An international multicenter cohort study on implantable cardioverter-defibrillators for the treatment of symptomatic children with catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) may cause sudden cardiac death (SCD) despite medical therapy. Therefore, implantable cardioverter-defibrillators (ICDs) are commonly advised. However, there are limited data on the outcomes of ICD use in children.

OBJECTIVE

The purpose of this study was to compare the risk of arrhythmic events in pediatric patients with CPVT with and without ICD.

METHODS

We compared the risk of SCD in patients with RYR2 (ryanodine receptor 2) variants and phenotype-positive symptomatic patients with CPVT with and without ICD who were younger than 19 years and had no history of sudden cardiac arrest at phenotype diagnosis. The primary outcome was SCD; secondary outcomes were composite end points of SCD, sudden cardiac arrest, or appropriate ICD shocks with or without arrhythmic syncope.

RESULTS

The study included 235 patients, 73 with ICD (31.1%) and 162 without ICD (68.9%). Over a median follow-up of 8.0 years (interquartile range 4.3-13.4 years), SCD occurred in 7 patients (3.0%), of whom 4 (57.1%) were noncompliant with medications and none had an ICD. Patients with ICD had a higher risk of both secondary composite outcomes (without syncope: hazard ratio 5.85; 95% confidence interval 3.40-10.09; P < .0001; with syncope: hazard ratio 2.55; 95% confidence interval 1.50-4.34; P = .0005). Thirty-one patients with ICD (42.5%) experienced appropriate shocks, 18 (24.7%) inappropriate shocks, and 21 (28.8%) device-related complications.

CONCLUSION

SCD events occurred only in the no ICD group and in those not on optimal medical therapy. Patients with ICD had a high risk of appropriate and inappropriate shocks, which may be reduced with appropriate device programming. Severe ICD complications were common, and risks vs benefits of ICDs need to be considered.

Clinical presentation of calmodulin mutations: the International Calmodulinopathy Registry

AIMS

Calmodulinopathy due to mutations in any of the three CALM genes (CALM1-3) causes life-threatening arrhythmia syndromes, especially in young individuals. The International Calmodulinopathy Registry (ICalmR) aims to define and link the increasing complexity of the clinical presentation to the underlying molecular mechanisms.

METHODS AND RESULTS

The ICalmR is an international, collaborative, observational study, assembling and analysing clinical and genetic data on CALM-positive patients. The ICalmR has enrolled 140 subjects (median age 10.8 years [interquartile range 5-19]), 97 index cases and 43 family members. CALM-LQTS and CALM-CPVT are the prevalent phenotypes. Primary neurological manifestations, unrelated to post-anoxic sequelae, manifested in 20 patients. Calmodulinopathy remains associated with a high arrhythmic event rate (symptomatic patients, n = 103, 74%). However, compared with the original 2019 cohort, there was a reduced frequency and severity of all cardiac events (61% vs. 85%; P = .001) and sudden death (9% vs. 27%; P = .008). Data on therapy do not allow definitive recommendations. Cardiac structural abnormalities, either cardiomyopathy or congenital heart defects, are present in 30% of patients, mainly CALM-LQTS, and lethal cases of heart failure have occurred. The number of familial cases and of families with strikingly different phenotypes is increasing.

CONCLUSION

Calmodulinopathy has pleiotropic presentations, from channelopathy to syndromic forms. Clinical severity ranges from the early onset of life-threatening arrhythmias to the absence of symptoms, and the percentage of milder and familial forms is increasing. There are no hard data to guide therapy, and current management includes pharmacological and surgical antiadrenergic interventions with sodium channel blockers often accompanied by an implantable cardioverter-defibrillator.

The long-term outcomes of cardiac implantable electronic devices implanted via the femoral route

Background

Conventional superior access for cardiac implantable electronic devices (CIEDs) is not always possible and femoral CIEDs (F‐CIED) are an alternative option when leadless systems are not suitable. The long‐term outcomes and extraction experiences with F‐CIEDs, in particular complex F‐CIED (ICD/CRT devices), remain poorly understood.

Methods

Patients referred for F‐CIEDs implantation between 2002 and 2019 at two tertiary centers were included. Early complications were defined as ≤30 days following implant and late complications >30 days.

Results

Thirty‐one patients (66% male; age 56 ± 20 years; 35% [11] patients with congenital heart disease) were implanted with F‐CIEDs (10 ICD/CRT and 21 pacemakers). Early complications were observed in 6.5% of patients: two lead displacements. Late complications at 6.8 ± 4.4 years occurred in 29.0% of patients. This was higher with complex F‐CIED compared to simple F‐CIED (60.0% vs. 14.3%, p = .02). Late complications were predominantly generator site related (n = 8, 25.8%) including seven infections/erosions and one generator migration. Eight femoral generators and 14 leads (median duration in situ seven [range 6–11] years) were extracted without complication.

Conclusions

Procedural success with F‐CIEDs is high with clinically acceptable early complication rates. There is a notable risk of late complications, particularly involving the generator site of complex devices following repeat femoral procedures. Extraction of chronic F‐CIED in experienced centers is feasible and safe.

An International Multi-Center Cohort Study on β-blockers for the Treatment of Symptomatic Children with Catecholaminergic Polymorphic Ventricular Tachycardia

Background: Symptomatic children with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for recurrent arrhythmic events. Beta-blockers (BBs) decrease this risk, but studies comparing individual BBs in sizeable cohorts are lacking. We aimed to assess the association between risk for arrhythmic events and type of BB in a large cohort of symptomatic children with CPVT. Methods: From two international registries of patients with CPVT, RYR2 variant-carrying symptomatic children (defined as syncope or sudden cardiac arrest prior to BB initiation and age at start of BB therapy <18 years), treated with a BB were included. Cox-regression analyses with time-dependent covariates for BB and potential confounders were used to assess the hazard ratio (HR). The primary outcome was the first occurrence of sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter-defibrillator shock, or syncope. The secondary outcome was the first occurrence of any of the primary outcomes except syncope. Results: We included 329 patients (median age at diagnosis 12 [interquartile range, 7-15] years, 35% females). Ninety-nine (30.1%) patients experienced the primary and 74 (22.5%) experienced the secondary outcome during a median follow-up of 6.7 [interquartile range, 2.8-12.5] years. Two-hundred sixteen patients (66.0%) used a non-selective BB (predominantly nadolol [n=140] or propranolol [n=70]) and 111 (33.7%) used a β1-selective BB (predominantly atenolol [n=51], metoprolol [n=33], or bisoprolol [n=19]) as initial BB. Baseline characteristics did not differ. The HR for both the primary and secondary outcomes were higher for β1-selective compared with non-selective BBs (HR, 2.04 95% CI, 1.31-3.17; and HR, 1.99; 95% CI, 1.20-3.30, respectively). When assessed separately, the HR for the primary outcome was higher for atenolol (HR, 2.68; 95% CI, 1.44-4.99), bisoprolol (HR, 3.24; 95% CI, 1.47-7.18), and metoprolol (HR, 2.18; 95% CI, 1.08-4.40) compared with nadolol, but did not differ from propranolol. The HR of the secondary outcome was only higher in atenolol compared with nadolol (HR, 2.68; 95% CI, 1.30-5.55). Conclusions: B1-selective BBs were associated with a significantly higher risk for arrhythmic events in symptomatic children with CPVT compared with non-selective BBs, specifically nadolol. Nadolol, or propranolol if nadolol is unavailable, should be the preferred BB for treating symptomatic children with CPVT.

Clinical and Functional Characterization of Ryanodine Receptor 2 Variants Implicated in Calcium-Release Deficiency Syndrome

Importance

Calcium-release deficiency syndrome (CRDS), which is caused by loss-of-function variants in cardiac ryanodine receptor 2 (RyR2), is an emerging cause of ventricular fibrillation. However, the lack of complex polymorphic/bidirectional ventricular tachyarrhythmias during exercise stress testing (EST) may distinguish it from catecholaminergic polymorphic ventricular tachycardia (CPVT). Recently, in the first clinical series describing the condition, mouse and human studies showed that the long-burst, long-pause, short-coupled ventricular extra stimulus (LBLPS) electrophysiology protocol reliably induced CRDS ventricular arrhythmias. Data from larger populations with CRDS and its associated spectrum of disease are lacking.

Objective

To further insight into CRDS through international collaboration.

Design, Setting, and Participants

In this multicenter observational cohort study, probands with unexplained life-threatening arrhythmic events and an ultrarare RyR2 variant were identified. Variants were expressed in HEK293 cells and subjected to caffeine stimulation to determine their functional impact. Data were collected from September 1, 2012, to March 6, 2021, and analyzed from August 9, 2015, to March 6, 2021.

Main Outcomes and Measures

The functional association of RyR2 variants found in putative cases of CRDS and the associated clinical phenotype(s).

Results

Of 10 RyR2 variants found in 10 probands, 6 were loss-of-function, consistent with CRDS (p.E4451del, p.F4499C, p.V4606E, p.R4608Q, p.R4608W, and p.Q2275H) (in 4 [67%] male and 2 [33%] female probands; median age at presentation, 22 [IQR, 8-34] years). In 5 probands with a documented trigger, 3 were catecholamine driven. During EST, 3 probands with CRDS had no arrhythmias, 1 had a monomorphic couplet, and 2 could not undergo EST (deceased). Relatives of the decedents carrying the RyR2 variant did not have EST results consistent with CPVT. After screening 3 families, 13 relatives were diagnosed with CRDS, including 3 with previous arrhythmic events (23%). None had complex ventricular tachyarrhythmias during EST. Among the 19 confirmed cases with CRDS, 10 had at least 1 life-threatening event at presentation and/or during a median follow-up of 7 (IQR, 6-18) years. Two of the 3 device-detected ventricular fibrillation episodes were induced by a spontaneous LBLPS-like sequence. β-Blockers were used in 16 of 17 surviving patients (94%). Three of 16 individuals who were reportedly adherent to β-blocker therapy (19%) had breakthrough events.

Conclusions and Relevance

The results of this study suggest that calcium-release deficiency syndrome due to RyR2 loss-of-function variants mechanistically and phenotypically differs from CPVT. Ventricular fibrillation may be precipitated by a spontaneous LBLPS-like sequence of ectopy; however, CRDS remains difficult to recognize clinically. These data highlight the need for better diagnostic tools and treatments for this emerging condition.

Clinical outcomes and programming strategies of implantable cardioverter-defibrillator devices in paediatric hypertrophic cardiomyopathy: a UK National Cohort Study

AIMS

Sudden cardiac death (SCD) is the most common mode of death in paediatric hypertrophic cardiomyopathy (HCM). This study describes the implant and programming strategies with clinical outcomes following implantable cardioverter-defibrillator (ICD) insertion in a well-characterized national paediatric HCM cohort.

METHODS AND RESULTS

Data from 90 patients undergoing ICD insertion at a median age 13 (±3.5) for primary (n = 67, 74%) or secondary prevention (n = 23, 26%) were collected from a retrospective, longitudinal multi-centre cohort of children (<16 years) with HCM from the UK. Seventy-six (84%) had an endovascular system [14 (18%) dual coil], 3 (3%) epicardial, and 11 (12%) subcutaneous system. Defibrillation threshold (DFT) testing was performed at implant in 68 (76%). Inadequate DFT in four led to implant adjustment in three patients. Over a median follow-up of 54 months (interquartile range 28-111), 25 (28%) patients had 53 appropriate therapies [ICD shock n = 45, anti-tachycardia pacing (ATP) n = 8], incidence rate 4.7 per 100 patient years (95% CI 2.9-7.6). Eight inappropriate therapies occurred in 7 (8%) patients (ICD shock n = 4, ATP n = 4), incidence rate 1.1/100 patient years (95% CI 0.4-2.5). Three patients (3%) died following arrhythmic events, despite a functioning device. Other device complications were seen in 28 patients (31%), including lead-related complications (n = 15) and infection (n = 10). No clinical, device, or programming characteristics predicted time to inappropriate therapy or lead complication.

CONCLUSION

In a large national cohort of paediatric HCM patients with an ICD, device and programming strategies varied widely. No particular strategy was associated with inappropriate therapies, missed/delayed therapies, or lead complications.

Outcomes From Pediatric Ablation: A Review of 20 Years of National Data

OBJECTIVES

This study set out to examine outcomes from pediatric supraventricular tachycardia ablations over a 20-year period. This study sought to examine success rates and repeat ablations over time and to evaluate whether modalities such as 3-dimensional (3D) mapping, contact force, and cryotherapy have improved outcomes.

BACKGROUND

Ablation of supraventricular tachycardia in pediatric patients is commonly performed in most congenital heart centers with excellent long-term results.

METHODS

Data were retrieved from the NICOR (National Institute of Clinical Outcomes Research) database in the United Kingdom. Outcomes over time were evaluated, and procedure-related details were compared.

RESULTS

There were 7,069 ablations performed from January 1, 1999, to December 31, 2018, at 10 centers. Overall, ablation success rates were 92% for accessory pathways, 97% for atrioventricular node re-entry tachycardia, and 89% for atrial tachycardia. There was an improvement in procedural success rates over time (p < 0.01). The use of 3D mapping did not alter success or need for repeat ablation but was associated with a higher proportion of lower fluoroscopy cases; 55% of 3D mapping cases used < 5 min of fluoroscopy (p < 0.01). Patients needing a repeat ablation were 341 (12%) for accessory pathways, 128 (7%) for atrioventricular node re-entry tachycardia, and 35 (7%) for atrial tachycardia. Overall, the risk of complete heart block was low (12 patients, <0.01%). The use of cryotherapy was associated with an increased risk of needing a repeat ablation.

CONCLUSIONS

Overall success rates from pediatric ablations are excellent and compare favorably to other registries. Introduction of newer technologies have likely made procedures safer and reduced radiation exposure, but they have not changed success rates or the need for a repeat procedure.

Atenolol is not effective in reducing ventricular arrhythmia severity on exercise stress test in patients with catecholaminergic polymorphic ventricular tachycardia

 

Patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for malignant ventricular arrhythmias during exercise and emotions which may lead to sudden cardiac death. Beta-blockers (BB) are the mainstay of therapy in patients with CPVT, but studies comparing the efficacy of different types of BB are scarce. Our objective was to determine the efficacy of different types of BB in reducing the ventricular arrhythmia (VA) severity on exercise stress test (EST) in patients with CPVT.

Data was derived from the International CPVT Registry, a large retrospective cohort study. We included patients who had an EST before (pre-EST) and after start of BB (post-EST). We divided the cohort into five groups based on the first prescribed BB and compared pre-EST and post-EST.

We included 428 patients (median age 18.5 [11.7–39.6] years, 240 (56.%) female), 155 (36.2%) probands) of whom 38 (8.9%) used atenolol, 131 (30.6%) bisoprolol, 82 (19.2%) metoprolol, 124 (29.0%) nadolol and 53 (12.4%) propranolol. Sex and history of aborted cardiac arrest were similar in all groups. The age at start of BB differed (p&lt;0,001): patients using bisoprolol were oldest (35.0 [15.7–35.3]) while patients using propranolol were youngest (12.3 [8.8–24.9]). Median daily BB dose in mg/kg was: 1.0 [0.8–2.3] for atenolol, 0.06 [0.05–0.10] for bisoprolol, 0.9 [0.6–1.5] for metoprolol, 1.1 [0.9–1.6] for nadolol and 1.5 [1.1–2.8] for propranolol. Resting heart rate on pre-EST and post-EST was similar in all groups. Patients using metoprolol had a significantly higher maximum heart rate post-EST compared to nadolol and propranolol (161±18 vs 136±19 and 130±22 bpm, p=0,002 and p=0,001, respectively). The VA severity decreased significantly after BB (147 (37.9%) (non-sustained) ventricular tachycardia ((NS)VT) and 120 (30.9%) no or isolated ventricular premature beat (iVPB) pre-EST vs 46 (11.4%) (NS)VT and 184 (45.7%) iVPB post-EST, p&lt;0,001). Examining the different groups, the VA severity decreased significantly after BB in all but atenolol (13 (40.6%) (NS)VT and 8 (25.0%) iVPB pre-EST vs 9 (25.0%) (NS)VT and 15 (41.7%) iVPB post-EST, p=0,103).

Based on these results we conclude that all beta-blockers except atenolol are effective in reducing the VA severity on EST in patients with CPVT.

Funding Acknowledgement

Type of funding source: Public grant(s) – EU funding. Main funding source(s): E-Rare Joint Transnational Call for Proposals 2015 “Improving Diagnosis and Treatment of Catecholaminergic Polymorphic Ventricular Tachycardia: Integrating Clinical and Basic Science”

Clinical outcomes and programming strategies of implantable cardioverter defibrillator (ICD) devices during childhood in hypertrophic cardiomyopathy: a UK national cohort study

Background

Sudden cardiac death (SCD) is the most common mode of death in childhood hypertrophic cardiomyopathy (HCM). ICDs have been shown to be effective at terminating malignant ventricular arrhythmias but at the expense of a high incidence of complications. The optimal device and programming strategies to reduce complications in this patient group are unknown.

Purpose

To describe the programming strategies and clinical outcomes of ICD implantation in childhood HCM.

Methods

Anonymised, non-invasive clinical data were collected from a retrospective, longitudinal multi-centre cohort of children (&lt;16 years) with HCM (n=687) and an ICD in-situ from the United Kingdom.

Results

96 patients (61 male (64%), 6 non-sarcomeric (6%)) underwent ICD implantation at a median age 14yr (IQR 11–16, range 3–16) and weight 52.3 kg (IQR 34.8–63.1). Indication for ICD was primary prevention in 72 (75%). 82 (85%) had an endovascular system, 3 (3%) epicardial and 11 (12%) subcutaneous system. 61 patients (74%) were receiving one or more cardioactive medications at implantation [B blockers n=66, 70%, disopyramide n=14, 15%, amiodarone n=7, 7%, calcium channel blocker n=7, 9%, other n=5, 6%]. Programming practices varied: all had VF therapies activated (median 220bpm, IQR 212–230); 70 (73%) had a VT zone programmed (median rate 187 bpm, SD 20.9), of which 26 (27%) had therapies activated. 50 patients (61%) had antitachycardia pacing (ATP) activated. Over a median follow up of 53.6 months (IQR 27.3,108.4), 4 patients (4.2%) died following arrhythmic events despite a functioning device. 25 patients had 53 appropriate therapies (ICD shock n=47, ATP n=8), incidence rate 5.22 (95% CI 3.5–7.8). On univariable analysis, secondary prevention indication for ICD implantation was the only predictor of therapy [16 (64%) vs 8 (11.3%), p value &lt;0.001]. 8 (8.3%) patients had 9 inappropriate therapies (ICD shock n=4, ATP n=5), incidence rate 1.37 (95% CI 0.65–2.8), caused by T wave oversensing (n=2), lead migration (n=1), supraventricular tachycardia (n=1). Device complications were seen in 30 patients (31%), including lead complications (n=16) and infection (n=10). No clinical characteristics predicted time to inappropriate therapy or lead complication.

Conclusions

In a contemporary cohort of children with HCM, the incidence of inappropriate therapies is lower than previously reported, yet complication rates remain higher than reported in adult patients. No clinical, device or programming strategies were associated with inappropriate therapies or lead complications.

Funding Acknowledgement

Type of funding source: Other. Main funding source(s): British Heart Foundation

An International Multicenter Evaluation of Inheritance Patterns, Arrhythmic Risks, and Underlying Mechanisms of CASQ2-Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

Genetic variants in calsequestrin-2 (CASQ2) cause an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT), although isolated reports have identified arrhythmic phenotypes among heterozygotes. Improved insight into the inheritance patterns, arrhythmic risks, and molecular mechanisms of CASQ2-CPVT was sought through an international multicenter collaboration.

METHODS

Genotype-phenotype segregation in CASQ2-CPVT families was assessed, and the impact of genotype on arrhythmic risk was evaluated using Cox regression models. Putative dominant CASQ2 missense variants and the established recessive CASQ2-p.R33Q variant were evaluated using oligomerization assays and their locations mapped to a recent CASQ2 filament structure.

RESULTS

A total of 112 individuals, including 36 CPVT probands (24 homozygotes/compound heterozygotes and 12 heterozygotes) and 76 family members possessing at least 1 presumed pathogenic CASQ2 variant, were identified. Among CASQ2 homozygotes and compound heterozygotes, clinical penetrance was 97.1% and 26 of 34 (76.5%) individuals had experienced a potentially fatal arrhythmic event with a median age of onset of 7 years (95% CI, 6-11). Fifty-one of 66 CASQ2 heterozygous family members had undergone clinical evaluation, and 17 of 51 (33.3%) met diagnostic criteria for CPVT. Relative to CASQ2 heterozygotes, CASQ2 homozygote/compound heterozygote genotype status in probands was associated with a 3.2-fold (95% CI, 1.3-8.0; P=0.013) increased hazard of a composite of cardiac syncope, aborted cardiac arrest, and sudden cardiac death, but a 38.8-fold (95% CI, 5.6-269.1; P<0.001) increased hazard in genotype-positive family members. In vitro turbidity assays revealed that p.R33Q and all 6 candidate dominant CASQ2 missense variants evaluated exhibited filamentation defects, but only p.R33Q convincingly failed to dimerize. Structural analysis revealed that 3 of these 6 putative dominant negative missense variants localized to an electronegative pocket considered critical for back-to-back binding of dimers.

CONCLUSIONS

This international multicenter study of CASQ2-CPVT redefines its heritability and confirms that pathogenic heterozygous CASQ2 variants may manifest with a CPVT phenotype, indicating a need to clinically screen these individuals. A dominant mode of inheritance appears intrinsic to certain missense variants because of their location and function within the CASQ2 filament structure.

Heart Rate Recovery After Exercise Is Associated With Arrhythmic Events in Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

Background:

Risk stratification in catecholaminergic polymorphic ventricular tachycardia remains ill defined. Heart rate recovery (HRR) immediately after exercise is regulated by autonomic reflexes, particularly vagal tone, and may be associated with symptoms and ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia. Our objective was to evaluate whether HRR after maximal exercise on the exercise stress test (EST) is associated with symptoms and ventricular arrhythmias.

Methods:

In this retrospective observational study, we included patients ≤65 years of age with an EST without antiarrhythmic drugs who attained at least 80% of their age- and sex-predicted maximal HR. HRR in the recovery phase was calculated as the difference in heart rate (HR) at maximal exercise and at 1 minute in the recovery phase (ΔHRR1′).

Results:

We included 187 patients (median age, 36 years; 68 [36%] symptomatic before diagnosis). Pre-EST HR and maximal HR were equal among symptomatic and asymptomatic patients. Patients who were symptomatic before diagnosis had a greater ΔHRR1′ after maximal exercise (43 [interquartile range, 25–58] versus 25 [interquartile range, 19–34] beats/min; P <0.001). Corrected for age, sex, and relatedness, patients in the upper tertile for ΔHRR1′ had an odds ratio of 3.4 (95% CI, 1.6–7.4) of being symptomatic before diagnosis ( P <0.001). In addition, ΔHRR1′ was higher in patients with complex ventricular arrhythmias at EST off antiarrhythmic drugs (33 [interquartile range, 22–48] versus 27 [interquartile range, 20–36] beats/min; P =0.01). After diagnosis, patients with a ΔHRR1′ in the upper tertile of its distribution had significantly more arrhythmic events as compared with patients in the other tertiles ( P =0.045).

Conclusions:

Catecholaminergic polymorphic ventricular tachycardia patients with a larger HRR following exercise are more likely to be symptomatic and have complex ventricular arrhythmias during the first EST off antiarrhythmic drug.

Linking the heart and the brain: Neurodevelopmental disorders in patients with catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an uncommon inherited arrhythmia disorder characterized by adrenergically evoked ventricular arrhythmias. Mutations in the cardiac calcium release channel/ryanodine receptor gene (RYR2) are identified in the majority of patients with CPVT. RyR2 is also the major RyR isoform expressed in the brain.

OBJECTIVE

The purpose of this study was to estimate the prevalence of intellectual disability (ID) and other neurodevelopmental disorders (NDDs) in RYR2-associated CPVT (CPVT1) and to study the characteristics of these patients.

METHODS

We reviewed the medical records of all CPVT1 patients from 12 international centers and analyzed the characteristics of all CPVT1 patients with concomitant NDDs. We functionally characterized the mutations to assess their response to caffeine activation. We did not correct for potential confounders.

RESULTS

Among 421 CPVT1 patients, we identified 34 patients with ID (8%; 95% confidence interval 6%-11%). Median age at diagnosis was 9.3 years (interquartile range 7.0-14.5). Parents for 24 of 34 patients were available for genetic testing, and 13 of 24 (54%) had a de novo mutation. Severity of ID ranged from mild to severe and was accompanied by other NDDs in 9 patients (26%). Functionally, the ID-associated mutations showed a markedly enhanced response of RyR2 to activation by caffeine. Seventeen patients (50%) also had supraventricular arrhythmias. During median follow-up of 8.4 years (interquartile range 1.8-12.4), 15 patients (45%) experienced an arrhythmic event despite adequate therapy.

CONCLUSION

Our study indicates that ID is more prevalent among CPVT1 patients (8%) than in the general population (1%-3%). This subgroup of CPVT1 patients reveals a malignant cardiac phenotype with marked supraventricular and ventricular arrhythmias.

Utility of Post-Mortem Genetic Testing in Cases of Sudden Arrhythmic Death Syndrome

BACKGROUND

Sudden arrhythmic death syndrome (SADS) describes a sudden death with negative autopsy and toxicological analysis. Cardiac genetic disease is a likely etiology.

OBJECTIVES

This study investigated the clinical utility and combined yield of post-mortem genetic testing (molecular autopsy) in cases of SADS and comprehensive clinical evaluation of surviving relatives.

METHODS

We evaluated 302 expertly validated SADS cases with suitable DNA (median age: 24 years; 65% males) who underwent next-generation sequencing using an extended panel of 77 primary electrical disorder and cardiomyopathy genes. Pathogenic and likely pathogenic variants were classified using American College of Medical Genetics (ACMG) consensus guidelines. The yield of combined molecular autopsy and clinical evaluation in 82 surviving families was evaluated. A gene-level rare variant association analysis was conducted in SADS cases versus controls.

RESULTS

A clinically actionable pathogenic or likely pathogenic variant was identified in 40 of 302 cases (13%). The main etiologies established were catecholaminergic polymorphic ventricular tachycardia and long QT syndrome (17 [6%] and 11 [4%], respectively). Gene-based rare variants association analysis showed enrichment of rare predicted deleterious variants in RYR2 (p = 5 × 10^-5). Combining molecular autopsy with clinical evaluation in surviving families increased diagnostic yield from 26% to 39%.

CONCLUSIONS

Molecular autopsy for electrical disorder and cardiomyopathy genes, using ACMG guidelines for variant classification, identified a modest but realistic yield in SADS. Our data highlighted the predominant role of catecholaminergic polymorphic ventricular tachycardia and long QT syndrome, especially the RYR2 gene, as well as the minimal yield from other genes. Furthermore, we showed the enhanced utility of combined clinical and genetic evaluation.

Histiocytoid cardiomyopathy and microphthalmia with linear skin defects syndrome: phenotypes linked by truncating variants in NDUFB11

Variants in NDUFB11, which encodes a structural component of complex I of the mitochondrial respiratory chain (MRC), were recently independently reported to cause histiocytoid cardiomyopathy (histiocytoid CM) and microphthalmia with linear skin defects syndrome (MLS syndrome). Here we report an additional case of histiocytoid CM, which carries a de novo nonsense variant in NDUFB11 (ENST00000276062.8: c.262C > T; p.[Arg88*]) identified using whole-exome sequencing (WES) of a family trio. An identical variant has been previously reported in association with MLS syndrome. The case we describe here lacked the diagnostic features of MLS syndrome, but a detailed clinical comparison of the two cases revealed significant phenotypic overlap. Heterozygous variants in HCCS (which encodes an important mitochondrially targeted protein) and COX7B, which, like NDUFB11, encodes a protein of the MRC, have also previously been identified in MLS syndrome including a case with features of both MLS syndrome and histiocytoid CM. However, a systematic review of WES data from previously published histiocytoid CM cases, alongside four additional cases presented here for the first time, did not identify any variants in these genes. We conclude that NDUFB11 variants play a role in the pathogenesis of both histiocytoid CM and MLS and that these disorders are allelic (genetically related).

Clinical Management of Catecholaminergic Polymorphic Ventricular Tachycardia

Background—

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic disorder causing life-threatening arrhythmias whenever sympathetic activity increases. β-Βlockers are the mainstay of therapy; when they fail, implantable cardioverter-defibrillators (ICDs) are used but often cause multiple shocks. Preliminary results with flecainide appear encouraging. We proposed left cardiac sympathetic denervation (LCSD) as useful additional therapy, but evidence remains anecdotal.

Methods and Results—

We report 63 patients with CPVT who underwent LCSD as secondary (n=54) or primary (n=9) prevention. The median post-LCSD follow-up was 37 months. The 9 asymptomatic patients remained free of major cardiac events. Of the 54 patients with prior major cardiac events either on (n=38) or off (n=16) optimal medical therapy, 13 (24%) had at least 1 recurrence: 0 patients had an aborted cardiac arrest, 2 patients had syncope only, 10 patients had ≥1 appropriate ICD discharges, and 1 patient died suddenly. The 1- and 2-year cumulative event-free survival rates were 87% and 81%. The percentage of patients with major cardiac events despite optimal medical therapy (n=38) was reduced from 100% to 32% ( P <0.001) after LCSD, and among 29 patients with a presurgical ICD, the rate of shocks dropped by 93% from 3.6 to 0.6 shocks per person per year ( P <0.001). Patients with an incomplete LCSD (n=7) were more likely to experience major cardiac events after LCSD (71% versus 17%; P <0.01) than those with a complete LCSD.

Conclusions—

LCSD is an effective antifibrillatory intervention for patients with CPVT. Whenever syncope occurs despite optimal medical therapy, LCSD could be considered the next step rather than an ICD and could complement ICDs in patients with recurrent shocks.

Effects of flecainide on exercise-induced ventricular arrhythmias and recurrences in genotype-negative patients with catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Conventional therapy with beta-blockers is incompletely effective in preventing arrhythmic events in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT). We have previously discovered that flecainide in addition to conventional drug therapy prevents ventricular arrhythmias in patients with genotype-positive CPVT.

OBJECTIVE

To study the efficacy of flecainide in patients with genotype-negative CPVT.

METHODS

We studied the efficacy of flecainide for reducing ventricular arrhythmias during exercise testing and preventing arrhythmia events during long-term follow-up.

RESULTS

Twelve patients with genotype-negative CPVT were treated with flecainide. Conventional therapy failed to control ventricular arrhythmias in all patients. Flecainide was initiated because of significant ventricular arrhythmias (n = 8), syncope (n = 3), or cardiac arrest (n = 1). At the baseline exercise test before flecainide, 6 patients had ventricular tachycardia and 5 patients had bigeminal or frequent ventricular premature beats. Flecainide reduced ventricular arrhythmias at the exercise test in 8 patients compared to conventional therapy, similar to that in patients with genotype-positive CPVT in our previous report. Notably, flecainide completely prevented ventricular arrhythmias in 7 patients. Flecainide was continued in all patients except for one who had ventricular tachycardia at the exercise test on flecainide. During a follow-up of 48±94 months, arrhythmia events (sudden cardiac death and aborted cardiac arrest) associated with noncompliance occurred in 2 patients. Flecainide was not discontinued owing to side effects in any of the patients.

CONCLUSIONS

Flecainide was effective in patients with genotype-negative CPVT, suggesting that spontaneous Ca(2+) release from ryanodine channels plays a role in arrhythmia susceptibility, similar to that in patients with genotype-positive CPVT.

Bloodspot acylcarnitine and amino acid analysis in cord blood samples: efficacy and reference data from a large cohort study

BACKGROUND

In order to test the feasibility of cord blood screening for inherited metabolic disease, a two-year cohort study of births in six obstetric units from five towns in the north of England was undertaken. These towns have a high prevalence of consanguineous marriages, largely among the immigrant Asian community. The purpose of the study was to determine whether early detection of metabolic disease was possible and whether early intervention would improve prognosis.

METHODS

Following parental consent, cord blood samples were collected at birth and analysed for acylcarnitine and amino acid profiles by tandem mass spectrometry in one of two laboratories. One laboratory used butylated derivatives, the other used underivatized samples. The same laboratories performed routine blood spot neonatal screening at 5-7 days of age on these babies. Patients with positive results were investigated and treated by a metabolic paediatrician as soon as possible.

RESULTS

24,983 births were examined. 12,952 samples were analysed as butyl derivatives, 12,031 samples were analysed underivatized. The following disorders were detected: medium-chain acyl-CoA dehydrogenase (MCAD) deficiency (1 case), 3-methylcrotonyl-CoA carboxylase (MCC) deficiency (2 cases), maternal carnitine transporter defect (2 cases), maternal MCC (1 case). The following disorders were diagnosed subsequently but were not detected by the cord blood screening: phenylketonuria (PKU) (1 case), maple syrup urine disease (MSUD) (2 cases), argininosuccinic aciduria (1 case), methylmalonic acidaemia (MMA) (1 case), glutaric aciduria type 2 (1 case), MCAD deficiency (2 cases), 3-hydroxy-3-methylglutaryl-CoA lyase deficiency (1 case). Comprehensive reference data for all analytes by both methods were obtained.

CONCLUSIONS

Cord blood testing is of limited value in detecting inherited metabolic disease. The metabolites associated with most disorders examined were not elevated in cord blood. Some maternal disorders, carnitine transporter defect and 3-methlycrotonyl-CoA carboxylase deficiency, are detected. These remain of uncertain clinical significance. Comprehensive reference data have been obtained that will facilitate future interpretation of studies in cord blood.

Hypocalcaemia mimicking long QT syndrome: case report

We describe a teenage girl who presented with syncope on exertion and prolonged QT on electrocardiogram (ECG). She was found to be hypocalcaemic due to hypoparathyroidism. Following oral calcium and vitamin D supplementation, there were no further episodes of syncope with normalization of the QT segment. This case highlights the need to consider all causes of a long QT segment.

Functional assessment of compound mutations in the KCNQ1 and KCNH2 genes associated with long QT syndrome

BACKGROUND

Long QT syndrome (LQTS) is a cardiovascular disorder characterized by prolonged QTc time, syncope, or sudden death caused by torsades de pointes and ventricular fibrillation. We investigated the clinical and electrophysiologic phenotype of individual mutations and the compound mutations in a family in which different genotypes could be found.

OBJECTIVES

The purpose of this study was to determine the impact of genotype-based diagnostic assessment in LQTS.

METHODS

We used cascade screening and functional analyses to investigate the phenotype in a family with LQTS. The contributions of the compound mutations in the KCNQ1 and KCNH2 genes (KCNQ1 R591H, KCNH2 R328C) were analyzed by heterologous expression in Xenopus laevis oocytes using two-electrode voltage clamp and by confocal imaging.

RESULTS

KCNH2 R328C did not show any functional phenotype whereas KCNQ1 R591H resulted in severe reduction of current. Neither wild-type nor mutant channels affected each other functionally in coexpression experiments. Therefore, a direct interaction between KCNQ1 and KCNH2 was ruled out under these conditions.

CONCLUSION

Assessment of novel mutational findings in LQTS should include accurate genetic and functional analysis. Notably, appropriate studies are needed if two or more mutations in different genes are present in one proband. Our findings prompt reconsideration of the impact of compound mutations in LQTS families and reinforce the need for thorough functional evaluation of novel ion channel mutations before assignment of pathogenic status.

Methylmalonic aciduria: follow-up and enzymology on the original case after 36 years

A 36-year follow-up on the original patient described with methylmalonic aciduria has shown that she has methylmalonyl-CoA apomutase deficiency. The main clinical problem associated with her methylmalonic aciduria is progressive renal impairment requiring commencement of haemodialysis at 42 years of age.

A new model for laser-induced thermal damage in the retina

We describe a new model for laser-induced retinal damage. Our treatment is prompted by the failure of the traditional approach to accurately describe the image size dependence of laser-induced retinal injuries and by a recently reported study which demonstrated that laser injuries to the retina might not appear for up to 48 h post exposure. We propose that at threshold a short-duration, laser-induced, temperature rise melts the membrane of the melanosomes found in the pigmented retinal epithelial cells. This results in the generation of free radicals which initiate a slow chain reaction. If more than a critical number of radicals are generated then cell death may occur at a time much later than the return of the retina to body temperature. We show that the equations consequent upon this mechanism result in a good fit to the recent image size data although more detailed experimental data for rate constants of elementary reactions is still required. This paper contributes to the current understanding of damage mechanisms in the retina and may facilitate the development of new treatments to mitigate laser injuries to the eye. The work will also help minimize the need for further animal experimentation to set laser eye safety standards.

Familial atrial standstill with coexistent atrial flutter

A child with familial atrial standstill and a ventricular pacemaker had syncope due to atrial flutter that was treated by His-bundle ablation. Bradycardia protection alone may be insufficient in patients with atrial standstill.

Strategies for the treatment of cystathionine beta-synthase deficiency: the experience of the Willink Biochemical Genetics Unit over the past 30 years

Strategies for the treatment of cystathionine beta-synthase (CBS) deficiency include (1) increasing residual enzyme activity by giving pyridoxine in those patients with vitamin responsive variants, (2) reducing the load on the affected pathway with a low methionine diet and supplementing the diet with cysteine; and (3) giving betaine in order to utilise alternative pathways to remove homocyst(e)ine. In our experience of over 30 years in the diagnosis and management of patients with CBS deficiency, a normal outcome can only be achieved in patients diagnosed and treated from infancy. Pyridoxine combined with folic acid prevents further deterioration in pyridoxine responsive patients. Dietary treatment of patients with non-pyridoxine responsive CBS deficiency becomes more difficult outside childhood but since late complications are not uncommon must be continued for life. Betaine can be effective in this group but compliance is often poor.

Assessment of QT dispersion in symptomatic patients with congenital long QT syndromes

It has been suggested that QT dispersion recorded on the surface electrocardiogram may be a predictor of arrhythmic events in patients with congenital QT prolongation. To evaluate this, 9 patients (6 female, mean age 17.6 years) with congenital long QT syndromes, all of whom had syncope and documented torsades de pointes, were studied. Patients were studied off treatment and during therapy with beta-blocking agents. Three patients were also studied after left stellate ganglionectomy. An age-matched control group was also studied. Good quality 12-lead electrocardiograms were recorded from all patients. For each lead, QT and RR intervals were measured, and QTc value was calculated. QT and QTc dispersions were calculated for each patient. Patients had a significantly longer mean QT interval compared with that of the control group (450 +/- 100 vs 359 +/- 63 ms; p = 0.015) at similar mean RR intervals (736 +/- 231 vs 783 +/- 289 ms), with a longer mean QTc value (0.53 +/- 0.08 vs 0.41 +/- 0.02 s1/2; p = 0.004). Patients also had longer QT and QTc dispersions compared with those of the control group (110 +/- 45 vs 43 +/- 12 ms [p = 0.004], and 0.108 +/- 0.03 vs 0.05 +/- 0.02 s1/2 [p = 0.002], respectively). QT and QTc dispersions on and off beta-blocking agents were not significantly different. Comparing patients with frequent and those with infrequent symptoms, there was no difference in QT or QTc dispersion either off treatment or during therapy with beta-blocking agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial flutter in the fetus and young infant: an association with accessory connections

OBJECTIVE

To highlight the association between atrial flutter and accessory connections in the fetus and young infant.

DESIGN

A retrospective review from January 1985 to January 1990.

PATIENTS

Fetuses, neonates, and young infants with atrial flutter.

RESULTS

Four fetuses and five infants presented with atrial flutter. In two fetuses and one infant sinus rhythm returned spontaneously. The other six required cardioversion. Three of them developed orthodromic atrioventricular re-entry tachycardia and each had evidence of an accessory connection.

CONCLUSIONS

Because atrial flutter in the fetus and neonate is rare, the high incidence of accessory connections in this group points to a possible aetiology of "idiopathic" atrial flutter in this age group.