Current status of class III antiarrhythmic drug therapy.

Studies in animal models, as well as clinical experience with amiodarone and sotalol, suggest that action potential prolongation may be a useful antiarrhythmic mode of action. A number of agents that produce this class III effect are currently under development. The single greatest liability for further development of this group of drugs is the occasional, and apparently unpredictable, development of exaggerated QT prolongation and polymorphic ventricular tachycardia (torsades de pointes). Available data suggest that QT interval prolongation is not a good indicator of whether or not a class III antiarrhythmic will suppress a target arrhythmia; however, exaggerated QT prolongation is a predictor of torsades de pointes. Further studies to delineate the mechanism underlying the development of torsades de pointes might lead to safer and more effective antiarrhythmic drugs.