The Prevalence and Association of Exercise Test Abnormalities With Sudden Cardiac Death and Transplant-Free Survival in Childhood Hypertrophic Cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) can be associated with an abnormal exercise response. In adults with HCM, abnormal results on exercise stress testing are predictive of heart failure outcomes. Our goal was to determine whether an abnormal exercise response is associated with adverse outcomes in pediatric patients with HCM. METHODS: In an international cohort study including 20 centers, phenotype-positive patients with primary HCM who were <18 years of age at diagnosis were included. Abnormal exercise response was defined as a blunted blood pressure response and new or worsened ST- or T-wave segment changes or complex ventricular ectopy. Sudden cardiac death (SCD) events were defined as a composite of SCD and aborted sudden cardiac arrest. Using Kaplan-Meier survival, competing outcomes, and Cox regression analyses, we analyzed the association of abnormal exercise test results with transplant and SCD event-free survival. RESULTS: Of 724 eligible patients, 630 underwent at least 1 exercise test. There were no major differences in clinical characteristics between those with or without an exercise test. The median age at exercise testing was 13.8 years (interquartile range, 4.7 years); 78% were male and 39% were receiving beta-blockers. A total of 175 (28%) had abnormal test results. Patients with abnormal test results had more severe septal hypertrophy, higher left atrial diameter z scores, higher resting left ventricular outflow tract gradient, and higher frequency of myectomy compared with participants with normal test results (P<0.05). Compared with normal test results, abnormal test results were independently associated with lower 5-year transplant-free survival (97% versus 88%, respectively; P=0.005). Patients with exercise-induced ischemia were most likely to experience all-cause death or transplant (hazard ratio, 4.86 [95% CI, 1.69-13.99]), followed by those with an abnormal blood pressure response (hazard ratio, 3.19 [95% CI, 1.32-7.71]). Exercise-induced ischemia was also independently associated with lower SCD event-free survival (hazard ratio, 3.32 [95% CI, 1.27-8.70]). Exercise-induced ectopy was not associated with survival. CONCLUSIONS: Exercise abnormalities are common in childhood HCM. An abnormal exercise test result was independently associated with lower transplant-free survival, especially in those with an ischemic or abnormal blood pressure response with exercise. Exercise-induced ischemia was also independently associated with SCD events. These findings argue for routine exercise testing in childhood HCM as part of ongoing risk assessment.

Current State of Cardiac Implantable Electronic Device Remote Monitoring in Pediatrics and Congenital Heart Disease: A PACES-Sponsored Quality Improvement Initiative.

Cardiac implantable electronic device (CIED) remote transmissions are an integral part of longitudinal follow-up in pediatric and adult congenital heart disease (ACHD) patients. To evaluate baseline CIED remote monitoring (RM) data among pediatric and ACHD centers prior to implementation of a Pediatric and Congenital Electrophysiology  Society (PACES)-sponsored quality improvement (QI) project. This is a cross-sectional study of baseline CIED RM. Centers self-reported baseline data: individual center RM compliance was defined as high if there was > 80% achievement and low if < 50%. A total of 22 pediatric centers in the USA and Australia submitted baseline data. Non-physicians were responsible for management of the RM program in most centers: registered nurse (36%), advanced practice provider (27%), combination (23%), and third party (9%). Fifteen centers (68%) reported that > 80% of their CIED patients are enrolled in RM and only two centers reported < 50% participation. 36% reported high compliance of device transmission within 14 days of implant and 77% of centers reported high compliance of CIED patients enrolled in RM. The number of centers achieving high compliance differed by device type: 36% for pacemakers, 50% for ICDs, and 55% for Implantable Cardiac Monitors (ICM). All centers reported at least 50% adherence to recommended follow-up for PM and ICD, with 23% low compliance rate for ICMs. Based on this cross-sectional survey of pediatric and ACHD centers, compliance with CIED RM is sub-optimal. The PACES-sponsored QI initiative will provide resources and support to participating centers and repeat data will be evaluated after PDSA cycles.

The effect of antipsychotic medications on QTc and delirium in paediatric cardiac patients with ICU delirium.

OBJECTIVE: Children with prolonged hospital admissions for CHD often develop delirium. Antipsychotic medications (APMs) have been used to treat delirium but are known to prolong the QTc duration. There is concern for prolongation of the QTc interval in cardiac patients who may be more vulnerable to electrocardiogram (ECG) changes and may have postoperative QTc prolongation already. The goal of this study was to determine the effect of APM on QTc duration in postoperative paediatric cardiac patients and determine the effect of quetiapine and risperidone in treating delirium and QTc prolongation. DESIGN: Retrospective study, July 1, 2017-May 31, 2022. SETTING: Tertiary children's hospital. PATIENTS: Included were patients admitted to the paediatric cardiac ICU at Children's Healthcare of Atlanta. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: ECGs, delirium scores, and drug information were collected. Delirium was defined as Cornell Assessment of Pediatric Delirium (CAPD) score >9. Mixed effect models were performed to evaluate the effect of surgery on QTc change and the effect of antipsychotics on QTc and CAPD changes. There were 139 children, 55% male and 67% surgical admissions. Median age was 5.9 months. Mean QTc increased after cardiac surgery by 18 ms (p = 0.014, 95% CI 3.65-32.4). There was no significant change in QTc after antipsychotic administration (p = 0.064). The mean CAPD score decreased (12.5-7.2; p < 0.001). Quetiapine had the most improvement in delirium, and risperidone had the least improvement (77.8%, n = 14; 37.8%, n = 34, respectively; p = 0.002). CONCLUSIONS: The QTc interval did not have a statistically significant change after the administration of antipsychotics, while there was improvement in the CAPD score. APMs may be administered safely without significant prolongation of the QTc and are an effective treatment for delirium.

Incidence and recovery of post-surgical heart block in children following cardiac surgery.

BACKGROUND: A subset of patients who develop post-surgical heart block have recovery of atrioventricular node function. Factors predicting recovery are not understood. We investigated our centre's incidence of post-surgical heart block and examine factors associated with recovery of atrioventricular node function. METHODS: We conducted a single-centre retrospective study of patients 0 - 21 years who underwent cardiac surgery between January 2010 and December 2019 and experienced post-operative heart block. Data including patient and clinical characteristics and operative variables were collected and analysed. RESULTS: Of 6333 surgical hospitalisations, 128 (2%) patients developed post-operative heart block. Of the 128 patients, 90 (70%) had return of atrioventricular node function, and 38 (30%) had pacemaker placement. Of the 38 patients who underwent pacemaker placement, 6 (15.8%) had recovery of atrioventricular node function noted on long-term follow-up. Median time from onset of heart block to late atrioventricular node recovery was 13 days (Interquartile range: 5 - 117). Patients with single-ventricle physiology (p = 0.04), greater weight (p = 0.03), and shorter cardiopulmonary bypass time (p = 0.015) were more likely to have recovery. The use of post-operative steroids was similar between all groups (p = 0.445). Infectious or wound complications were similar between pacemaker groups (p = 1). CONCLUSIONS: Two per cent of patients who underwent congenital cardiac surgery developed post-operative heart block, and 0.6% underwent pacemaker placement. Early recovery of atrioventricular node was associated with greater weight at the time of surgery, single-ventricle physiology, and shorter cardiopulmonary bypass time. Late recovery of atrioventricular node conduction following pacemaker placement occurred in 15.8% of patients.

Exercise Recommendations in Pediatric HCM: Variation and Influence of Provider Characteristics.

Pediatric Hypertrophic Cardiomyopathy (HCM) is associated with sudden cardiac death (SCD) that can be related to physical activity. Without pediatric specific guidelines, recommendations for activity restriction may be varied. Therefore, our aim is to determine the current practice and variability surrounding exercise clearance recommendations (ER) in pediatric HCM referral centers as well as provider and patient characteristics that influence them. We designed a survey that was distributed to the Pediatric Heart Transplant Study (PHTS) providers and members of the Pediatric and Adult Congenital Electrophysiology Society (PACES) querying provider demographics and patient variables from 2 patient vignettes. The study is a multicenter survey of current practice of specialized providers caring for pediatric HCM patients. Survey of PHTS and PACES providers via email to the respective listservs with a response rate of 28% and 91 overall completing the entire survey after self-identifying as providers for pediatric HCM patients at their center. ER varies for pediatric HCM and is associated with provider training background as well as personal and professional history. Of the 91 providers who completed the survey, 42% (N = 38) trained in pediatric electrophysiology (EP), and 40% (N = 36) in pediatric heart failure (HF). Responses varied and only 53% of providers cleared for mild to moderate activity for the patient in Vignette 1, which is more in line with recent published adult guidelines. ER in both vignettes was significantly associated with type of training background. EP providers were more likely to recommend no restriction (27.8% vs 5.9%) than HF providers even when controlling for provider age and time out of training. Syncope with exercise was deemed "Most Important" by 81% of providers when making ER. ER for pediatric HCM are variable and the majority of providers make ER outside of previously published adult guidelines. Furthermore, ER are influenced by provider background and experience. Further study is needed for risks and benefits of physical activity in this population to inform the development of pediatric specific guidelines.

A Validated Model for Sudden Cardiac Death Risk Prediction in Pediatric Hypertrophic Cardiomyopathy.

BACKGROUND: Hypertrophic cardiomyopathy 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 hypertrophic cardiomyopathy to guide SCD prevention strategies. METHODS: In an international multicenter observational cohort study, phenotype-positive patients with isolated hypertrophic cardiomyopathy <18 years of age 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, and aborted SCD, that is, appropriate shock following primary prevention implantable cardioverter defibrillators. 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 10 repeated 4-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 by using the c-statistic for competing risk models. The final model was validated in an independent external cohort (SHaRe [Sarcomeric Human Cardiomyopathy Registry], 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 sudden cardiac arrests, and 14 aborted SCD). Risk predictors included age at diagnosis, documented nonsustained ventricular tachycardia, unexplained syncope, septal diameter z-score, left ventricular posterior wall diameter z score, left atrial diameter z score, peak left ventricular outflow tract gradient, and presence of a pathogenic variant. Unlike in adults, left ventricular outflow tract 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 between 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). CONCLUSION: Our study provides a validated SCD risk prediction model with >70% prediction accuracy and incorporates risk factors that are unique to pediatric hypertrophic cardiomyopathy. An individualized risk prediction model has the potential to improve the application of clinical practice guidelines and shared decision making for implantable cardioverter defibrillator insertion. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT0403679.

Lead age as a predictor for failure in pediatrics and congenital heart disease.

BACKGROUND: Pediatric and congenital heart disease (CHD) patients have a high rate of transvenous (TV) lead failure. OBJECTIVE: To determine whether TV lead age can aid risk assessment for lead failure to guide the decision of whether a lead should be replaced or reused at the time of a generator change. METHODS: Retrospective cohort study of patients <21 years old undergoing TV device implant from 2000 to 2014 at our institution. Patient, device, and lead variables were collected. Leads were compared in groups based on how many generator changes were completed. RESULTS: A total of 393 leads in 257 patients met inclusion criteria, 60 leads failed (15%). Failed leads were more likely to have not yet undergone generator change (p = .048). CHD (p = .045), Tendril lead type (p = .02) and silicone insulation (p = .02) were associated with failure. In multivariate analysis, younger leads (p = .022), number of generator changes (p = .003), CHD (p = .005) and silicone insulation (p = .004) remained significant while Tendril lead type did not (p = .052). Survival curves show an early decline around 4 years. CONCLUSIONS: Lead failure rate in pediatric and CHD patients is high. Leads that have not yet undergone a generator change were more likely to fail in this cohort. The strategy of serial replacement based on lead age needs further research to justify in this population.

Myocardial deformation as a predictor of right ventricular pacing-induced cardiomyopathy in the pediatric population.

INTRODUCTION: Right ventricular pacing is associated with pacemaker induced cardiomyopathy and lesser degrees of pacing-induced LV dysfunction (PIVD) manifested by a reduction in left ventricular ejection fraction (LVEF). Our objective was to determine whether apical 4 chamber strain (A4C) by echocardiography can identify patients at risk of PIVD before LVEF declines. METHODS AND RESULTS: A retrospective chart review of patients (0-21 years) who had a pacemaker with a ventricular lead placed between 2011 and 2017 was performed. Patients were divided into group A (LVEF <55% and/or >10% decline in LVEF within 12 months of pacemaker placement) and group B. Data have collected before and 1 and 12 months postpacemaker implantation. There were 30 patients in the group A and 60 in group B. At 1 and 12 months postpacemaker implantation, the LVEF was significantly lower while the A4C and QRS duration on electrocardiogram were significantly higher in the group A. While the LVEF and A4C became markedly abnormal in group A as early as 1 month, the A4C did not seem to demonstrate such marked abnormalities in group B. However, a sub-analysis of patients in the group A with preserved LVEF at 1 month demonstrated significant worsening in their A4C at that time. CONCLUSION: Myocardial deformation imaging may be a clinically useful tool for the prediction of a decline in LV systolic function following pacemaker implantation. Abnormalities in A4C seem to appear before LVEF decline and as soon as 1-month postpacemaker implantation.

Chemical cardioversion of atrial flutter and fibrillation in the pediatric population with Ibutilide.

INTRODUCTION: Atrial flutter (AFL) and atrial fibrillation (AF) are common in pediatric patients with congenital heart disease and structurally normal hearts as well. Chemical cardioversion is attractive for patients with AFL/AF for a short period of time because of the ability to avoid sedation. We review a single center's experience with Ibutilide in pediatric patients in an effort to report on its safety and efficacy. METHODS: We performed a retrospective chart review of pediatric patients (0-21 years) who underwent chemical cardioversion for AFL/AF with Ibutilide (January 2011-February 2019). Patients on another antiarrhythmic medication or attempted chemical cardioversion with another drug were excluded. RESULTS: There were 21 patients who met inclusion criteria. Thirteen of the 21 (62%) patients were successfully cardioverted with Ibutilide (10 out of 13 had AF and four out of 13 required a second dose). There were no significant differences in baseline characteristics between those who were successfully cardioverted compared to those who were not. Administration of magnesium prior to administration did not appear to have an effect on the success rate. There was a significant increase in rate corrected QT interval (QTc) post Ibutilide administration, which returned to baseline prior to discharge. One patient had symptomatic bradycardia needing intravenous fluids and another had torsades requiring electrical cardioversion during Ibutilide administration. CONCLUSIONS: The success rate of chemical cardioversion with Ibutilide was similar in our experience as compared to studies in the adult population and the other lone pediatric study. Although adverse events were uncommon, Ibutilide administration warrants close monitoring and fully defining its efficacy warrants further pediatric experience.

Recurrent single echo beats after cryoablation of atrioventricular nodal reentrant tachycardia: The pediatric population.

BACKGROUND: Cryoablation for atrioventricular nodal reentrant tachycardia (AVNRT) is effective and safe with a reported limitation of lower success and higher recurrence rates. We have observed cases in which slow pathway conduction was eliminated as demonstrated by atrial extra-stimulus testing within 1 min of cryo-energy delivery but returned following tissue rewarming. Frequently, slow pathway conduction persisted despite multiple acutely successful lesions over a broad anatomic region. We aimed to determine if return of slow pathway conduction after elimination during cryoablation represents a risk for recurrent AVNRT with the same intermediate term results as slow pathway ablation. We hypothesize that remnant single echo beats in the absence of sustained slow pathway conduction and inducible AVNRT is an acceptable end point after clear slow pathway elimination during cryoablation. METHODS: Retrospective chart review of patients undergoing attempted slow pathway ablation for AVNRT using solely cryoablation between January 2015-January 2018. RESULTS: Forty-four patients met inclusion criteria with at-least 2 features of dual AVN physiology. 19 patients had return of slow pathway conduction shortly after clear elimination during cryoablation (Group A) while 25 did not (Group B). All in Group A had recurrent single echo beats but none had sustained slow pathway conduction at the end of the procedure nor AVNRT recurrence at 1 year. CONCLUSION: Recurrent single echo beats with absent sustained slow pathway conduction and non-inducible AVNRT may be an acceptable endpoint for slow pathway ablation of AVNRT using cryoablation when there is elimination of slow pathway demonstrated during energy delivery.

Voltage mapping to guide pacemaker placement in patients with CHD.

Transvenous pacemaker implantation for sinus node dysfunction in patients with Fontan palliation presents the difficulty of finding suitable pacing tissue and the potential of causing vascular obstruction in a low-flow circuit. We describe a patient who underwent electro-anatomic voltage mapping to guide a transvenous single chamber lead within her Fontan baffle. This highlights the use of advanced mapping technologies for pacemaker implantation in complex cyanotic heart disease.

Safety of same-day discharge without anticoagulation for left-sided radiofrequency catheter ablations in pediatrics.

BACKGROUND: For left-sided radiofrequency catheter ablation (LCA) in pediatrics, significant practice variability exists regarding anticoagulation and discharge practices. Given the lack of data in pediatric patients, the risks and benefits of these practices are not well defined. OBJECTIVE: The purpose of this study was to evaluate the safety of same-day discharge and use of aspirin (ASA) in pediatric patients following LCA. METHODS: We performed a retrospective cohort study of pediatric patients who underwent LCA from 2010 to 2020 at our institution. Discharge timing and ASA usage were based on operator preference. The primary outcome was incidence of postablation anticoagulation complications reported within 1 month of the procedure. RESULTS: Three hundred seventy-six patients underwent LCA and met inclusion criteria. Median [25th, 75th percentiles] age was 13.9 [10.5, 16.2] years; 18 (4.7%) had a history of structural heart disease. The most common substrates for ablation were Wolff-Parkinson-White syndrome (183 patients [48.7%]), concealed accessory pathway (159 patients [42.3%]), and ectopic atrial tachycardia (10 patients [2.7%]). Three hundred thirty-eight patients (89.9%) were discharged on the day of LCA. Seventy-six patients (20.2%) were prescribed ASA at discharge. Of those who underwent follow-up (273 patients [72.6%]), 7 (2.7%) reported an anticoagulation complication (5 with hematoma, 2 with headache). One of these patients was prescribed ASA; none required readmission. There was no correlation between anticoagulation complications and same-day discharge or with ASA usage. CONCLUSION: Given the rare incidence of anticoagulation complications in pediatric patients undergoing LCAs, same-day discharge from the electrophysiology laboratory without anticoagulation should be considered.

Epidemiology of Postoperative Junctional Ectopic Tachycardia in Infants Undergoing Cardiac Surgery.

BACKGROUND: Junctional ectopic tachycardia (JET) complicates congenital heart surgery in 2% to 8.3% of cases. JET is associated with postoperative morbidity in single-center studies. We used the Pediatric Cardiac Critical Care Consortium data registry to provide a multicenter epidemiologic description of treated JET. METHODS: This is a retrospective study (February 2019-August 2022) of patients with treated JET. Inclusion criteria were (1) <12 months old at the index operation, and (2) treated for JET <72 hours after surgery. Diagnosis was defined by receiving treatment (pacing, cooling, and medications). A multilevel logistic regression analysis with hospital random effect identified JET risk factors. Impact of JET on outcomes was estimated by margins/attributable risk analysis using previous risk-adjustment models. RESULTS: Among 24,073 patients from 63 centers, 1436 (6.0%) were treated for JET with significant center variability (0% to 17.9%). Median time to onset was 3.4 hours, with 34% present on admission. Median duration was 2 days (interquartile range, 1-4 days). Tetralogy of Fallot, atrioventricular canal, and ventricular septal defect repair represented >50% of JET. Patient characteristics independently associated with JET included neonatal age, Asian race, cardiopulmonary bypass time, open sternum, and early postoperative inotropic agents. JET was associated with increased risk-adjusted durations of mechanical ventilation (incidence rate ratio, 1.6; 95% CI, 1.5-1.7) and intensive care unit length of stay (incidence rate ratio, 1.3; 95% CI, 1.2-1.3), but not mortality. CONCLUSIONS: JET is treated in 6% of patients with substantial center variability. JET contributes to increased use of postoperative resources. High center variability warrants further study to identify potential modifiable factors that could serve as targets for improvement efforts to ameliorate deleterious outcomes.

The Effect of Udenafil on Heart Rate and Blood Pressure in Adolescents With the Fontan Circulation.

The Fontan Udenafil Exercise Longitudinal (FUEL) trial showed that treatment with udenafil was associated with improved exercise performance at the ventilatory anaerobic threshold in children with Fontan physiology. However, it is not known how the initiation of phosphodiesterase 5 inhibitor therapy affects heart rate and blood pressure in this population. These data may help inform patient selection and monitoring after the initiation of udenafil therapy. The purpose of this study is to evaluate the effects of udenafil on vital signs in the cohort of patients enrolled in the FUEL trial. This international, multicenter, randomized, double-blind, placebo-controlled trial of udenafil included adolescents with single ventricle congenital heart disease who had undergone Fontan palliation. Changes in vital signs (heart rate [HR], systolic [SBP] and diastolic blood pressure [DBP]) were compared both to subject baseline and between the treatment and the placebo groups. Additional exploratory analyses were performed to evaluate changes in vital signs for prespecified subpopulations believed to be most sensitive to udenafil initiation. Baseline characteristics were similar between the treatment and placebo cohorts (n = 200 for each). The groups demonstrated a decrease in HR, SBP, and DBP 2 hours after drug/placebo administration, except SBP in the placebo group. There was an increase in SBP from baseline to after 6-min walk test in the treatment and placebo groups, and the treatment group showed an increase in HR (87.4 ± 15.0 to 93.1 ± 19.4 beats/min, p <0.01) after exercise. When comparing changes from baseline to the 26-week study visit, small decreases in both SBP (-1.9 ± 12.3 mm Hg, p = 0.03) and DBP (-3.0 ± 9.6 mm Hg, p <0.01) were seen in the treatment group. There were no clinically significant differences between treatment and placebo group in change in HR or blood pressure in the youngest age quartile, lightest weight quartile, or those on afterload-reducing agents. In conclusion, initiation of treatment with udenafil in patients with Fontan circulation was not associated with clinically significant changes in vital signs, implying that for patients similar to those enrolled in the FUEL trial, udenafil can be started without the requirement for additional monitoring after initial administration.

Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration.

BACKGROUND: Atrial standstill (AS) is a rare condition characterized by absence of electrical activity within the atria. Studies to date have been limited. OBJECTIVES: The authors sought to describe the clinical characteristics, genetics, and outcomes of patients with AS. METHODS: This was a retrospective multicenter study of patients <18 years at AS diagnosis, defined as absence of atrial activity documented during an electrophysiology study, device placement, or noninvasive rhythm tracings and confirmed by echocardiogram. Patients with acquired disorders were excluded. Clinical details and genetic variants were recorded and analyzed. RESULTS: Twenty patients were diagnosed at a median age of 6.6 years (IQR: 2.9-10.8 years). Arrhythmias included 16 (80%) with atrial/supraventricular arrhythmias and 8 (40%) with ventricular tachycardia, including 4 with cardiac arrests. A type 1 Brugada pattern was documented in 4. Pacemakers were implanted in 18 (90%). Although atrial leads were attempted in 15, only 4 achieved pacing at implantation. During a median follow-up of 6.9 years (IQR: 1.2-13.3 years), 7 (35%) had thromboembolic events. Of these, none had atrial pacing, 6 were not on anticoagulation, and 1 was on aspirin. Genetic testing identified SCN5A variants in 13 patients (65%). Analyses suggest SCN5A loss-of-function may be one mechanism driving AS. Ventricular arrhythmias and cardiac arrest were more commonly seen in patients with biallelic SCN5A variants. CONCLUSIONS: AS may be associated with loss-of-function SCN5A variants. Patients demonstrate atrial and ventricular arrhythmias, and may present challenges during device placement. Patients without the capacity for atrial pacing are at risk for thromboembolic events and warrant anticoagulation.

Transcatheter Leadless Pacing in Children: A PACES Collaborative Study in the Real-World Setting.

BACKGROUND: Transcatheter Leadless Pacemakers (TLP) are a safe and effective option for adults with pacing indications. These devices may be an alternative in pediatric patients and patients with congenital heart disease for whom repeated sternotomies, thoracotomies, or transvenous systems are unfavorable. However, exemption of children from clinical trials has created uncertainty over the indications, efficacy, and safety of TLP in the pediatric population. The objectives of this study are to evaluate clinical indications, procedural characteristics, electrical performance, and outcomes of TLP implantation in children. METHODS: Retrospective data were collected from patients enrolled in the Pediatric and Congenital Electrophysiology Society TLP registry involving 15 centers. Patients ≤21 years of age who underwent Micra (Medtronic Inc, Minneapolis, MN) TLP implantation and had follow-up of ≥1 week were included in the study. RESULTS: The device was successfully implanted in 62 of 63 registry patients (98%) at a mean age of 15±4.1 years and included 20 (32%) patients with congenital heart disease. The mean body weight at TLP implantation was 55±19 kg and included 8 patients ≤8 years of age and ≤30 kg in weight. TLP was implanted by femoral (n=55, 87%) and internal jugular (n=8, 12.6%) venous approaches. During a mean follow-up period of 9.5±5.3 months, there were 10 (16%) complications including one cardiac perforation/pericardial effusion, one nonocclusive femoral venous thrombus, and one retrieval and replacement of TLP due to high thresholds. There were no deaths, TLP infections, or device embolizations. Electrical parameters, including capture thresholds, R wave sensing, and pacing impedances, remained stable. CONCLUSIONS: Initial results from the Pediatric and Congenital Electrophysiology Society TLP registry demonstrated a high level of successful Micra device implants via femoral and internal venous jugular approaches with stable electrical parameters and infrequent major complications. Long-term prospective data are needed to confirm the reproducibility of these initial findings.

Risk of Sudden Death in Patients With RASopathy Hypertrophic Cardiomyopathy.

BACKGROUND: Genetic defects in the RAS/mitogen-activated protein kinase pathway are an important cause of hypertrophic cardiomyopathy (RAS-HCM). Unlike primary HCM (P-HCM), the risk of sudden cardiac death (SCD) and long-term survival in RAS-HCM are poorly understood. OBJECTIVES: The study's objective was to compare transplant-free survival, incidence of SCD, and implantable cardioverter-defibrillator (ICD) use between RAS-HCM and P-HCM patients. METHODS: In an international, 21-center cohort study, we analyzed phenotype-positive pediatric RAS-HCM (n = 188) and P-HCM (n = 567) patients. The between-group differences in cumulative incidence of all outcomes from first evaluation were compared using Gray's tests, and age-related hazard of all-cause mortality was determined. RESULTS: RAS-HCM patients had a lower median age at diagnosis compared to P-HCM (0.9 years [IQR: 0.2-5.0 years] vs 9.8 years [IQR: 2.0-13.9 years], respectively) (P < 0.001). The 10-year cumulative incidence of SCD from first evaluation was not different between RAS-HCM and P-HCM (4.7% vs 4.2%, respectively; P = 0.59). The 10-year cumulative incidence of nonarrhythmic deaths or transplant was higher in RAS-HCM compared with P-HCM (11.0% vs 5.4%, respectively; P = 0.011). The 10-year cumulative incidence of ICD insertions, however, was 5-fold lower in RAS-HCM compared with P-HCM (6.9% vs 36.6%; P < 0.001). Nonarrhythmic deaths occurred primarily in infancy and SCD primarily in adolescence. CONCLUSIONS: RAS-HCM was associated with a higher incidence of nonarrhythmic death or transplant but similar incidence of SCD as P-HCM. However, ICDs were used less frequently in RAS-HCM compared to P-HCM. In addition to monitoring for heart failure and timely consideration of advanced heart failure therapies, better risk stratification is needed to guide ICD practices in RAS-HCM.

Relation of Norwood Shunt Type and Frequency of Arrhythmias at 6 Years (from the Single Ventricle Reconstruction Trial).

The Norwood procedure with a right ventricular to pulmonary artery shunt (RVPAS) decreases early mortality, but requires a ventriculotomy, possibly increasing risk of ventricular arrhythmias (VAs) compared with the modified Blalock-Taussig shunt (MBTS). The effect of shunt and Fontan type on arrhythmias by 6 years of age in the SVRII (Single Ventricle Reconstruction Extension Study) was assessed. SVRII data collected on 324 patients pre-/post-Fontan and annually at 2 to 6 years included antiarrhythmic medications, electrocardiography (ECG) at Fontan, and Holter/ECG at 6 years. ECGs and Holters were reviewed for morphology, intervals, atrioventricular conduction, and arrhythmias. Isolated VA were seen on 6-year Holter in >50% of both cohorts (MBTS 54% vs RVPAS 60%), whereas nonsustained ventricular tachycardia was rare and observed in RVPAS only (2.7%). First-degree atrioventricular block was more common in RVPAS than MBTS (21% vs 8%, p = 0.01), whereas right bundle branch block, QRS duration, and QTc were similar. Antiarrhythmic medication usage was common in both groups, but most agents also supported ventricular function (e.g., digoxin, carvedilol). Of the 7 patients with death or transplant between 2 and 6 years, none had documented VAs, but compared with transplant-free survivors, they had somewhat longer QRS (106 vs 93 ms, p = 0.05). Atrial tachyarrhythmias varied little between MBTS and RVPAS but did vary by Fontan type (lateral tunnel 41% vs extracardiac conduit 29%). VAs did not vary by Fontan type. In conclusion, at 6-year follow-up, benign VAs were common in the SVRII population. However, despite the potential for increased VAs and sudden death in the RVPAS cohort, these data do not support significant differences or increased risk at 6 years. The findings highlight the need for ongoing surveillance for arrhythmias in the SVR population.

Adverse event rate during inpatient sotalol initiation for the management of supraventricular and ventricular tachycardia in the pediatric and young adult population.

BACKGROUND: Sotalol is an important antiarrhythmic drug in the pediatric population. Given the risk of proarrhythmia, sotalol is initiated in inpatient settings, with adult studies as recent as 2015 supporting this practice. OBJECTIVE: The purpose of this study was to determine the frequency of adverse events (AEs) during sotalol initiation for the management of atrial, supraventricular, or ventricular arrhythmias in pediatric patients. METHODS: A retrospective cohort analysis of pediatric patients 21 years or younger initiated on oral sotalol for supraventricular tachycardia or ventricular tachycardia (VT) at Boston Children's Hospital from January 1, 2007, through July 1, 2016, was performed. The primary end point was an AE defined as significant bradycardia, new or increased ventricular arrhythmias, conduction block, or corrected QT interval (QTc) prolongation, resulting in dose reduction or cessation. RESULTS: There were 190 patients who met inclusion criteria, with 110 patients (58%) 6 months or younger. A total of 115 patients (60%) had congenital heart disease. Arrhythmias for which sotalol was initiated included atrioventricular reciprocating tachycardia/atrioventricular nodal reciprocating tachycardia (n = 105 [55%]), atrial flutter (n = 31 [16%]), ectopic atrial tachycardia (n = 26 [14%]), VT (n = 21 [11%]), and atrial fibrillation (n = 7 [4%]). The median pre-sotalol QTc was 438 ms (interquartile range 348-530 ms). Five patients (3%) (aged 0.1-18 years) had AEs including bradycardia <40 beats/min (n = 2) and <100 beats/min (n = 1) and QTc prolongation (n = 2). All 5 patients with AEs had repaired congenital heart disease. CONCLUSION: The incidence of AEs in pediatric patients initiating sotalol for atrial tachycardia, supraventricular tachycardia, or VT is low (3%), with no deaths or malignant rhythms reported in this series.

Stroke After Cardiac Catheterization in Children.

BACKGROUND: Children with cardiac disease are at high risk for stroke. Approximately one-quarter of strokes in children with cardiac disease occur in the peri-procedural period; yet, the risk factors, clinical presentation, and treatment of post-catheterization stroke in children have not been well defined. METHODS: We conducted a retrospective review of the medical records of patients aged zero to 18 years with a new clinically-apparent arterial ischemic stroke after cardiac catheterization at a tertiary children's hospital from 2006 to 2016. We excluded patients who had cardiac surgery, a cardiac arrest, extracorporeal membrane oxygenation, a ventricular assist device, or an arrhythmia proximate to their stroke. RESULTS: Twenty children had a new clinically-apparent post-catheterization arterial ischemic stroke. The median age was one year (range, two days to 16 years). The most common procedures were balloon dilation for pulmonary vein stenosis (n = 6) and systemic pulmonary collateral closure (n = 5). The most common presenting symptoms were arm weakness (n = 10) and seizure (n = 8). The median time from catheterization to symptom discovery was 31.5 hours (interquartile range, 16.2 to 47.8 hours; n = 18). The median Pediatric Stroke Outcome Measure score 12 months post-stroke was 0.75 (range, 0 to 2; n = 6). CONCLUSIONS: Although arterial ischemic stroke after cardiac catheterization is rare, better understanding this entity is important as children with cardiac disease and stroke have ongoing morbidity. Ameliorating this morbidity requires efforts aimed at preventing and rapidly detecting stroke, thereby enabling timely institution of neuroprotective measures and treatment with hyperacute therapies.