OUTCOME OF PEDIATRIC UNEXPLAINED CARDIAC ARREST SURVIVORS: A REPORT FROM THE CANADIAN PEDIATRIC HEART RHYTHM NETWORK

Unexplained cardiac arrest (UCA) is a rare occurrence in children. Despite clinical advancements, the cause in up to half can remain undiagnosed. We sought to assess the management and outcomes of pediatric UCAs in Canada. We performed a retrospective case series analysis. Children (age 1-19 years) presenting with an UCA between January 1, 2004 and November 1, 2017 from 8 Canadian centres were included. Age at UCA, genetic test results (categorized according to the 2015 ACMG guidelines), subsequent diagnoses, and outcome of family screening were collected. Implantable cardioverter defibrillator (ICD) data was included. Patients with known heart disease prior to the UCA were excluded. Forty-six patients (61% male) met inclusion criteria. Median age was 13.5 years at UCA (IQR 8.8-15.7). One patient did not survive to discharge post-arrest and 5 patients were lost to follow-up. Baseline investigations included electrocardiogram (87%), echocardiogram (80%), cardiac MRI (48%), exercise stress test (35%), and Holter (33%). Twenty-eight patients (61%) underwent genetic testing, with a range of 29-100% utilization across centres. Twenty-four variants in 9 genes were identified (54% pathogenic/likely pathogenic, 21% variants of unknown significance). The presumed etiology for the UCA was identified in 26 patients (56.5%; Table 1) after a median of 1.5 months (IQR 0.2-5.3). The most common diagnoses were Long QT syndrome (23%) and Catecholaminergic Polymorphic Ventricular Tachycardia (19%). Diagnoses were based on clinical evidence in 54% or clinical and genetic results in 46%. Families of 25 probands underwent screening (54.3%) leading to a diagnosis in 6/25 families assessed (24%). Thirty-four probands (74%) received ICDs, with a range of 50-100% use across centres. Over a median follow-up of 34.5 months (IQR 8.5-57.3), 8 patients experienced shocks (n = 13 shocks). Of ICD treatments with sufficient data, the majority (8/9) were appropriate therapies. Three patients (6.5%) had arrhythmic syncope during follow-up; 2 received appropriate ICD shocks at the time of syncope. No further cardiac arrests or deaths were reported. A cause for UCA, distributed between channelopathy and cardiomyopathy, is identified in only ∼50% of cases despite a systematic approach. Investigation and treatment of UCA varies across centres. Use of genetic testing and cascade screening is inconsistent. A standardized genetic testing approach may improve diagnostic yield.