True idiopathic ventricular fibrillation in out-of-hospital cardiac arrest survivors in the Swiss Canton Ticino: Prevalence, clinical features, and long-term follow-up

Aims Out-of-hospital cardiac arrest (OHCA) in the absence of evident structural heart disease is rare and can be due to subclinical cardiomyopathy and primary electrical disorders, including idiopathic ventricular fibrillation (IVF) with early repolarization (ER) pattern. Aim of this study was to investigate prevalence, clinical features, and long-term prognosis of IVF in OHCA survivors with otherwise normal 12-lead electrocardiograms (ECGs). Methods and results Patients with IVF in the absence of ER pattern or atrioventricular conduction abnormalities were considered eligible for this study. A total of 3407 OHCAs occurred in our region from 2000 to 2014. Out-of-hospital cardiac arrests of presumed cardiac origin were 2192; of them, 644 presented with a ventricular arrhythmia (VT/VF) as first shockable rhythm. Among them, a total of 74 implantable cardioverter-defibrillators were implanted for secondary prevention. Ventricular arrhythmia was considered idiopathic in 11 (15%) of these patients. Over a mean follow-up time of 85+47 months (median: 42 months), ECG was found abnormal in three cases. In the remaining eight patients (6 males; median age: 45 years), no ECG or structural abnormalities were detected during the follow-up. Prevalence of IVF in OHCA survivors with first-shockable rhythm was 1.2%. During the long-term follow-up, no patient died or experienced ICD interventions. No new echocardiographic abnormal findings were revealed. Conclusions Idiopathic ventricular fibrillation is rare occurring in 1.2% of OHCA survivors presenting with a shockable rhythm. The initial diagnosis can change in up to 27% of cases. Patients with IVF and no ER pattern or AV conduction disturbances have a good prognosis during a long-term follow-up.