Proarrhythmic responses during electrophysiologic testing.

Antiarrhythmic drugs may worsen ventricular arrhythmias in certain patients. This effect, termed proarrhythmia, aggravation or provocation of arrhythmia, can be investigated with either noninvasive or invasive techniques. Using electrophysiologic study, 160 patients with ventricular tachycardia or ventricular fibrillation were evaluated during treatment with 432 different antiarrhythmic regimens. Proarrhythmic responses were noted in 68 drug trials (16%), and at least 1 event was observed in 51 patients (32%). Nonsustained ventricular tachycardia was converted to sustained ventricular tachycardia in 17% of these studies. Hemodynamically stable ventricular tachycardia was converted to an arrhythmia that required cardioversion for termination in 5% of the studies. Ventricular tachyrhythmia was more easily induced in 12% of trials. These proarrhythmic responses were not related to changes in QRS duration, QT interval or JT interval measured at baseline or to changes produced by antiarrhythmic drugs.