Intravenous magnesium has been used to prevent and treat many different types of cardiac arrhythmia. It has diverse electrophysiological actions on the conduction system of the heart; including prolonging sinus node recovery time, and reducing automaticity, atrioventricular nodal conduction, antegrade and retrograde conduction over an accessory pathway, and His-ventricular conduction. Intravenous magnesium can also homogenise transmural ventricular repolarisation. Because of its unique and diverse electrophysiological actions, intravenous magnesium has been reported to be useful in preventing atrial fibrillation and ventricular arrhythmias after cardiac and thoracic surgery; in reducing the ventricular response in acute onset atrial fibrillation, including for patients with Wolff-Parkinson-White syndrome; in the treatment of digoxin induced supraventricular and ventricular arrhythmias, multifocal atrial tachycardia, and polymorphic ventricular tachycardia or ventricular fibrillation from drug overdoses. Intravenous magnesium is, however, not useful in monomorphic ventricular tachycardia and shock-resistant ventricular fibrillation. Large randomised controlled studies are needed to confirm whether intravenous magnesium can improve patient centre outcomes in different cardiac arrhythmias.

Magnes Res 2008 Mar;21(1):65-8
PMID: 18557136