NCT01597557.