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Altered ventricular depolarization due to manifest accessory pathway conduction (ie, Wolff-Parkinson-White syndrome) leads to repolarization abnormalities that persist after pathway ablation. The term T-wave memory (TWM) has been applied to these changes, as the postablation T-wave vector "remembers" the pre-excited QRS vector. In adults, these abnormalities can be misinterpreted as ischemia leading to unnecessary interventions. To date, no comprehensive studies have evaluated this phenomenon in the pediatric population.The purpose of this study was to define TWM in the pediatric population, identify preablation risk factors, and delineate the timeline of recovery.Pre- and postablation electrocardiograms (ECGs) in patients ≤25 years were analyzed over a 5-year period. Frontal plane QTc interval, T-wave axis, QRST angle, and T-wave inversions were used to identify patients with TWM. Univariate analysis was performed to determine the association of preablation ECG features with the outcome of TWM.TWM was present in 42% of pediatric patients, with resolution occurring within 3 months of ablation. Preablation QRS axis0° was a strong predictor of TWM (odds ratio [OR] 15.2; 95% confidence interval [CI] 5.7-40), followed by posteroseptal pathway location (right posteroseptal-OR 8.9; 95% CI 4.2-18.8; left posteroseptal-OR 6.1; 95% CI 1.7-22.3). The degree of pre-excitation had a modest association with the development of TWM. No adverse events were observed.TWM is less common in children compared to adults, and normalization occurred within 3 months postablation. The most predictive features for the development of TWM include a leftward pre-excited QRS axis and posteroseptal pathway location.

Decreased physical activity is associated with cardiovascular, metabolic and mental health disease. While decreases in physical activity during the COVID-19 pandemic have been described in the general population, there is a paucity of data regarding children with underlying cardiovascular disease. We hypothesized there would be a decrease in physical activity at the onset of the COVID-19 pandemic. Performed a single-center, retrospective cohort study of children aged 80% of dates from February 3, 2020 through June 30, 2020. Patients with significant neurologic/neuromuscular disease were excluded. We identified 144 patients with a median age of 15.4 years. 47% were female. 34% had congenital heart disease, 20% had cardiomyopathy, 19% had an inherited arrhythmia syndrome and 5% had atrioventricular block without congenital heart disease. 47% of patients had an implantable loop recorder, 29% had a permanent pacemaker and 24% had an implantable cardioverter-defibrillator. We observed a significant decrease in device-measured physical activity from baseline (February 3–March 9), with up to a 21% decrease in physical activity during mid-March through early May. Activity levels returned to pre-pandemic levels in June. Physical activity sharply declined in children with cardiac rhythm management devices at the onset of the COVID-19 pandemic. These data highlight the importance of finding strategies to maintain physical activity during the current pandemic and future public health crises.

Catheter ablation of accessory pathways (APs) in Ebstein anomaly (EA) has been associated with a high recurrence risk.The purpose of this study was to compare outcomes of AP ablation in EA in an early (1990-2004) vs a recent (2005-2019) era and identify variables associated with recurrence.A retrospective review of all catheter ablations for supraventricular tachycardia in EA at our institution was performed.We identified 76 patients with median (25th-75th quartiles) age 9 (2.6-13.3) years. Of these patients, 52 had AP alone, 12 had atrial flutter, 3 had atrioventricular nodal reentrant tachycardia, and 9 had AP plus at least 1 additional arrhythmia. Of the 61 patients with APs, a total of 78 separate APs were identified: 40 right-sided, 37 septal, and 1 left-sided. Acute success for AP first procedure was 89% and did not differ between early and recent eras (89% vs 88%; P = .48). However, 19 patients (31%) required repeat procedures (average 1.4 per patient) due to AP recurrence or ablation failure at first attempt. In comparison to early era, recent era ablations had significantly lower recurrence rates at 1 year (62% vs 19%; P = .005). At median follow-up of 2.5 (0.2-7) years, ultimate AP elimination after all procedures was 93%. Younger age at time of electrophysiological study (2 vs 12-47 years: hazard ratio [HR] 7.3; P = .003) and ablation era (early era vs recent era: HR 3.65; P = .009) predicted recurrence.Outcomes for AP ablation in patients with EA have improved, but there is still a relatedly high recurrence risk requiring repeat procedures.

Introduction:Reflex-mediated syncope occurs in 15% of children and young adults. In rare instances, pacemakers are required to treat syncopal episodes associated with transient sinus pauses or atrioventricular block. This study describes a single centre experience in the use of permanent pacemakers to treat syncope in children and young adults.Materials and methods:Patients with significant pre-syncope or syncope and pacemaker implantation from 1978 to 2018 were reviewed. Data collected included the age of presentation, method of diagnosis, underlying rhythm disturbance, age at implant, type of pacemaker implanted, procedural complications and subsequent symptoms.Results:Fifty patients were identified. Median age at time of the first syncopal episode was 10.2 (range 0.3–20.4) years, with a median implant age of 14.9 (0.9–34.3) years. Significant sinus bradycardia/pauses were the predominant reason for pacemaker implant (54%), followed by high-grade atrioventricular block (30%). Four (8%) patients had both sinus pauses and atrioventricular block documented. The majority of patients had dual-chamber pacemakers implanted (58%), followed by ventricular pacemakers (38%). Median follow-up was 6.7 (0.4–33.0) years. Post-implant, 4 (8%) patients continued to have syncope, 7 (14%) had complete resolution of their symptoms, and the remaining reported a decrease in their pre-syncopal episodes and no further syncope. Twelve (24%) patients had complications, including two infections and eight lead malfunctions.Conclusions:Paediatric patients with reflex-mediated syncope can be treated with pacing. Complication rates are high (24%); as such, permanent pacemakers should be reserved only for those in whom asystole from sinus pauses or atrioventricular block has been well documented.

Background Adult survivors of Hodgkin lymphoma (HL) are at increased risk of cardiovascular (CV) events secondary to mediastinal radiation therapy (RT). Objectives In this group of patients, we assessed the association between cardiopulmonary exercise testing (CPET), as determined by percent-predicted peak Vo2 (ppVo2peak), and clinical outcomes, as well as the rate of ppVo2peak decline and sex differences. Methods All survivors of HL who were >10 years post chest RT and who underwent ≥1 CPET were enrolled from a single center. Traditional CV and treatment risk factors, along with CV events, were ascertained. Results A total of 64 patients (67% female; median age 51 years [range 26 to 70 years]) with a median follow-up time after RT of 23 years (range 11 to 41 years), and 141 CPET studies, were included. Median initial ppVo2peak was 91% (range 58% to 138%). ppVo2peak in survivors declined by 7.5 percentage points every 10-year period after RT, as compared with age- and sex-based norms (P = 0.001), even after adjusting for hypertension and history of anthracycline. Both male and female patients had a similar rate of ppVo2peak decline. However, women had a lower ppVo2peak at all times, and they developed abnormal ppVo2peak (≤85%) on average earlier than men (24.1 years vs 47.0 years after RT). Patients with abnormal ppVo2peak vs normal ppVo2peak (>85%), had an increased risk of CV events (59% vs 16%). Abnormal ppVo2peak was independently associated with the risk of CV events (adjusted HR: 6.37; 95% CI: 2.06-19.80; P = 0.001). Conclusions Percent-predicted Vo2peak in long-term survivors of HL who were treated with chest RT progressively declined as compared with population- and sex-based norms. Importantly, women developed abnormal ppVo2peak more than 2 decades earlier than male survivors. Abnormal ppVo2peak was associated with an increased risk of CV events in this group of patients., Central Illustration

Prior studies have characterized children with supraventricular tachycardia (SVT) in inpatient settings, however there is a paucity of data regarding pediatric SVT in the Emergency Department (ED) setting. We sought to describe pediatric ED visits for SVT and assess whether variability exists in care. We performed a cross-sectional study of ED visits for SVT among children

OBJECTIVE To determine the impact of provocative electrophysiology testing in postoperative congenital heart disease (CHD) patients on the management of supraventricular tachycardia (SVT) and clinical outcomes. METHODS This is a retrospective study including patients

Children and adolescents with congenital heart disease often do not have the opportunity, inclination, or education to participate in safe and effective exercise. The consequences of this behavioral pattern affect not only cardiopulmonary parameters, but also psychosocial factors, especially when lack of participation in peer activities or sports leads to isolation and further sedentary behaviors. Importantly, unlike cardiac rehabilitation programs for adults with atherosclerotic disease, the goal for congenital heart disease patients was less about "rehabilitation" and more about promotion of optimal fitness. We thus developed a comprehensive "Cardiac Fitness Program" at Boston Children's Hospital to promote exercise training, enhanced self-confidence, and motivation for patients with congenital heart disease. Since much of sustained fitness relates to consistency and behavior change, we crafted a progressive, goal-oriented exercise curriculum and augmented it with a self-learning workbook of targeted positive mindset practices to develop self-efficacy, an app for motivation and data collection, and exercise videos to demonstrate mechanics and to reiterate a positive message. We now report our experience including program structure and framework, navigating insurance, curriculum development, and outcome measures. Methods employed and barriers encountered in the initial development and execution of this program are reviewed. Key take-aways and further considerations including virtual and home-based programs are discussed.

Objectives: To describe a single institutional experience managing fetuses with supraventricular tachycardia (SVT) and to identify associations between patient characteristics and fetal and postnatal outcomes. Background: Sustained fetal SVT is associated with significant morbidity and mortality if untreated, yet the optimal management strategy remains unclear. Methods: Retrospective cohort study including fetuses diagnosed with sustained SVT (>50% of the diagnostic echocardiogram) between 1985 and 2018. Fetuses with congenital heart disease were excluded. Results: Sustained SVT was diagnosed in 65 fetuses at a median gestational age of 30 weeks (range, 14-37). Atrioventricular re-entrant tachycardia and atrial flutter were the most common diagnoses, seen in 41 and 16 cases, respectively. Moderate/severe ventricular dysfunction was present in 20 fetuses, and hydrops fetalis was present in 13. Of the 57 fetuses initiated on transplacental drug therapy, 47 received digoxin first-line, yet 39 of 57 (68%) required advanced therapy with sotalol, flecainide, or amiodarone. Rate or rhythm control was achieved in 47 of 57 treated fetuses. There were no cases of intrauterine fetal demise. Later gestational age at fetal diagnosis (odds ratio [OR], 1.1, 95% confidence interval [CI], 1.01-1.2, P = .02) and moderate/severe fetal ventricular dysfunction (OR, 6.1, 95% CI, 1.7-21.6, P = .005) were associated with postnatal SVT. Two postnatal deaths occurred. Conclusions: Fetuses with structurally normal hearts and sustained SVT can be effectively managed with transplacental drug therapy with minimal risk of intrauterine fetal demise. Treatment requires multiple antiarrhythmic agents in over half of cases. Later gestational age at fetal diagnosis and the presence of depressed fetal ventricular function, but not hydrops, predict postnatal arrhythmia burden.

Objectives This study sought to evaluate for the presence of and characterize the interdigitating and entrapped myocardium within cardiac fibromas (CF) and correlate tissue findings with symptoms and surgical outcomes. Background The mechanism of ventricular tachycardia (VT) in CF is unclear. The authors hypothesized that CF harbor tongues of interdigitating myocardium, which could be a substrate for episodes of arrhythmia analogous to peri-infarct zones. Methods A total of 29 patients (14 boys) with CF were identified; all subjects had undergone at least partial tumor resection. A semiquantitative grading system was used to assess the degree of myocardial interdigitation and entrapment, myocyte morphology (hematoxylin and eosin stain and immunohistochemical stain for desmin), tumor collagen density, and cellularity (trichrome stain). The subjects’ ages at presentation, types of arrhythmia, and responses to surgery were correlated with histology. Results CF consistently demonstrated interdigitating and entrapped myocardium, and the extent correlated negatively with age at surgery, as did cellularity, whereas collagen increased with age. Median age at arrhythmia recognition was 8 months. Sustained VT was present in 18 of 29 patients (62%), and 5 of 6 patients with prenatally diagnosed conditions developed VT before 8 months. All 8 patients who experienced cardiac arrest had clinically significant arrhythmia events. Sustained arrhythmia episodes correlated with more diffuse myocyte interdigitation. Ten patients had abnormal karyotype: chromosomes 9 (n = 3) and 3 (n = 1) deletions; isolated translocations: t(4;13), t(5;11) and t(1;9); and undefined aberrations (n = 3). All patients who underwent complete resection were cured of arrhythmias, whereas 2 of 14 patients who had subtotal resections had recurrence, with resolution following re-resection in 1 patient. Conclusions Interdigitating myocardium represents a potential histopathologic substrate for VT and cardiac arrest in CF, which may also explain the occasional recurrence of arrhythmia following incomplete resection.

This study sought to determine the practical use of the recently introduced LINQ implantable loop recorder (LINQ-ILR) in a cohort of pediatric and adult congenital arrhythmia patients.Correlating symptoms to a causative arrhythmia is a key aspect of diagnosis and management in clinical electrophysiology.Retrospective review of clinical data, implantation indications, findings, and therapeutic decisions in patients who underwent LINQ-ILR implantation from April 1st, 2014 to January 30th, 2017 at Boston Children's Hospital.A total of 133 patients were included, of which 76 (57%) were male. The mean age at implantation was 15.7 ± 9.1 years with a duration of follow-up of 11.8 months. Congenital heart disease was present in 34 patients (26%), a confirmed genetic diagnosis in 50 (38%), and cardiomyopathy in 22 (26%), and the remainder were without a previous diagnosis. Syncope was the most common indication for LINQ-ILR implantation, occurring in 59 patients (44%). The median time to diagnosis was 4.5 months, occurring in 78 patients (59%). Cardiac device placement occurred in 17 patients (22%), a medication change in 9 (12%), electrophysiology study/ablation in 5 (6%), or LINQ-ILR explantation in 42 (54%). Infection or erosion occurred in 5 patients. Syncope was correlated with a diagnostic transmission (54% vs. 31%, p = 0.01).The LINQ-ILR is an important diagnostic tool, providing useful data in more than one-half of patients in 6 months. Adverse events are low. Patient selection is critical and undiagnosed syncope represents an important presenting indication for which a LINQ-ILR implant should be considered.

Introduction Current pediatric PACU practice administering low dose IV haloperidol for post-operative nausea and vomiting (PONV) unresponsive to other interventions for specific pediatric populations varies by anesthesia team. Identification of the problem Anecdotally, low dose haloperidol had been used safely in pediatric PACUs. Formulary recommendations for intensive monitoring were based on higher dose haloperidol used for the treatment of psychosis and the potential for QTc prolongation. QI question/Purpose of the study To clarify the magnitude of both QT prolongation and therapeutic benefit for PONV in pediatric PACU patients given low dose haloperidol. Those data would inform potential changes to the hospital formulary to differentiate guidelines for low dose IV haloperidol in the PACU from higher dose haloperidol used for psychiatric intervention. Methods An interdisciplinary QI project was developed to provide evidence to support proposed changes in the formulary. Data were collected over a six month period including pre- and post-haloperidol administration QTc and BARF scores. Descriptive statistics were used to analyze this data. Outcomes/Results During the project period, pre therapy QTc was 430±43msec (range 480-355) with heart rates of 82±16. Two patients had dosing deferred because of clinical QTc ≥ 480 (N=29). Post treatment QTc readings had an average increase of 2±22 msec, with 1 ECG exceeding the QTc cutoff of Discussion It is critical for nurses to question and evaluate practice using evidence based guidelines and quality improvement methodology. Conclusion Low dose IV haloperidol is effective at limiting PONV and has a low incidence of QT prolongation. The high monitoring environment of a pediatric PACU suggests that it can be used safely in that setting for select populations. Implications for perianesthesia nurses and future research This work resulted in developing evidence based changes to the formulary that are consistent with clinical practice. Further research is needed to determine if low-dose haloperidol can be administered safely for a younger population.

Background: Prior ECG standards in children have largely been defined without echo confirmation of normal anatomy. The Pediatric Heart Network Normal Echocardiogram Z-score Project provides a racially diverse age/sex classified group of healthy children with normal echos that included 2170 matched contemporaneous digitally acquired ECGs. We hypothesized that ECG measures and z-scores of left ventricular (LV) dimensions are correlated in healthy children. Methods: This was a secondary analysis of the previously described cohort. Six ECG measures historically associated with LV size (R V5, R V6, S V1, Q III, axis, R V6+S V1), and 13 paired echo measures were identified a-priori with LV Mass (LVMass-z) and left ventricular end diastolic volume (LVEDV-z) z-scores serving as primary echo measurement predictors. Pearson or Spearman correlations were calculated for each of the 78 ECG- echo pairs. Regression analyses were performed to assess how much variance in ECG measures was explained by variation in LV dimensions and by demographic variables (age, sex, race). Results: ECG and echo measurement correlations were significant and concordant in 41/78 (53%), though many were significant and discordant in 13, (17%) or not correlated in 24 (31%). Of the 6 ECG measures of LV size, 5 correlated in the clinically predicted direction for LV Mass-z and LVEDV-z. While many of the correlations were statistically significant, the correlations were weak (0.05-0.25). R 2 was higher for demographic variables than for echo measures in all pairs, but even with demographic variables included, the overall R 2 was < 0.17. Conclusions: In a large, diverse cohort of healthy children, there was a positive association between echo measures of LV dimension and mass and the most commonly used ECG measures of LVH. However, these correlations were weak and most of the variability in ECG measures was explained by factors other than echo derived mass or volume or measured patient demographic variables. These data question the utility of traditional ECG measurements of LV size as standalone indications for further cardiac evaluation in healthy children.

Introduction: Hypertrophic cardiomyopathy (HCM) accounts for nearly half of pediatric cardiomyopathies. While impaired exercise function has been described in adults with HCM, little is known about exercise function in children with HCM. Hypothesis: Children with HCM have impaired exercise function. Methods: A retrospective cohort study was performed. Pts Results: We identified 124 pts with 240 CPETs. The average age at time of CPET was 14.8 ± 3.0 years. Average %predicted peak VO2 (78 ± 20%) was significantly less than the population average (p 100% in 13% of tests. The %predicted peak O2 pulse (88 ± 21%; p Conclusions: Exercise function is at least moderately impaired in a substantial portion of children with HCM and this impairment tends to worsen over time. However, there is a significant subset of patient with remarkably well-preserved exercise function. Echocardiographic measurements did not correlate with exercise function in our cohort.

Background: Atrioventricular reentrant tachycardia is common in children. Catheter ablation is increasingly used as a first-line therapy with a high acute success rate, but recurrence during follow-up remains a concern. The aim of this study was to identify risk factors for recurrence after accessory pathway (AP) ablation. Methods: Retrospective cohort study including patients who underwent AP ablation between 2013 and 2018. Cox proportional hazards model was used to examine the association between patient and procedural characteristics and recurrence during follow-up. Results: From 558 AP ablation procedure, 542 (97%) were acutely successful. During a median follow-up of 0.4 (interquartile range, 0.1–1.4) years, there were 42 (8%) patients with documented recurrence. On univariate analysis, early recurrence was associated with younger age, congenital heart disease, multiple AP, AP location (right sided and posteroseptal versus left sided), cryoablation (versus radiofrequency), empirical ablation, the lack of full power radiofrequency lesions ( Conclusions: In our institutional experience, radiofrequency consolidation time

Supplemental Digital Content is available in the text., Introduction: Variability exists in the management of childhood syncope as clinicians balance resource utilization with the need to identify serious diseases. Limited evidence exists regarding the long-term impact of evidence-based guidelines (EBGs) on clinical practices. This study’s objective was to measure long-term changes in the management of syncope after implementing a syncope EBG in a single pediatric emergency department following the redistribution of resources to facilitate compliance over time. Methods: We included healthy patients aged 8–22 years, presenting to the pediatric emergency department with syncope between 2009 and 2017. Interrupted time series analysis compared testing rates and length of stay among the pre-EBG, short-term follow-up, and long-term follow-up periods. Results: The study included 1,294 subjects. From the pre-EBG period to the long-term follow-up period, recommended electrocardiogram and urine pregnancy test rose significantly [level change odds ratio (95% confidence interval) 5.56 (1.73–17.91) and 3.15 (1.07–9.32), respectively]. Testing and management not recommended by the EBG decreased significantly, including complete blood count, electrolytes, point-of-care glucose, chest radiograph, and intravenous fluids [level change odds ratio (95% confidence interval) 0.19 (0.09–0.40), 0.15 (0.07–0.32), 0.38 (0.18–0.81), 0.17 (0.06–0.49), and 0.18 (0.08–0.39), respectively]. Length of stay declined significantly. No delayed diagnoses occurred. Conclusions: Sustained improvements in syncope management persisted during long-term follow-up of the EBG despite minimal resources. The EBG was associated with increased focused evaluation and decreased low yield testing. EBGs may be useful tools to influence sustained clinical practices to promote safe, cost-effective, and high-quality care.

Objectives This study sought to determine the long-term effect of dual-site ventricular pacing (i.e., cardiac resynchronization therapy [CRT]) versus single-site pacing in patients with Fontan physiology and high-grade atrioventricular block (AVB). Background Chronic single-site ventricular pacing in Fontan patients is associated with significant morbidity and mortality. Methods The study conducted a retrospective review of all Fontan patients with high-grade AVB who received pacemakers at a single institution between 1990 and 2016 with follow-up of 12 months or greater. The primary study outcome was a composite of death or heart transplantation. Results Nineteen patients received CRT devices and 43 patients received single-site ventricular pacemakers (SVPMs), with a median follow-up of 4.9 years (range 1.1 to 11.3 years) and 10.4 years (range 1.1 to 26.8 years), respectively. One (5.3%) CRT patient and 11 (25.6%) SVPM patients reached the composite endpoint of death or transplant (odds ratio: 0.16; 95% confidence interval: 0.02 to 1.36; p = 0.09). Kaplan-Meier analysis showed similar rates of freedom from death or transplant between the 2 study groups over a 5-year follow-up period (p = 0.08). The proportion of SVPM patients with abnormal ventricular systolic function before device implantation (9.5%) and at follow-up (33.3%) significantly increased (p=0.009). The CRT cohort had less change in their ventricular function (42.1% before device implant, 36.8% at follow-up; p = 1.00); however, a Kaplan-Meier analysis over a 5-year follow-up period found no difference in the presence of abnormal ventricular systolic function between groups (p = 0.27). Conclusions There was no significant difference in long-term outcomes between Fontan patients who were single- or dual-site paced for high-grade AVB.

Background Left ventricular false tendons (FT) traverse the ventricular cavity and are thought to have some association with idiopathic left ventricular tachycardia (ILVT). However, reported prevalence of FT varies widely, making correlation difficult. Superior echocardiographic windows of pediatric patients may permit better analysis of FT in ILVT. Our study describes the relationship between FT and ILVT in young patients. Methods Retrospective case-control study of 30 ILVT patients with 98 controls compared for FT. Diagnosis of ILVT was made by electrocardiogram and clinical history, and for 25 patients was further confirmed by electrophysiology study (EPS). Presence of FT was identified by one blinded observer and verified by a second blinded observer. Presence of FT was then compared between ILVT patients and controls using Fisher's exact test. Results Presence of FT did not differ significantly between patients and controls (53% vs 43%, P = 0.40). Twelve FT patients (19%) had multiple FTs detected, though the incidence of ILVT was no higher in the setting of multiple FTs. A total of 25 patients with ILVT underwent EPS for intended ablation therapy, with ultimate success in 22/25 (88%) after one or more ablation sessions. Of the 25 EPS patients, FTs were present in 11, but precise correlation between successful ablation location and FT location was not possible since intraprocedural echocardiography was not performed in this patient group. Conclusions Presence of FTs did not differ between ILVT patients and controls. While FTs are not absolutely required for ILVT, they may still play a role in some cases.

Objective This study evaluates the ability of experienced pediatric electrophysiologists (EPs) to reliably classify incomplete right bundle branch block (IRBBB) and assesses its clinical utility as an isolated ECG finding in a group of healthy outpatient children without prior cardiac evaluation. Design We performed a retrospective analysis of all electrocardiographic and echocardiographic records at Boston Children's Hospital between January 1, 2005, and December 31, 2014. Echocardiographic diagnoses were identified if registered between the date of the index electrocardiogram and the ensuing year. A selected subset of 473 ECGs was subsequently reanalyzed in a blinded manner by six pediatric EPs to determine the consistency with which the finding of IRBBB could be assigned. Results Of the 331 278 ECGs registered in the BCH database, 32 127 (9.7%) met inclusion criteria and were analyzed for the prevalence of isolated right bundle conduction disturbance findings. The mean age was 12.1 ± 4.0 years, and the population was 49% male. Of the 32 127 ECGs, 72.5% were coded normal, 3.0% were coded IRBBB, and 0.5% were coded complete right bundle branch block (CRBBB). A total of 7.3% of patients coded as normal had an ensuing echocardiogram, compared to 12.5% coded IRBBB. Echo findings were recorded in 0.1% of normal and 0.2% of IRBBB. Patients with ASD-secundum type were no more likely to have isolated IRBBB on previous ECG than the general population (2.5% vs 3.0%). Analysis of inter-reader variability in ECG findings and conduction disturbance identification was high (range of IRBBB prevalence 1-20% among readers). Reinterpretation of ECGs using explicit diagnostic criteria did not demonstrate consistent discrimination of IRBBB and Normal ECGs. Conclusions IRBBB is not uncommon in a healthy school age population and is observed to have high inter-reader variability. It was associated with increased use of echocardiographic exam but was not associated with increased rate of echocardiographic findings when compared with rates for normal ECGs.

Objective To examine the association between electrocardiographic (ECG) evidence of carditis at the time of Lyme disease evaluation and a diagnosis of Lyme disease. Study design We performed an 8-center prospective cohort study of children undergoing emergency department evaluation for Lyme disease limited to those who had an ECG obtained by their treating clinicians. The study cardiologist reviewed all ECGs flagged as abnormal by the study sites to assess for ECG evidence of carditis. We defined Lyme disease as the presence of an erythema migrans lesion or a positive 2-tier Lyme disease serology. We used logistic regression to measure the association between Lyme disease and atrioventricular (AV) block or any ECG evidence of carditis. Results Of the 546 children who had an ECG obtained, 214 (39%) had Lyme disease. Overall, 42 children had ECG evidence of carditis, of whom 24 had AV block (20 first-degree). Of the patients with ECG evidence of carditis, only 21 (50%) had any cardiac symptoms. The presence of AV block (OR 4.7, 95% CI 1.8-12.1) and any ECG evidence of carditis (OR 2.3, 95% CI 1.2-4.3) were both associated with diagnosis of Lyme disease. Conclusions ECG evidence of carditis, especially AV block, was associated with a diagnosis of Lyme disease. ECG evidence of carditis can be used as a diagnostic biomarker for Lyme disease to guide initial management while awaiting Lyme disease test results.

Objective To measure the efficacy of mecasermin (recombinant human insulin‐like growth factor 1, rhIGF‐1), for treating symptoms of Rett syndrome (RTT) in a pediatric population using a double‐blind crossover study design. Methods Thirty girls with classic RTT in postregression stage were randomly assigned to placebo or rhIGF‐1 in treatment period 1 and crossed over to the opposite assignment for period 2 (both 20 weeks), separated by a 28‐week washout period. The primary endpoints were as follows: Anxiety Depression and Mood Scale (ADAMS) Social Avoidance subscale, Rett Syndrome Behaviour Questionnaire (RSBQ) Fear/Anxiety subscale, Parent Target Symptom Visual Analog Scale (PTSVAS) top three concerns, Clinical Global Impression (CGI), Parent Global Impression (PGI), and the Kerr severity scale. Cardiorespiratory‐ and electroencephalography (EEG)‐based biomarkers were also analyzed. Results There were no significant differences between randomization groups. The majority of AEs were mild to moderate, although 12 episodes of serious AEs occurred. The Kerr severity scale, ADAMS Depressed Mood subscale, Visual Analog Scale Hyperventilation, and delta average power change scores significantly increased, implying worsening of symptoms. Electroencephalography (EEG) parameters also deteriorated. A secondary analysis of subjects who were not involved in a placebo recall confirmed most of these findings. However, it also revealed improvements on a measure of stereotypic behavior and another of social communication. Interpretation As in the phase 1 trial, rhIGF‐1 was safe; however, the drug did not reveal significant improvement, and some parameters worsened.

Background Outcomes for catheter ablation of accessory pathways in pediatric patients have steadily improved, with the exception of pathways located in the anteroseptal (AS) and midseptal (MS) regions, where success is limited by the close proximity of normal atrioventricular conduction. Objective The purpose of this study was to evaluate the efficacy of different catheter approaches and ablation energy modalities used for catheter ablation at these sites. Methods A retrospective review was performed of all electrophysiology studies conducted between July 2001 and July 2017. Acute success and recurrence rates were assessed by comparing catheter approaches and energy modalities used for ablation. Results A total of 255 electrophysiology procedures were performed in 223 patients (178 AS, 72 MS, 5 unspecified). Ablation was attempted in 241 procedures, with acute success in 87% (AS 89%, MS 83%). Recurrence was evident in 18% of successful ablation procedures (AS 18%, MS 19%). Success rates were higher with repeat procedures than with primary procedures (P = .006). Multiple approaches were more often used for AS pathways, though no single approach was superior. There was no difference in success when comparing energy modalities, though the overall recurrence rate was higher for cryoablation. Significant complications occurred in 1.2% of procedures, though no patient had complete heart block. Conclusion Ablation of AS and MS pathways remains challenging. Multiple approaches are often necessary to successfully ablate AS pathways. While both ablation energy modalities were equally successful, cryoablation may be associated with a higher chance of recurrence. Recurrences and repeat procedures may be anticipated to minimize risk to normal atrioventricular conduction during ablation in these regions.

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.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.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.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 bradycardia40 beats/min (n = 2) and100 beats/min (n = 1) and QTc prolongation (n = 2). All 5 patients with AEs had repaired congenital heart disease.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.

Left atrial (LA) dilation has been shown to be associated with atrial fibrillation (AF) in the adult population, with some studies indicating that larger LAs are more prone to AF recurrence. The relation of LA size to AF in the pediatric and young adult population has not been investigated. In this study, all pediatric patients (aged ≤22 years) who presented to Boston Children's Hospital from January 2002 to December 2012 with AF were reviewed. Patients with significant congenital heart disease, cardiomyopathies, proven channelopathies, previous cardiac surgery, end-stage renal disease, or severe lung disease/cystic fibrosis were excluded. LA measurements were taken using the echocardiogram performed at the initial presentation. In total, 48 patients with AF were identified. The median age at presentation was 17.1 years (range 3.7 to 22.9 years); 38 patients (79%) were men. Eleven patients (23%) had at least 1 recurrence of their AF. There was no difference in body mass index, prevalence of systemic hypertension, alcohol, stimulant, or illicit drug use between those who had an isolated episode of AF and those who had a recurrence. There was no significant difference in LA dimension Z -scores between groups, with only 2 patients (1 isolated AF, 1 recurrent AF) having Z -scores >2. In conclusion, AF in the young without underlying heart disease is not associated with LA dilation.

BACKGROUND Radiofrequency identification (RFID) detection systems are used to detect retained surgical sponges and may cause electromagnetic interference (EMI), altering intended function of cardiac pacing systems. Three pediatric patients requiring temporary pacing for postoperative atrioventricular block experienced transient inhibition of ventricular pacing during the use of RFID detection system. Bench testing was performed to evaluate the mechanism of pacemaker inhibition. METHODS Impedance of temporary pacing wires was obtained using a pacing system analyzer. Temporary pacemakers (Medtronic 5388, Medtronic 5392, and Biotronik Reocor D) at nominal settings (VVI 120 bpm, output 10 mA) were attached at the ventricular terminal to temporary pacing wires and a resistor for sham impedance in physiologic range. An RFID detection system and wand (RF Assure, model 200) or mat was tested over wires. Induced current and voltages were recorded via an oscilloscope attached to lead terminals. Inhibition of pacing was determined for the following variables: distance from wires, sham impedance, and programmed sensitivity. RESULTS In bench testing, the RFID system induced a stereotyped EMI signal in temporary pacing wires with peak root-mean-square voltage demonstrating an exponential decay relationship with increasing distance from pacing wires. Induced voltages overlapped with normal sensing range of temporary pacemakers, resulting in pacemaker inhibition at nominal settings (ventricular sensitivity 2.0 mV, distance from wand

Publicly available data from the Pediatric Heart Network's Single Ventricle Reconstruction Trial was analyzed to determine the prevalence, timing, risk factors for, and impact of second- and third-degree heart block (HB) on outcomes in patients who underwent stage 1 palliation (S1P) for hypoplastic left heart syndrome (HLHS).The presence and date of onset of post-S1P HB occurring within the first year of life, potential risk factors for HB, and factors known to predict poor outcomes after S1P were extracted. Multivariable logistic and Cox regression analyses were performed to identify risk factors for HB and to determine the effect of HB on 3-year transplantation-free survival.Among the 549 patients in the cohort, 33 (6%) developed HB after S1P. The median interval between S1P and HB was 8 days (interquartile range, 0-133 days). Regression analysis showed that tricuspid valve repair during S1P and obstruction of pulmonary venous drainage requiring pre-S1P intervention were independently associated with HB (adjusted odds ratio [aOR], 11.6, 95% confidence interval [CI] 3.3-40; P .001 and aOR, 5.1; 95% CI, 1.3-20.6; P = .02, respectively). Transplantation-free survival at 3 years was lower for those with HB (39% vs 65%; P = .004). HB remained associated with transplantation-free survival after controlling for known risk factors (adjusted hazard ratio, 3.1; 95% CI, 1.9-5.0; P .001). Nine children (27%) had a pacemaker implanted, and 7 of these children (78%) died or underwent heart transplantation.HB after S1P is rare but heralds a poor outcome. Careful monitoring of these patients is recommended given their significantly increased risks of death and heart transplantation.

Patients with life-threatening conditions that present with syncope can be recognized promptly and appropriately with history, physical electrocardiogram (EKG), and echocardiography. Once diseases are recognized, exercise testing may be part of disease characterization and management. Exercise testing has a critical role in patients with high-risk histories of syncope, to evaluate for catecholaminergic polymorphic ventricular tachycardia (CPVT) and other unusual arrhythmia syndromes. Most patients with low severity, typical syncope will not benefit from exercise testing (or any substantial testing). For patients with more problematic symptoms, exercise testing represents a relatively low barrier test that can identify multiple contributors to symptoms. This includes deconditioning, abnormal or potentially abnormal blood pressure responses, and incidental or potentially important arrhythmias. The differences between normal and abnormal exercise responses in those with potential orthostatic syndrome overlap with normal physiology. Testing always needs to be interpreted in context.

While a substantial minority of patients with repaired tetralogy of Fallot (rTOF) have normal exercise performance, as a group their performance is mild-moderately decreased, and there is a cohort with markedly decreased exercise capacity. The factors responsible for the rTOF patient’s exercise intolerance are probably diverse and may vary from patient to patient. In most cases, residual cardiovascular lesions (pulmonary stenosis, pulmonary regurgitation, and especially right ventricular dysfunction) are the most important issues. The dynamic interplay between these variables and their effect on exercise function is complex, however, and can vary over time. The combination of an incompetent pulmonary valve and residual pulmonary artery stenoses is particularly deleterious and results in interesting physiology that is uniquely appreciated in the exercise physiology laboratory. Exercise testing can be safely performed in a wide range of TOF patients. Data from exercise testing in rTOF patients has important prognostic and clinical implications.

Atrial and ventricular arrhythmias are commonly seen with exercise stress testing (EST); these are almost always nonsustained, and the significance of those findings is, at best, modest. For patients with structurally normal hearts and combinations of isolated and repetitive ventricular ectopy, EST offers some mechanistic data and some marginal long-term prognostic data. Patients with increased ectopy during exercise or immediately post exercise deserve enhanced follow-up.

Wolff-Parkinson-White (WPW) syndrome is a ventricular pre-excitation syndrome affecting approximately 1–3 in 1000 individuals and carries a low, but clinically important, risk of sudden cardiac death. The clinical presentation can vary from asymptomatic WPW to cardiac arrest as the sentinel event. Practice guidelines have been developed for the management of patients with asymptomatic WPW. These guidelines include noninvasive and invasive testing and have ascribed an important role to exercise testing.

Introduction: Direct comparison of the effects of antiarrhythmic agents on myocardial performance may be useful in choosing between medications in critically ill patients. Studies directly comparing multiple antiarrhythmic medications are lacking. The use of an experimental heart preparation permits examination of myocardial performance under constant loading conditions. Methods: Hearts of Sprague Dawley rats (n = 35, 402-507 g) were explanted and cannulated in working heart model with fixed preload and afterload. Each heart was then exposed to a 3-hour infusion of procainamide (20 µg/kg/min), esmolol (100 or 200 µg/kg/min), amiodarone (10 or 20 mg/kg/d), sotalol (80 mg/m2/d), or placebo infusions (n = 5 per dose). Cardiac output, contractility (dP/dTmax), diastolic performance (dP/dTmin), and heart rate were compared between groups over time by linear mixed modeling. Results: Compared with placebo, sotalol decreased contractility by an average of 24% ( P < .001) over the infusion period, as did amiodarone (low dose by 13%, P = .029; high dose by 14%, P = .013). Compared with placebo, mean cardiac output was significantly lower in animals treated with sotalol (by 22%, P = .016) and esmolol 200 μg/kg/min (by 23%, P = .012). Over time, amiodarone decreased cardiac output (20 mg/kg/d, β = −89 [−144, −33] μL/min2 decrease, P = .002) and also worsened diastolic function, decreasing dP/dTmin by ∼18% and 22% ( P = .032 and P = .011, low and high doses, respectively). Procainamide did not have a significant effect on any measures of systolic or diastolic performance. Conclusions: In isolated hearts, amiodarone and sotalol depressed myocardial contractility, cardiac output, and diastolic function. However, procainamide did not negatively affect myocardial performance and represents a favorable agent in settings of therapeutic equivalence.

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 P P ≤0.006), and greater compared with a commonly used public data set for age groups ≥12 years ( P 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.

Objectives This study quantified the incidence of arrhythmias during pediatric exercise stress tests (ESTs) and evaluated criteria to identify patients at risk of clinically important arrhythmias. Background The incidence of clinically important arrhythmias during pediatric ESTs and criteria for identifying high-risk patients are poorly characterized. Methods A retrospective review of ESTs performed from 2013 to 2015 was studied. Arrhythmias were categorized into 4 classes based on need for test termination and intervention. Risk factors evaluated included having an implantable cardioverter-defibrillator (ICD), cardiomyopathy, severe ventricular dysfunction, complex arrhythmia history, coronary disease with concern for ischemia, pulmonary hypertension, select poorly palliated congenital heart disease (CHD), and concerning symptoms. Negative predictive values (NPVs) were calculated. Results During the study period, 5307 ESTs were performed. Median age of the subjects was 16 years (interquartile range: 13 to 24 years); 20% had complex CHD. At least 1 high-risk criterion was present in 507 tests (10%); having an ICD (37%) and cardiomyopathy (36%) were the most common criteria. Some arrhythmias were seen in 46% of tests, but only 33 events (0.6%) required test termination. Three events (0.06%) required cardiopulmonary resuscitation, all with high-risk criteria. Absence of a high-risk criterion had a 99.7% (95% confidence interval [CI]: 99.5% to 99.8%) NPV for an arrhythmia that required test termination and a 99.96% (95% CI: 99.85% to 99.99%) NPV for an arrhythmia that required intervention beyond test termination. Conclusions Although self-terminating arrhythmias are common, dangerous arrhythmias are rare during ESTs in a high-volume pediatric cardiology program. Pre-defined high-risk criteria identified all patients with the most serious events. The absence of any criteria predicted a low risk for arrhythmias that required test termination. These data permitted informed choices regarding supervision of ESTs.

Objective(s) To assess the impact of univentricular versus biventricular pacing (BiVP) on systemic ventricular function in patients with congenitally corrected transposition of the great arteries (ccTGA). Methods We performed a retrospective review of all patients with a diagnosis of ccTGA who underwent pacemaker insertion. From 1993 to 2014, 53 patients were identified from the cardiology database and surgical records. Results Overall mortality was 7.5% (n = 4). One patient required transplantation and 3 late deaths occurred secondary to end-stage heart failure. Median follow-up was 3.7 years (range, 4 days to 22.5 years). Twenty-five (47%) underwent univentricular pacing only, of these, 8 (32%) developed significant systemic ventricular dysfunction. Twenty-eight (53%) received BiVP, 17 (26%) were upgraded from a dual-chamber system, 11 (21%) received primary BiVP. Fourteen (82%) of the 17 undergoing secondary BiVP demonstrated systemic ventricular dysfunction at the time of pacer upgrade, with 7 (50%) demonstrating improved systemic ventricular function after pacemaker upgrade. Overall, 42 (79%) patients underwent univentricular pacing, with 22 (52%) developing significant systemic ventricular dysfunction. In contrast, the 11 (21%) who received primary BiVP had preserved systemic ventricular function at latest follow-up. Conclusions Late-onset systemic ventricular dysfunction is a major complication associated with the use of univentricular pacing in patients with ccTGA. All patients with ccTGA who develop heart block should undergo primary biventricular pacing, as this prevents late systemic ventricular dysfunction. Preemptive placement of BiVP leads at the time of anatomical repair or other permanent palliative procedure will facilitate subsequent BiVP should heart block develop.

The first patients to undergo a successful arterial switch operation (ASO) for d-transposition of the great arteries (D-TGA) are now entering their fourth decade of life. Past studies of ASO survivors' exercise function have yielded conflicting results. We therefore undertook this study to describe the current function of ASO survivors, to identify factors related to inferior exercise performance and to determine whether their exercise function tends to deteriorate over time. A retrospective cohort study was designed examining all patients with D-TGA after the ASO who underwent comprehensive cardiopulmonary exercise testing (CPET). Patients with palliative surgery prior to ASO, ventricular hypoplasia or severe valvar dysfunction were excluded from the study. Data from CPETs in which the peak respiratory exchange ratio was

Background:Neosaxitoxin (NeoSTX) is a site-1 sodium channel blocker that produces prolonged local anesthesia in animals and humans. Under a Food and Drug Administration–approved phase 1 Investigational New Drug trial, the authors evaluated safety and efficacy of NeoSTX alone and combined with 0.2% bupivacaine (Bup) with and without epinephrine.Methods:The authors conducted a double-blind, randomized, controlled trial involving healthy male volunteers aged 18 to 35 yr receiving two 10-ml subcutaneous injections. Control sites received Bup. In part 1, active sites received (1) 5 to 40 μg NeoSTX+Saline (NeoSTX-Saline), (2) 5 to 40 μg NeoSTX+Bup (NeoSTX-Bup), or (3) placebo (Saline). In part 2, active sites received 10 or 30 μg NeoSTX+Bup+Epinephrine (NeoSTX-Bup-Epi) or placebo. Primary outcome measures were safety and adverse events associated with NeoSTX. Secondary outcomes included clinical biochemistry, NeoSTX pharmacokinetics, and cutaneous hypoesthesia.Results:A total of 84 subjects were randomized and completed the two-part trial with no serious adverse events or clinically significant physiologic impairments. Perioral numbness and tingling increased with NeoSTX dose for NeoSTX-Saline and NeoSTX-Bup. All symptoms resolved without intervention. NeoSTX-Bup-Epi dramatically reduced symptoms compared with other NeoSTX combinations (tingling: 0 vs. 70%, P = 0.004; numbness: 0 vs. 60%, P = 0.013) at the same dose. Mean peak plasma NeoSTX concentration for NeoSTX-Bup-Epi was reduced at least two-fold compared with NeoSTX-Saline and NeoSTX-Bup (67 ± 14, 134 ± 63, and 164 ± 81 pg/ml, respectively; P = 0.016). NeoSTX-Bup showed prolonged cutaneous block duration compared with Bup, NeoSTX-Saline, or placebo, at all doses. Median time to near-complete recovery for 10 μg NeoSTX-Bup-Epi was almost five-fold longer compared with Bup (50 vs. 10 h, P = 0.007).Conclusion:NeoSTX combinations have a tolerable side effect profile and appear promising for prolonged local anesthesia.

Adult CRT Criteria for Pediatric Dilated Cardiomyopathy Introduction Cardiac resynchronization therapy (CRT) is an effective device-based intervention for adults with heart failure (HF) with specific indications, based on large, multicenter randomized clinical trials. The criteria for CRT in adult HF include significant symptoms, ventricular systolic dysfunction, prolonged QRS duration, and left bundle branch block (LBBB) pattern on electrocardiogram (ECG). Despite having less data, CRT is also being widely utilized in children with HF. The shortage of evidence-based CRT criteria in pediatrics prompted us to review a cohort of children with dilated cardiomyopathy and evaluate their potential eligibility for CRT using the traditional adult criteria. Methods Single-center data of all pediatric patients with dilated cardiomyopathy were extracted from the heart failure registry and retrospectively reviewed. Patients who had at least 2 separate visits that included HF scoring, electrocardiogram, and echocardiogram were included. Patients who were ventricular paced were excluded. Results Data for 52 patients meeting inclusion criteria were analyzed. The mean ejection fraction was 25% on the first clinical evaluation and 27% on the second visit. No patient and 2 patients met the adult criteria for prolonged QRS on the first and second encounters, respectively. No patients had an LBBB pattern on ECG. Conclusions None of the pediatric HF patients in our study met the published Class I criteria for CRT device therapy in adults. These findings suggest that extrapolation of adult HF data to pediatrics is not sufficient for CRT criteria. Specific guidelines for device implantation in children must be based on scientific investigation including pediatric clinical trials.

This drug safety review provides an update on the long-term cardiovascular risks of therapeutic stimulant class medication for children and adults with attention-deficit/hyperactivity disorder (ADHD).Relevant literature on the long-term (defined as ≥ 12 months) cardiovascular effects of stimulant class medications for ADHD was sought using PubMed searches for clinical literature, epidemiological reports, as well as reviews of post-marketing data and clinical guidelines/consensus statements. Comparison was made to the non-stimulant atomoxetine.Long-term cardiovascular risks of stimulants for healthy children and adults with ADHD are limited to minor mean elevations in blood pressure (≤ 7 mmHg) and heart rate (≤ 10 bpm). In a sizeable minority of individuals these elevations are greater and/or reach a clinical threshold. Subjective complaints may also be anticipated during long-term treatment, yet without an increase in serious cardiac outcomes above background rates per age. Future research is needed on possible latent or cumulative cardiovascular risks in healthy individuals, as well as the longer-term cardiovascular safety in vulnerable populations.

Background The 2005 Bethesda Conference Guidelines advise patients with long QT syndrome against competitive sports. We assessed cardiac event rates during competitive and recreational sports, and daily activities among treated long QT syndrome patients. Methods and Results Long QT syndrome patients aged ≥4 years treated with anti‐adrenergic therapy were included. Demographics included mechanism of presentation, corrected QT interval pretreatment, symptom history, medication compliance, and administration of QT‐prolonging medications. Corrected QT interval ≥550 ms or prior cardiac arrest defined high risk. Sports were categorized by cardiovascular demand per the 2005 Bethesda Conference Guidelines. Each was classified as recreational or competitive. One hundred seventy‐two patients (90; 52% female) with median age 15.2 years (interquartile range 11.4, 19.4) were included. Evaluation was performed for family history (102; 59%), incidental finding (34; 20%), and symptoms (36; 21%). Median corrected QT interval was 474 ms (interquartile range 446, 496) and 14 patients (8%) were deemed high risk. Treatment included β‐blockers (171; 99%), implantable cardioverter‐defibrillator (27; 16%), left cardiac sympathetic denervation (7; 4%), and pacemaker (3; 2%). Sports participation was recreational (66; 38%) or competitive (106; 62%), with 92 (53%) exercising against the Bethesda Conference Guidelines. There were no cardiac events in competitive athletes and no deaths. There were 13 cardiac events in 9 previously symptomatic patients during either recreational exercise or activities of daily life. Conclusions In this cohort of appropriately managed children with long QT syndrome, cardiac event rates were low and occurred during recreational but not competitive activities. This study further supports the need for increased assessment of arrhythmia risk during exercise in this patient population.

Background— Implantable cardioverter defibrillators (ICDs) used to prevent sudden cardiac arrest in children not only provide appropriate therapy in 25% of patients but also result in a significant incidence of inappropriate shocks and other device complications. ICDs placed for secondary prevention have higher rates of appropriate therapy than those placed for primary prevention. Pediatric patients with primary prevention ICDs were studied to determine time-dependent incidence of appropriate use and adverse events. Methods and Results— A total of 140 patients aged Conclusions— Primary prevention ICDs were associated with appropriate therapy in 19% and adverse event in 36% in this cohort. The incidence of both first appropriate therapy and device-related adverse events decreased during longer periods of follow-up after implantation. This suggests that indications for continued device therapy in pediatric primary prevention ICD patients might be reconsidered after a period of nonuse.

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder mainly affecting females and is associated with mutations in MECP2, the gene encoding methyl CpG-binding protein 2. Mouse models suggest that recombinant human insulin-like growth factor 1 (IGF-1) (rhIGF1) (mecasermin) may improve many clinical features. We evaluated the safety, tolerability, and pharmacokinetic profiles of IGF-1 in 12 girls with MECP2 mutations (9 with RTT). In addition, we performed a preliminary assessment of efficacy using automated cardiorespiratory measures, EEG, a set of RTT-oriented clinical assessments, and two standardized behavioral questionnaires. This phase 1 trial included a 4-wk multiple ascending dose (MAD) (40-120 μg/kg twice daily) period and a 20-wk open-label extension (OLE) at the maximum dose. Twelve subjects completed the MAD and 10 the entire study, without evidence of hypoglycemia or serious adverse events. Mecasermin reached the CNS compartment as evidenced by the increase in cerebrospinal fluid IGF-1 levels at the end of the MAD. The drug followed nonlinear kinetics, with greater distribution in the peripheral compartment. Cardiorespiratory measures showed that apnea improved during the OLE. Some neurobehavioral parameters, specifically measures of anxiety and mood also improved during the OLE. These improvements in mood and anxiety scores were supported by reversal of right frontal alpha band asymmetry on EEG, an index of anxiety and depression. Our data indicate that IGF-1 is safe and well tolerated in girls with RTT and, as demonstrated in preclinical studies, ameliorates certain breathing and behavioral abnormalities.

As mortality in patients with D-loop transposition of the great arteries (D-TGA) has decreased after the arterial switch operation (ASO), the focus has shifted to higher risk groups and outcomes that impact long-term morbidity and mortality, such as left ventricular (LV) dysfunction. We sought to examine the perioperative factors associated with LV dysfunction in patients with D-TGA and ventricular septal defects (VSD) after ASO.A retrospective study was made of all patients with D-TGA/VSD who underwent ASO/VSD closure from 2001 to 2011. Patients with prematurity, L-looped ventricles, and straddling atrioventricular valves were excluded. The primary endpoint was moderate or severe LV dysfunction measured by echocardiogram 2 months or more after surgery.A total of 112 patients underwent ASO/VSD closure at a median age of 5 days. Median time of follow-up was 6.5 months, with no mortality noted. Six patients (8%) were noted to have at least moderate LV dysfunction. Risk factors were heart block requiring pacemaker placement (p0.001) and length of intensive care unit admission (p=0.04). All 6 patients with heart block had an epicardial lead on the right ventricular free wall; 4 had moderate or severe LV dysfunction and underwent upgrade to cardiac resynchronization therapy (CRT); median time from initial pacemaker to CRT was 5 months. With a median follow-up of 5 months after CRT, LV function improved to normal (2 patients) or mild dysfunction (2 patients).Left ventricular dysfunction after surgical repair for D-TGA/VSD is low, with heart block and pacemaker insertion playing a significant role. The LV function improved after patients were upgraded to a CRT device.

Aims Non-fluoroscopic imaging (NFI) devices are increasingly used in ablations. The objective was to determine the utility of intracardiac echocardiography (ICE) in ablating paediatric supraventricular tachycardias (SVTs) and assess whether its integrated use with electroanatomic mapping (EAM) resulted in lower radiation exposure than use of EAM alone. Methods and results Prospective, controlled, single-centre study of patients (pts) age ≥10 years, weight ≥35 kg, with SVT and normal cardiac anatomy. Patients were randomized to ICE + EAM (ICE) or EAM only (no ICE). Both had access to fluoroscopy as needed. Eighty-four pts were enroled (42 ICE, 42 no ICE). Median age was 15 years (range 10.4–23.7 years); 57% had accessory pathways, 42% atrioventricular nodal reentry tachycardia. There was no difference in radiation dose (9 mGy ICE vs. 23 mGy no ICE, P = 0.37) or fluoroscopy time (1.1 min ICE vs. 1.5 min no ICE, P = 0.38). Transseptal punctures were performed in 25 pts (16 ICE, 9 no ICE), with ICE reducing radiation (8 mGy ICE vs. 62 mGy no ICE, P = 0.002) and fluoroscopy time (1.1 min ICE vs. 4.5 min no ICE, P = 0.01). Zero fluoroscopy was achieved in 13 pts (15% of total, 5 ICE, 8 no ICE), and low-dose cases (