ELECTROPHYSIOLOGIC MECHANISMS OF ADVERSE-EFFECTS OF CLASS-I ANTIARRHYTHMIC DRUGS (CIBENZOLINE, PILSICAINIDE, DISOPYRAMIDE, PROCAINAMIDE) ININDUCTION OF ATRIOVENTRICULAR REENTRANT TACHYCARDIA

We evaluated the electrophysiological mechanisms of adverse effects of class I antiarrhythmic drugs (cibenzoline in seven patients, pilsicai nide in two, and disopyramide in two, and procainamide in three) in th e induction of orthodromic atrioventricular re-entrant tachycardia (AV RT). In 14 patients (10 males, 4 females; mean age 37 +/- 18 years) wh o had inducible AVRT despite the administration of class I drugs, elec trophysiological effects of class I antiarrhythmic drugs were evaluate d using programmed electrical stimulation techniques. In 4 out of 6 pa tients with a manifest accessory pathway, class I drugs induced unidir ectional conduction block of the accessory pathway (antegrade conducti on block associated with preserved retrograde conduction) and enhanced the induction of AVRT with atrial extrastimulation. In eight patients with a concealed accessory pathway, the outward or inward expansion o f the tachycardia induction zone was observed in patients who had grea ter prolongation of the conduction time than the refractory period of the retrograde accessory pathway after class I drugs. During ventricul ar extrastimulation, the induction of bundle branch reentry after clas s I drugs initiated the AVRT in patients with either manifest or conce aled accessory pathways. We conclude that the adverse effects of class I drugs are mainly due to induction of unidirectional retrograde cond uction of the manifest accessory pathway and the greater prolongation of the retrograde conduction time of the concealed accessory pathway t han the refractory period, regardless of the sub-classification of cla ss I drugs.