Comparison of class I and class III action in atrial fibrillation.
Antiarrhythmic agents with class I action have been available for decades, and those with class III mode of action for more than 10 years. However, no randomized, controlled, direct comparison between agents with class I and class III mode of action was performed until recently. In patients with successful DC conversion of chronic atrial fibrillation, sotalol proved to be as effective as quinidine in maintaining sinus rhythm but was better tolerated and provided beneficial rate control during atrial fibrillation in those patients who relapsed. In other clinical settings, such as the pharmacological conversion of acute or paroxysmal atrial fibrillation and the termination of and/or prophylaxis against atrial fibrillation after coronary artery bypass surgery, less reliable data is available. Both commonly-available agents with a class III mode of action, amiodarone and sotalol, also have other significant antiarrhythmic properties; for sotalol, the combination of class III activity and beta blockade may prove to be favourable. Therefore, the available data is not necessarily representative of a pure class III mode of action. Ongoing studies with d-sotalol in patients with atrial fibrillation will provide the first important information on the clinical usefulness of a class III mode of action without subsidiary effects. Whether d-sotalol or other new class III agents will, in the future, be compared to class I agents still remains an open question.