Background: Hypertrophic cardiomyopathy (HCM) is the leading cause of sudden cardiac death (SCD) in children and young adults. Our objective was to develop and validate a SCD risk prediction model in pediatric HCM to guide SCD prevention strategies. Methods: In an international multi-center observational cohort study, phenotype-positive patients with isolated HCM <18 years at diagnosis were eligible. The primary outcome variable was the time from diagnosis to a composite of SCD events at 5-year follow-up: SCD, resuscitated sudden cardiac arrest (SCA), and aborted SCD, i.e. appropriate shock following primary prevention ICD. Competing risk models with cause-specific hazard regression were used to identify and quantify clinical and genetic factors associated with SCD. The cause-specific regression model was implemented using boosting, and tuned with ten repeated four-fold cross-validations. The final model was fitted using all data with the tuned hyperparameter value that maximizes the c-statistic, and its performance was characterized using c-statistic for competing risk models. The final model was validated in an independent external cohort (SHaRe, n=285). Results: Overall, 572 patients met eligibility criteria with 2855 patient-years of follow-up. The 5-year cumulative proportion of SCD events was 9.1% (14 SCD, 25 resuscitated SCA, 14 aborted SCD). Risk predictors included age at diagnosis, documented non-sustained ventricular tachycardia, unexplained syncope, septal diameter z-score, LV posterior wall diameter z-score, LA diameter z-score, peak LV outflow tract (LVOT) gradient, and presence of a pathogenic variant. Unlike adults, LVOT gradient had an inverse association, and family history of SCD had no association with SCD. Clinical and clinical/genetic models were developed to predict 5-year freedom from SCD. Both models adequately discriminated patients with and without SCD events with a c-statistic of 0.75 and 0.76 respectively and demonstrated good agreement between predicted and observed events in the primary and validation cohorts (validation c-statistic 0.71 and 0.72 respectively). Conclusions: Our study provides a validated SCD risk prediction model with over 70% prediction accuracy and incorporates risk factors that are unique to pediatric HCM. An individualized risk prediction model has the potential to improve the application of clinical practice guidelines and shared decision-making for ICD insertion. Clinical Trial Registration: URL: https://clinicaltrials.gov Unique Identifier: NCT04036799

Background Left ventricular noncompaction (LVNC) is a distinct form of cardiomyopathy characterized by hypertrabeculation of the left ventricle. The LVNC phenotype may occur in isolation or with other cardiomyopathy phenotypes. Prognosis is incompletely characterized in children. Methods and Results Using diagnoses from the National Heart, Lung, and Blood Institute-funded Pediatric Cardiomyopathy Registry from 1990-2008, 155 of 3219 children (4.8%) had LVNC. Each LVNC patient was also classified as having an associated echocardiographically diagnosed cardiomyopathy phenotype (dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restrictive cardiomyopathy (RCM), isolated, or indeterminate). The time to death or transplant differed among the phenotypic groups (P = 0.035). Time to listing for cardiac transplantation significantly differed by phenotype (P < 0.001), as did time to transplantation (P = 0.015). The hazard ratio for death/transplant (with isolated LVNC as the reference group) was 4.26 (95% confidence interval [CI], 0.78 to 23.3) for HCM, 6.35 (95% CI, 1.52 to 26.6) for DCM, and 5.66 (95% CI, 1.04 to 30.9) for the indeterminate phenotype. Most events occurred in the first year after diagnosis. Conclusion LVNC is present in at least 5% of children with cardiomyopathy. The specific LVNC-associated cardiomyopathy phenotype predicts the risk of death/transplant and should inform clinical management.

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect. We explore "hot topics" to highlight areas of emerging science for clinicians and scientists in moving toward a better understanding of the long-term management of patients with repaired TOF. From a genetic perspective, the etiology of TOF is multifactorial, with a familial recurrence risk of 3%. Cardiac magnetic resonance is the gold standard assessment tool based on its superior imaging of the right ventricular (RV) outflow tract, pulmonary arteries, aorta, and aortopulmonary collaterals, and on its ability to quantify biventricular size and function, pulmonary regurgitation (PR), and myocardial viability. Atrial re-entrant tachycardia will develop in more than 30% of patients, and high-grade ventricular arrhythmias will be seen in about 10% of patients. The overall incidence of sudden cardiac death is estimated at 0.2%/yr. Risk stratification, even with electrophysiologic testing and cardiac magnetic resonance, remains imperfect. Drug therapy has largely been abandoned, and defibrillator placement, despite its high risks for complications and inappropriate discharges, is often recommended for patients at higher risk. Definitive information about optimal surgical strategies for primary repair to preserve RV function, reduce arrhythmia, and optimize functional status is lacking. Post-operative lesions are often amenable to transcatheter intervention. In selected cases, PR may be treated with transcatheter valve insertion. Ongoing surveillance of RV function is a crucial component of clinical assessment. Except for resynchronization with biventricular pacing, no medical therapies have been shown to be effective after RV dysfunction occurs. In patients with significant PR with RV dilation, optimal timing of pulmonary valve replacement remains uncertain, although accepted criteria are emerging.

Objectives To establish the incidence of, and risk factors for, SCD in pediatric DCM. Background The incidence of SCD in children with DCM is unknown. The ability to predict patients at high risk for SCD will help define who may benefit most from ICDs. Methods The cohort was 1803 children in the PCMR diagnosed with DCM from 1990-2009. Cumulative incidence competing-risks event rates were estimated. We achieved risk stratification using CART methodology. Results Five-year incidence rates were 29% for heart transplant, 12.1% non-sudden cardiac death (non-SCD), 4.0% death from unknown cause, and 2.4% for SCD. Of 280 deaths, 35 were SCD and cause was unknown for 56. The 5-year rate for SCD incorporating a subset of the unknown deaths is 3%. Patients receiving anti-arrhythmic medication were at higher risk of SCD (hazard ratio 3.0, 95% CI 1.1-8.3, p =0.025). A risk stratification model based on most recent echocardiographic values had 86% sensitivity and 57% specificity. Thirty of 35 SCDs occurred in patients who met all of these criteria: LV end-systolic dimension z score > 2.6, age at diagnosis <14.3 years, and ratio of LVPWT:EDD <0.14. Sex, ethnicity, cause of DCM, and family history were not associated with SCD. Conclusions The 5-year incidence of SCD in children with DCM is 3%. A risk stratification rule (86% sensitivity) included diagnosis age < 14.3 years, LV dilation, and LV posterior wall thinning. Patients who consistently meet these criteria should be considered for ICD placement.