Bundle branch reentry tachycardia: a possible mechanism of flecainide proarrhythmia effect

A 42-year old man with non-obstructive myocardiopathy complicated by paroxysmal atrial fibrillation treated with amiodarone (200 mg per day) received flecainide in daily doses of 400 mg for undocumented palpitations. Ten syncopes and numerous malaises occurred during the following two months. Electrophysiological testing was performed, showing prolongation of HV to 80 ms and discreet widening of QRS to 100 ms. Programmed atrial stimulation failed to demonstrate a second degree subnodal block and to induce tachycardia. In contrast, ventricular stimulation elicited a critical SH delay (260 ms), always followed by a left delay-type complex preceded by His bundle deflection which suggested reentry within the His-Purkinje system. Three extrasystoles on imposed rhythm started sustained ventricular tachycardia with the same 270 ms cycle morphology and reproducing the symptoms. Each V wave was preceded by an H potential, with HV varying from 100 to 300 ms. Three weeks after flecainide was discontinued, HV was 60 ms, and no ventricular tachycardia could be triggered by programmed stimulation. The patient remained symptom-free throughout the 5-month follow-up. This case illustrates the proarrhythmic effect of the flecainide-amiodarone combination. The mechanism of provoked tachycardia probably involves ventricular reentry through the His bundle branches, induced by a critical depression of conduction below the His bundle.