How to evaluate class III antiarrhythmic drug efficacy clinically: the benefits and shortcomings of the invasive approach.

Ventricular tachycardia and ventricular fibrillation are frequent complications of organic heart disease. There is sufficient evidence that serial electrophysiologic testing is able to predict long-term efficacy of antiarrhythmic agents in patients with malignant ventricular tachyarrhythmias. This approach has not only been useful for the evaluation of class I drugs, but recent studies have shown that this invasive method may also be useful for the management of patients undergoing treatment with class III antiarrhythmic agents such as amiodarone and sotalol. The results of several studies suggest that class III agents are more effective than class I drugs in patients presenting with ventricular tachycardia or ventricular fibrillation. Proarrhythmic complications in patients treated with class III antiarrhythmic drugs are mainly characterized by torsades de pointes. Their incidence does not exceed 5%. Further studies are necessary to elucidate the mechanisms underlying this type of proarrhythmia. By the use of currently available stimulation techniques, patients who might develop torsades de pointes while on therapy with a class III agent cannot be identified.