The proposed study is designed to evaluate the effect of an intravenous infusion of magnesium sulfate in facilitating successful cardioversion of atrial fibrillation and in decreasing the energy threshold (in J) required for successful cardioversion of atrial fibrillation into sinus rhythm.

Patients with atrial fibrillation may suffer from disabling symptoms such as palpitations, shortness of breath or worsening heart failure. In such patients, it may be beneficial to convert their rhythm to sinus rhythm. Cardioversion can be achieved either pharmacologically or electrically. Pharmacological cardioversion is less successful acutely than electrical cardioversion and may be associated with complications such as prolongation of the QT interval and torsades de pointes (polymorphic ventricular tachycardia). Thus, cardioversion is most often accomplished electrically, using biphasic synchronized shocks of 75-200 Joules. Biphasic electrical cardioversion in atrial fibrillation has shown to be successful (i.e., converting to sinus rhythm) about 88% of the time, on average. The success rate appears to largely depend upon the duration of the arrhythmia and the presence and severity of structural heart disease.

In this study, we will evaluate the effect of intravenous magnesium sulfate on the success rate of electrical cardioversion, and also assess its effect in decreasing the energy levels needed for successful cardioversion. If the study is successful, we will have shown that a simple and inexpensive intervention can increase the success rate of electrical cardioversion, increasing the proportion of patients who can be restored to sinus rhythm. In addition, success with lower energy levels may improve the safety of cardioversion, as high energy levels are more likely to be associated with side effects

Inclusion Criteria:

• Patient with new onset Atrial fibrillation less than 48 hours after onset undergoing electrical cardioversion.
• Patients with atrial fibrillation longer than 48 hours on warfarin with documented therapeutic INR levels >2 for at least 3 weeks prior to the cardioversion, or been on dabigatran for 3 weeks, or a transesophageal echocardiogram on the day of the procedure that excludes intracardiac thrombi, undergoing electrical cardioversion.

Exclusion Criteria:

• Creatinine >2.0 mg/dl
• Potassium level less than 3.5 mmol/dl
• TSH < 0.5
• Magnesium levels >3.0 mg/dl
• Urgent need for cardioversion (e.g., hemodynamic instability, unstable angina, pulmonary edema)
• Patients with recent (less than 6 weeks) acute myocardial infarction
• Patients post-cardiac surgery
• Pregnant women
• Patients who are being treated with antiarrhythmic drugs who have received less than five doses of the drug. For amiodarone, patients who have received less than three weeks prior to cardioversion are excluded.

Very few patients in paroxysmal AF, majority failed earlier rhythm control strategies making the study population a resistant population to treat, only one dose of Mg infusion was tested and the monitoring period was only 1 hour post cardioversion