Proarrhythmic effects of antiarrhythmic drugs assessed by electrophysiologic study in recurrent sustained ventricular tachycardia.

Proarrhythmic responses were evaluated in repeated electrophysiologic studies (EPS) in 27 patients with inducible ventricular tachycardia (VT). Class Ia drugs were administered to 23, Ib to 6, Ic to 4, III to 5 and IV to 9 patients. The mean age was 53 years, and 18 patients had structural heart diseases. Pleomorphism was observed in 11 patients. In 4 patients (15%), the VT cycle length (CL) shortened by 50 ms or more in EPS during the administration of antiarrhythmic drugs. VT was inducible by a less aggressive induction mode than the control study in 9 patients (33%). In 4 patients (15%), the induced VT changed to the incessant form, and the other 2 patients (7%) required DC shocks due to hemodynamic deterioration. Patients with pleomorphic VT and/or structural heart diseases seemed to develop proarrhythmia more frequently. In total, some proarrhythmic response was observed in 13 (48%) of the 27 patients. Therefore, it should be kept in mind that proarrhythmic effects are frequently observed during antiarrhythmic therapy in patients with sustained VT. The action of the drugs on the slow conduction zone may vary, which may provide a basis for the development of proarrhythmia.