Ventricular fibrillation induced by rapid atrial rates in patients with hypertrophic cardiomyopathy.

AIMS: To describe the mechanisms of induction of ventricular fibrillation (VF) by rapid atrial rates in patients with hypertrophic cardiomyopathy (HCM). METHODS: Electrophysiological studies, management and follow-up in three patients with HCM with VF induced by atrial pacing. RESULTS: In one patient, spontaneous sinus tachycardia triggered VF. In another patient, VF occurred after verapamil infusion during rapid atrial fibrillation, and in the remaining patient there was no clinical VF. In all three patients, short runs of atrial pacing (cycle length 272-380 ms) induced VF, and QRS widening preceded fibrillation in all patients. Marked ventricular electrogram fragmentation was documented in one patient during atrial pacing and in another patient during late ventricular extra-stimuli. Hypotension was associated with sinus tachycardia in one patient. The two patients developing clinical VF underwent atrioventricular (AV) junctional ablation; a ventricular defibrillator was implanted in one, and a mode-switching dual-chamber pacemaker in the other. No arrhythmic events occurred during 34- and 35-month follow-up, respectively. In the other patient, postatrial fibrillation pauses caused syncope, and he is asymptomatic 52 months after implantation of a dual-chamber pacemaker. CONCLUSIONS: Rapid atrial rates can trigger VF in some patients with HCM, probably through a combination of electrophysiological and ischaemic mechanisms. AV junctional ablation may prevent VF in selected cases.