Initially unexplained cardiac arrest in children and adolescents: A national experience from the Canadian Pediatric Heart Rhythm Network.

Background: Unexplained cardiac arrest (UCA) is rare in children. Despite investigations, the etiology in up to one-half of patients remains unknown.

Objective: The purpose of this study was to assess the management and outcomes of pediatric UCA survivors through the Canadian Pediatric Heart Rhythm Network.

Methods: A retrospective case series of children (age 1-19 years) who presented with UCA between January 1, 2004, and November 1, 2017, was conducted. Patients with known heart disease pre-UCA were excluded. UCA details, investigations, genetic test results, treatment, implantable cardioverter-defibrillator (ICD) data, subsequent diagnoses, and family screening data were collected.

Results: Forty-six patients (61% male) were survivors of sudden unexpected death and met inclusion criteria at 8 participating sites. Median age at UCA was 13.8 years (interquartile range [IQR] 9-16 years). Baseline retrievable investigations included electrocardiogram (96%), echocardiogram (85%), exercise stress test (73%), and cardiac magnetic resonance imaging (57%). The presumed etiology for the UCA was identified in 24 (52%), mainly long QT syndrome or catecholaminergic polymorphic ventricular tachycardia. Genetic testing was performed in 33 of 46 (72%), with pathogenic/likely pathogenic variants identified in 13 of 33 (39%) and variants of uncertain significance in 8 of 33 (24%). ICDs were implanted in 35 of 46 (76%). Over median follow-up of 36 months (IQR 17-57 months), 8 of 35 had arrhythmia events captured on device interrogation. Families of 26 of 46 patients(57%) underwent screening, leading to a cardiac diagnosis in 6 of 26 families.

Conclusion: A cause for UCA was not identified in nearly 50% of patients despite extensive investigations, including cascade screening. A large proportion (75%) of ICD shocks occurred in patients without a diagnosis.