COMPARISON IN THE SAME PATIENT OF ABERRANT CONDUCTION AND BUNDLE-BRANCH REENTRY AFTER DOFETILIDE, A NEW SELECTIVE CLASS-III ANTIARRHYTHMIC AGENT

Dofetilide may induce aberrant intraventricular conduction due to its Class III effect. This report describes an atrial fibrillation patient in whom intraventricular conduction was studied before and after dofe tilide using multiple endocardial recordings. Dofetilide provoked aber rant conduction during atrial fibrillation, and aberrancy could be mim icked with programmed atrial stimulation after restoration of sinus rh ythm. However, during right ventricular stimulation, isolated bundle b ranch reentrant beats were recorded after induction of critical retrog rade conduction delays. This occurred in the setting of relatively lar ge differences in refractoriness between the right bundle branch and t he right ventricular myocardium. This favored distal retrograde bundle branch block during ventricular extrastimulation, in turn enhancing b undle branch reentry. This potential proarrhythmic mechanism deserves close attention in the further development of dofetilide and also of o ther new ''pure'' Class III agents.