Background:

Initially unexplained cardiac arrest (UCA) is rare in youth and young adults. However, UCA is one of the most important non-traumatic reasons of death in this population. Often, despite further investigations, underlying etiology remains unknown. Also, less is known about long-term clinical outcome in patients surviving UCA.

Methods:

All patients under 40 years of age admitted to our clinic with sudden cardiac arrest without known cardiac disease were included in our analysis. We collected data from clinical workup, genetic testing and ICD interrogations at baseline and of all follow-up presentations with the aim to analyze etiology, clinical management and outcome of UCA patients.

Results:

38 survivors of UCA (median age at UCA 24.0±8.8 years, 63% female) had cardiac magnetic imaging (74%), cardiac catheterization (84%), electrophysiological study (45%) and endomyocardial biopsy (10%) during the diagnostic workup. Of 10 patients with genetic testing, 7(26%) showed pathogenic results. ICDs were implanted in 34/38 patients (89%). Most frequent diagnoses were Long-QT-Syndrome (18%) and hypertrophic cardiomyopathy (10%). In nearly half of the patients (45%), no explanation for UCA was found. After a median follow-up of 7.5±6.5 years, 36 patients (92%) were still alive with a mean event-free survival of 20.6±1.3 years. 32% had an event of documented ventricular fibrillation in ICD interrogations.

25 patients (64%) had an ICD replacement and 9 out of 38 patients (24%) had multiple ICD replacement procedures. Interestingly, of 17 patients without explaining diagnosis after diagnostic workup, 23% developed another ventricular fibrillation in further course.

Conclusion:

UCA is rare event and underlying disease remains unknown in a large number of patients. Mortality after an UCA event is low.