Partial Heart Transplant in a Neonate With Irreparable Truncal Valve Dysfunction.

Importance: The treatment of neonates with irreparable heart valve dysfunction remains an unsolved problem because there are no heart valve implants that grow. Therefore, neonates with heart valve implants are committed to recurrent implant exchanges until an adult-sized valve can fit. Objective: To deliver the first heart valve implant that grows. Design, Setting, and Participants: Case report from a pediatric referral center, with follow-up for more than 1 year. Participants were a recipient neonate with persistent truncus arteriosus and irreparable truncal valve dysfunction and a donor neonate with hypoxic-ischemic brain injury. Intervention: First-in-human transplant of the part of the heart containing the aortic and pulmonary valves. Main Outcomes and Measures: Transplanted valve growth and hemodynamic function. Results: Echocardiography demonstrated adaptive growth and excellent hemodynamic function of the partial heart transplant valves. Conclusions and Relevance: In this child, partial heart transplant delivered growing heart valve implants with a good outcome at age 1 year. Partial heart transplants may improve the treatment of neonates with irreparable heart valve dysfunction.

Variability in radiation dose and image quality: A comparison across fluoroscopy-system vendors, generations of equipment and institutions.

OBJECTIVES: To evaluate differences in radiation dose and image quality across institutions, fluoroscope vendors and generations of fluoroscopes for pediatric cardiac catheterization. BACKGROUND: Increased recognition of the potentially harmful effects of ionizing radiation has spurred technological advances in fluoroscopes, as well as increased focus on optimizing fluoroscope performance. There is currently little understanding of variability in the dose-image quality relationship across institutions, fluoroscope vendor and/or generation of equipment. METHODS: We evaluated latest generation fluoroscopes from Phillips, Siemens, GE, and Toshiba, and an older generation Phillips fluoroscope (release date 2003) at three different institutions. Radiation dose was measured using an anthropomorphic dose-assessment phantom with effective dose in mSv estimated from Monte Carlo simulations. Image quality phantom images were scored on a 12-point scale by three blinded reviewers. RESULTS: Fluoroscope effective doses ranged from 0.04 to 0.14 mSv/1,000 pulses for fluoroscopy with associated composite image quality scores ranging from 8.0 ± 0.6 to 10.4 ± 1.3. For cineangiography, effective doses ranged from 0.17 to 0.57 mSv/1,000 frames with image quality scores ranging from 10.1 ± 0.3 to 11.1 ± 0.3. There was modest correlation between effective dose and image quality (r = 0.67, P = 0.006). The older generation fluoroscope delivered consistently higher doses than the newer generation systems (2.3- to 3.5-fold higher for fluoroscopy; 1.1- to 3.4-fold higher for cineangiography) without appreciable differences in image quality. CONCLUSION: Technological advances have markedly improved fluoroscope performance. Comparing latest generation systems across vendors and institutions, we found variability in the dose-IQ relationship and speculate that this reflects both equipment and institutional optimization practices.

Abstract 12670: Variability in Radiation Dose and Image Quality: A Comparison Across Fluoroscopy-system Vendors and Generations of Equipment.

INTRODUCTION: Increased recognition of the potentially harmful effects of ionizing radiation has spurred technological advances to reduce exposure during fluoroscopy. However there is currently little understanding of the dose-image quality (IQ) relationship between fluoroscopy vendors and across generations of equipment used for imaging during pediatric catheterization. METHODS: We evaluated latest generation fluoroscopy systems from Phillips, Siemens, GE and Toshiba, and an older generation Phillips system (2004 release). Fluoroscopy and cineangiography were performed on a tissue simulation anthropomorphic phantom using a standardized imaging approach. Phantom surface exposures were used for Monte Carlo simulations to calculate radiation effective dose, accounting for differences in beam parameters. We also imaged a fluoroscopy IQ phantom to assess contrast-detail and line-per-inch visualization. IQ images were scored by 3 blinded reviewers with scores averaged to produce a composite rating (scale 0-18). To assess the impact of imaging approach we then simulated a neonatal cardiac catheterization incorporating "typical" imaging protocols provided by institutions using the various systems. RESULTS: Effective doses and IQ scores are summarized in the table. Effective doses varied by >400% with the older generation system consistently delivering markedly higher doses. The associated figure summarizes dose and IQ for a simulated neonatal cardiac catheterization which accounts for measured doses as well as the reported institutional imaging parameters summarized in the figure legend. CONCLUSION: These data demonstrate substantial technological improvements in fluoroscopy equipment and may be useful to justify institutional "upgrades". Comparing latest generation systems across vendors and institutions, we found variability in the dose-IQ relationship that reflects both equipment and imaging approach.

Brugada-like syndrome in infancy presenting with rapid ventricular tachycardia and intraventricular conduction delay.

BACKGROUND: Brugada syndrome is a potentially serious channelopathy that usually presents in adulthood and has only rarely been described in infancy. In the absence of metabolic or structural cardiac disease, rapid ventricular tachycardia (>200 bpm) and primary cardiac conduction disease are uncommon in infancy. We hypothesized that infants having rapid ventricular tachycardia and conduction abnormalities and not having structural or metabolic pathogeneses were likely to have mutations in depolarizing current channels. METHODS AND RESULTS: A retrospective review of all clinical materials from a single institution over a 9-year period from all infants <2 years old and having a discharge diagnosis of ventricular tachycardia or ventricular fibrillation was performed. Among 32 infants fulfilling inclusion criteria, 12 had a structurally normal heart, and 9 of them had either prolonged QRS duration or Brugada pattern while in sinus rhythm. Of those 5 infants not having a definitive pathogenesis, electrophysiological testing had been performed in 4, and genetic testing had been performed in all 5 of those infants. During electrophysiological testing, a prolonged HV interval was present in 2 of 4, inducible ventricular tachycardia was present in 1 of 4, and a type 1 Brugada pattern was induced by intravenous procainamide in 3 of 4. Genetic testing revealed disease-causing mutations in depolarizing sodium (SCN5A) or calcium (CaCNB2b) channels in all 5 infants. CONCLUSIONS: Infants having rapid ventricular tachycardia and conduction abnormalities in the absence of structural or metabolic abnormalities are likely to have disease-causing mutations in cardiac depolarizing channels.

Laser lead extraction in congenital heart disease: a case-controlled study.

INTRODUCTION: Patients with congenital heart disease (CHD) and implanted cardiac rhythm management devices have a high rate of endocardial lead issues requiring lead extraction. Laser lead extraction (LLE) is a promising modality for lead management though few studies have evaluated this technique in CHD. METHODS: This is a retrospective, case-controlled (gender- and age-matched, without CHD) analysis of all CHD patients from 2002-2010 at a single institution who underwent LLE as a primary extraction modality. The aim is to evaluate the utility of LLE in patients with CHD compared with controls without CHD. The primary outcome is LLE clinical success. Secondary outcomes include procedural success, complications, and factors related to LLE failure. RESULTS: Twenty-two patients with CHD underwent 24 LLE procedures to extract 35 leads. These were compared with 22 patients without CHD who underwent 24 LLE procedures to extract 37 leads. LLE clinical success was achieved for 26 of 35 leads (74%) in patients with CHD versus 35 of 37 leads (92%) in patients without CHD [P = 0.02]. No factors within the CHD group predicted LLE failure. Six of the nine leads for which LLE was unsuccessful were extracted using other methods. No complications were observed in the CHD group. CONCLUSIONS: Patients with CHD are less likely to have successful LLE than gender- and age-matched controls without CHD. LLE failures in CHD may be related to calcified adhesions. Mechanical-rotational devices and the femoral snare technique are useful for LLE failures. LLE provides an effective first-line approach for patients with CHD.

Racial and socioeconomic disparities in pediatric heart transplant outcomes in the era of anti-thymocyte globulin induction.

BACKGROUND: Black race is associated with worse outcomes across solid organ transplantation. Augmenting immunosuppression through antithymocyte globulin (ATG) induction may mitigate organ rejection and graft loss. We investigated whether racial and socioeconomic outcome disparities persist in children receiving ATG induction. METHODS: Using the Pediatric Heart Transplant Society registry, we compared outcomes in Black and White children who underwent heart transplant with ATG induction between 2000 and 2020. The primary outcomes of treated rejection, rejection with hemodynamic compromise (HC), and graft loss (death or re-transplant). We explored the association of these outcomes with race and socioeconomic disparity, assessed using a neighborhood deprivation index [NDI] score at 1-year post-transplant (high NDI score implies more socioeconomic disadvantage). RESULTS: The study cohort included 1,719 ATG-induced pediatric heart transplant recipients (22% Black, 78% White). There was no difference in first year treated rejection (Black 24.5%, White 28.1%, p = 0.2). During 10 year follow up, the risk of treated rejection was similar; however, Black recipients were at higher risk of HC rejection (p = 0.009) and graft loss (p = 0.02). Black recipients had a higher mean NDI score (p < 0.001). Graft loss conditional on 1-year survival was associated with high NDI score in both White and Black recipients (p < 0.0001). In a multivariable Cox model, both high NDI score (HR 1.97, 95% CI 1.23-3.17) and Black race (HR 2.22, 95% CI 1.40-3.53) were associated with graft loss. CONCLUSION: Black race and socioeconomic disadvantage remain associated with late HC rejection and graft loss in children with ATG induction. These disparities represent important opportunities to improve long term transplant outcomes.

Relationship of ventricular assist device support duration with pediatric heart transplant outcomes.

BACKGROUND: There is wide variability in the timing of heart transplant (HTx) after pediatric VAD implant. While some centers wait months before listing for HTx, others accept donor heart offers within days of VAD surgery. We sought to determine if HTx within 30 days versus ≥ 30 after VAD impacts post-HTx outcomes. METHODS: Children on VAD pre-HTx were extracted from the Pediatric Heart Transplant Study database. The primary endpoints were post-HTx length of hospital stay (LOS) and one-year survival. Confounding was addressed by propensity score weighting using inverse probability of treatment. Propensity scores were calculated based on age, blood type, primary cardiac diagnosis, decade, VAD type, and allosensitization status. RESULTS: A total of 1064 children underwent VAD prior to HTx between 2000 to 2018. Most underwent HTx ≥ 30 days post-VAD (70%). Infants made up 22% of both groups. Patients ≥ 12 years old were 42% of the < 30 days group and children 1 to 11 years comprised 47% of the ≥ 30 days group (p < 0.001). There was no difference in the prevalence of congenital heart disease vs. cardiomyopathy (p = 0.8) or high allosensitization status (p = 0.9) between groups. Post-HTx LOS was similar between groups (p = 0.11). One-year survival was lower in the < 30 days group (adjusted mortality HR 1.76, 95% CI 1.11-2.78, p = 0.016). CONCLUSIONS: A longer duration of VAD support prior to HTx is associated with a one-year survival benefit in children, although questions of patient complexity, post-VAD complications and the impact on causality remain. Additional studies using linked databases to understand these factors will be needed to fully assess the optimal timing for post-VAD HTx.

Preoperative diagnosis of long QT syndrome in an infant with tetralogy of Fallot.

Long QT syndrome is a well-described entity in infants. Its presentation in the context of congenital heart disease is rare and is almost exclusively diagnosed postoperatively. For patients undergoing surgical intervention, preoperative knowledge of the diagnosis and appropriate perioperative management can be life-saving. We present the rare case of an infant with tetralogy of Fallot who was preoperatively diagnosed with long QT syndrome and discuss the implications of this diagnosis for his perioperative management.

ATP1A3-Encoded Sodium-Potassium ATPase Subunit Alpha 3 D801N Variant Is Associated With Shortened QT Interval and Predisposition to Ventricular Fibrillation Preceded by Bradycardia.

Background Pathogenic variation in the ATP1A3-encoded sodium-potassium ATPase, ATP1A3, is responsible for alternating hemiplegia of childhood (AHC). Although these patients experience a high rate of sudden unexpected death in epilepsy, the pathophysiologic basis for this risk remains unknown. The objective was to determine the role of ATP1A3 genetic variants on cardiac outcomes as determined by QT and corrected QT (QTc) measurements. Methods and Results We analyzed 12-lead ECG recordings from 62 patients (male subjects=31, female subjects=31) referred for AHC evaluation. Patients were grouped according to AHC presentation (typical versus atypical), ATP1A3 variant status (positive versus negative), and ATP1A3 variant (D801N versus other variants). Manual remeasurements of QT intervals and QTc calculations were performed by 2 pediatric electrophysiologists. QTc measurements were significantly shorter in patients with positive ATP1A3 variant status (P<0.001) than in patients with genotype-negative status, and significantly shorter in patients with the ATP1A3-D801N variant than patients with other variants (P<0.001). The mean QTc for ATP1A3-D801N was 344.9 milliseconds, which varied little with age, and remained <370 milliseconds throughout adulthood. ATP1A3 genotype status was significantly associated with shortened QTc by multivariant regression analysis. Two patients with the ATP1A3-D801N variant experienced ventricular fibrillation, resulting in death in 1 patient. Rare variants in ATP1A3 were identified in a large cohort of genotype-negative patients referred for arrhythmia and sudden unexplained death. Conclusions Patients with AHC who carry the ATP1A3-D801N variant have significantly shorter QTc intervals and an increased likelihood of experiencing bradycardia associated with life-threatening arrhythmias. ATP1A3 variants may represent an independent cause of sudden unexplained death. Patients with AHC should be evaluated to identify risk of sudden death.

Two children with "dropped head" syndrome due to lamin A/C mutations.

LMNA-related congenital muscular dystrophy (L-CMD) is a recently described disorder characterized by infantile-onset myopathy due to mutations in the lamin A/C (LMNA) gene. We report the genetic and clinical characteristics of two unrelated L-CMD patients. Patient 1 harbored a novel, L35P mutation and patient 2 a previously reported R249W mutation. The striking phenotype associated with L-CMD is important to recognize, as molecular diagnostic testing can spare patients unnecessary procedures and prompt the physician to monitor for associated cardiac arrhythmias.

Arrhythmias in children having a single left superior vena cava and minimal structural heart disease.

BACKGROUND: The presence of a single left superior vena cava in the absence of complex congenital heart disease is uncommon, and, in the absence of hemodynamic consequences, it would not be expected to result in cardiovascular signs or symptoms. Single case reports and our anecdotal experience suggested to us that this anomaly is highly associated with cardiac arrhythmias. OBJECTIVE: We sought to describe the clinically important arrhythmias in a population of young patients having this anomaly. METHODS: A retrospective chart review was performed from all patients <20 years old and who were determined by echocardiography over an 11-year-period to have a single left superior vena cava and minor or no coexisting congenital heart defects. The prevalence of nonsinus pacemaker, age-corrected sinus rate percentile, and prevalence of brady- or tachyarrhythmias was compared with a control group of patients having bilateral superior vena cavae. RESULTS: Eight patients having a single left and 55 patients having bilateral superior vena cava(e) were identified. The existence of this anomaly tended to be associated with a lower age-corrected sinus rate percentile (17.5% vs 75%, P = 0.09), and was associated with a higher prevalence of arrhythmias (50% vs 7%, P = 0.014) compared with the control group. In the study group, one patient each had clinically relevant sinus node dysfunction, third-degree AV block, Wolff-Parkinson-White syndrome and atrial fibrillation, and AV nodal reentrant tachycardia. CONCLUSION: Even in the absence of symptoms, patients found to have a single left superior vena cava should be monitored long-term for clinically important arrhythmias.

Long QT syndrome, Brugada syndrome, and conduction system disease are linked to a single sodium channel mutation.

The function of the 12 positive charges in the 53-residue III/IV interdomain linker of the cardiac Na(+) channel is unclear. We have identified a four-generation family, including 17 gene carriers with long QT syndrome, Brugada syndrome, and conduction system disease with deletion of lysine 1500 (DeltaK1500) within the linker. Three family members died suddenly. We have examined the functional consequences of this mutation by measuring whole-cell and single-channel currents in 293-EBNA cells expressing the wild-type and DeltaK1500 mutant channel. The mutation shifted V(1/2)h( infinity ) to more negative membrane potentials and increased k(h) consistent with a reduction of inactivation valence of 1. The shift in h( infinity ) was the result of an increase in closed-state inactivation rate (11-fold at -100 mV). V(1/2)m was shifted to more positive potentials, and k(m) was doubled in the DeltaK1500 mutant. To determine whether the positive charge deletion was the basis for the gating changes, we performed the mutations K1500Q and K1500E (change in charge, -1 and -2, respectively). For both mutations, V(1/2)h was shifted back toward control; however, V(1/2)m shifted progressively to more positive potentials. The late component of Na(+) current was increased in the DeltaK1500 mutant channel. These changes can account for the complex phenotype in this kindred and point to an important role of the III/IV linker in channel activation.

Efficacy of Flecainide in the Treatment of Catecholaminergic Polymorphic Ventricular Tachycardia: A Randomized Clinical Trial.

Importance: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal genetic arrhythmia syndrome characterized by polymorphic ventricular tachycardia with physical or emotional stress, for which current therapy with ß-blockers is incompletely effective. Flecainide acetate directly suppresses sarcoplasmic reticulum calcium release-the cellular mechanism responsible for triggering ventricular arrhythmias in CPVT-but has never been assessed prospectively. Objective: To determine whether flecainide dosed to therapeutic levels and added to ß-blocker therapy is superior to ß-blocker therapy alone for the prevention of exercise-induced arrhythmias in CPVT. Design, Setting, and Participants: This investigator-initiated, multicenter, single-blind, placebo-controlled crossover clinical trial was conducted from December 19, 2011, through December 29, 2015, with a midtrial protocol change at 10 US sites. Patients with a clinical diagnosis of CPVT and an implantable cardioverter-defibrillator underwent a baseline exercise test while receiving maximally tolerated ß-blocker therapy that was continued throughout the trial. Patients were then randomized to treatment A (flecainide or placebo) for 3 months, followed by exercise testing. After a 1-week washout period, patients crossed over to treatment B (placebo or flecainide) for 3 months, followed by exercise testing. Interventions: Patients received oral flecainide or placebo twice daily, with the dosage guided by trough serum levels. Main Outcomes and Measures: The primary end point of ventricular arrhythmias during exercise was compared between the flecainide and placebo arms. Exercise tests were scored on an ordinal scale of worst ventricular arrhythmia observed (0 indicates no ectopy; 1, isolated premature ventricular beats; 2, bigeminy; 3, couplets; and 4, nonsustained ventricular tachycardia). Results: Of 14 patients (7 males and 7 females; median age, 16 years [interquartile range, 15.0-22.5 years]) randomized, 13 completed the study. The median baseline exercise test score was 3.0 (range, 0-4), with no difference noted between the baseline and placebo (median, 2.5; range, 0-4) exercise scores. The median ventricular arrhythmia score during exercise was significantly reduced by flecainide (0 [range, 0-2] vs 2.5 [range, 0-4] for placebo; P < .01), with complete suppression observed in 11 of 13 patients (85%). Overall and serious adverse events did not differ between the flecainide and placebo arms. Conclusions and Relevance: In this randomized clinical trial of patients with CPVT, flecainide plus ß-blocker significantly reduced ventricular ectopy during exercise compared with placebo plus ß-blocker and ß-blocker alone. Trial Registration: clinicaltrials.gov Identifier: NCT01117454.

Transthoracic percutaneous access for electroanatomic mapping and catheter ablation of atrial tachycardia in patients with a lateral tunnel Fontan.

BACKGROUND: The incidence of atrial tachycardia following Fontan surgery is high, but access to the pulmonary venous atrium, a frequent site of arrhythmia origin, is limited. OBJECTIVES: The purpose of this study is to report our results with a novel transthoracic percutaneous technique that provides direct access to the pulmonary venous atrium for electrophysiologic procedures. METHODS: Six transthoracic ablation procedures were performed in five patients (age 1.2-17 years, weight 9.2-68.4 kg) with a lateral tunnel Fontan. Under biplane fluoroscopy, a percutaneous needle was advanced at the selected intercostal space toward the pulmonary venous atrium. Once access was confirmed, a sheath was placed over a wire and a Navistar CARTO catheter advanced for mapping and ablation. Additional catheters were placed in the baffle and esophagus for pacing and reference. Atrial tachycardia was induced, electroanatomic mapping performed, and candidate areas tested with entrainment techniques. Radiofrequency ablation was performed and success defined as the inability to reinduce tachycardia using the initiating protocol. RESULTS: All tachycardias were ablated. Procedure time ranged from 3.7 to 4.9 hours, and fluoroscopy time ranged from 31 to 70 minutes. Hospital stay was 2 days. One patient had a pneumothorax and two had a hemothorax that was drained. Tachycardia recurred in one patient at 3 months. Ablation was repeated successfully. Four patients are free of tachycardia at follow-up ranging from 6 to 29 months. Follow-up is not available for one child. CONCLUSION: Transthoracic percutaneous access provided a direct route to the pulmonary venous atrium for successful mapping and radiofrequency ablation in Fontan patients.

Outcomes after percutaneous coronary artery revascularization procedures for cardiac allograft vasculopathy in pediatric heart transplant recipients: A multi-institutional study.

BACKGROUND: Cardiac allograft vasculopathy is an important cause of long-term graft loss. In adults, percutaneous revascularization procedures (PRPs) have variable success with high restenosis rates and little impact on graft survival. Limited data exist in pediatric recipients of transplants. METHODS: Data from the Pediatric Heart Transplant Study (PHTS) were used to explore associations between PRPs and outcomes after heart transplant in patients listed ≤18 years old who received a first heart transplant between 1993 and 2009. RESULTS: Revascularization procedures were done in 28 of 3,156 (0.9%) patients; 13 patients had multiple PRPs giving a total of 51 PRPs performed across 15 centers. Mean recipient age at time of transplant was 7.7 ± 6.7 years; mean donor age was 15.9 ± 15.4 years. The mean time to first PRP was 5.7 ± 3.2 years. Vessels involved were left anterior descending artery (41%), right coronary artery (25%), circumflex artery (18%), other coronary branches/unknown (16%). PRPs consisted of 38 (75%) stent implantations and 13 (25%) balloon angioplasties with an overall procedural success rate of 73%. Freedom from graft loss after PRPs was 89%, 75%, and 61% at 1, 3, and 12 months. In addition, patients with transplants from donors >30 years old were found to have less freedom from the need for a revascularization procedure than patients with transplants from younger donors (p < 0.0001). CONCLUSIONS: In this large pediatric heart transplant cohort, use of PRPs for cardiac allograft vasculopathy was rare, likely related to procedural feasibility of the interventions. Despite technically successful interventions, graft loss occurred in 39% within 1 year post-procedure; relisting for heart transplant should be considered.

Improved Detection of Cardiac Allograft Vasculopathy: A Multi-Institutional Analysis of Functional Parameters in Pediatric Heart Transplant Recipients.

BACKGROUND: Recent guidelines recommend assessment of systolic function and filling pressures to augment angiographic grading of cardiac allograft vasculopathy (CAV); however, no data exist on the utility of these guidelines. OBJECTIVES: The aims of this study were to evaluate whether the assessment of systolic and diastolic graft function, in addition to angiography, improves recognition of patients at high risk of graft loss and to assess the ability of adult filling-pressure thresholds to discriminate graft dysfunction in pediatric patients. METHODS: This study reviewed Pediatric Heart Transplant Study data from 1993 to 2009. Graft dysfunction was defined as significant systolic dysfunction (ejection fraction [EF] <45%) or the presence of restrictive hemodynamic features. Additional pediatric hemodynamic cutpoints of right atrial pressure (RAP) >12 mm Hg or pulmonary capillary wedge pressure (PCWP) >15 mm Hg were analyzed. RESULTS: In the study, 8,122 angiograms were performed in 3,120 patients, and 70% of patients had at least 1 angiogram. Angiographic incidence of CAV was 5%, 15%, and 28% at 2, 5, and 10 years, respectively, and most disease was mild. The presence of graft dysfunction identified patients at greater risk for graft loss even in children with mild angiographic vasculopathy (p < 0.0001). An RAP >12 mm Hg or a PCWP >15 mm Hg was sufficient to detect patients at high risk of graft loss even with mild angiographic disease. CONCLUSIONS: Patients with only mild angiographic CAV have significantly better outcomes than do patients with moderate or severe disease. The presence of an EF <45%, an RAP >12 mm Hg, or a PCWP >15 mm Hg identifies children at increased risk of graft loss even in the presence of only mild angiographic vasculopathy.

Management of pediatric tachyarrhythmias on mechanical support.

BACKGROUND: Pediatric patients with persistent arrhythmias may require mechanical cardiopulmonary support. We sought to classify the population, spectrum, and success of current treatment strategies. METHODS AND RESULTS: A multicenter retrospective chart review was undertaken at 11 sites. Inclusion criteria were (1) patients <21 years, (2) initiation of mechanical support for a primary diagnosis of arrhythmias, and (3) actively treated on mechanical support. A total of 39 patients were identified with a median age of 5.5 months and median weight of 6 kg. A total of 69% of patients were cannulated for supraventricular tachycardia with a median rate of 230 beats per minute. A total of 90% of patients were supported with extracorporeal membrane oxygenation for an average of 5 days. The remaining 10% were supported with ventricular assist devices for an average of 38 (20-60) days. A total of 95% of patients were treated with antiarrhythmics, with 43% requiring >1 antiarrhythmic. Amiodarone was the most frequently used medication alone or in combination. A total of 33% patients underwent electrophysiology study/transcatheter ablation. Radiofrequency ablation was successful in 9 patients on full flow extracorporeal membrane oxygenation with 3 radiofrequency-failures/conversion to cryoablation. One patient underwent primary cryoablation. A total of 15% of complications were related to electrophysiology study/ablation. At follow-up, 23 patients were alive, 8 expired, and 8 transplanted. CONCLUSIONS: Younger patients were more likely to require support in the presented population. Most patients were treated with antiarrhythmics and one third required electrophysiology study/ablation. Radiofrequency ablation is feasible without altering extracorporeal membrane oxygenation flows. There was a low frequency of acute adverse events in patients undergoing electrophysiology study/ablation, while on extracorporeal membrane oxygenation.