Aggravation of electrically provoked ventricular tachycardia during treatment with propafenone.

Propafenone is a new class Ic antiarrhythmic agent currently being investigated in the United States. It is generally well tolerated. We administered propafenone to 16 patients with ventricular tachycardia (VT) that had been refractory to conventional antiarrhythmic drug therapy. Three of these 16 patients developed electrically provoked incessant VT during treatment with propafenone without other evidence of toxicity. These arrhythmias subsided after lidocaine was administered. Propafenone therapy was discontinued in each case. Incessant VT did not develop in any of these patients in the absence of antiarrhythmic drugs or on antiarrhythmic drugs other than propafenone. Alternative effective treatment was identified for each patient. Although VT was initially provoked by pacing in each of these patients, these observations suggest that propafenone, like some other class Ic drugs, may favor the development of incessant VT in occasional patients. This appears most likely to occur in patients with ventricular dysfunction and prior sustained VT or ventricular fibrillation.