A 27-year-old man with complex congenital heart disease (double discordance and complete congenital atrioventricular block) previously implanted with a single-chamber pacemaker was successfully resuscitated from sudden death due to ventricular fibrillation (VF). A dual-chamber implantable cardioverter-defibrillator (ICD) (Biotronik) was implanted for secondary prevention. Four months later, patient collapsed during sport activity. Device interrogation documented new VF episode, successfully detected and treated by the device. At the beginning of recording, sinus tachycardia at 153bpm adapted to exercise is observed and atrial sensed (As) events are normally followed by ventricular pacing (Vp) (because of the complete AV block). The primum movens of this VF is a longer paced AV delay triggered by the device. The device extended its nominal paced AV delay because a pacemaker-mediated tachycardia (PMT) was suspected due to the repetitive “As-Vp” sequence close to the maximal tracking rate which unfortunately led to a cascade of events triggering VF. In order to avoid a recurrence we searched for retrograde VA conduction which was absent in this patient with complete antegrade AV block and PMT algorithm was deactivated. The patient was discharged from the hospital, restarted playing sport and remained free of VF.
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