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Electrophysiological studies can be useful in the presence of idiopathic ventricular fibrillation (VF) and may be used when selecting antiarrhythmic drugs. However, the yield, the mode, and the long-term reproducibility of the induction of VF have not yet been fully elucidated. Eight patients with idiopathic VF underwent electrophysiological study. The mean age (+/- SD) was 45 +/- 17 years. Six were males and two were females. Diagnosis was done by exclusion. VF was induced in 6 (75%) of 8 patients using double extra stimuli at coupling intervals of 233 +/- 39 and 191 +/- 20 ms for the first and second extra stimuli, respectively. Of note, VF was induced by stimulation exclusively at the origin of the premature ventricular beat, which was the first complex of VF in two patients. In another patient, VF was initiated by two premature stimuli and also by a pause produced by rapid pacing. The inducibility of VF was reproduced 9-18 months after the first induction in all of the four patients studied. When the ability of antiarrhythmic drugs to suppress VF inducibility was confirmed, no recurrence was observed during the follow-up period of 40-160 months, but a recurrence of VF was observed in one of two nonresponders. In one patient, amiodarone administration failed in preventing VF induction 9 months after initiation of therapy, and reassessment of long-term drug-efficacy might be indicated in some patients. In conclusion, idiopathic VF was highly inducible (75%) with double extra stimuli. In this study, it was induced from a specific site (2/8) or by a pause (1/8). Induction of VF seemed to be reproduced 9-18 months after the first study. The outcome was considered favorable when the inducibility of VF was suppressed by antiarrhythmic drugs.

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