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Background: Patients with CHD can be exposed to high levels of cumulative ionising radiation. Utilisation of electroanatomic mapping during catheter ablation leads to reduced radiation exposure in the general population but has not been well studied in patients with CHD. This study evaluated the radiation sparing benefit of using three-dimensional mapping in patients with CHD., Methods: Data were retrospectively collected from the Catheter Ablation with Reduction or Elimination of Fluoroscopy multi-institutional registry. Patients with CHD were selected. Those with previous ablations, concurrent diagnostic or interventional catheterisation and unknown arrhythmogenic foci were excluded. The control cohort was matched for operating physician, arrhythmia mechanism, arrhythmia location, weight and age. The procedure time, rate of fluoroscopy use, fluoroscopy time, procedural success, complications, and distribution of procedures per year were compared between the two groups., Results: Fifty-six patients with congenital heart disease and 56 matched patients without CHD were included. The mean total procedure time was significantly higher in patients with CHD (212.6 versus 169.5 minutes, p = 0.003). Their median total fluoroscopy time was 4.4 minutes (compared to 1.8 minutes), and their rate of fluoroscopy use was 23% (compared to 13%). The acute success and minor complication rates were similar and no major complications occurred., Conclusions: With the use of electroanatomic mapping during catheter ablation, fluoroscopy use can be reduced in patients with CHD. The majority of patients with CHD received zero fluoroscopy.

Background: Data on atrial fibrillation (AF) ablation and outcomes are limited in patients with congenital heart disease (CHD). We aimed to investigate the characteristics of patients with CHD presenting for AF ablation and their outcomes., Methods: A multicenter, retrospective analysis was performed of patients with CHD undergoing AF ablation between 2004 and 2020 at 13 participating centers. The severity of CHD was classified using 2014 Pediatric and Congenital Electrophysiology Society/Heart Rhythm Society guidelines. Clinical data were collected. One-year complete procedural success was defined as freedom from atrial tachycardia or AF in the absence of antiarrhythmic drugs or including previously failed antiarrhythmic drugs (partial success)., Results: Of 240 patients, 127 (53.4%) had persistent AF, 62.5% were male, and mean age was 55.2±13.3 years. CHD complexity categories included 147 (61.3%) simple, 68 (28.3%) intermediate, and 25 (10.4%) severe. The most common CHD type was atrial septal defect (n=78). More complex CHD conditions included transposition of the great arteries (n=14), anomalous pulmonary veins (n=13), tetralogy of Fallot (n=8), cor triatriatum (n=7), single ventricle physiology (n=2), among others. The majority (71.3%) of patients had trialed at least one antiarrhythmic drug. Forty-six patients (22.1%) had reduced systemic ventricular ejection fraction <50%, and mean left atrial diameter was 44.1±8.2 mm. Pulmonary vein isolation was performed in 227 patients (94.6%); additional ablation included left atrial linear ablations (40%), complex fractionated atrial electrogram (19.2%), and cavotricuspid isthmus ablation (40.8%). One-year complete and partial success rates were 45.0% and 20.5%, respectively, with no significant difference in the rate of complete success between complexity groups. Overall, 38 patients (15.8%) required more than one ablation procedure. There were 3 (1.3%) major and 13 (5.4%) minor procedural complications., Conclusions: AF ablation in CHD was safe and resulted in AF control in a majority of patients, regardless of complexity. Future work should address the most appropriate ablation targets in this challenging population.

As a result of remarkable progress in operative techniques and cardiology care during childhood, Fontan patients continue to age and require team-based multidisciplinary expertise to manage complications encountered in adulthood. They face particular challenges in terms of altered hemodynamic stressors, cardiac and hepatic failure, and arrhythmias. Arrhythmias in Fontan patients are highly prevalent and associated with underlying anatomy, surgical technique, and postoperative sequelae. Diagnostic tools, treatments, and device strategies for arrhythmias in Fontan patients should be adapted to the specific anatomy, type of surgical repair, and clinical status. Great strides in our understanding of arrhythmia mechanisms, options and techniques to obtain access to relevant cardiac structures, and application of both old and new technologies have contributed to improving cardiac implantable electronic device (CIED) therapies for this unique population. In this state-of-the-art review, we discuss the various arrhythmias encountered in Fontan patients, their diagnosis, and options for treatment and prevention, with a focus on CIEDs. Throughout, access challenges particular to the Fontan circulation are considered. Recently developed technologies, such as the subcutaneous implantable cardioverter defibrillator, carry the potential to be transformative but require awareness of Fontan-specific issues. Moreover, new leadless pacing technology represents a promising strategy that may soon become applicable to Fontan patients with sinus-node dysfunction. CIEDs are essential tools in managing Fontan patients, but the complex clinical scenarios that arise in this patient population are among the most challenging for the electrophysiologist treating patients with congenital heart disease., (Copyright © 2022 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Objectives: This study sought to describe the electrophysiologic properties and catheter ablation outcomes for atrioventricular reciprocating tacchycardia via twin atrioventricular nodes (T-AVRT)., Background: Although catheter ablation for T-AVRT is an established entity, there are few data on the electrophysiological properties and outcomes of this procedure., Methods: An international, multicenter study was conducted to collect retrospective procedural and outcomes data for catheter ablation of T-AVRT., Results: Fifty-nine patients with T-AVRT were identified (median age at procedure, 8 years [interquartile range: 4.4-17.0 years]; 49% male). Of these, 55 (93%) were diagnosed with heterotaxy syndrome (right atrial isomerism in 39, left atrial isomerism in 8, and indeterminate in 8). Twenty-three (39%) had undergone Fontan operation (12 extracardiac, 11 lateral tunnel). After the Fontan operation, atrial access was conduit or baffle puncture in 15 (65%), fenestration in 5 (22%), and retrograde in 3 (13%). Acute success was achieved in 43 (91%) of 47 attempts (targeting an anterior node in 23 and posterior node in 24). There was no high-grade AV block or change in QRS duration. Over a median of 3.8 years, there were 3 recurrences. Of 7 patients with failed index procedure or recurrent T-AVRT, 6 (86%) were associated with anatomical hurdles such as prior Fontan or catheter course through an interrupted inferior vena cava-to-azygous vein continuation (P = 0.11)., Conclusions: T-AVRT can be targeted successfully with low risk for recurrence. Complications were rare in this population. Anatomical challenges were common among patients with reduced short and long-term efficacy, representing opportunities for improvement in procedural timing and planning., Competing Interests: Funding Support and Author Disclosures The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Published by Elsevier Inc.)

Background: Catheter ablation outcomes for adults with congenital heart disease (ACHD) are described, but recurrence mechanisms remain largely unknown., Objective: The purpose of this study was to identify the electrophysiological characteristics of atrial tachycardia (AT) recurrence in ACHD., Methods: ACHD atrial tachycardia procedures over a 10-year period were explored for AT or atrial fibrillation (AF) recurrence., Results: At 299 procedures in 250 ACHD (mean age 39 ± 15 years; 130 [52%] male), 464 ATs (360 intra-atrial reentrant tachycardia, 104 focal AT; median 2 [IQR 1-3] ATs per procedure) were targeted. Complete (n = 256 [86%]) or partial (n = 37 [12%]) success was achieved in 98% of procedures. Over a median of 3.0 (IQR 1.4-5.3) years of follow-up, 67 patients (27%) developed AT/AF recurrence after the index procedure. Repeat vs index tachycardias were more often focal AT (26/69 [38%] vs 73/378 [19%]; P < .001), demonstrated longer cycle length (325 ms vs 280 ms; P = .003), required isoproterenol (34/69 [50%] vs 121/378 [32%]; P = .03), and involved the pulmonary venous atrium (PVA)/septum (26/69 [38%] vs 67/378 [18%]; P < .001). AF history (hazard ratio [HR] 2.0; interquartile range [IQR] 1.2-3.4; P = .01), incomplete success (HR 3.6; IQR 2.1-6.4; P < .001), and PVA substrate (HR 2.1; IQR 1.2-3.5; P = .006) were independently associated with AT/AF recurrence. With complete index procedure success and no AF history, 5-year actuarial freedom from AT/AF and AT alone were 77% and 80%., Conclusion: After catheter ablation in ACHD, repeat ATs were more frequently focal, required isoproterenol administration, or involved intra-atrial reentrant tachycardia within the PVA or atrial septum. Negative factors were partial success, index PVA substrate, and remote history of AF. These data support aggressive pharmacological provocation to eliminate all inducible tachycardias and coexisting PVA substrates at index procedures for ACHD., (Published by Elsevier Inc.)

Background: Biatrial tachycardia (BiAT) is a rare form of macroreentry not previously characterized in adults with congenital heart disease (ACHD)., Objective: The purpose of this study was to determine the prevalence, mechanisms, and outcomes of catheter ablation for BiAT in ACHD., Methods: All ACHD undergoing catheter ablation for macroreentrant atrial tachycardia over a 10-year period were evaluated for evidence of BiAT. Patients were categorized as prior Senning, Fontan, or other biventricular operation. A novel biatrial global activation histogram (GAH) analysis was used to demonstrate the presence of interatrial connections (IACs)., Results: Among 263 ACHD, BiAT was identified at 11 procedures in 10 patients (4.2%; median age 35 years; 30% male). The congenital category was Fontan in 6, Senning in 3, and biventricular in 2. Diagnosis of BiAT was associated with ablation era and mapping technology (P <.001) and could be confirmed with a novel GAH mapping approach for normally septated atrial connections. Catheter ablation targeted an IAC in 5 cases (Bjork Fontan and biventricular operations), a posterior isthmus in 3 (Senning operation), and the cavotricuspid isthmus or equivalent in 3 (lateral tunnel [LT] Fontan). Recurrence was isolated to ablation to sites at the expected location of the Bachmann bundle, and durable success could be achieved after repeat ablation., Conclusion: BiAT occurs in approximately 4% of ACHD but is likely underrecognized. BiAT could be targeted at an IAC for normally septated atria and at a conventional critical isthmus after Senning and LT Fontan operations., (Published by Elsevier Inc.)

Background Ultra-high-density mapping enables detailed mechanistic analysis of atrial reentrant tachycardia but has yet to be used to assess circuit conduction velocity (CV) patterns in adults with congenital heart disease. Methods and Results Circuit pathways and central isthmus CVs were calculated from consecutive ultra-high-density isochronal maps at 2 tertiary centers over a 3-year period. Circuits using anatomic versus surgical obstacles were considered separately and pathway length <50th percentile identified small circuits. CV analysis was used to derive a novel index for prediction of postablation conduction block. A total of 136 supraventricular tachycardias were studied (60% intra-atrial reentrant, 14% multiple loop). Circuits with anatomic versus surgical obstacles featured longer pathway length (119 mm; interquartile range [IQR], 80-150 versus 78 mm; IQR, 63-95; P <0.001), faster central isthmus CV (0.1 m/s; IQR, 0.06-0.25 versus 0.07 m/s; IQR, 0.05-0.10; P =0.016), faster non-isthmus CV (0.52 m/s; IQR, 0.33-0.71 versus 0.38 m/s; IQR, 0.27-0.46; P =0.009), and fewer slow isochrones (4; IQR, 2.3-6.8 versus 6; IQR 5-7; P =0.008). Both central isthmus ( R 2 =0.45; P <0.001) and non-isthmus CV ( R 2 =0.71; P <0.001) correlated with pathway length, whereas central isthmus CV <0.15 m/s was ubiquitous for small circuits. Non-isthmus CV in tachycardia correlated with CV during block validation ( R 2 =0.94; P <0.001) and a validation map to tachycardia conduction time ratio >85% predicted isthmus block in all cases. Over >1 year of follow-up, arrhythmia-free survival was better for homogeneous CV patterns (90% versus 57%; P =0.04). Conclusions Ultra-high-density mapping-guided CV analysis distinguishes atrial reentrant patterns in adults with congenital heart disease with surgical obstacles producing slower and smaller circuits. Very slow central isthmus CV may be essential for atrial tachycardia maintenance in small circuits, and non-isthmus conduction time in tachycardia appears to be useful for rapid assessment of postablation conduction block.

Background: Total cavopulmonary connection (TCPC) is associated with a lower risk of incident atrial arrhythmias as compared to atriopulmonary Fontan, but the risk of recurrent atrial arrhythmias is unknown in this population. The purpose of this study was to determine the incidence and risk factors for recurrent atrial arrhythmias and thromboembolic complications in patients with TCPC., Methods: This is a retrospective multicenter study conducted by the Alliance for Adult Research in Congenital Cardiology (AARCC), 2000-2018. The inclusion criteria were TCPC patients (age > 15 years) with prior history of atrial arrhythmia., Results: A total of 103 patients (age 26 ± 7 years; male 58 [56%]) met inclusion criteria. The mean age at initial arrhythmia diagnosis was 13 ± 5 years, and atrial arrhythmias were classified as atrial flutter/tachycardia in 85 (83%) and atrial fibrillation in 18 (17%). The median duration of follow-up from the first episode of atrial arrhythmia was 14.9 (12.1-17.3) years, and during this period 64 (62%) patients had recurrent atrial arrhythmias (atrial flutter/tachycardia 51 [80%] and atrial fibrillation 13 [20%]) with annual incidence of 4.4%. Older age was a risk factor for arrhythmia recurrence while the use of a class III anti-arrhythmic drug was associated with a lower risk of recurrent arrhythmias. The incidence of thromboembolic complication was 0.6% per year, and the cumulative incidence was 4% and 7% at 5 and 10 years respectively from the time of first atrial arrhythmia diagnosis. There were no identifiable risk factors for thromboembolic complications in this cohort., Conclusions: Although TCPC provides superior flow dynamics and lower risk of incident atrial arrhythmias, there is a significant risk of recurrent arrhythmias among TCPC patients with a prior history of atrial arrhythmias. These patients may require more intensive arrhythmia surveillance as compared to other TCPC patients., (© 2021 The Author(s).)

Objectives: The primary goal of this study was to evaluate the implant experience and midterm results of subcutaneous implantable cardioverter-defibrillators (S-ICDs) in pediatric patients and those with congenital heart disease., Background: The S-ICD was developed to avoid the lead-related complications associated with transvenous systems. The absence of intravascular or intracardiac components offers potential advantages to pediatric patients and those with congenital heart disease., Methods: This international, multicenter, retrospective, standard-of-care study was conducted through the Pediatric & Congenital Electrophysiology Society. Complications at 30 and 360 days, inappropriate shocks, and delivery of appropriate therapy were assessed., Results: The study included 115 patients with a median follow-up of 32 (19 to 52) months. Median age was 16.7 years (14.8 to 19.3 years), 29% were female, and 55% had a primary prevention indication. Underlying disease substrate was cardiomyopathy (40%), structural heart disease (32%), idiopathic ventricular fibrillation (16%), and channelopathy (13%). The complication rate was 7.8% at 30 days and 14.7% at 360 days. Overall, inappropriate shocks occurred in 15.6% of patients, with no single clinical characteristic reaching statistical significance. At implant, 97.9% of patients had successful first shock conversion with 96% requiring ≤65 J. Appropriate therapy was delivered to 11.2% of patients with an annual incidence of 3.9% and an acute first shock conversion success rate of 92.5%., Conclusions: This study found that in a heterogeneous population of pediatric patients and those with congenital heart disease, the S-ICD had comparable rates of complications, inappropriate shocks, and conversion efficacy compared with previously published studies on transvenous systems in similar populations., Competing Interests: Author Disclosures The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2020 American College of Cardiology Foundation. All rights reserved.)

Objectives: This study sought to determine the relationship between long QT syndrome (LQTS) subtype (LTQ1, LTQ2, LTQ3) and postnatal cardiac events (CEs)., Background: LQTS presenting with 2:1 atrioventricular block or torsades de pointes in the fetus and/or neonate has been associated with risk for major CEs, but overall outcomes and predictors remain unknown., Methods: A retrospective study involving 25 international centers evaluated the course of fetuses/newborns diagnosed with congenital LQTS and either 2:1 atrioventricular block or torsades de pointes. The primary outcomes were age at first CE after dismissal from the newborn hospitalization and death and/or cardiac transplantation during follow-up. CE was defined as aborted cardiac arrest, appropriate shock from implantable cardioverter-defibrillator, or sudden cardiac death., Results: A total of 84 fetuses and/or neonates were identified with LQTS (12 as LQT1, 35 as LQT2, 37 as LQT3). Median gestational age at delivery was 37 weeks (interquartile range: 35 to 39 weeks) and age at hospital discharge was 3 weeks (interquartile range: 2 to 5 weeks). Fetal demise occurred in 2 and pre-discharge death in 1. Over a median of 5.2 years, there were 1 LQT1, 3 LQT2, and 23 LQT3 CEs (13 aborted cardiac arrests, 5 sudden cardiac deaths, and 9 appropriate shocks). One patient with LQT1 and 11 patients with LQT3 died or received cardiac transplant during follow-up. The only multivariate predictor of post-discharge CEs was LQT3 status (LQT3 vs. LQT2: hazard ratio: 8.4; 95% confidence interval: 2.6 to 38.9; p < 0.001), and LQT3, relative to LQT2, genotype predicted death and/or cardiac transplant (p < 0.001)., Conclusions: In this large multicenter study, fetuses and/or neonates with LQT3 but not those with LQT1 or LQT2 presenting with severe arrhythmias were at high risk of not only frequent, but lethal CEs., Competing Interests: Author Relationship With Industry Dr. Strasburger has received support from the National Institutes of Health grant RO1HL143485. Dr. Wakai has received support from the National Institutes of Health grant RO1HL063174. Dr. Miyake has received support from the National Heart, Lung, and Blood Institute grant K23HL136932 and American Heart Association grant 17SDG33410183. Dr. Schwartz has received support from the National Institutes of Health grant HL083374 and Italian Ministry of Health grant (Sindrome della morte improvvisa del lattante: meccanismi e prevenzione). All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Published by Elsevier Inc.)

Background: Although they are at lower risk, patients with previous extracardiac conduit (EC) Fontan still may require catheter ablation for supraventricular arrhythmia., Objective: The purpose of this study was to determine the optimal approach to pulmonary venous atrium (PVA) access after EC Fontan operation., Methods: All electrophysiological procedures requiring PVA over a 10-year period at the UCLA Medical Center were reviewed. PVA was grouped by transcaval cardiac puncture (TCP) or direct conduit puncture. Procedural characteristics and outcomes were compared., Results: Between June 2009 and November 2019, 23 electrophysiological procedures requiring PVA access were performed in 17 EC Fontan patients (53% male; median age 25 years; interquartile range 11-34). Cavoatrial overlap was identified in 14 patients by preprocedural imaging (10 cardiac computed tomography, 4 cardiac magnetic resonance). PVA access was obtained via TCP in 11, direct conduit puncture in 6, pre-existing fenestration in 5, and pulmonary artery puncture in 1. Time to PVA was significantly shorter for TCP vs direct conduit puncture (0.2 vs 1.1 hours, respectively; P = .03). The only predictor of successful TCP was the length of cavoatrial overlap by preprocedural imaging (14 vs 3 mm; P = .02). No procedural complications occurred. No change in oxygen saturation was noted, and no evidence of residual shunting was detected by follow-up echocardiography., Conclusion: TCP is feasible in most patients after EC Fontan surgery and can be predicted by preprocedural advanced imaging. TCP is associated with shorter time to PVA and was uncomplicated in this single-center study. Preoperative assessment of cavoatrial overlap should be considered before catheter ablation for EC Fontan., (Published by Elsevier Inc.)

Background: Abrupt loss of ventricular preexcitation on noninvasive evaluation, or nonpersistent preexcitation, in Wolff-Parkinson-White syndrome (WPW) is thought to indicate a low risk of life-threatening events., Objective: The purpose of this study was to compare accessory pathway (AP) characteristics and occurrences of sudden cardiac arrest (SCA) and rapidly conducted preexcited atrial fibrillation (RC-AF) in patients with nonpersistent and persistent preexcitation., Methods: Patients 21 years or younger with WPW and invasive electrophysiology study (EPS) data, SCA, or RC-AF were identified from multicenter databases. Nonpersistent preexcitation was defined as absence/sudden loss of preexcitation on electrocardiogram, Holter monitoring, or exercise stress test. RC-AF was defined as clinical preexcited atrial fibrillation with shortest preexcited R-R interval (SPERRI) ≤ 250 ms. AP effective refractory period (APERP), SPERRI at EPS , and shortest preexcited paced cycle length (SPPCL) were collected. High-risk APs were defined as APERP, SPERRI, or SPPCL ≤ 250 ms., Results: Of 1589 patients, 244 (15%) had nonpersistent preexcitation and 1345 (85%) had persistent preexcitation. There were no differences in sex (58% vs 60% male; P=.49) or age (13.3±3.6 years vs 13.1±3.9 years; P=.43) between groups. Although APERP (344±76 ms vs 312±61 ms; P<.001) and SPPCL (394±123 ms vs 317±82 ms; P<.001) were longer in nonpersistent vs persistent preexcitation, there was no difference in SPERRI at EPS (331±71 ms vs 316±73 ms; P=.15). Nonpersistent preexcitation was associated with fewer high-risk APs (13% vs 23%; P<.001) than persistent preexcitation. Of 61 patients with SCA or RC-AF, 6 (10%) had nonpersistent preexcitation (3 SCA, 3 RC-AF)., Conclusion: Nonpersistent preexcitation was associated with fewer high-risk APs, though it did not exclude the risk of SCA or RC-AF in children with WPW., (Copyright © 2020 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Arrhythmia management in adult congenital heart disease (ACHD) encompasses a wide range of problems from bradyarrhythmia to tachyarrhythmia, sudden death, and heart failure-related electrical dyssynchrony. Major advances in the understanding of the pathophysiology and treatments of these problems over the past decade have resulted in improved therapeutic strategies and outcomes. This article attempts to define these problems and review contemporary management for the patient with ACHD presenting with cardiac arrhythmia., Competing Interests: Disclosure The author has nothing to disclose., (Published by Elsevier Inc.)

Background Patients with Eisenmenger syndrome are known to have a high incidence of sudden cardiac death (SCD), yet the underlying causes are not well understood. We sought to define the predictors of SCD in this population. Methods and Results A retrospective analysis of all patients with Eisenmenger syndrome from 2 large tertiary referral centers was performed. ECGs, prolonged ambulatory recordings, echocardiograms, and clinical histories were reviewed; and the cause of death was identified. A total of 246 patients (85 [34.6%] men) with a mean age of 37.3 (±14.2) years were followed up for a median of 7 years. Over the study period, 136 patients died, with 40 experiencing SCD and 74 experiencing cardiac death (sudden and nonsudden). Age, atrial fibrillation, prolonged QRS duration, complete heart block, right atrial enlargement, right bundle branch block, increased right atrial pressure, impaired biventricular function, and the presence of a pacemaker were associated with increased risk of SCD, whereas advanced pulmonary hypertension therapies were protective. Atrial fibrillation (11.45-fold increased risk; P <0.001) and QRS duration ≥120 ms (2.06-fold increased risk; P =0.034) remained significant predictors of SCD in the multivariate analysis, whereas advanced pulmonary hypertension therapies were strongly protective against SCD ( P <0.001). Conclusions Atrial arrhythmias, impaired ventricular function, and conduction system disease were associated with increased risk of SCD in this cohort of patients with Eisenmenger syndrome, providing an opportunity for early risk stratification and potential intervention. Clinical heart failure symptoms (New York Heart Association class ≥II) were predictive of increased mortality but not of SCD, suggesting a potential arrhythmic cause behind SCD.

Background: Congenitally corrected transposition of the great arteries (CCTGA) is associated with spontaneous atrioventricular block and pacing-induced cardiomyopathy. Conduction system pacing is a potential alternative to conventional cardiac resynchronization therapy (CRT)., Objective: The purpose of this study was to determine the outcomes of conduction system pacing for CCTGA., Methods: Retrospective data were collected from 10 international centers., Results: His bundle (HBP) or left bundle branch pacing (LBBP) was attempted in 15 CCTGA patients (median age 23 years; 87% male). Previous surgery had been performed in 8 and chronic ventricular pacing in 7. Conduction system pacing (11 HBP, 2 LBBP 2; nonselective in 10, selective in 3) was acutely successful in 13 (86%) without complication. In 9 cases, electroanatomic mapping was available and identified the distal His bundle and proximal left bundle branches within the morphologic left ventricle below the pulmonary valve separate from the mitral annulus. Median implant HV interval was 42 ms (interquartile range [IQR] 35-48), R wave 6 mV (IQR 5-18), and threshold 0.5 V (IQR 0.5-1.2) at median 0.5 ms. QRSd was unchanged compared to junctional escape rhythm (124 vs 110 ms; P = .17) and decreased significantly compared to baseline ventricular pacing (112 vs 164 ms; P <.01). At a median of 8 months, all patients were alive without significant change in pacing threshold or lead dysfunction. New York Heart Association functional class improved in 5 patients., Conclusion: Permanent conduction system pacing is feasible in CCTGA by either HBP or proximal LBBP. Narrow paced QRS and stable lead thresholds were observed at intermediate follow-up. Unique anatomic characteristics may favor this approach over conventional CRT., (Published by Elsevier Inc.)

Background: Tricuspid valve (TV) surgery is often required for adult congenital heart disease (ACHD), but may hinder catheter ablation when an artificial material or imbricated tissue covers the tricuspid annulus., Objective: The purpose of this study was to determine the outcomes of catheter ablation after TV surgery in a large ACHD cohort., Methods: An international retrospective study involving 7 centers was conducted. Patients who did and did not undergo TV surgery were matched for age, lesion classification, and postsurgical duration. TV operations were classified as valve ring/replacement vs repair., Results: One hundred thirty-six patients (42 ring/replacement, 39 repair, and 55 no TV surgery; median 32 years [IQR 20 - 46]) underwent 180 procedures targeting 239 tachycardias (cavotricuspid-isthmus dependent intraatrial reentrant tachycardia 36%, other intraatrial reentrant tachycardia 29%, focal atrial tachycardia 18%, and other supraventricular tachyarrhythmia 17%). Post-TV surgery, procedures were longer (4.3 hours vs 3.3 hours; P = .003) and required longer fluoroscopy time (31 minutes vs 18 minutes; P = .001). At least partial acute success was achieved in 81% of procedures in the TV ring/replacement group vs 94% in both TV repair and no TV surgery groups (P = .03). The difference was driven mainly by ablation of annular substrates, with acute success in 73% of TV ring/replacement, 92% of TV repair, and 94% of no TV surgery groups (P = .01). Over a median of 3.0 years, tachycardia recurred after 26% of procedures. TV ring/replacement predicted recurrence in the multivariable analysis (hazard ratio 2.4; 95% confidence interval 1.2-5.2; P = .009)., Conclusion: After surgery for ACHD, catheter ablation success was lower and tachycardia recurrence was higher after TV valve ring/replacement surgery. The findings of this retrospective report support future larger multicenter series and prospective evaluation to determine the role of empirical annular substrate ablation., (Published by Elsevier Inc.)

Background: Predictors of risk of lethal arrhythmic events (LAE) is poorly understood and may differ from adults in children with hypertrophic cardiomyopathy (HCM)., Objective: The purpose of this study was to determine predictors of LAE in children with HCM., Methods: A retrospective data collection was performed on 446 children and teenagers 20 years and younger (290 [65%] male; mean age 10.1 ± 5.7 years) with idiopathic HCM from 35 centers. Patients were classified as group 1 (HCM with LAE) if having a secondary prevention implantable cardioverter-defibrillator (ICD) or primary prevention ICD with appropriate interventions or group 2 (HCM without LAE) if having a primary prevention ICD without appropriate interventions., Results: There were 152 children (34%) in group 1 and 294 (66%) in group 2. Risk factors for group 1 by univariate analysis were septal thickness, posterior left ventricular (LV) wall thickness, lower LV outflow gradient, and Q wave > 3 mm in inferior electrocardiographic leads. Factors not associated with LAE were family history of SCD, abnormal blood pressure response to exercise, and ventricular tachycardia on ambulatory electrocardiographic monitoring. Risk factors for SCD by multivariate analysis were age at ICD placement (hazard ratio [HR] 0.9; P = .0025), LV posterior wall thickness z score (HR 1.02; P < .005), and LV outflow gradient < 30 mm Hg (HR 2.0; P < .006). LV posterior wall thickness z score ≥ 5 was associated with LAE., Conclusion: Risk factors for LAE appear different in children compared to adults. Conventional adult risk factors were not significant in children. Further prospective studies are needed to improve risk stratification for LAE in children with HCM., (Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: An increasing number of adults with congenital heart disease (CHD) are undergoing catheter ablation for atrial fibrillation (AF). Data on ablation strategy and outcomes in CHD are limited. Rhythm control is often believed to be of greater importance among patients with complex CHD., Objective: The purpose of this study was to examine the safety and efficacy of AF ablation in adult patients with CHD., Methods: A multicenter retrospective analysis was performed of CHD patients undergoing AF ablation. Clinical data were collected, including AF and CHD type, procedural data, and outcomes. Patients were divided into 3 groups (simple, moderate, and severe) based on CHD complexity, as defined by the 2014 PACES/HRS (Pediatric and Congenital Electrophysiology Society/Heart Rhythm Society) consensus statement. One-year procedural success was defined as freedom from recurrent AF, off antiarrhythmic drugs (complete) or off/on previously failed antiarrhythmic drugs (partial)., Results: Overall, 84 CHD patients (mean age 51.5 ± 12.1 years; 65.5% male; 45.2% with paroxysmal AF) undergoing AF ablation (51 simple, 22 moderate, 11 severe complexity) were included. Pulmonary vein isolation was performed in 80 (95.2%), of whom 30 (35.7%) underwent pulmonary vein isolation alone. Overall, complete and complete/partial freedom was achieved at 1 year in 53.1% and 71.6%, respectively, with no significant differences between those with simple, moderate, or severe complexity. There were no major complications and 7 minor complications, and 2 patients died during follow-up., Conclusion: There are dramatic differences in the degree of CHD complexity among patients referred for AF ablation. When performed at experienced centers, AF ablation is safe and effective even among patients with the most complex forms of CHD., (Copyright © 2018 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Objectives: The purpose of this study was to determine the ventricular arrhythmia (VA) substrates in patients with unoperated and post-surgical Ebstein's Anomaly (EA)., Background: EA is associated with variable atrialization of the right ventricle and a propensity for VA and sudden death. There are scant data on catheter ablation for VA in this population., Methods: This was a retrospective study involving 11 congenital heart disease centers., Results: A total of 24 patients (median age 17 [interquartile range (IQR): 11 to 37] years; age range 1 to 68 years; 42% men) with EA undergoing catheter ablation were identified. Prior tricuspid valve (TV) surgery had been performed in 12 (50%). Presenting symptoms were palpitations in 15, syncope in 4, aborted cardiac arrest in 4, and none in 1. At procedure, 28 VA substrates were encountered and 25 were completely characterized (median 1 per patient; cycle length 305 [IQR: 268 to 400] ms). In 3 cases, premature ventricular contraction (PVC) foci were targeted (1 with a history of PVC-induced ventricular fibrillation). VA mechanisms were focal in 15 and macro-re-entrant in 10, and did not differ significantly between those with and those without prior TV surgery (p = 0.7). Focal VAs predominantly localized to the atrialized right ventricle ARV in unoperated patients and to diseased myocardium or Purkinje tissue after TV surgery. Macro-re-entry was related to isolated scar or split potentials in the ARV in unoperated patients, and larger, more diffuse scar after TV surgery. Complete success was achieved in 22 (92%). There were 2 of 13 complications in patients <18 years of age and none in patients >18 years of age. There was a single recurrence over a median follow-up of 3.4 years., Conclusions: VA in EA may be either focal or macro-re-entrant. In the absence of surgery, substrates chiefly involve the ARV. After surgery, focal VA involves injured myocardium or Purkinje tissue and re-entrant ventricular tachycardia is related to post-surgical scar. Catheter ablation is a reasonable therapeutic approach for these patients., (Copyright © 2018 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Objectives: This study sought to characterize risk in children with Wolff-Parkinson-White (WPW) syndrome by comparing those who had experienced a life-threatening event (LTE) with a control population., Background: Children with WPW syndrome are at risk of sudden death., Methods: This retrospective multicenter pediatric study identified 912 subjects ≤21 years of age with WPW syndrome, using electrophysiology (EPS) studies. Case subjects had a history of LTE: sudden death, aborted sudden death, or atrial fibrillation (shortest pre-excited RR interval in atrial fibrillation [SPERRI] of ≤250 ms or with hemodynamic compromise); whereas subjects did not. We compared clinical and EPS data between cases and subjects., Results: Case subjects (n = 96) were older and less likely than subjects (n = 816) to have symptoms or documented tachycardia. Mean age at LTE was 14.1 ± 3.9 years of age. The LTE was the sentinel symptom in 65%, consisting of rapidly conducted pre-excited atrial fibrillation (49%), aborted sudden death (45%), and sudden death (6%). Three risk components were considered at EPS: SPERRI, accessory pathway effective refractory period (APERP), and shortest paced cycle length with pre-excitation during atrial pacing (SPPCL), and all were shorter in cases than in control subjects. In multivariate analysis, risk factors for LTE included male sex, Ebstein malformation, rapid anterograde conduction (APERP, SPERRI, or SPPCL ≤250 ms), multiple pathways, and inducible atrial fibrillation. Of case subjects, 60 of 86 (69%) had ≥2 EPS risk stratification components performed; 22 of 60 (37%) did not have EPS-determined high-risk characteristics, and 15 of 60 (25%) had neither concerning pathway characteristics nor inducible atrioventricular reciprocating tachycardia., Conclusions: Young patients may experience LTE from WPW syndrome without prior symptoms or markers of high-risk on EPS., (Copyright © 2018 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

The position and course of the conduction system in congenital heart disease are intricately tied to the underlying congenital malformation. Although only subtle differences exist between the anatomy of the conduction axis for simple congenital heart lesions and normal anatomy, almost every patient with congenital heart disease harbors some important anatomic variation. This article summarizes the body of literature by retaining original classical concepts and by attempting to translate the available knowledge into useful points for the congenital heart disease specialist. This discussion spans the entire spectrum of simple to complex congenital heart disease., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Tachycardia-induced cardiomyopathy (TIC) is a treatable cause of heart failure in children, but there is little information as to which clinical variables best discriminate TIC from other forms of cardiomyopathy. TIC cases with dilated cardiomyopathy (DC) from 16 participating centers were identified and compared with controls with other forms of DC. Presenting clinical, echocardiographic, and electrocardiographic characteristics were collected. Heart rate (HR) percentile was defined as HR/median HR for age, and PR index as the PR/RR interval. P-wave morphology (PWM) was defined as possible sinus or nonsinus based on a predefined algorithm. Eighty TIC cases and 135 controls were identified. Cases demonstrated lower LV end-diastolic diameter and LV end-systolic diameter than DC controls (4.3 vs 6.5, p <0.001; 7.4 vs 10.9, p <0.001) and were less likely to receive inotropic medication at presentation (p <0.001 for both). Multivariable logistic regression identified HR percentile (OR 2.1 per 10% increase, CI 1.3 to 4.6; p = 0.014), PR index (OR 1.2, CI 1.1 to 1.4; p = 0.004), and nonsinus PWM (OR 104.9, CI 15.2 to 1,659.8; p <0.001) as predictive of TIC status. A risk score using HR percentile >130%, PR index >30%, and nonsinus PWM was associated with a sensitivity of 100% and specificity of 87% for the diagnosis of TIC. Model training and validation area under the curves were similar at 0.97 and 0.94, respectively. In conclusion, pediatric TIC may be accurately discriminated from other forms of DC using simple electrocardiographic parameters. This may allow for rapid diagnosis and early treatment of this condition., (Published by Elsevier Inc.)