Diagnostic Approach to Unexplained Cardiac Arrest (from the FIVI-Gen Study)

Molecular genetic screening after non-ischaemic sudden cardiac arrest and no overt cardiomyopathy in real life: A major tool for the aetiological diagnostic work-up

BACKGROUND

With the development of advanced sequencing techniques, genetic testing has emerged as a valuable tool for the work-up of non-ischaemic sudden cardiac arrest (SCA).

AIMS

To evaluate the effectiveness of genetic testing in patients with unexplained SCA, according to clinical phenotype.

METHODS

All patients who underwent molecular genetic testing for non-ischaemic SCA with no left ventricular cardiomyopathy between 2012 and 2021 in two French university hospitals were included.

RESULTS

Of 66 patients (mean age 36.7±11.9years, 54.5% men), 21 (31.8%; 95% confidence interval 22.4-45.3%) carried a genetic variant: eight (12.1%) had a pathogenic or likely pathogenic (P/LP) variant and 13 (19.7%) had a variant of uncertain significance (VUS). Among 37 patients (56.1%) with no phenotypic clues, genetic testing identified a P/LP variant in five (13.5%), mainly in RYR2 (n=3) and SCN5A (n=2), and a VUS in nine (24.3%). None of the nine patients with phenotypic evidence of channelopathies had P/LP variants, but two had VUS in RYR2 and NKX2.5. Among the 20 patients with suspected arrhythmogenic cardiomyopathy, three P/LP variants (15.0%) and two VUS (10.0%) were found in DSC2, PKP2, SCN5A and DSG2, TRPM4, respectively. Genetic testing was performed sooner after cardiac arrest (P<0.001) and results were obtained more rapidly (P=0.02) after versus before 2016.

CONCLUSION

This study highlights the utility of molecular genetic testing with a genetic variant of interest identified in one-third of patients with unexplained SCA. Genetic testing was beneficial even in patients without phenotypic clues, with one-fourth of patients carrying a P/LP variant that could have direct implications.

Inherited Arrhythmias in the Pediatric Population: An Updated Overview

Pediatric cardiomyopathies (CMs) and electrical diseases constitute a heterogeneous spectrum of disorders distinguished by structural and electrical abnormalities in the heart muscle, attributed to a genetic variant. They rank among the main causes of morbidity and mortality in the pediatric population, with an annual incidence of 1.1-1.5 per 100,000 in children under the age of 18. The most common conditions are dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). Despite great enthusiasm for research in this field, studies in this population are still limited, and the management and treatment often follow adult recommendations, which have significantly more data on treatment benefits. Although adult and pediatric cardiac diseases share similar morphological and clinical manifestations, their outcomes significantly differ. This review summarizes the latest evidence on genetics, clinical characteristics, management, and updated outcomes of primary pediatric CMs and electrical diseases, including DCM, HCM, arrhythmogenic right ventricular cardiomyopathy (ARVC), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT syndrome (LQTS), and short QT syndrome (SQTS).

Explaining the Unexplained: A Practical Approach to Investigating the Cardiac Arrest Survivor

Sudden cardiac arrest (SCA) is a common cause of death. The majority of SCA is caused by ventricular arrhythmia due to underlying CHD. Aborted SCA with no apparent diagnosis after initial assessment with ECG, echocardiography and coronary assessment is referred to as unexplained cardiac arrest (UCA). Systematic evaluation of such patients may reveal a specific diagnosis in up to half of patients before a diagnosis of idiopathic VF is assigned. Specific diagnoses include inherited cardiac conditions, such as latent cardiomyopathies or inherited primary electrical disease. Identifying the cause of UCA is therefore not only critical for appropriate management of the SCA survivors to prevent recurrence, but also for their family members who may be at risk of the same condition. This review provides a tiered, systematic approach for the investigation of UCA.

The genetic basis of apparently idiopathic ventricular fibrillation: a retrospective overview

AIMS

During the diagnostic work-up of patients with idiopathic ventricular fibrillation (VF), next-generation sequencing panels can be considered to identify genotypes associated with arrhythmias. However, consensus for gene panel testing is still lacking, and variants of uncertain significance (VUS) are often identified. The aim of this study was to evaluate genetic testing and its results in idiopathic VF patients.

METHODS AND RESULTS

We investigated 419 patients with available medical records from the Dutch Idiopathic VF Registry. Genetic testing was performed in 379 (91%) patients [median age at event 39 years (27-51), 60% male]. Single-gene testing was performed in 87 patients (23%) and was initiated more often in patients with idiopathic VF before 2010. Panel testing was performed in 292 patients (77%). The majority of causal (likely) pathogenic variants (LP/P, n = 56, 15%) entailed the DPP6 risk haplotype (n = 39, 70%). Moreover, 10 LP/P variants were found in cardiomyopathy genes (FLNC, MYL2, MYH7, PLN (two), TTN (four), RBM20), and 7 LP/P variants were identified in genes associated with cardiac arrhythmias (KCNQ1, SCN5A (2), RYR2 (four)). For eight patients (2%), identification of an LP/P variant resulted in a change of diagnosis. In 113 patients (30%), a VUS was identified. Broad panel testing resulted in a higher incidence of VUS in comparison to single-gene testing (38% vs. 3%, P < 0.001).

CONCLUSION

Almost all patients from the registry underwent, albeit not broad, genetic testing. The genetic yield of causal LP/P variants in idiopathic VF patients is 5%, increasing to 15% when including DPP6. In specific cases, the LP/P variant is the underlying diagnosis. A gene panel specifically for idiopathic VF patients is proposed.

The Importance of Systematic Diagnostic Testing in Idiopathic Ventricular Fibrillation: Results From the Dutch iVF-Registry

BACKGROUND

Idiopathic ventricular fibrillation (iVF) is a diagnosis of exclusion. Systematic diagnostic testing is important to exclude alternative causes for VF. The early use of "high yield" testing, including cardiac magnetic resonance (CMR), exercise testing, and sodium channel blocker provocation, has been increasingly recognized.

OBJECTIVES

The purpose of this study was to investigate the importance and consistency of systematic diagnostic testing in iVF.

METHODS

This study included 423 iVF patients from 11 large secondary and tertiary hospitals in the Netherlands. Clinical characteristics and diagnostic testing data were ascertained.

RESULTS

IVF patients experienced the index event at a median age of 40 years (IQR: 28-52 years), and 61% were men. The median follow-up time was 6 years (IQR: 2-12 years). Over the years, "high yield" diagnostic tests were increasingly performed (mean 68% in 2000-2010 vs 75% in 2011-2021; P < 0.001). During follow-up, 38 patients (9%) originally labeled as iVF received an alternative diagnosis. Patients in whom "high-yield" diagnostic tests were consistently performed during the initial work-up received an alternative diagnosis less frequently during follow-up (HR: 0.439; 95% CI: 0.219-0.878; P = 0.020). Patients who received an alternative diagnosis during follow-up had a worse prognosis in terms of cardiac death (P = 0.012) with a trend toward more implantable cardioverter-defibrillator therapy (P = 0.055).

CONCLUSIONS

Although adherence to (near) complete diagnostic testing in this population of iVF patients increased over the years, patients with iVF still undergo varying levels of diagnostic evaluation. The latter leads to initial underdiagnosis of alternative conditions and is associated with a worse prognosis. Our results underscore the importance of early systematic diagnostic assessment in patients with apparent iVF.

State-of-the-Art Multimodality Imaging in Sudden Cardiac Arrest with Focus on Idiopathic Ventricular Fibrillation: A Review

Idiopathic ventricular fibrillation is a rare cause of sudden cardiac arrest and a diagnosis by exclusion. Unraveling the mechanism of ventricular fibrillation is important for targeted management, and potentially for initiating family screening. Sudden cardiac arrest survivors undergo extensive clinical testing, with a growing role for multimodality imaging, before diagnosing “idiopathic” ventricular fibrillation. Multimodality imaging, considered as using multiple imaging modalities as diagnostics, is important for revealing structural myocardial abnormalities in patients with cardiac arrest. This review focuses on combining imaging modalities (echocardiography, cardiac magnetic resonance and computed tomography) and the electrocardiographic characterization of sudden cardiac arrest survivors and discusses the surplus value of multimodality imaging in the diagnostic routing of these patients. We focus on novel insights obtained through electrostructural and/or electromechanical imaging in apparently idiopathic ventricular fibrillation patients, with special attention to non-invasive electrocardiographic imaging.

Prevalence of Inherited Cardiac Conditions in Pediatric First-Degree Relatives of Patients with Idiopathic Ventricular Fibrillation

Idiopathic ventricular fibrillation (IVF) is diagnosed in out-of-hospital VF survivors after comprehensive investigations have excluded structural heart disease or inherited channelopathies. Current guidelines recommend clinical screening of first-degree relatives of IVF survivors, but this approach has not been validated in children. This study aimed to assess the yield of clinical cardiac screening in child first-degree relatives of IVF victims. A retrospective observational study was conducted of all consecutive pediatric first-degree relatives of IVF patients referred to our center between December 2007 and April 2020. Patients underwent systematic evaluation including medical and family history; 12-lead resting, signal-averaged, and ambulatory electrocardiogram (ECG); echocardiogram; exercise testing; cardiac magnetic resonance imaging; and ajmaline provocation testing. Sixty child first-degree relatives of 32 IVF survivors were included [median follow-up time of 55 months (IQR 27.0-87.0 months); 30 (50%) females]. Eight patients (13.3%) from 6 families (18.8%) received a cardiac diagnosis: long QT syndrome (n = 4); Brugada syndrome (n = 3); and dilated cardiomyopathy (n = 1). There were no deaths during follow-up. This study demonstrates a high yield of clinical screening for inherited cardiac disease in child first-degree relatives of IVF survivors. These findings highlight the variable expression of inherited cardiac conditions and the importance of comprehensive clinical evaluation in pediatric relatives, even when extensive investigations in the proband have not identified a clear etiology. Moreover, our results support the validity of the investigations proposed by current guidelines in family relatives of IVF survivors.

OUP accepted manuscript

Aims

Genetic testing is recommended in specific inherited heart diseases but its role remains unclear and it is not currently recommended in unexplained cardiac arrest (UCA). We sought to assess the yield and clinical utility of genetic testing in UCA using whole-exome sequencing (WES).

Methods and results

Survivors of UCA requiring external defibrillation were included from the Cardiac Arrest Survivor with Preserved Ejection fraction Registry. Whole-exome sequencing was performed, followed by assessment of rare variants in previously reported cardiovascular disease genes. A total of 228 UCA survivors (mean age at arrest 39 ± 13 years) were included. The majority were males (66%) and of European ancestry (81%). Following advanced clinical testing at baseline, the likely aetiology of cardiac arrest was determined in 21/228 (9%) cases. Whole-exome sequencing identified a pathogenic or likely pathogenic (P/LP) variant in 23/228 (10%) of UCA survivors overall, increasing the proportion of ‘explained’ cases from 9% only following phenotyping to 18% when combining phenotyping with WES. Notably, 13 (57%) of the 23 P/LP variants identified were located in genes associated with cardiomyopathy, in the absence of a diagnosis of cardiomyopathy at the time of arrest.

Conclusions

Genetic testing identifies a disease-causing variant in 10% of apparent UCA survivors. The majority of disease-causing variants was located in cardiomyopathy-associated genes, highlighting the arrhythmogenic potential of such variants in the absence of an overt cardiomyopathy diagnosis. The present study supports the use of genetic testing including assessment of arrhythmia and cardiomyopathy genes in survivors of UCA.

Non-ischemic sudden cardiac arrest: Role of 12 lead Holter, family screening and genetic testing

OBJECTIVE AND BACKGROUND

To evaluate the diagnostic and prognostic yield of a comprehensive protocol involving clinical and broad genetic testing in consecutive sudden cardiac arrest (SCA) population. Determining the pathogenesis of non-ischemic SCA is crucial for management and SCA prevention in other family members METHODS: Families with unexplained non-ischemic SCA event underwent rigorous clinical and genetic protocol after referral to our inherited arrhythmia clinic, during 2011-2017.

RESULTS

One hundred and four index cases, 29 ± 16 years, and 421 family members were studied. After a thorough evaluation, diagnosis was made in 80 (77%) of families. The most prevalent 47/104 (45%) diagnosis was inherited channelopathy. The genetic test was positive, in 37 /69 (54%) of patients. Using the Mann Whitney test, we found that electrocardiography (ECG) (effect size 0.5, p < .001), 12 lead Holter (effect size 0.33, p = .001) and family screening (effect size 0.4, p = .001) had the highest yield in reaching the final diagnosis. Family screening, genetic testing, and cardiac MRI were the exclusive modalities for final diagnosis in 14%, 9%, and 2% of families, respectively. Among 421 family members evaluated through cascade screening, 127 (30%), were diagnosed and medically treated. Nine family members from 25 (40%) patients who underwent implantable cardioverter defibrillator (ICD) implantation have experienced appropriate ICD shock.

CONCLUSIONS

A rigorous, systematic protocol in a specialized inherited arrhythmia clinic has a high diagnostic and prognostic yield. ECG, 12 lead Holter and family screening significantly increased the diagnostic yield. In nine families, without genetic testing, the diagnosis would have been missed.

2020 APHRS/HRS expert consensus statement on the investigation of decedents with sudden unexplained death and patients with sudden cardiac arrest, and of their families

This international multidisciplinary document intends to provide clinicians with evidence-based practical patient-centered recommendations for evaluating patients and decedents with (aborted) sudden cardiac arrest and their families. The document includes a framework for the investigation of the family allowing steps to be taken, should an inherited condition be found, to minimize further events in affected relatives. Integral to the process is counseling of the patients and families, not only because of the emotionally charged subject, but because finding (or not finding) the cause of the arrest may influence management of family members. The formation of multidisciplinary teams is essential to provide a complete service to the patients and their families, and the varied expertise of the writing committee was formulated to reflect this need. The document sections were divided up and drafted by the writing committee members according to their expertise. The recommendations represent the consensus opinion of the entire writing committee, graded by Class of Recommendation and Level of Evidence. The recommendations were opened for public comment and reviewed by the relevant scientific and clinical document committees of the Asia Pacific Heart Rhythm Society (APHRS) and the Heart Rhythm Society (HRS); the document underwent external review and endorsement by the partner and collaborating societies. While the recommendations are for optimal care, it is recognized that not all resources will be available to all clinicians. Nevertheless, this document articulates the evaluation that the clinician should aspire to provide for patients with sudden cardiac arrest, decedents with sudden unexplained death, and their families.

Precision Medicine in Catecholaminergic Polymorphic Ventricular Tachycardia: JACC Focus Seminar 5/5

In this final of a 5-part Focus Seminar series on precision medicine, we focus on catecholaminergic polymorphic ventricular tachycardia (CPVT). This focus on CPVT allows us to take a "deep dive" and explore the full extent of the precision medicine opportunities for a single cardiovascular condition at a level that was not possible in the preceding articles. As a new paradigm presented in this article, it has become clear that CPVT can occur as either a typical or atypical form. Although there is a degree of overlap between the typical and atypical forms, it is notable that they arise due to different underlying genetic changes, likely exhibiting differing mechanisms of action, and presenting with different phenotypic features. The recognition of these differing forms of CPVT and their different etiologies and mechanisms is an important step toward implementing rapidly emerging precision medicine approaches that will tailor novel therapies to specific gene defects.

Defining idiopathic ventricular fibrillation: A systematic review of diagnostic testing yield in apparently unexplained cardiac arrest

BACKGROUND

Idiopathic ventricular fibrillation (IVF) is diagnosed in patients with apparently unexplained cardiac arrest (UCA) after varying degrees of evaluation. This is largely due to the lack of a standardized approach to UCA.

OBJECTIVE

We sought to develop an evidence-based diagnostic algorithm for IVF by systematically examining the yield of diagnostic testing in UCA probands.

METHODS

Studies reporting the yield of diagnostic testing in UCA were identified in MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and conference abstracts. Their methodological quality was assessed by the National Institutes of Health quality assessment tool. Meta-analyses were performed using the random effects model.

RESULTS

A total of 21 studies were included. The pooled comprehensive diagnostic testing yield was 43% (95% confidence interval 39%-48%). A lower yield was seen when only definite diagnoses based on the prespecified criteria were used (32% vs 47%; P = .15). Epinephrine challenge, Holter monitoring, and family screening were associated with low yield (<5%), whereas cardiac magnetic resonance imaging, exercise treadmill test, and sodium-channel blocker challenge were associated with high yield (≥5%). Coronary spasm provocation, electrophysiology study, and systematic genetic testing were reported to be abnormal in a high proportion of UCA probands (>10%).

CONCLUSION

We developed a stepwise algorithm for UCA evaluation and criteria to assess the strength of IVF diagnosis on the basis of the diagnostic yield of UCA testing.

2020 APHRS/HRS expert consensus statement on the investigation of decedents with sudden unexplained death and patients with sudden cardiac arrest, and of their families

This international multidisciplinary document intends to provide clinicians with evidence-based practical patient-centered recommendations for evaluating patients and decedents with (aborted) sudden cardiac arrest and their families. The document includes a framework for the investigation of the family allowing steps to be taken, should an inherited condition be found, to minimize further events in affected relatives. Integral to the process is counseling of the patients and families, not only because of the emotionally charged subject, but because finding (or not finding) the cause of the arrest may influence management of family members. The formation of multidisciplinary teams is essential to provide a complete service to the patients and their families, and the varied expertise of the writing committee was formulated to reflect this need. The document sections were divided up and drafted by the writing committee members according to their expertise. The recommendations represent the consensus opinion of the entire writing committee, graded by Class of Recommendation and Level of Evidence. The recommendations were opened for public comment and reviewed by the relevant scientific and clinical document committees of the Asia Pacific Heart Rhythm Society (APHRS) and the Heart Rhythm Society (HRS); the document underwent external review and endorsement by the partner and collaborating societies. While the recommendations are for optimal care, it is recognized that not all resources will be available to all clinicians. Nevertheless, this document articulates the evaluation that the clinician should aspire to provide for patients with sudden cardiac arrest, decedents with sudden unexplained death, and their families.

Diagnostic yield and long-term outcome of nonischemic sudden cardiac arrest survivors and their relatives: Results from a tertiary referral center

BACKGROUND

Cardiac arrest may be the first manifestation of most inherited cardiac diseases. International guidelines recommend screening of relatives of sudden cardiac arrest (SCA) survivors if an inherited cardiac disorder is suspected.

OBJECTIVE

The purpose of this study was to assess the prevalence and spectrum of inherited cardiac diseases and the long-term outcome in a consecutive cohort of nonischemic SCA survivors (probands) and their relatives.

METHODS

This retrospective study consecutively included probands and their relatives referred to our tertiary center for family screening between 2005 and 2018. All participants underwent a systematic workup and follow-up protocol. Data were retrieved from medical records.

RESULTS

We included 155 probands (age 41.2 ± 15.5 years; 61% male) and 282 relatives (age 35.7 ± 18.8 years; 51% male). Mean follow-up was 7.1 years for probands and 4.4 years for relatives. We identified an inherited cardiac disease in 76 (49%) probands and 42 (15%) relatives. An implantable cardioverter-defibrillator was inserted in 147 (95%) probands and 9 (3%) relatives. During follow-up, 4 (3%) probands and 3 (1%) relatives died, and 37 probands and 2 relatives received appropriate shock therapy. All relatives received genetic counseling, and 18 (6%) relatives started pharmacologic treatment during follow-up.

CONCLUSION

Systematic workup of nonischemic SCA survivors and their relatives identified an inherited cardiac disease in 49% of referred probands and 15% of their relatives. The favorable long-term prognosis of diagnosed relatives probably not only reflects lower age but also the effects of early diagnosis, treatment, and follow-up. These findings support systematic workup of SCA survivors and their relatives.

Prognostic impact of misdiagnosis of cardiac channelopathies as epilepsy

INTRODUCTION

Cardiac channelopathies are a frequent cause of sudden cardiac death (SCD) and often manifest with convulsive syncope, leading to a misdiagnosis of epilepsy. We aim to evaluate the clinical impact of epilepsy misdiagnosis in a cohort of patients with cardiac channelopathies.

METHODS

Fifty probands/families with a cardiac channelopathy were included. We retrospectively collected information from medical records to identify all patients who presented with convulsive syncope and were diagnosed with epilepsy after neurological evaluation. Clinical data and outcome were compared with those of patients without a previous epilepsy diagnosis.

RESULTS

Eight patients had a previous diagnosis of epilepsy. At first episode, 3 of them presented a positive family history of SCD and 5 showed a pathological electrocardiogram; half presented with sudden cardiac arrest (SCA) and the rest with recurrent syncope despite treatment with 1 or more anti-epileptic drugs. Five patients had long QT syndrome, 2 had catecholaminergic polymorphic ventricular tachycardia, and 1 had Brugada syndrome. Epilepsy misdiagnosis was associated with an increased risk of SCA/SCD (OR 6.92, P = .04), a delay of 12 years (P = .047) in correct diagnosis, and a delay from first symptom to channelopathy diagnosis of 18.45 years (P < .0001).

CONCLUSION

Cardiac channelopathy patients can be misdiagnosed with epilepsy. This involves a delayed diagnosis, a delay from the first symptom to a correct diagnosis, and an increased risk of SCA/SCD.

Epidemiology of inherited arrhythmias

The primary electrical disorders are a group of inherited cardiac ventricular arrhythmias that are a major cause of sudden cardiac death in young individuals. Inherited ventricular arrhythmias result from mutations in genes encoding cardiac ion channels or their modulatory subunits. Advances in genetic screening in the past three decades have led to the assembly of large patient cohorts with these disorders. Studies in these patients, as well as in the general population, have striven to define the prevalence of these inherited arrhythmias and the characteristics of patients with different genetic subtypes of the disease. In this Review, we provide a comprehensive update on the epidemiology of inherited ventricular arrhythmias, focusing on natural history, prevalence and patient demographics. In addition, we summarize the various founder populations (groups of individuals with a disease that is caused by a genetic defect inherited from a common ancestor) that have been identified for some of these disorders and which lead to increased prevalence in some geographical regions. To date, although numerous studies have markedly increased our understanding of the epidemiology of these disorders, demographic data, especially from non-Western countries, remain scarce. Furthermore, defining the true prevalence of these disorders remains challenging. International collaboration will undoubtedly accelerate the collection of demographic information and improve the accuracy of prevalence data.

Interplay between Triadin and Calsequestrin in the Pathogenesis of CPVT in the Mouse

Recessive forms of catecholaminergic polymorphic ventricular tachycardia (CPVT) are induced by mutations in genes encoding triadin or calsequestrin, two proteins that belong to the Ca²⁺ release complex, responsible for intracellular Ca²⁺ release triggering cardiac contractions. To better understand the mechanisms of triadin-induced CPVT and to assay multiple therapeutic interventions, we used a triadin knockout mouse model presenting a CPVT-like phenotype associated with a decrease in calsequestrin protein level. We assessed different approaches to rescue protein expression and to correct intracellular Ca²⁺ release and cardiac function: pharmacological treatment with kifunensine or a viral gene transfer-based approach, using adeno-associated virus serotype 2/9 (AAV2/9) encoding the triadin or calsequestrin. We observed that the levels of triadin and calsequestrin are intimately linked, and that reduction of both proteins contributes to the CPVT phenotype. Different combinations of triadin and calsequestrin expression level were obtained using these therapeutic approaches. A full expression of each is not necessary to correct the phenotype; a fine-tuning of the relative re-expression of both triadin and calsequestrin is required to correct the CPVT phenotype and rescue the cardiac function. AAV-mediated gene delivery of calsequestrin or triadin and treatment with kifunensine are potential treatments for recessive forms of CPVT due to triadin mutations.

Usefulness of Genetic Testing in Sudden Cardiac Arrest Survivors With or Without Previous Clinical Evidence of Heart Disease

Genetic testing in survivors of sudden cardiac arrest (SCA) with a suspicious cardiac phenotype is considered clinically useful, whereas its value in the absence of phenotype is disputed. We aimed to evaluate the clinical utility of genetic testing in survivors of SCA with or without cardiac phenotype. Sixty unrelated SCA survivors (median age: 34 [interquartile range 20 to 43] years, 82% male) without coronary artery disease were included: 24 (40%) with detectable cardiac phenotype (Ph(+)SCA) after the SCA event and 36 (60%) with no clear cardiac phenotype (Ph(-)SCA). The targeted exome sequencing was performed using the TruSight-One Sequencing Panel (Illumina). Variants in 185 clinically relevant cardiac genes with minor allele frequency <1% were analyzed. A total of 32 pathogenic or likely pathogenic variants were found in 27 (45%) patients: 17 (71%) in the Ph(+)SCA group and 10 (28%) in the Ph(-)SCA group. Sixteen (67%) Ph(+)SCA patients hosted mutations congruent with the suspected phenotype, in which 12 (50%) were cardiomyopathies and 4 (17%) channelopathies. In Ph(-)SCA cases, 6 (17%) carried a mutation in cardiac ion channel genes that could explain the event. The additional 4 (11%) mutations in this group, could not explain the phenotype and require additional studies. In conclusion, cardiac genetic testing was positive in nearly 2/3 patients of the Ph(+)SCA group and in 1/6 of the Ph(-)SCA group. The test was useful in both groups to identify or confirm an inherited heart disease, with an important impact on the patient care and first-degree relatives at risk.

Catecholaminergic Polymorphic Ventricular Tachycardia as the Etiology of Emergency Medical Services-Reported Traumatic Arrest

A 13-year-old girl had a witnessed loss of consciousness after a scuffle with another student at school and was found in ventricular fibrillation at the time of arrival of emergency medical services personnel. The patient was successfully defibrillated in the field and was transported to the emergency department as a presumed "traumatic arrest". The patient's initial electrocardiogram was remarkable for a prolonged QT interval, and it was discovered that multiple family members had died of cardiac events as young adults. Genetic testing subsequently revealed a mutation in the RYR2 gene, which is implicated in catecholaminergic polymorphic ventricular tachycardia.

Recommendations for genetic testing and counselling after sudden cardiac death: practical aspects for Swiss practice

There is a need to standardise, within a coordinated Swiss framework, the practical aspects of genetic testing and genetic counselling on possibly inherited cardiovascular disorders in relatives of a sudden cardiac death (SCD) victim. Because of the major advances in genetic investigation techniques and recent publication of international guidelines in the field of cardiology, genetics and pathology, we consider it important to summarise the current evidence and propose an optimal approach to post-mortem genetic investigation for SCD victims and their families in Switzerland. In this article, we discuss important technical, financial and medico-ethical aspects, and provide updated information on specific situations in which forensic pathologists, general practitioners and cardiologists should suspect a genetic origin of the SCD. At present, the principles of benefit, the duty to warn and the impact of genetic information for family members at risk are considered as strong justifications for post-mortem disclosure and prevail over the arguments of respect for a deceased person’s privacy and confidentiality. This paper underlines also the need to update and improve the general knowledge concerning the genetic risk of cardiovascular pathologies, the importance to perform an autopsy and post-mortem genetic testing in SCD victims, and to develop standardized post-mortem disclosure policy at national and international levels for SCD cases and relatives.

Characteristics and clinical assessment of unexplained sudden cardiac arrest in the real-world setting: focus on idiopathic ventricular fibrillation

Aims

Recent studies have shown that in more than half of apparently unexplained sudden cardiac arrests (SCA), a specific aetiology can be unmasked by a careful evaluation. The characteristics and the extent to which such cases undergo a systematic thorough investigation in real-life practice are unknown.

Methods and results

Data were analysed from an ongoing study, collecting all cases of out-of-hospital cardiac arrest in Paris area. Investigations performed during the index hospitalization or planned after discharge were gathered to evaluate the completeness of assessment of unexplained SCA. Between 2011 and 2016, among the 18 622 out-of-hospital cardiac arrests, 717 survivors (at hospital discharge) fulfilled the definition of cardiac SCA. Of those, 88 (12.3%) remained unexplained after electrocardiogram, echocardiography, and coronary angiography. Cardiac magnetic resonance imaging yielded the diagnosis in 25 (3.5%) cases, other investigations accounted for 14 (2.4%) additional diagnoses, and 49 (6.8%) patients were labelled as idiopathic ventricular fibrillation (IVF) (48.7 ± 15 years, 69.4% male). Among those labelled IVF, only 8 (16.3%) cases benefited from a complete workup (including pharmacological testing). Younger patients [odds ratio (OR) 6.00, 95% confidence interval (CI) 1.80-22.26] and those admitted to university centres (OR 3.60, 95% CI 1.12-12.45) were more thoroughly investigated. Genetic testing and family screening were initiated in only 9 (18.4%) and 12 (24.5%) cases, respectively.

Conclusion

Our findings suggest that complete investigations are carried out in a very low proportion of unexplained SCA. Standardized, systematic approaches need to be implemented to ensure that opportunities for specific therapies and preventive strategies (including relatives) are not missed.

Next generation sequencing applications for cardiovascular disease

The Human Genome Project (HGP), as the primary sequencing of the human genome, lasted more than one decade to be completed using the traditional Sanger's method. At present, next-generation sequencing (NGS) technology could provide the genome sequence data in hours. NGS has also decreased the expense of sequencing; therefore, nowadays it is possible to carry out both whole-genome (WGS) and whole-exome sequencing (WES) for the variations detection in patients with rare genetic diseases as well as complex disorders such as common cardiovascular diseases (CVDs). Finding new variants may contribute to establishing a risk profile for the pathology process of diseases. Here, recent applications of NGS in cardiovascular medicine are discussed; both Mendelian disorders of the cardiovascular system and complex genetic CVDs including inherited cardiomyopathy, channelopathies, stroke, coronary artery disease (CAD) and are considered. We also state some future use of NGS in clinical practice for increasing our information about the CVDs genetics and the limitations of this new technology. Key messages Traditional Sanger's method was the mainstay for Human Genome Project (HGP); Sanger sequencing has high fidelity but is slow and costly as compared to next generation methods. Within cardiovascular medicine, NGS has been shown to be successful in identifying novel causative mutations and in the diagnosis of Mendelian diseases which are caused by a single variant in a single gene. NGS has provided the opportunity to perform parallel analysis of a great number of genes in an unbiased approach (i.e. without knowing the underlying biological mechanism) which probably contribute to advance our knowledge regarding the pathology of complex diseases such as CVD.

Brugada syndrome in children - Stepping into unchartered territory

Brugada syndrome (BrS) is an autosomal dominant inherited channelopathy. It is associated with a typical pattern of ST-segment elevation in the precordial leads V1-V3 and potentially lethal ventricular arrhythmias in otherwise healthy patients. It is frequently seen in young Asian males, in whom it has previously been described as sudden unexplained nocturnal death syndrome. Although it typically presents in young adults, it is also known to present in children and infants, especially in the presence of fever. Our understanding of the genetic pathogenesis and management of BrS has grown substantially considering that it has only been 24 years since its first description as a unique clinical entity. However, there remains much to be learned, especially in the pediatric population. This review aims to discuss the epidemiology, genetics, and pathogenesis of BrS. We will also discuss established standards and new innovations in the diagnosis, prognostication, risk stratification, and management of BrS. Literature search was run on the National Center for Biotechnology Information's website, using the Medical Subject Headings (MeSH) database with the search term "Brugada Syndrome" (MeSH), and was run on the PubMed database using the age filter (birth-18 years), yielding 334 results. The abstracts of all these articles were studied, and the articles were categorized and organized. Articles of relevance were read in full. As and where applicable, relevant references and citations from the primary articles were further explored and read in full.

[Sudden cardiac death: A better understanting for a better prevention]

Sudden cardiac death is defined as a natural and unexpected death, in a previous apparently healthy individual. It represents a major public health issue, with up to 50% of the cardiovascular mortality. Using data from the Paris Sudden Death Expertise Centre registry, this article summarises the main cardiovascular abnormalities associated with sudden cardiac death, the different preventives approaches, and provides a systematic diagnostic approach.

Clinical and Genetic Diagnosis of Nonischemic Sudden Cardiac Death

INTRODUCTION AND OBJECTIVES

Nonischemic sudden cardiac death (SCD) is predominantly caused by cardiomyopathies and channelopathies. There are many diagnostic tests, including some complex techniques. Our aim was to analyze the diagnostic yield of a systematic diagnostic protocol in a specialized unit.

METHODS

The study included 56 families with at least 1 index case of SCD (resuscitated or not). Survivors were studied with electrocardiogram, advanced cardiac imaging, exercise testing, familial study, genetic testing and, in some cases, pharmacological testing. Families with deceased probands were studied using the postmortem findings, familial evaluation, and molecular autopsy with next-generation sequencing (NGS).

RESULTS

A positive diagnosis was obtained in 80.4% of the cases, with no differences between survivors and nonsurvivors (P=.53). Cardiac channelopathies were more prevalent among survivors than nonsurvivors (66.6% vs 40%, P=.03). Among the 30 deceased probands, the definitive diagnosis was given by autopsy in 7. A diagnosis of cardiomyopathy tended to be associated with a higher event rate in the family. Genetic testing with NGS was performed in 42 index cases, with a positive result in 28 (66.6%), with no differences between survivors and nonsurvivors (P=.21).

CONCLUSIONS

There is a strong likelihood of reaching a diagnosis in SCD after a rigorous protocol, with a more prevalent diagnosis of channelopathy among survivors and a worse familial prognosis in cardiomyopathies. Genetic testing with NGS is useful and its value is increasing with respect to the Sanger method.

Genomic-based diagnosis of arrhythmia disease in a personalized medicine era

INTRODUCTION

Although thousands of potentially disease-causing mutations have been identified in a handful of genes, the genetic heterogeneity has led to diagnostic confusions, stemming directly from the limitations in our arsenal of genetic tools.

AREAS COVERED

We discuss the genetic basis of cardiac ion channelopathies, the gaps in our knowledge and how Next-generation sequencing technology (NGS) and can be used to bridge them, and how induced pluripotent stem cell (iPSC) derived-cardiomyocytes can be used for drug discovery.

EXPERT COMMENTARY

Univariate, arrhythmogenic arrhythmias can explain some congenital arrhythmias, however, it is far from a comprehensive understanding of the complexity of many arrhythmias. Mutational screening is a critical step in personalized medicine and is critical to the management of patients with arrhythmias. The success of personalized medicine requires a more efficient way to identify a high number of genetic variants potentially implicated in cardiac arrhythmogenic diseases than traditional sequencing methods (eg, Sanger sequencing). Next-generation sequencing technology provides us with unprecedented opportunities to achieve high-throughput, rapid, and cost-effective detection of congenital arrhythmias in patients. Moreover, in personalized medicine era, IPSC derived-cardiomyocytes can be used as 'cardiac arrhythmia in a dish' model for drug discovery, and help us improve management of arrhythmias in patients by developing patient-specific drug therapies with target specificity.

Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac arrhythmia disorder that is characterized by emotion- and exercise-induced polymorphic ventricular arrhythmias and may lead to sudden cardiac death (SCD). CPVT plays an important role in SCD in the young and therefore recognition and adequate treatment of the disease are of vital importance. In the past years tremendous improvements have been made in the diagnostic methods and treatment of the disease. In this review, we summarize the clinical characteristics, genetics, and diagnostic and therapeutic strategies of CPVT and describe the most recent advances and some of the current challenges. (Circ J 2016; 80: 1285-1291).

Calmodulin 2 Mutation N98S Is Associated with Unexplained Cardiac Arrest in Infants Due to Low Clinical Penetrance Electrical Disorders

Background

Calmodulin 1, 2 and 3 (CALM) mutations have been found to cause cardiac arrest in children at a very early age. The underlying aetiology described is long QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia (CPVT) and idiopathic ventricular fibrillation (IVF). Little phenotypical data about CALM2 mutations is available.

Objectives

The aim of this paper is to describe the clinical manifestations of the Asn98Ser mutation in CALM2 in two unrelated children in southern Spain with apparently unexplained cardiac arrest/death.

Methods

Two unrelated children aged 4 and 7, who were born to healthy parents, were studied. Both presented with sudden cardiac arrest. The first was resuscitated after a VF episode, and the second died suddenly. In both cases the baseline QTc interval was within normal limits. Peripheral blood DNA was available to perform targeted gene sequencing.

Results

The surviving 4-year-old girl had a positive epinephrine test for LQTS, and polymorphic ventricular ectopic beats were seen on a previous 24-hour Holter recording from the deceased 7-year-old boy, suggestive of a possible underlying CPVT phenotype. A p.Asn98Ser mutation in CALM2 was detected in both cases. This affected a highly conserved across species residue, and the location in the protein was adjacent to critical calcium binding loops in the calmodulin carboxyl-terminal domain, predicting a high pathogenic effect.

Conclusions

Human calmodulin 2 mutation p.Asn98Ser is associated with sudden cardiac death in childhood with a variable clinical penetrance. Our results provide new phenotypical information about clinical behaviour of this mutation.

Clinical Challenges in Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inheritable cardiac disorder associated with exercise- and stress-induced sudden death in young individuals. Although important steps forward have been made in the comprehension and treatment of this disease, several aspects remain unclear. Firstly, from an epidemiological standpoint the actual prevalence of CPVT is still unknown and possibly underestimated. In addition, the diagnostic process remains very challenging and can be supported by genetic analysis in only about half of the cases. Finally, up to one third of CPVT patients continue to present complex arrhythmias despite beta blocker treatment; the role of newer therapeutic options, such as flecainide and left cardiac sympathetic denervation, needs to be further elucidated. All these points constitute challenges for the cardiologist in the management of CPVT patients and fuel research into new diagnostic, prognostic and therapeutic approaches.