Variations in cardiac implantable electronic device surveillance and ancillary testing in the paediatric and congenital heart disease population: an international multi-centre survey from the Paediatric and Congenital Electrophysiology Society.

BACKGROUND: Expert guidance from scientific societies and regulatory agencies recommend a framework of principles for frequency of in-person evaluations and remote monitoring for patients with cardiac implantable electronic devices. However, there are limited data regarding adherence to recommendations among paediatric electrophysiologists, and there are no data regarding cardiac implantable electronic device-related ancillary testing. METHODS: To assess current clinical practices for cardiac implantable electronic device in-person evaluation, remote monitoring, and cardiac implantable electronic device-related ancillary testing, the Paediatric and Congenital Electrophysiology Society members were surveyed. The main outcome measures were variations in frequency of in person evaluation, frequency of remote monitoring, and cardiac implantable electronic device-related ancillary testing. RESULTS: All respondents performed in-person evaluation at least once a year, but <50% of respondents performed an in-person evaluation within 2 weeks of cardiac implantable electronic device implantation. Remote monitoring was performed every 3 months for pacemakers and implantable cardioverter defibrillators by 71 and 75% respondents, respectively. Follow-up echocardiography was performed every 2-3 years by 53% respondents for patients with >50% ventricular pacing. Majority of respondents (75%) did not perform either an exercise stress test or ambulatory Holter monitoring or chest X-ray (65%) after cardiac implantable electronic device implantation. CONCLUSION: This survey identified significant practice variations in cardiac implantable electronic device in- person evaluation, remote monitoring, and ancillary testing practices among paediatric electrophysiologists. Cardiac implantable electronic device management may be optimised by development of a paediatric-specific guidelines for follow-up and ancillary testing.

Calmodulin mutations and life-threatening cardiac arrhythmias: insights from the International Calmodulinopathy Registry.

AIMS: Calmodulinopathies are rare life-threatening arrhythmia syndromes which affect mostly young individuals and are, caused by mutations in any of the three genes (CALM 1-3) that encode identical calmodulin proteins. We established the International Calmodulinopathy Registry (ICalmR) to understand the natural history, clinical features, and response to therapy of patients with a CALM-mediated arrhythmia syndrome. METHODS AND RESULTS: A dedicated Case Report File was created to collect demographic, clinical, and genetic information. ICalmR has enrolled 74 subjects, with a variant in the CALM1 (n = 36), CALM2 (n = 23), or CALM3 (n = 15) genes. Sixty-four (86.5%) were symptomatic and the 10-year cumulative mortality was 27%. The two prevalent phenotypes are long QT syndrome (LQTS; CALM-LQTS, n = 36, 49%) and catecholaminergic polymorphic ventricular tachycardia (CPVT; CALM-CPVT, n = 21, 28%). CALM-LQTS patients have extremely prolonged QTc intervals (594 ± 73 ms), high prevalence (78%) of life-threatening arrhythmias with median age at onset of 1.5 years [interquartile range (IQR) 0.1-5.5 years] and poor response to therapies. Most electrocardiograms (ECGs) show late onset peaked T waves. All CALM-CPVT patients were symptomatic with median age of onset of 6.0 years (IQR 3.0-8.5 years). Basal ECG frequently shows prominent U waves. Other CALM-related phenotypes are idiopathic ventricular fibrillation (IVF, n = 7), sudden unexplained death (SUD, n = 4), overlapping features of CPVT/LQTS (n = 3), and predominant neurological phenotype (n = 1). Cardiac structural abnormalities and neurological features were present in 18 and 13 patients, respectively. CONCLUSION: Calmodulinopathies are largely characterized by adrenergically-induced life-threatening arrhythmias. Available therapies are disquietingly insufficient, especially in CALM-LQTS. Combination therapy with drugs, sympathectomy, and devices should be considered.

A Precision Medicine Approach to the Rescue of Function on Malignant Calmodulinopathic Long-QT Syndrome.

RATIONALE: Calmodulinopathies comprise a new category of potentially life-threatening genetic arrhythmia syndromes capable of producing severe long-QT syndrome (LQTS) with mutations involving CALM1, CALM2, or CALM3. The underlying basis of this form of LQTS is a disruption of Ca2+/calmodulin (CaM)-dependent inactivation of L-type Ca2+ channels. OBJECTIVE: To gain insight into the mechanistic underpinnings of calmodulinopathies and devise new therapeutic strategies for the treatment of this form of LQTS. METHODS AND RESULTS: We generated and characterized the functional properties of induced pluripotent stem cell-derived cardiomyocytes from a patient with D130G-CALM2-mediated LQTS, thus creating a platform with which to devise and test novel therapeutic strategies. The patient-derived induced pluripotent stem cell-derived cardiomyocytes display (1) significantly prolonged action potentials, (2) disrupted Ca2+ cycling properties, and (3) diminished Ca2+/CaM-dependent inactivation of L-type Ca2+ channels. Next, taking advantage of the fact that calmodulinopathy patients harbor a mutation in only 1 of 6 redundant CaM-encoding alleles, we devised a strategy using CRISPR interference to selectively suppress the mutant gene while sparing the wild-type counterparts. Indeed, suppression of CALM2 expression produced a functional rescue in induced pluripotent stem cell-derived cardiomyocytes with D130G-CALM2, as shown by the normalization of action potential duration and Ca2+/CaM-dependent inactivation after treatment. Moreover, CRISPR interference can be designed to achieve selective knockdown of any of the 3 CALM genes, making it a generalizable therapeutic strategy for any calmodulinopathy. CONCLUSIONS: Overall, this therapeutic strategy holds great promise for calmodulinopathy patients as it represents a generalizable intervention capable of specifically altering CaM expression and potentially attenuating LQTS-triggered cardiac events, thus initiating a path toward precision medicine.

The clinical and genetic spectrum of catecholaminergic polymorphic ventricular tachycardia: findings from an international multicentre registry.

Aims: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an ion channelopathy characterized by ventricular arrhythmia during exertion or stress. Mutations in RYR2-coded Ryanodine Receptor-2 (RyR2) and CASQ2-coded Calsequestrin-2 (CASQ2) genes underlie CPVT1 and CPVT2, respectively. However, prognostic markers are scarce. We sought to better characterize the phenotypic and genotypic spectrum of CPVT, and utilize molecular modelling to help account for clinical phenotypes. Methods and results: This is a Pediatric and Congenital Electrophysiology Society multicentre, retrospective cohort study of CPVT patients diagnosed at <19 years of age and their first-degree relatives. Genetic testing was undertaken in 194 of 236 subjects (82%) during 3.5 (1.4-5.3) years of follow-up. The majority (60%) had RyR2-associated CPVT1. Variant locations were predicted based on a 3D structural model of RyR2. Specific residues appear to have key structural importance, supported by an association between cardiac arrest and mutations in the intersubunit interface of the N-terminus, and the S4-S5 linker and helices S5 and S6 of the RyR2 C-terminus. In approximately one quarter of symptomatic patients, cardiac events were precipitated by only normal wakeful activities. Conclusion: This large, multicentre study identifies contemporary challenges related to the diagnosis and prognostication of CPVT patients. Structural modelling of RyR2 can improve our understanding severe CPVT phenotypes. Wakeful rest, rather than exertion, often precipitated life-threatening cardiac events.

Utility of preoperative Holter monitoring in children undergoing extracardiac conduit Fontan operation.

BACKGROUND: In patients undergoing extracardiac conduit Fontan (ECF) who require postoperative pacing, epicardial leads are usually required because of anatomical constraints. If indicated, these could be conveniently placed at the time of ECF. We have routinely performed ambulatory 24-hour Holter monitoring before ECF to determine the presence or absence of preoperative sinus node dysfunction, in an attempt to avoid repeat sternotomy at a later time. METHODS: We performed a retrospective study of all patients undergoing ECF from January 2000 to December 2015. RESULTS: Two hundred sixteen patients met inclusion criteria. Patients were separated into two groups, those with preoperative Holter monitoring (PHM, n = 150) and those without (No-PHM, n = 66). Ten patients (4.6%) underwent permanent pacemaker implantation at the time of ECF (eight patients [5.3%] in PHM vs two patients [3.0%] in No-PHM, P = 0.46). There were seven (3.2%) patients who underwent pacemaker implantation after ECF requiring repeat sternotomy (four patients [2.7%] in PHM vs three patients [4.5%] in No-PHM, P = 0.47). Fourteen (6.5%) patients underwent permanent epicardial lead placement without a pulse generator at the time of ECF. None from this group underwent pacemaker implantation to date (median follow-up of 5.7 years). The overall incidence of pacemaker implantation was 9.3% (20 patients). CONCLUSIONS: In our series, arrhythmia disturbances requiring pacing after ECF occurred in just over 9% of patients. While PHM in those patients may help predict which patients might require postoperative pacing, this approach did not result in a significant decrease in those patients requiring repeat sternotomy for pacemaker implantation.

Sudden cardiac arrest in patients following surgery for CHD.

The prevalence of sudden cardiac arrest after surgery for CHD is primarily related to the complexity of the congenital defect and the presence of residual defects, especially ventricular dysfunction. Among all causes of death in patients having CHD, about 19% lead to sudden mortality. The specific risk factors associated with the various congenital defects are poorly understood. The lone exception is tetralogy of Fallot, largely due to its high prevalence and the historically high post-operative survival rate. In tetralogy of Fallot, historical, haemodynamic, and electrical features contribute to risk, and electrophysiologic testing may be helpful, particularly to rule out risk. An implantable cardioverter-defibrillator is highly effective for secondary prevention in most forms of CHD, and future advances will improve its role in primary prevention.

Screening the apparently healthy athlete for risk: a paradigm in transition.

It has largely been accepted that pre-participation screening for student athletes is necessary, but there is still no consensus on the most effective and efficient ways to accomplish this. Most clinical strategies are based on retrospective case series. By applying the European Society of Cardiology and Seattle criteria, electrocardiography appears to afford the lowest false-positive rate for identifying potentially dangerous cardiac abnormalities in athletes. Prospective, randomised trials may help determine the most effective primary prevention. Normative data for age, gender, and ethnicity for screening tools need to be formulated to further reduce false-positive results. Targeted advanced screening aimed at the highest risk groups may be the most beneficial and cost-effective application of primary prevention.

A novel NaV1.5 voltage sensor mutation associated with severe atrial and ventricular arrhythmias.

BACKGROUND: Inherited autosomal dominant mutations in cardiac sodium channels (NaV1.5) cause various arrhythmias, such as long QT syndrome and Brugada syndrome. Although dozens of mutations throughout the protein have been reported, there are few reported mutations within a voltage sensor S4 transmembrane segment and few that are homozygous. Here we report analysis of a novel lidocaine-sensitive recessive mutation, p.R1309H, in the NaV1.5 DIII/S4 voltage sensor in a patient with a complex arrhythmia syndrome. METHODS AND RESULTS: We expressed the wild type or mutant NaV1.5 heterologously for analysis with the patch-clamp and voltage clamp fluorometry (VCF) techniques. p.R1309H depolarized the voltage-dependence of activation, hyperpolarized the voltage-dependence of inactivation, and slowed recovery from inactivation, thereby reducing the channel availability at physiologic membrane potentials. Additionally, p.R1309H increased the "late" Na(+) current. The location of the mutation in DIIIS4 prompted testing for a gating pore current. We observed an inward current at hyperpolarizing voltages that likely exacerbates the loss-of-function defects at resting membrane potentials. Lidocaine reduced the gating pore current. CONCLUSIONS: The p.R1309H homozygous NaV1.5 mutation conferred both gain-of-function and loss-of-function effects on NaV1.5 channel activity. Reduction of a mutation-induced gating pore current by lidocaine suggested a therapeutic mechanism.

Defibrillation Testing Strategies of Pediatric and Adult Congenital Electrophysiologists during ICD Implantation.

BACKGROUND: Recently, there has been an increasing number of internal medicine-trained electrophysiologists who choose not to test for acute defibrillation efficacy during implantable cardioverter defibrillator (ICD) implantation. It is not known whether this same trend is seen in pediatric electrophysiologists, who care primarily for patients with congenital heart disease or primary electrical problems. METHODS: Through a 14-question survey created on Survey Monkey, we asked the members of the Pediatric and Adult Congenital Electrophysiology Society (PACES) for their approach to ICD implantation. In particular, respondents were asked for their individual practice preferences on testing for acute defibrillation efficacy, including methods used for testing. RESULTS: There were 108 survey respondents. Thirty-nine percent test acute defibrillation efficacy at all implants, while 46% test in most patients, barring any clinical concerns. Another 14% routinely test during initial ICD system implants but not during generator changes with existing leads. Less than 1% of respondents do not routinely test acute defibrillation efficacy. CONCLUSIONS: The practice preferences of pediatric electrophysiologists in evaluating for acute defibrillation efficacy during ICD implants are in contrast to the recent trend in their internal medicine-trained counterparts. More studies are needed to determine if practice changes should be considered in the pediatric and adult congenital patient population.

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.

Rationale and Design of the Multicenter Catheter Ablation of Ventricular Tachycardia Before Transcatheter Pulmonary Valve Replacement in Repaired Tetralogy of Fallot Study.

Patients with repaired tetralogy of Fallot are at elevated risk for ventricular arrhythmia and sudden cardiac death. Over the past decade, the pathogenesis and natural history of ventricular tachycardia has become increasingly understood, and catheter ablation has emerged as an effective treatment modality. Concurrently, there has been great progress in the development of a versatile array of transcatheter valves that can be placed in the native right ventricular outflow tract for the treatment of long-standing pulmonary regurgitation. Although such valve platforms may eliminate the need for repeat cardiac operations, they may also impede catheter access to the myocardial substrates responsible for sustained macro-reentrant ventricular tachycardia. This manuscript provides the rationale and design of a recently devised multicenter study that will examine the clinical outcomes of a uniform, preemptive strategy to eliminate ventricular tachycardia substrates before transcatheter pulmonary valve implantation in patients with tetralogy of Fallot.

Multicenter Outcomes of Catheter Ablation for Atrioventricular Reciprocating Tachycardia Mediated by Twin Atrioventricular Nodes.

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.

Arrhythmias in patients with hypoplastic left heart syndrome.

BACKGROUND: Mortality between stage I and II palliation for hypoplastic left heart syndrome (HLHS) has been associated with arrhythmias. The stage-related proportion, associations, and clinical impact of arrhythmias in patients with HLHS have not been evaluated. In addition, arrhythmia subtypes have not been described in this patient group. METHODS: We performed a retrospective analysis of all patients at Duke University Medical Center who received one or more palliative stages for HLHS from September 2000 to October 2008. RESULTS: Overall, 49 (57%) of 86 patients had 63 arrhythmias. The majority of arrhythmias occurred between stage I and II, with 44 (51%) of 86 patients manifesting a new arrhythmia. Arrhythmias occurring in this interval tended to be associated with a higher mortality compared with arrhythmias occurring after stage II (odds ratio = 3.2 [95% CI 0.84-12.0], P = .09). Overall mortality was similar in patients with and without arrhythmias (P = .99). Supraventricular tachycardia was the most common arrhythmia (16/63; 25%), but persistent bradycardias (sinus node dysfunction or high-grade atrioventricular block) had the worst clinical outcome with 73% mortality (8/11). There was no association between arrhythmia occurrence and degree of tricuspid regurgitation, left ventricular hypertension, genetic syndrome, type of stage I operation, or need for extracorporeal membrane oxygenation. CONCLUSIONS: A large proportion of patients with HLHS experience serious arrhythmias requiring therapy, especially between stage I and II. Persistent bradycardia following stage I is associated with a high mortality rate. Considering all arrhythmia patients, overall mortality was not different compared with the arrhythmia-free group.

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.

Pearls for ablation in congenital heart disease.

Tachyarrhythmias occur in patients having congenital heart disease most commonly related to surgically created or naturally occurring conduction obstacles, and to postoperative hemodynamic effects on cardiac muscle. Less frequently, the underlying disease is associated with tachycardia substrates. Thorough knowledge of the patient's congenital anatomy and surgical procedures is required before considering catheter ablation. In many instances, procedural considerations should include meticulous hemodynamic surveillance, analogous to patients having structurally normal heart but cardiomyopathy. This includes careful selection of sedating and anesthetic agents. Congenital heart defects that have a higher than expected incidence of naturally occurring tachyarrhythmia substrates include Ebstein anomaly of the tricuspid valve, congenitally corrected transposition, and some of the heterotaxies. Intraatrial reentry tachycardia and atrial flutter are especially prevalent following the Mustard or Senning operations for d-transposition of the great arteries and the earlier Fontan type operations. Although these tachyarrhythmias are not as frequent following atrial septal defect repair, the high incidence of this defect also makes these patients germaine to this discussion. Focal atrial tachyacrdia and atrioventricular nodal reentry tachycardia also occur in these patient groups. Macroreentry ventricular tachycardia occurs most frequently following right ventricular outflow tract surgery, especially following repair of tetralogy of Fallot. This article focuses on the technical aspects of catheter ablation of these arrhythmias, due to the challenges presented by the underlying anatomy compared with patients having normal hearts.

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.