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Radiofrequency (RF) ablation is a relatively safe and effective method for treatment of atrioventricular nodal re-entry tachycardia (AVNRT), but carries a 1-2% risk of AV nodal injury. Cryothermal ablation reduces the risk of AV block, but has had decreased procedural success and increased recurrence of tachycardia. We sought to evaluate the technique of linear lesion cryoablation (LLC) for treatment of AVNRT. Single institution retrospective cohort study. Each patient underwent slow pathway modification using either RF, single lesion cryoablation, or LLC. Procedural success, recurrence, freedom from tachycardia 12 months following ablation and fluoroscopy time were compared between ablation methods. A total of 125 patients, median age 15.5 (4.7-23.1) years, underwent ablation: 32 RF energy, 31 single lesion cryoablation, 62 LLC. Procedural success was obtained in 94% of the LLC group compared to 58% using single lesion cryoablation (P ≤ 0.001). Ninety-seven percent of the LLC group was free from tachycardia recurrence, significantly higher than with single lesion cryoablation (68%, P = 0.001) and equal to that of RF (97%, P = NS). Fluoroscopy time was reduced in the LLC group compared to both single lesion and RF groups (P = 0.02). There was no permanent AV nodal injury in the cryoablation groups. LLC is an effective means of treatment for AVNRT and is associated with significantly improved procedural success and freedom from recurrence compared to single lesion methods, while at the same time obtaining equivalent efficacy to RF. (PACE 2010; 1304-1311) [ABSTRACT FROM AUTHOR]

There is a growing awareness that diversity, health equity, and inclusion play a significant role in improving patient outcomes and advancing knowledge. The Pediatric Heart Network launched an initiative to incorporate diversity, health equity, and inclusion into its 2021 Scholar Award Funding Opportunity Announcement. This manuscript describes the process of incorporating diversity, health equity, and inclusion into the Pediatric Heart Network Scholar Award and the lessons learned. Recommendations for future Pediatric Heart Network grant application cycles are made which could be replicated by other funding agencies.

Background: Selection of radiofrequency ablation (RF) or cryoablation (Cryo) for atrioventricular nodal re-entrant tachycardia (AVNRT) in children remains controversial due to a lack of contemporary comparison studies in this population., Objectives: This study sought to compare outcomes of RF and Cryo for AVNRT in the pediatric population., Methods: AVNRT ablation outcomes were retrospectively analyzed utilizing the National Cardiovascular Data Registry IMPACT (Improving Pediatric and Adult Congenital Treatment) Registry from April 2016 to March 2019. Data from subjects 1 to 21 years of age undergoing elective first-time slow pathway (SP) modification for AVNRT were included. Exclusion criteria included <1 year of age, congenital heart disease, and >1 ablation target. Cases were analyzed by ablation energy: 1) RF only; 2) Cryo only; 3) radiofrequency ablation switching to cryoablation (RF→Cryo); and 4) cryoablation switching to radiofrequency ablation (Cryo→RF). The primary outcome was acute ablation failure. Secondary outcomes included in-hospital adverse events., Results: Among 2,448 patients (mean age 13.6 ± 3.4 years, 60% female), RF only was employed in 43% (n = 1,046), Cryo only in 49% (n = 1,201), RF→Cryo in 6% (n = 135), and Cryo→RF in 66 (3%). Acute ablation failure occurred in 1.3% (n = 33), with no difference by energy source (1% in RF only, 1.5% in Cryo only, 1.5% in RF→Cryo, 3% in Cryo→RF; P = 0.5). Atrioventricular (AV) block requiring permanent pacemaker did not occur in any group; transient AV block occurred in 0.4% of the cohort, with no difference by group., Conclusions: In this largest pediatric study of AVNRT ablation, RF and Cryo demonstrated comparable high acute success and rare documentation of AV block that did not result in temporary or permanent pacing. Longitudinal data are important for further comparison of these modalities with regard to recurrence risk and late complications., Competing Interests: Funding Support and Author Disclosures The specific analysis described in this manuscript was funded by the American College of Cardiology and National Cardiovascular Data Registry. The proposed project and manuscript were reviewed by the IMPACT Research and Publications Committee. The funding agencies had no role in the drafting of the manuscript or influencing its content. The views expressed in this manuscript represent those of the author(s), and do not necessarily represent the official views of the NCDR or its associated professional societies identified at CVQuality.ACC.org/ NCDR. The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Whether vigorous exercise increases risk of ventricular arrhythmias for individuals diagnosed and treated for congenital long QT syndrome (LQTS) remains unknown., Methods: The National Institutes of Health-funded LIVE-LQTS study (Lifestyle and Exercise in the Long QT Syndrome) prospectively enrolled individuals 8 to 60 years of age with phenotypic and/or genotypic LQTS from 37 sites in 5 countries from May 2015 to February 2019. Participants (or parents) answered physical activity and clinical events surveys every 6 months for 3 years with follow-up completed in February 2022. Vigorous exercise was defined as ≥6 metabolic equivalents for >60 hours per year. A blinded Clinical Events Committee adjudicated the composite end point of sudden death, sudden cardiac arrest, ventricular arrhythmia treated by an implantable cardioverter defibrillator, and likely arrhythmic syncope. A National Death Index search ascertained vital status for those with incomplete follow-up. A noninferiority hypothesis (boundary of 1.5) between vigorous exercisers and others was tested with multivariable Cox regression analysis., Results: Among the 1413 participants (13% <18 years of age, 35% 18-25 years of age, 67% female, 25% with implantable cardioverter defibrillators, 90% genotype positive, 49% with LQT1, 91% were treated with beta-blockers, left cardiac sympathetic denervation, and/or implantable cardioverter defibrillator), 52% participated in vigorous exercise (55% of these competitively). Thirty-seven individuals experienced the composite end point (including one sudden cardiac arrest and one sudden death in the nonvigorous group, one sudden cardiac arrest in the vigorous group) with overall event rates at 3 years of 2.6% in the vigorous and 2.7% in the nonvigorous exercise groups. The unadjusted hazard ratio for experience of events for the vigorous group compared with the nonvigorous group was 0.97 (90% CI, 0.57-1.67), with an adjusted hazard ratio of 1.17 (90% CI, 0.67-2.04). The upper 95% one-sided confidence level extended beyond the 1.5 boundary. Neither vigorous or nonvigorous exercise was found to be superior in any group or subgroup., Conclusions: Among individuals diagnosed with phenotypic and/or genotypic LQTS who were risk assessed and treated in experienced centers, LQTS-associated cardiac event rates were low and similar between those exercising vigorously and those not exercising vigorously. Consistent with the low event rate, CIs are wide, and noninferiority was not demonstrated. These data further inform shared decision-making discussions between patient and physician about exercise and competitive sports participation., Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02549664., Competing Interests: Dr Lampert reports honoraria and research support from Medtronic, Abbott-St. Jude, and Boston Scientific, as well as serving on the Advisory Board for Medtronic. Dr Day received consulting and grant funding from Lexicon Pharmaceuticals, grant funding from Bristol Myers Squibb, and DMC from Cytokinetics. L. Salberg consulted for Biomarin. Dr Tome Esteban consulted for BMS and Cytokinetics. Dr Abrams served on the Scientific Advisory Board for Thryv Therapeutics and consulted for Rocket Pharmaceuticals. Dr Aziz served on the Medtronic Advisory Committee. Dr Behr consulted for Boston Scientific. Dr Berul received research funding from Medtronic. Dr Cerrone provided teaching and CME activities for Abbott and Medtronic. Dr Erickson received funding from Integer. Dr Estes reports consulting for Boston Scientific and Medtronic. Dr Ethridge reports funding from Spauling Research (ECG reading) and UpToDate. Dr James was a consultant for Pfizer and Lexeo Therapeutics and received research funding from Lexeo Therapeutics and StrideBio. Dr Law was a consultant for Medtronic and St. Jude and a speaker for Boston Scientific. Dr Olshansky, AstraZeneca DSMB (Data Safety Monitoring Board). Dr Noseworthy and Mayo Clinic have filed patents related to the application of artificial intelligence to the ECG for diagnosis and risk stratification and have licensed several A-ECG algorithms to Anumana. Dr Noseworthy and Mayo Clinic have a relationship with AliveCor related to the measurement of the QT interval on the Kardia device. Dr Shah was a consultant for Medtronic and Tenaya. Dr Ware received research support and/or consultancy fees from MyoKardia, Bristol Myers Squibb, Foresite Labs, Pfizer, and Health Lumen. Dr Ware is supported by Medical Research Council (UK), British Heart Foundation (RE/18/4/34215), and the NIHR Imperial College Biomedical Research Centre. Dr Ackerman has served as a consultant for Abbott, BioMarin Pharmaceuticals, Boston Scientific, Bristol Myers Squibb, Daiichi-Sankyo, Illumina, Invitae, Medtronic, Tenaya Therapeutics, and UpToDate. Dr Ackerman and Mayo Clinic are involved in an equity/royalty relationship with AliveCor, Anumana, ARMGO Pharma, Pfizer, and Thryv Therapeutics. The other authors report no conflicts.

Supraventricular tachycardia (SVT) is the most common arrhythmia in infants. Once diagnosed, infants are admitted for antiarrhythmic therapy and discharged after observation. There are limited data on risk factors for readmission and readmission rates, while on medication. The objective of this study was to investigate risk factors for readmission and outcomes in infants diagnosed with SVT. This is a single-center retrospective study over a 10-year period of infants under 6 months of age with documented SVT. Infants with congenital heart disease requiring surgical or catheter intervention, gestational age less than 32 weeks or diagnosis of atrial flutter or fibrillation were excluded. The primary outcome was readmission within 31 days of hospital discharge. Long term need for ablation and eventual discontinuation of medications were assessed. Ninety patients were included. Beta blockers were the initial therapy in 66 and 28 required a medication change. Nineteen were readmitted within 31 days of discharge. The only clinical factor associated with early readmission was presence of ventricular pre-excitation (6/19 vs. 8/71, p = 0.03). Patients who were readmitted within 31 days had a longer length of treatment (12 [11.5, 22.0] vs. 10 [7.5, 12.0] months, p = 0.007) and were more likely to undergo ablation (4/19 vs. 2/71, p = 0.017). In this cohort of infants with SVT, readmission was common and ventricular pre-excitation was identified as a risk factor for readmission. Infants who were readmitted within 31 days of discharge had longer length of antiarrhythmic therapy and were more likely to undergo catheter ablation., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

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., (Copyright © 2024 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Pediatric ECG standards have been defined without echocardiographic confirmation of normal anatomy. The Pediatric Heart Network Normal Echocardiogram Z-score Project provides a racially diverse group of healthy children with normal echocardiograms. We hypothesized that ECG and echocardiographic measures of left ventricular (LV) dimensions are sufficiently correlated in healthy children to imply a clinically meaningful relationship. This was a secondary analysis of a previously described cohort including 2170 digital ECGs. The relationship between 6 ECG measures associated with LV size were analyzed with LV Mass (LVMass-z) and left ventricular end-diastolic volume (LVEDV-z) along with 11 additional parameters. Pearson or Spearman correlations were calculated for the 78 ECG-echocardiographic pairs with regression analyses assessing the variance in ECG measures explained by variation in LV dimensions and demographic variables. ECG/echocardiographic measurement correlations were significant and concordant in 41/78 (53%), though many were significant and discordant (13/78). Of the 6 ECG parameters, 5 correlated in the clinically predicted direction for LV Mass-z and LVEDV-z. Even when statistically significant, correlations were weak (0.05-0.24). R 2 was higher for demographic variables than for echocardiographic measures or body surface area in all pairs, but remained weak (R 2  ≤ 0.17). In a large cohort of healthy children, there was a positive association between echocardiographic measures of LV size and ECG measures of LVH. These correlations were weak and dependent on factors other than echocardiographic or patient derived variables. Thus, our data support deemphasizing the use of solitary, traditional measurement-based ECG markers traditionally thought to be characteristic of LVH as standalone indications for further cardiac evaluation of LVH in children and adolescents., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Background: A growing number of patients with tetralogy of Fallot develop left ventricular systolic dysfunction and heart failure, in addition to right ventricular dysfunction. Although cardiac resynchronization therapy (CRT) is an established treatment option, the effect of CRT in this population is still not well defined. This study aimed to investigate the early and late efficacy, survival, and safety of CRT in patients with tetralogy of Fallot., Methods: Data were analyzed from an observational, retrospective, multicenter cohort, initiated jointly by the Pediatric and Congenital Electrophysiology Society and the International Society of Adult Congenital Heart Disease. Twelve centers contributed baseline and longitudinal data, including vital status, left ventricular ejection fraction (LVEF), QRS duration, and NYHA functional class. Outcomes were analyzed at early (3 months), intermediate (1 year), and late follow-up (≥2 years) after CRT implantation., Results: A total of 44 patients (40.3±19.2 years) with tetralogy of Fallot and CRT were enrolled. Twenty-nine (65.9%) patients had right ventricular pacing before CRT upgrade. The left ventricular ejection fraction improved from 32% [24%-44%] at baseline to 42% [32%-50%] at early follow-up ( P <0.001) and remained improved from baseline thereafter ( P ≤0.002). The QRS duration decreased from 180 [160-205] ms at baseline to 152 [133-182] ms at early follow-up ( P <0.001) and remained decreased at intermediate and late follow-up ( P ≤0.001). Patients with upgraded CRT had consistent improvement in left ventricular ejection fraction and QRS duration at each time point ( P ≤0.004). Patients had a significantly improved New York Heart Association functional class after CRT implantation at each time point compared with baseline ( P ≤0.002). The transplant-free survival rates at 3, 5, and 8 years after CRT implantation were 85%, 79%, and 73%., Conclusions: In patients with tetralogy of Fallot treated with CRT consistent improvement in QRS duration, left ventricular ejection fraction, New York Heart Association functional class, and reasonable long-term survival were observed. The findings from this multicenter study support the consideration of CRT in this unique population., Competing Interests: Disclosures None.

Competing Interests: Funding Support and Author Disclosures The authors have reported that they have no relationships relevant to the contents of this paper to disclose.

Patients with Trisomy 18 have a high incidence of cardiac anomalies and are associated with early death. Because of early mortality, electrical system disease and arrhythmia has been difficult to delineate and the incidence remain unknown. We sought to describe the association and clinical outcomes of electrical system disease and cardiac tachy-arrhythmias in patients with Trisomy 18. This was a retrospective, single institutional study. All patients with Trisomy 18 were included in the study. Patient characteristics, congenital heart disease (CHD), conduction system and clinical tachy-arrhythmia data were collected on all patients. Outcomes including cardiac surgical interventions, electrical system interventions and death were collected until the time of study. Patients with tachy-arrhythmias/electrical system involvement were compared to those without to identify potential associated variables. A total of 54 patients with Trisomy 18 were included in analysis. The majority of patients was female and had associated CHD. AV nodal conduction system abnormalities with either first or second degree AV block were common (15%) as was QTc prolongation (37%). Tachy-arrhythmias were common with 22% of patients having at least one form of tachy-arrhythmia and associated with concomitant conduction system disease (p = 0.002). Tachy-arrhythmias were typically treatable with monitoring or medication with eventual resolution without need for procedural intervention. Although early death was common, there were no causes of death associated with tachy-arrhythmia or conduction system disease. In conclusion, patients with Trisomy 18 have a high incidence of conduction system abnormalities and burden of clinical tachy-arrhythmias. Although frequent, electrical system disease did not affect patient outcome or difficultly of care delivery., (© 2023 The Authors. American Journal of Medical Genetics Part A published by Wiley Periodicals LLC.)

Importance: Whether vigorous intensity exercise is associated with an increase in risk of ventricular arrhythmias in individuals with hypertrophic cardiomyopathy (HCM) is unknown., Objective: To determine whether engagement in vigorous exercise is associated with increased risk for ventricular arrhythmias and/or mortality in individuals with HCM. The a priori hypothesis was that participants engaging in vigorous activity were not more likely to have an arrhythmic event or die than those who reported nonvigorous activity., Design, Setting, and Participants: This was an investigator-initiated, prospective cohort study. Participants were enrolled from May 18, 2015, to April 25, 2019, with completion in February 28, 2022. Participants were categorized according to self-reported levels of physical activity: sedentary, moderate, or vigorous-intensity exercise. This was a multicenter, observational registry with recruitment at 42 high-volume HCM centers in the US and internationally; patients could also self-enroll through the central site. Individuals aged 8 to 60 years diagnosed with HCM or genotype positive without left ventricular hypertrophy (phenotype negative) without conditions precluding exercise were enrolled., Exposures: Amount and intensity of physical activity., Main Outcomes and Measures: The primary prespecified composite end point included death, resuscitated sudden cardiac arrest, arrhythmic syncope, and appropriate shock from an implantable cardioverter defibrillator. All outcome events were adjudicated by an events committee blinded to the patient's exercise category., Results: Among the 1660 total participants (mean [SD] age, 39 [15] years; 996 male [60%]), 252 (15%) were classified as sedentary, and 709 (43%) participated in moderate exercise. Among the 699 individuals (42%) who participated in vigorous-intensity exercise, 259 (37%) participated competitively. A total of 77 individuals (4.6%) reached the composite end point. These individuals included 44 (4.6%) of those classified as nonvigorous and 33 (4.7%) of those classified as vigorous, with corresponding rates of 15.3 and 15.9 per 1000 person-years, respectively. In multivariate Cox regression analysis of the primary composite end point, individuals engaging in vigorous exercise did not experience a higher rate of events compared with the nonvigorous group with an adjusted hazard ratio of 1.01. The upper 95% 1-sided confidence level was 1.48, which was below the prespecified boundary of 1.5 for noninferiority., Conclusions and Relevance: Results of this cohort study suggest that among individuals with HCM or those who are genotype positive/phenotype negative and are treated in experienced centers, those exercising vigorously did not experience a higher rate of death or life-threatening arrhythmias than those exercising moderately or those who were sedentary. These data may inform discussion between the patient and their expert clinician around exercise participation.

Background: Supraventricular tachycardia (SVT) is a common arrhythmia. Infants with SVT are often admitted to initiate antiarrhythmics. Transesophageal pacing (TEP) studies can be used to guide therapy prior to discharge., Objective: The objective of this study was to investigate the impact of TEP studies on length of stay (LOS), readmission, and cost in infants with SVT., Methods: This was a 2-site retrospective review of infants with SVT. One site (Center TEPS) utilized TEP studies in all patients. The other (Center NOTEP) did not. Patients with structural heart disease, patients with gestational age <34 weeks, and patients diagnosed after 6 months were excluded. At Center TEPS, repeat TEP studies were performed after titration of medication until SVT was not inducible. Primary endpoints were LOS and readmission for breakthrough SVT within 31 days of discharge. Hospital reimbursement data were utilized for cost-effectiveness analysis., Results: The cohort included 131 patients, 59 in Center TEPS and 72 in Center NOTEP. One patient was readmitted in Center TEPS vs 17 in Center NOTEP (1.6% vs 23.6%; P ≤ .001). Median LOS was longer for Center TEPS at 118.0 (interquartile range [IQR] 74.0-189.5) hours vs Center NOTEP at 66.9 (IQR 45.5-118.3) hours ( P = .001). Twenty-one patients had multiple TEP studies. Median length of readmission for Center NOTEP was 65 (IQR 41-101) hours. Including readmission costs, utilization of TEP studies resulted in a probability-weighted cost of $45,531 per patient compared with $31,087 per patient without TEP studies., Conclusion: Utilization of TEP studies was associated with decreased readmission rates but longer LOS and greater cost compared with SVT management without TEP studies., (© 2023 Heart Rhythm Society. Published by Elsevier Inc.)

Background: Dyssynchrony-associated left ventricular systolic dysfunction is a major contributor to heart failure in congenital heart disease (CHD). Although conventional cardiac resynchronization therapy (CRT) has shown benefit, the comparative efficacy of cardiac conduction system pacing (CSP) is unknown., Objectives: The purpose of this study was compare the clinical outcomes of CSP vs conventional CRT in CHD with biventricular, systemic left ventricular anatomy., Methods: Retrospective CSP data from 7 centers were compared with propensity score-matched conventional CRT control subjects. Outcomes were lead performance, change in left ventricular ejection fraction (LVEF), and QRS duration at 12 months., Results: A total of 65 CSP cases were identified (mean age 37 ± 21 years, 46% men). The most common CHDs were tetralogy of Fallot (n = 12 [19%]) and ventricular septal defect (n = 12 [19%]). CSP was achieved after a mean of 2.5 ± 1.6 attempts per procedure (38 patients with left bundle branch pacing, 17 with HBP, 10 with left ventricular septal myocardial). Left bundle branch area pacing [LBBAP] vs HBP was associated with a smaller increase in pacing threshold (Δ pacing threshold 0.2 V vs 0.8 V; P = 0.05) and similar sensing parameters at follow-up. For 25 CSP cases and control subjects with baseline left ventricular systolic dysfunction, improvement in LVEF was non-inferior (Δ LVEF 9.0% vs 6.0%; P = 0.30; 95% confidence limits: -2.9% to 10.0%) and narrowing of QRS duration was more pronounced for CSP (Δ QRS duration 35 ms vs 14 ms; P = 0.04). Complications were similar (3 [12%] CSP, 4 [16%] conventional CRT; P = 1.00)., Conclusions: CSP can be reliably achieved in biventricular, systemic left ventricular CHD patients with similar improvement in LVEF and greater QRS narrowing for CSP vs conventional CRT at 1 year. Among CSP patients, pacing electrical parameters were superior for LBBAP vs HBP., Competing Interests: Funding Support and Author Disclosures Dr Cano has received consultant fees from Medtronic, Biotronik, and Boston Scientific. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Published by Elsevier Inc.)

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., Competing Interests: Funding Support and Author Disclosures Dr Miyake is supported by National Heart, Lung, and Blood Institute grant K23HL136932. Dr Chiang is supported by the Leducq Foundation and a National Institutes of Health T32 grant from the National Human Genome Research Institute (#1T32HG010464). The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2023 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background The objective of this international multicenter study was to investigate both early and late outcomes of cardiac resynchronization therapy (CRT) in patients with a systemic right ventricle (SRV) and to identify predictors for congestive heart failure readmissions and mortality. Methods and Results This retrospective international multicenter study included 13 centers. The study population comprised 80 adult patients with SRV (48.9% women) with a mean age of 45±14 (range, 18-77) years at initiation of CRT. Median follow-up time was 4.1 (25th-75th percentile, 1.3-8.3) years. Underlying congenital heart disease consisted of congenitally corrected transposition of the great arteries and dextro-transposition of the great arteries in 63 (78.8%) and 17 (21.3%) patients, respectively. CRT resulted in significant improvement in functional class (before CRT: III, 25th-75th percentile, II-III; after CRT: II, 25th-75th percentile, II-III; P =0.005) and QRS duration (before CRT: 176±27; after CRT: 150±24 milliseconds; P =0.003) in patients with pre-CRT ventricular pacing who underwent an upgrade to a CRT device (n=49). These improvements persisted during long-term follow-up with a marginal but significant increase in SRV function (before CRT; 30%, 25th-75th percentile, 25-35; after CRT: 31%, 25th-75th percentile, 21-38; P =0.049). In contrast, no beneficial change in the above-mentioned variables was observed in patients who underwent de novo CRT (n=31). A quarter of all patients were readmitted for heart failure during follow-up, and mortality at latest follow-up was 21.3%. Conclusions This international experience with CRT in patients with an SRV demonstrated that CRT in selected patients with SRV dysfunction and pacing-induced dyssynchrony yielded consistent improvement in QRS duration and New York Heart Association functional status, with a marginal increase in SRV function.

Background: Arrhythmias are common in single ventricle patients though their effect on outcomes during stage I palliation (S1P) is unclear., Objectives: The authors sought to study associated risks for arrhythmia in patients undergoing S1P for single ventricle disease and evaluate the outcome of arrhythmias and their treatment strategies on survival., Methods: Retrospective patient, surgical, medication, and arrhythmia data were obtained from the NPC-QIC (National Pediatric Cardiology Quality Improvement Collaborative) database. Bivariate analysis of variables associated with arrhythmias, as well as those associated with survival, was performed at the time of stage II palliation. Appropriate variables were included in multivariate modeling., Results: Of the 2,048 patients included in the study, 36% had arrhythmia noted during their S1P hospitalization, with supraventricular tachycardia (12%) and focal atrial tachycardia (11%) the most common. At S1P discharge, 11% of patients were on an antiarrhythmic medication. Arrhythmias were associated with lower survival and increased hospital length of stay. Heterotaxy syndrome, younger age at S1P, male sex, and additional anomalies were associated with increased risk of arrhythmia in multivariable modeling (P ≤ 0.01). Arrhythmia and female sex were associated with increased mortality, whereas antiarrhythmic medication and digoxin use were associated with decreased mortality (P ≤ 0.003, model area under the curve = 0.79). The use of antiarrhythmic medications within the subcohort of arrhythmia patients was also associated with decreased risk of mortality (P &lt; 0.0001; odds ratio: 2.0-7.2)., Conclusions: Arrhythmias are common during admission for S1P and associated with poor outcomes. The use of antiarrhythmic medications may improve survival, though future studies are needed., Competing Interests: Funding Support and Author Disclosures This work was conducted with support from the Heart Institute Research Core (HIRC) at Cincinnati Children’s Hospital. Current funding sources for National Pediatric Cardiology Quality Improvement Collaborative include participation fees from enrolled centers; a grant from the Children’s Heart Association of Cincinnati; a federal grant to the pediatric Center for Education and Research in Therapeutics at Cincinnati Children’s Hospital Medical Center, funded by the federal Agency for Healthcare, Research and Quality (#U19HS021114 AHRQ). The content is solely the responsibility of the authors and does not necessarily represent the official views of the Agency for Healthcare Research and Quality. Dr Webster is partially supported by National Institutes of Health grant K23HL130554. The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2022 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Palliation of the single ventricle (SV) circulation is associated with a burden of lifelong complications. Previous studies have identified that the need for a permanent ventricular pacing system (PPM v ) may be associated with additional adverse long-term outcomes., Objectives: The goal of this study was to quantify the attributable risk of PPM v in patients with SV, and to identify modifiable risk factors., Methods: This international study was sponsored by the Pediatric and Congenital Electrophysiology Society. Centers contributed baseline and longitudinal data for functionally SV patients with PPM v . Enrollment was at implantation. Controls were matched 1:1 to PPM v subjects by ventricular morphology and sex, identified within center, and enrolled at matched age. Primary outcome was transplantation or death., Results: In total, 236 PPM v subjects and 213 matched controls were identified (22 centers, 9 countries). Median age at enrollment was 5.3 years (quartiles: 1.5-13.2 years), follow-up 6.9 years (3.4-11.6 years). Median percent ventricular pacing (Vp) was 90.8% (25th-75th percentile: 4.3%-100%) in the PPM v cohort. Across 213 matched pairs, multivariable HR for death/transplant associated with PPM v was 3.8 (95% CI 1.9-7.6; P < 0.001). Within the PPM v population, higher Vp (HR: 1.009 per %; P = 0.009), higher QRS z-score (HR: 1.19; P = 0.009) and nonapical lead position (HR: 2.17; P = 0.042) were all associated with death/transplantation., Conclusions: PPM v in patients with SV is associated with increased risk of heart transplantation and death, despite controlling for increased associated morbidity of the PPM v cohort. Increased Vp, higher QRS z-score, and nonapical ventricular lead position are all associated with higher risk of adverse outcome and may be modifiable risk factors., Competing Interests: Funding Support and Author Disclosures Drs Janousek and Fumanelli were supported by the Ministry of Health, Czech Republic: conceptual development of research organization, Motol University Hospital, Prague, Czech Republic. Dr Balaji has been a medical advisor/consultant to “yoR labs” (stock options). All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2022 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

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., Competing Interests: Disclosures The authors have no conflicts of interest to declare., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Patients with left ventricular noncompaction (LVNC) are at risk of clinically significant arrhythmias and sudden death. We evaluated whether implantable loop recorders could detect significant arrhythmias that might be missed in these patients during annual Holter monitoring. Selected pediatric and adult patients with LVNC who consented to implantable loop recorder placement were monitored for 3 years (study duration, 10 April 2014-9 December 2019). Fourteen subjects were included (age range, 6.5-36.4 yr; 8 males). Of 13 patients who remained after one device extrusion, one underwent implantable cardioverter-defibrillator placement. Four patients (31%) had significant arrhythmias: atrial tachycardia (n=2), nonsustained ventricular tachycardia (n=1), and atrial fibrillation (n=1). All 4 events were clinically asymptomatic and not associated with left ventricular ejection fraction. In addition, a high frequency of benign arrhythmic patterns was detected. Implantable loop recorders enable continuous, long-term detection of important subclinical arrhythmias in selected patients who have LVNC. These devices may prove to be most valuable in patients who have LVNC and moderate or greater ventricular dysfunction., (© 2022 by the Texas Heart® Institute, Houston.)

Background: Understanding the overall variant burden in pediatric patients with left ventricular noncompaction (LVNC) has clinical implications. Whole exome sequencing (WES) allows detection of coding variants in both candidate cardiomyopathy genes and those included on commercial panels. Other lines of evidence, including in silico analysis, are necessary to reduce the overwhelming number of variants to those most likely having a phenotypic impact., Methods: Five families, including five pediatric probands with LVNC, 5 other affected, and 10 unaffected family members, had WES performed, followed by bioinformatics filtering and Sanger sequencing. Review of the HGMD, variant classification by ACMG guidelines, and clinical information were used to further refine complex genotypes., Results: One nonsense and eleven missense variants were identified. In Family 1, affected siblings carried digenic heterozygous variants: E1350K-MYH7 and A276V-ANKRD1. The proband also carried heterozygous W143X-NRG1. Four affected members of Family 2 carried K184Q-MYH7 while unaffected members did not. In Family 3, homozygous A161T-MYH7 and heterozygous P4935T-OBSCN variants were identified in the proband with the latter being absent in his unaffected brother. In Family 4, proband's father and half-sibling have mild hypertrabeculation and carry T3796I-PLEC. The proband, carrying T3796I-PLEC and V2878A-OBSCN, demonstrated higher trabeculation burden. The proband in Family 5 carried four variants, R3247W-PLEC, C92Y-ERG, T1233M-NCOR2, and E54K-HIST1H4B. Application of ACMG criteria and clinical data revealed that W143X-NRG1, P4935T-OBSCN, and V2878A-OBSCN likely have no phenotypic role., Conclusions: We report nine variants, including novel T3796I-PLEC and biallelic A161T-MYH7, likely contributing to phenotypes ranging from asymptomatic hypertrabeculation to severe LVNC with heart failure., (Copyright © 2021. Published by Elsevier B.V.)

Rhythm-symptom correlation in pediatric patients with syncope/palpitations or at risk cohorts can be difficult, but important given potential associations with treatable or malignant arrhythmia. We sought to evaluate the use, efficacy and outcomes of implantable loop recorders (ILR) in pediatrics. We conducted a retrospective study of pediatric patients (<21 years) with implanted ILR. Patient/historical characteristics and ILR indication were obtained. Outcomes including symptom documentation, arrhythmia detection and ILR based changes in medical care were identified. Comparison of outcomes were performed based on implant indication. Additional sub-analyses were performed in syncope-indication patients comparing those with and without changes in clinical management. A total of 116 patients with ILR implant were identified (79 syncope/37 other). Symptoms were documented 58% of patients (syncope 68% vs nonsyncope 35%; p = 0.002). A total of 37% of patients had a documented clinically significant arrhythmia and 25% of patients had a resultant change in clinical management independent of implant indication. Arrhythmia type was dependent on implant indication with nonsyncope patients having more ventricular arrhythmias. Pacemaker/defibrillator implantation and mediation management were the majority of the clinical changes. In conclusion, IRL utilization in selected pediatric populations is associated with high efficacy and supports clinical management. ILR efficacy is similar regardless of indication although patients with nonsyncope indications had a higher frequency of ventricular arrhythmias as opposed to asystole and heart block in syncope indications. The majority of arrhythmic findings occurred in the first 12 months, and new technology that would allow for less invasive monitoring for 6 to 12 months may be of value., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Mortality in cohorts with a single ventricle remains high with multiple associated factors. The effect of heart block during stage I palliation remains unclear., Objective: The purpose of this study was to study patient and surgical risks of heart block and its effect on 12-month transplant-free survival in patients with a single ventricle., Methods: Patient, surgical, outcome data and heart block status (transient and permanent) were obtained from the National Pediatric Cardiology Quality Improvement Collaborative single ventricle database. Bivariate analysis was performed comparing patients with and without heart block, and multivariate modeling was used to identify variables associated with block. One-year outcomes were analyzed to identify variables associated with lower 12-month transplant-free survival., Results: In total, 1423 patients were identified, of whom 28 (2%) developed heart block (second degree or complete) during their surgical admission. Associated risk factors for block included heterotaxy syndrome (odds ratio [OR] 6.4) and atrial flutter/fibrillation (OR 3.8). Patients with heart block had lower 12-month survival, though only in patients with complete heart block as opposed to second degree block. At 12 months of age, 43% (12/28) of patients with heart block died and were more likely to experience mortality at 12 months than patients without block (OR 4.9; 95% confidence interval 1.4-17.5; P = .01)., Conclusion: Although rare, complete heart block after stage I palliation represents an additional risk of poor outcomes in this high-risk patient population. Heterotaxy syndrome was the most significant risk factor for the development of heart block after stage I palliation. The role of transient block in outcomes and potential rescue with long-term pacing remains unknown and requires additional study., (Copyright © 2021 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

We describe an adolescent with Streptococcus pneumoniae meningitis and symptomatic high-grade, second-degree atrioventricular block requiring permanent pacemaker placement. It is difficult to ascertain if these two diagnoses were independent or had a causal relationship though ongoing symptoms were not present prior to the infection. Because of this uncertainty, awareness that rhythm disturbances can be cardiac in origin but also secondary to other aetiologies, such as infection, is warranted.

Background: Accelerated idioventricular rhythm (AIVR) is an uncommon and typically benign dysrhythmia with similarities to more malignant forms of ventricular tachycardia (VT). It is often seen in adults after myocardial infarctions, although it also arises in the newborn period, as well as in children with and without congenital heart disease., Case Report: We describe a presentation of AIVR in an otherwise healthy 13-year-old girl, discovered on arrival to the pediatric emergency department in the setting of post-tonsillectomy bleeding. The case reviews the diagnostic criteria of AIVR, associated symptoms, the pathophysiologic origin of AIVR, and potential treatment strategies. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Given its morphologic similarities to life-threatening forms of VT, AIVR can be misdiagnosed in the emergency department or primary care settings. With an understanding of the dysrhythmia's unique features, emergency physicians can avoid unnecessary interventions and provide the correct diagnosis, workup, and management of AIVR for pediatric patients., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Pacemakers are a mainstay of therapy for patients with congenital and acquired heart block, but ventricular pacing is related to ventricular dysfunction. We sought to evaluate patient and device characteristics associated with ventricular dysfunction in pediatric patients with chronic ventricular pacing. This was a retrospective cohort of pediatric patients with heart block and chronic ventricular pacing. Patient, ECG, and device characteristics were analyzed to determine factors associated with ventricular dysfunction. Longitudinal ECG and echocardiogram parameters were obtained to track changes in QRS and systemic ventricular systolic function over time. In total, 82 patients were included (median age at implant 0.81 years). Over a follow-up time of 6.1 years, 18% developed ventricular dysfunction. Patients with dysfunction had greater current QRS duration (p = 0.002) compared to those with preserved function with a similar time from device implantation. There was no difference between lead location or age at device implantation. QRS duration increased with time from implant and the resultant ΔQRS was associated with ventricular dysfunction (p = 0.01). QRS duration >162 ms was associated with a 5.8 (2-9)-fold increased risk for dysfunction. Transvenous leads were associated with longer QRS duration with no difference compared to epicardial leads in development of ventricular dysfunction. This study demonstrated that the absolute paced QRS duration and Δpaced QRS were association with long-term ventricular dysfunction independent of how long a given patient was paced. Patients in high-risk categories may benefit from close echocardiographic monitoring. Whether permissive junctional rhythm or His bundle/biventricular pacing decreases the rate of dysfunction needs further study.

Background: Implantable cardioverter defibrillators (ICD) are recommended for secondary prevention after sudden cardiac arrest (SCA). The outcomes of pediatric patients receiving an ICD after SCA remain unclear. The objective of this study is to evaluate outcomes, future risk for appropriate shocks, and identify characteristics associated with appropriate ICD therapy during follow-up., Methods: Multicenter retrospective analysis of patients (age ≤21 years) without prior cardiac disease who received an ICD following SCA. Patient/device characteristics, cardiac function, and underlying diagnoses were collected, along with SCA event characteristics. Patient outcomes including complications and device therapies were analyzed., Results: In total, 106 patients were included, median age 14.7 years. Twenty (19%) received appropriate shocks and 16 (15%) received inappropriate shocks (median follow-up 3 years). First-degree relative with SCA was associated with appropriate shocks ( P <0.05). In total, 40% patients were considered idiopathic. Channelopathy was the most frequent late diagnosis not made at time of presentation. Neither underlying diagnosis nor idiopathic status was associated with increased incidence of appropriate shock. Monomorphic ventricular tachycardia (hazard ratio, 4.6 [1.2-17.3]) and family history of sudden death (hazard ratio, 6.5 [1.4-29.8]) were associated with freedom from appropriate shock in a multivariable model (area under the receiver operating characteristic curve, 0.8). Time from diagnoses to evaluation demonstrated a nonlinear association with freedom from appropriate shock ( P =0.015). In patients >2 years from implantation, younger age ( P =0.02) and positive exercise test ( P =0.04) were associated with appropriate shock., Conclusions: The risk of future device therapy is high in pediatric patients receiving an ICD after SCA, irrelevant of underlying disease. Lack of a definitive diagnosis after SCA was not associated with lower risk of subsequent events and does not obviate the need for secondary prophylaxis.

Background: Patients with repaired tetralogy of Fallot (rTOF) have increased risk for mortality, sudden cardiac death, and ventricular tachycardia (VT). The aim of this systematic review and meta-analysis is to offer an updated analysis of risk factors following significant changes in surgical and perioperative management., Methods: A meta-analysis based on the published literature between 2008 and 2018 was conducted. Endpoints were VT, cardiac mortality/VT, and all-cause mortality/VT. Studies with ≥100 patients and ≥10 events were included., Results: Fifteen studies including 7218 patients (average age 27.5 years) were analyzed. Risk factors for VT included older age (per 1 year, odds ratio [OR]: 1.039; 95% confidence interval [CI]: 1.025-1.053), older age at corrective surgery (per 1 year, OR: 1.034; CI: 1.017-1.051), previous palliative shunt (OR: 3.063; CI: 1.525-6.151), number of thoracotomies (OR: 1.416; CI: 1.249-1.604), longer QRS duration (per 1 ms, OR: 1.031; CI: 1.008-1.055), and at least moderate right-ventricular dysfunction (OR: 2.160; CI&#95; 1.311-3.560). Additional risk factors for cardiac death/VT were previous ventriculotomy (OR: 2.269; CI: 1.226-4.198), lower left-ventricular ejection fraction (per 1%, OR: 1.049; CI: 1.029-1.071), and higher right-ventricular end diastolic volume (per 1 mL/m 2 , OR: 1.009; CI: 1.002-1.016). Supraventricular tachycardia/atrial fibrillation was an additional risk factor for all-cause mortality/VT (OR: 1.939; CI: 1.088-3.457)., Conclusions: The study highlights the importance of preservation of biventricular systolic function on late outcomes. Ventricular function appears to have a greater impact on outcomes than the severity of pulmonary regurgitation alone in this patient population., (Copyright © 2020 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Neonates can have different types of arrhythmias that range from benign to life-threatening. The evaluation, approach to acute presentation, and long-term management depend on correct identification of the arrhythmia. A systematic approach to analyzing the electrocardiogram and the telemetry monitor, if available, is often sufficient to diagnose the type of arrhythmia., (Copyright © 2020 by the American Academy of Pediatrics.)

Objectives: Extracorporeal membrane oxygenation is used to support refractory cardiorespiratory failure. Outcomes and complications when extracorporeal membrane oxygenation is used to support cardiorespiratory failure secondary to arrhythmia in pediatric patients remain poorly defined. Our purpose is to describe pediatric patients requiring extracorporeal membrane oxygenation support for supraventricular arrhythmias in the context of normal cardiac anatomy and congenital heart disease and identify patient/peri-extracorporeal membrane oxygenation variables associated with extracorporeal membrane oxygenation-related complications and survival., Design: Retrospective multicenter review from 1993 to 2016., Setting: Extracorporeal Life Support Organization registry., Subjects: Patients younger than 21 years old requiring extracorporeal membrane oxygenation support for supraventricular arrhythmias., Interventions: None., Measurements and Main Results: A total of 342 patients were identified (weight, 3.8 kg [3.2-7.5 kg]; age at extracorporeal membrane oxygenation initiation, 24 d [6-222]; 61% male). Sixty-five percentage survived to hospital discharge. Complications were frequent (85%) and most commonly cardiac related (31%). In multivariable modeling, mortality was associated with congenital heart disease, time from intubation to extracorporeal membrane oxygenation initiation, use of bicarbonate prior to extracorporeal membrane oxygenation, extracorporeal membrane oxygenation duration, and the presence of a complication. The presence of any complication was associated with a three-fold increase in the odds of death. In subgroup analysis of isolated supraventricular arrhythmias patients, similar patient and extracorporeal membrane oxygenation characteristics were associated with outcome. A lower pre-extracorporeal membrane oxygenation pH and PCO2 and site of venous cannulation were associated with complications (p < 0.02)., Conclusions: Extracorporeal membrane oxygenation use for medically refractory supraventricular arrhythmias was associated with a 65% survival to hospital discharge. However, there was a high rate of complications, the presence of which was associated with decreased survival. Complications appeared to be related to pre-extracorporeal membrane oxygenation clinical status and whether earlier extracorporeal membrane oxygenation cannulation prior to patient deterioration would improve outcomes needs additional evaluation.

We aimed to compare salient characteristics and antecedents of quality of life (QOL) in adolescents and young adults with implantable cardioverter-defibrillators (ICDs) from qualitative methods with quantitative measurement of QOL and correlations between QOL (PedsQL) and measured participant characteristics. Concurrent parallel mixed methods design was used to collect survey data from the PedsQL electronic health record, demographic questionnaire, and semistructured interview data. A convenience sample of 16 individuals with ICDs, aged 13 to 25 years, was obtained from a tertiary pediatric facility. Overall QOL and subdomains of physical, psychosocial, and academic/work were examined by PedsQL and visual analog scale. Select demographics were collected to develop a participant profile. Females with ICDs appear to be at risk of poor QOL given some unknown factors. Financial status of the individual and the family was positively related to QOL. For new ICD persons involved in physical activities that must be stopped, peer support appears to improve QOL.

Background: Dilated cardiomyopathy (DCM) is the most common cardiomyopathy in children. Patients with severe cardiac dysfunction are thought to be at risk of sudden cardiac arrest (SCA). After diagnosis, a period of medical optimization is recommended before permanent implantable cardioverter-defibrillator (ICD) implantation. Wearable cardioverter-defibrillators (WCDs) provide an option for arrhythmia protection as an outpatient during this optimization., Objective: The purpose of this study was to determine the strategy that optimizes cost and survival during medical optimization of a patient with DCM before ICD placement., Methods: A Markov state transition model was constructed for the 3 clinical approaches to compare costs, clinical outcomes, and quality of life: (1) "Inpatient," (2) "Home-WCD," and (3) "Home-No WCD." Transitional probabilities, costs, and utility metrics were extracted from the existing literature. Cost-effectiveness was assessed comparing each paradigm's incremental cost-effectiveness ratio against a societal willingness-to-pay threshold of $50,000 per quality-adjusted life year., Results: The cost-utility analysis illustrated that Home-WCD met the willingness-to-pay threshold with an incremental cost-effectiveness ratio of $20,103 per quality-adjusted life year and 4 mortalities prevented per 100 patients as compared with Home-No WCD. One-way sensitivity analyses demonstrated that Home-No WCD became the most cost-effective solution when the probability of SCA fell below 0.2% per week, the probability of SCA survival with a WCD fell below 9.8%, or the probability of SCA survival with Home-No WCD quadrupled from base-case assumptions., Conclusion: Based on the existing literature probabilities of SCA in pediatric patients with DCM undergoing medical optimization before ICD implantation, sending a patient home with a WCD may be a cost-effective strategy., (Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: The presence of anterograde conduction through an accessory pathway (AP) has been linked to sudden cardiac death. Unfortunately, pre-excitation associated with classic pathways can be difficult to differentiate from benign APs such as nodofascicular fibers., Objective: Identifying characteristics on electrocardiogram (ECG) and exercise that differentiate classic and benign AP connections in suggested pre-excitation patterns., Methods: Retrospective review of patients presenting between 1995 and 2017 with ventricular pre-excitation on ECG, determined to have either typical left-lateral AP during electrophysiology study (EPS), or benign, or no AP determined by either transesophageal electrophysiology study (TEP), or EPS., Results: A total of 96 patients were included, 14.2 years (4-24), 45% female, 90% Caucasian. Of these, 60 (63%) had a classic APs identified on EPS and 58 (97%) underwent successful ablation. Conversely, 36 (37%) had benign pathways identified. ECG findings differed between the groups: PR-interval 102 versus 120 ms (P < .0001), QRS-duration 110 versus 102 ms (P < .0001), QRS-axis 74 versus 59 degrees (P = .0005), and QRS onset to peak R/S in limb leads 64 versus 42 ms (P < .0001), and precordial leads 66 versus 46 ms (P < .0001). Change in QRS duration during exercise differed between the groups: 25 versus 2 ms (P < .0001) and ECG characteristics identified the presence of an AP with 97% sensitivity and 94% negative predictive value., Conclusion: Classic and benign APs exhibit different ECG characteristics, though clinical overlap does not allow for absolute differentiation. These data may help with risk stratification decision making though does not obviate the need for additional invasive testing., (© 2019 Wiley Periodicals, Inc.)

Background: Pediatric restrictive cardiomyopathy (RCM) has high mortality in historical cohorts, and traditional management often involves early referral for heart transplantation (HTx). This study sought to determine outcomes of pediatric RCM at a center that has favored medical management over early listing for HTx., Methods: All patients (N = 43) with pure RCM phenotype (RCM, N = 26) and hypertrophic cardiomyopathy with restrictive physiology (RCM/HCM, N = 17) managed at our center over a 15-year period were investigated. Outcomes of those listed for HTx (N = 18) were compared to a benchmark of contemporaneous pediatric RCM patients in the UNOS database (N = 377). Proportional hazards models were used to determine predictors of adverse outcomes., Results: The mean age was 11 ± 9 years and 49% were male. 14 of 18 patients listed received HTx. Overall mortality (12%) was identical between the phenotypes; however, RCM patients were more likely to be listed (P = 0.001) and receive HTx (P = 0.02) compared to RCM/HCM. Prior to HTx, 60% had documented arrhythmia, 16% had cardiac arrest, and 7% required mechanical circulatory support. 4 of 17 patients with an ICD/PM received device therapies (four of five shocks appropriate for VT/VF, and two effective anti-tachycardia pacing interventions). Outcomes of those listed for HTx at our center were similar to the UNOS benchmark. In multivariate analysis, markers of congestive heart failure were associated with adverse outcomes., Conclusion: Heart failure and arrhythmia treatments can delay or possibly prevent the need for HTx in some cases of pediatric RCM. Survival post-HTx is not compromised using this approach.

Background: Traditional indices to evaluate biventricular (BiV) pacing are load dependent, fail to assess dynamic changes, and may not be appropriate in patients with congenital heart disease (CHD). We therefore measured the force-frequency relationship (FFR) using tissue Doppler-derived isovolumic acceleration (IVA) to assess the dynamic adaption of the myocardium and its variability with different ventricular pacing strategies., Methods: This was a prospective pilot study of pediatric and young adult CHD patients with biventricular or multisite pacing systems. Color-coded myocardial velocities were recorded at the base of the systemic ventricular free wall. IVA was calculated at resting heart rate and with incremental pacing. FFR curves were obtained by plotting IVA against heart rate for different ventricular pacing strategies., Results: Ten patients were included (mean: 22 ± 7 years). The FFR identified a best and worst ventricular pacing strategy for each patient, based on the AUC at baseline, submaximal, and peak heart rates (P < .001). However, there was no single best ventricular pacing strategy that was optimal for all patients. Additionally, the best ventricular pacing strategy often differed within the same patient at different heart rates., Conclusion: This novel assessment demonstrates a wide variability in optimal ventricular pacing strategy. These inherent differences may play a role in the unpredictable clinical response to BiV pacing in CHD, and emphasizes an individualized approach. Furthermore, the optimal ventricular pacing varies with heart rate within individuals, suggesting that rate-responsive ventricular pacing modulation may be required to optimize ventricular performance., (© 2018 Wiley Periodicals, Inc.)

Background: Axillary implant location is an alternative implant location in patients for cardiac implantable electronic devices (CIEDs) for the purposes of improved cosmetic outcome. The impact from the patient's perspective is unknown. The purpose of this study was to compare scar perception scores and quality of life (QOL) in pediatric patients with axillary CIED implant location versus the standard infraclavicular approach., Methods: This is a multicenter prospective study conducted at eight pediatric centers and it includes patients aged from 8 to 18 years with a CIED. Patients with prior sternotomy were excluded. Scar perception and QOL outcomes were compared between the infraclavicular and axillary implant locations., Results: A total of 141 patients (83 implantable cardioverter defibrillator [ICD]/58 pacemakers) were included, 55 with an axillary device and 86 with an infraclavicular device. Patients with an ICD in the axillary position had better perception of scar appearance and consciousness. Patients in the axillary group reported, on average, a total Pediatric QOL Inventory score that was 6 (1, 11) units higher than the infraclavicular group, after adjusting for sex and race (P = 0.02)., Conclusions: QOL is significantly improved in axillary in comparison to the infraclavicular CIED position, regardless of device type. Scar perception is improved in patients with ICD in the axillary position., (© 2018 Wiley Periodicals, Inc.)

Patients with the Marfan syndrome (MFS) are at risk for sudden death. The contribution of arrhythmias is unclear. This study examines the prevalence of arrhythmias in children with the MFS and their relation to clinical and/or echocardiographic factors. Data from the Pediatric Heart Network randomized trial of atenolol versus losartan in MFS were analyzed (6 months to 25 years old, aortic root diameter z-score > 3.0, no previous aortic surgery and/or dissection). Baseline 24-hour ambulatory electrocardiographic monitoring was performed. Significant ventricular ectopy (VE) and supraventricular ectopy (SVE) were defined as ≥10 VE or SVE/hour, or the presence of high-grade ectopy. Three-year composite clinical outcome of death, aortic dissection, or aortic root replacement was analyzed. There were 274 analyzable monitors on unique patients from 11 centers. Twenty subjects (7%) had significant VE, 13 (5%) significant SVE; of these, 2 (1%) had both. None had sustained ventricular or supraventricular tachycardia. VE was independently associated with increasing number of major Ghent criteria (odds ratio [OR] = 2.13/each additional criterion, p = 0.03) and greater left ventricular end-diastolic dimension z-score (OR = 1.47/each 1 unit increase in z-score, p = 0.01). SVE was independently associated with greater aortic sinotubular junction diameter z-score (OR = 1.56/each 1 unit increase in z-score, p = 0.03). The composite clinical outcome (14 events) was not related to VE or SVE (p ≥ 0.3), but was independently related to heart rate variability (higher triangular index). In conclusion, in this cohort, VE and SVE were rare. VE was related to larger BSA-adjusted left ventricular size. Routine ambulatory electrocardiographic monitoring may be useful for risk stratification in select MFS patients., (Copyright © 2018. Published by Elsevier Inc.)

Background Implantable cardioverter defibrillators (ICDs) are an important part of therapy for many patients, yet there is little data on population characteristics, complications, or system survival in pediatric patients. Methods A retrospective review of ICD recipients in the National Cardiovascular Data Registry ICD Registry was performed from 2010 to 2016. Patient characteristics and complications between pediatric (≤21 years) and adult populations (>21 years) were compared. Variables associated with complications and early device interventions within the pediatric cohort were evaluated using multivariate modeling. Results There were 562 209 total ICD implants, of which 3461 occurred in the pediatric cohort. Among the pediatric patients, 60% of implants were for primary prevention, and nonischemic cardiomyopathy was the most common underlying disease (60%). Over time, there was an increasing trend of both primary and secondary prevention ICD implantations ( P<0.05). Compared with adults, pediatric patients were more likely to have structural heart disease, hypertrophic cardiomyopathy, and channelopathy, and to receive a single-chamber device (all P<0.001). There was no difference in inhospital complications between the adult and pediatric cohorts (2.4% versus 2.6%, P=0.3). However, among the pediatric patients, lower weight, Ebstein anomaly, worse New York Heart Association class, dual chamber, and cardiac resynchronization therapy-defibrillator were associated with greater risk of complications. Although reintervention for generator replacement or upgrade was more common in adults, the time to reintervention was shorter in the pediatric cohort. Conclusions We observed an increasing trend in ICD device implantation among pediatric patients. The pediatric cohort had similar inhospital complication rates compared with adults but had a shorter time to reintervention.

Multifocal atrial tachycardia (MAT) has a well-known association with Costello syndrome, but is rarely described with related RAS/MAPK pathway disorders (RASopathies). We report 11 patients with RASopathies (Costello, Noonan, and Noonan syndrome with multiple lentigines [formerly LEOPARD syndrome]) and nonreentrant atrial tachycardias (MAT and ectopic atrial tachycardia) demonstrating overlap in cardiac arrhythmia phenotype. Similar overlap is seen in RASopathies with respect to skeletal, musculoskeletal and cutaneous abnormalities, dysmorphic facial features, and neurodevelopmental deficits. Nonreentrant atrial tachycardias may cause cardiac compromise if sinus rhythm is not restored expeditiously. Typical first-line supraventricular tachycardia anti-arrhythmics (propranolol and digoxin) were generally not effective in restoring or maintaining sinus rhythm in this cohort, while flecainide or amiodarone alone or in concert with propranolol were effective anti-arrhythmic agents for acute and chronic use. Atrial tachycardia resolved in all patients. However, a 4-month-old boy from the cohort was found asystolic (with concurrent cellulitis) and a second patient underwent cardiac transplant for heart failure complicated by recalcitrant atrial arrhythmia. While propranolol alone frequently failed to convert or maintain sinus rhythm, fleccainide or amiodarone, occasionally in combination with propranolol, was effective for RASopathy patient treatment for nonreentrant atrial arrhythmia. Our analysis shows that RASopathy patients may have nonreentrant atrial tachycardia with and without associated cardiac hypertrophy. While nonreentrant arrhythmia has been traditionally associated with Costello syndrome, this work provides an expanded view of RASopathy cardiac arrhythmia phenotype as we demonstrate mutant proteins throughout this signaling pathway can also give rise to ectopic and/or MAT., (© 2018 Wiley Periodicals, Inc.)

Background: Interpretation of pediatric ECGs is limited by lack of accurate sex- and race-specific normal reference values obtained with modern technology for all ages. We sought to obtain contemporary digital ECG measurements in healthy children from North America, to evaluate the effects of sex and race, and to compare our results to commonly used published datasets., Methods: Digital ECGs (12-lead) were retrospectively collected for children ≤18 years old with normal echocardiograms at 19 centers in the Pediatric Heart Network. Patients were classified into 36 groups: 6 age, 2 sex, and 3 race (white, black, and other/mixed) categories. Standard intervals and amplitudes were measured; mean±SD and 2nd/98th percentiles were determined by age group, sex, and race. For each parameter, multivariable analysis, stratified by age, was conducted using sex and race as predictors. Parameters were compared with 2 large pediatric ECG data sets., Results: Among ECGs from 2400 children, significant differences were found by sex and race categories. The corrected QT interval in lead II was greater for girls compared with boys for age groups ≥3 years ( P ≤0.03) and for whites compared with blacks for age groups ≥12 years ( P <0.05). The R wave amplitude in V6 was greater for boys compared with girls for age groups ≥12 years ( P <0.001), for blacks compared with white or other race categories for age groups ≥3 years ( P ≤0.006), and greater compared with a commonly used public data set for age groups ≥12 years ( P <0.0001)., Conclusions: In this large, diverse cohort of healthy children, most ECG intervals and amplitudes varied by sex and race. These differences have important implications for interpreting pediatric ECGs in the modern era when used for diagnosis or screening, including thresholds for left ventricular hypertrophy., (© 2018 American Heart Association, Inc.)

Background: Certain pediatric patients are at risk for sudden cardiac death. The wearable cardioverter-defibrillator (WCD) can be used in clinical situations in which implantable cardioverter-defibrillator placement is not ideal. The objectives of the study are to examine the effectiveness, safety, and compliance of the WCD in the identification and treatment of life-threatening ventricular arrhythmias in pediatric patients., Methods: All United States pediatric patients <18 years who wore a WCD, from 2009 to 2016 were retrospectively reviewed., Results: In total, 455 patients were identified. The median age was 15 (3-17) years, median duration of WCD use was 33 (1-999) days and median patient wear time was 20.6 (0.3-23.8) hours per day. The population was divided into 2 groups: (1) patients with implantable cardioverter-defibrillator problem, n=63 and (2) patients with nonimplantable cardioverter-defibrillator problem, n=392. Wear time per day was >20 hours in both groups. Wear duration was shorter in the implantable cardioverter-defibrillator problem group, 26 days versus 35 days, P <0.05. There were 7 deaths (1.5%); all not wearing WCD at time of death. Eight patients (1.8%) received at least 1 WCD shock treatment. Of the 6 patients (1.3%) who had appropriate therapy, there were 7 episodes of either polymorphic ventricular tachycardia or ventricular fibrillation with a total of 13 treatments delivered. All episodes were successfully converted and the patients survived., Conclusions: The WCD has overall adequate compliance with appropriate wear times and wear durations in pediatric patients. The WCD is safe and effective in treating ventricular arrhythmias that can lead to sudden cardiac death in pediatric patients., (© 2018 American Heart Association, Inc.)

Background: The Pediatric Heart Network designed a career development award to train the next generation of clinician scientists in paediatric-cardiology-related research, a historically underfunded area. We sought to identify the strengths/weaknesses of the programme and describe the scholars' academic achievements and the network's return on investment., Methods: Survey questions designed to evaluate the programme were sent to applicants - 13 funded and 19 unfunded applicants - and 20 mentors and/or principal investigators. Response distributions were calculated. χ2 tests of association assessed differences in ratings of the application/selection processes among funded scholars, unfunded applicants, and mentors/principal investigators. Scholars reported post-funding academic achievements., Results: Survey response rates were 88% for applicants and 100% for mentor/principal investigators. Clarity and fairness of the review were rated as "clear/fair" or "very clear/very fair" by 98% of respondents, but the responses varied among funded scholars, unfunded applicants, and mentors/principal investigators (clarity χ2=10.85, p=0.03; fairness χ2=16.97, p=0.002). Nearly half of the unfunded applicants rated feedback as "not useful" (47%). "Expanding their collaborative network" and "increasing publication potential" were the highest-rated benefits for scholars. Mentors/principal investigators found the programme "very" valuable for the scholars (100%) and the network (75%). The 13 scholars were first/senior authors for 97 abstracts and 109 manuscripts, served on 22 Pediatric Heart Network committees, and were awarded $9,673,660 in subsequent extramural funding for a return of ~$10 for every scholar dollar spent., Conclusions: Overall, patient satisfaction with the Scholar Award was high and scholars met many academic markers of success. Despite this, programme challenges were identified and improvement strategies were developed.

Objectives: Evaluate the efficacy, outcomes, and complications associated with direct current cardioversion (DCCV) in the treatment of arrhythmias in pediatric and adult congenital heart disease (CHD) populations and identify patient and procedural characteristics associated with adverse events., Background: Pediatric and adult patients with CHD are at risk of atrial arrhythmias. DCCV is effective but is associated with potential complications., Methods: In this single-center retrospective series, patients who underwent DCCV between January 2010 and May 2015 were identified and categorized as pediatric (<18 years) or adult (> 18 years). Records were reviewed for demographic, arrhythmic, and CHD-specific characteristics; acute efficacy; and 3-month arrhythmia recurrence. Complications were categorized as life-threatening (LT) or non-life-threatening (NLT). Univariate followed by multiple variable and logistic regression (LR) analyses were used to identify characteristics associated with complications., Results: We identified 104 patients with 152 discrete DCCV events with median age 17.4 years (0.15-62.2). DCCV efficacy was 89% with 3-month recurrence of 46%. There were 52 complications among 24 patients, median age 17.7 years (0.15-49). Risks associated with NLT complications are as follows: moderate-severe systolic dysfunction (8/152 encounters, P = < 0.01) and more than one shock per DCCV encounter (P = < 0.01). Six of eight encounters with moderate-severe systolic dysfunction were <18 years (P = 0.1). Risks for LT complications included age >18 years and associated NLT complication. Adults had more frequent arrhythmia recurrence within 3 months than children (P = < 0.01)., Conclusions: DCCV is effective for arrhythmias but is associated with frequent recurrence, particularly in adult patients. Complications associated with DCCV may be greater than previously reported. Additional support and precautions should be in place for those at greatest risk., (© 2018 Wiley Periodicals, Inc.)