Review : Restoring Sinus Rhythm in Patients with Atrial Flutter and Fibrillation: Pharmacologic or Electrical Cardioversion?

Abstract

Atrial fibrillation and atrial flutter, the most frequently encountered tachyarrhythmias requir ing treatment, have become a major focus for clinical and basic research in recent years. Restoration and maintenance of sinus rhythm, having been shown to improve exercise capac ity, alleviate symptoms, and reduce the incidence of thromboembolic events, may be the opti mal management strategy. Identification of the safest, most efficacious and cost-effective means of restoring sinus rhythm is necessary prior to the institution of optimal antiarrhyth mic therapy to maintain sinus rhythm. Potential advantages of pharmacologic compared with electrical cardioversion include lack of need for general anesthesia and likely lower cost. Pharmacologic conversion has been accomplished with drugs that prolong atrial refractori ness, including class Ia (quinidine, procainamide, disopyramide), class Ic (flecainide, propafenone), and class III (sotalol, amiodarone) compounds. The so-called pure class III agents were created to overcome the blocker side effects of sotalol and the complex pharma codynamic profile of amiodarone. Two such agents are dofetilide, which selectively blocks the rapid component of the delayed rectifier current (Ikr) and ibutilide, which augments the slow inward sodium current, with a smaller component of action mediated by the block of Ikr. Reported overall conversion rates for recent onset atrial fibrillation and atrial flutter were 31 % and 54% for dofetilide, respectively, and 29-31 % and 38-63%, respectively, for ibu tilide. Proarrhythmia, manifested as polymorphic ventricular tachycardia requiring cardiover sion, was a significant early side effect of both agents. Data from clinical trials with these new agents, combined with increasing knowledge of the electrophysiologic substrate for these arrhythmias, has renewed interest in the development of safer, more efficacious class III drugs for atrial fibrillation and atrial flutter conversion.