Cardiac Channelopathies Research Articles

Penetrancia familiar en la parada cardíaca en ausencia de cardiopatía aparente: observaciones del estudio FIVI-Gen

Introduction and objectiveFamilial inheritance and penetrance of disorders causing unexplained cardiac arrest is not well known. Our aim is to describe clinical and diagnostic methods in a sample of unexplained cardiac arrest relatives. Material and methodsWe studied first to third degree relatives of unexplained cardiac arrest patients with electrocardiogram and echocardiogram. In all cases with a definitive diagnosis in the index case, phenotype directed unmasking tests were performed in all available relatives. ResultsWe included 88 subjects belonging to 35 families (mean of 2.5 relatives per family), with a mean age of 38,4 years, and 52,8% males. 55,6% were first degree relatives, and the remaining were second and third degree. A definitive diagnosis was achieved in 19 relatives (21,5%), consisting of Brugada Syndrome (10 cases), long QT syndrome (3 cases), catecholaminergic polymorphic ventricular tachycardia (5 cases) and one case of possible short QT syndrome. In 4 families, the diagnosis in the proband was reached thanks to the familial assesment. ConclusionsPrevalence of cardiac channelopathies among relatives of unexplained cardiac arrest patients was high, using a multitest approach including unmasking pharmacological tests and genetic study.

Eligibility and Disqualification Recommendations for Competitive Athletes With Cardiovascular Abnormalities: Task Force 10: The Cardiac Channelopathies: A Scientific Statement From the American Heart Association and American College of Cardiology.

The cardiac channelopathies are a collection of primary, genetically mediated heart rhythm disorders (also referred to as the primary electrical disorders) that are generally associated with a structurally normal heart and a propensity for syncope, seizures, or sudden cardiac arrest precipitated by a channelopathy-mediated episode of nonsustained or sustained polymorphic ventricular tachycardia (torsade de pointes) or ventricular fibrillation. These cardiac channelopathies include long-QT syndrome (LQTS), catecholaminergic polymorphic ventricular tachycardia (CPVT), Brugada syndrome (BrS), early repolarization syndrome, short-QT syndrome, and potentially idiopathic ventricular fibrillation. Approximately 1 in 1000 people are affected by a cardiac channelopathy, with LQTS being most common, involving an estimated 1 in 2000 people.1 Presently, these channelopathies should be viewed as potentially lethal but highly treatable conditions. However, unlike the various bradyarrhythmias and tachyarrhythmias detailed in the Task Force 9 report,2 there remains significant variability and heterogeneity among pediatric and adult heart rhythm specialists in terms of their ability to diagnose, risk stratify, and treat patients with these conditions. For example, in 1 study, 40% of the patients who received a second opinion evaluation at a LQTS specialty center for a previously rendered diagnosis of LQTS by a heart rhythm specialist were reclassified as otherwise normal, having insufficient evidence to merit that diagnostic consideration.3 This is explained in part by the advanced knowledge and training required to evaluate and treat these less common channelopathies. Accordingly, any return-to-play decision for an athlete suspected of having a cardiac channelopathy necessitates that the athlete be evaluated, risk stratified, treated, and counseled by a heart rhythm specialist or genetic cardiologist with sufficient experience and expertise in these syndromes.4 For the most part, restriction from virtually all competitive sports has been the guideline-based recommendation since 2005 for athletes with a cardiac channelopathy, regardless of the underlying channelopathy.5, …

Abstract 15933: Scn5a Gating Pore Current Causes Cardiac Arrhythmias Associated With Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is a structural heart disease that causes dilatation of cardiac chambers, impairs cardiac contractility and systolic function leading to heart failure. SCN5A gene encodes the cardiac sodium channel (Nav1.5) in which mutations have been identified in patients with arrhythmic disorders associated with DCM. However, it is not understood how a dysfunction in SCN5A may cause very atypical cardiac arrhythmias associated with dilatation remodeling of the heart. We generated control and patient specific human induced pluripotent cells (hiPS) carrying the Nav1.5/R219H mutation. hiPS were differentiated to obtain cardiomyocytes derived from hiPS (hiPS-CM). Molecular dynamic simulations experiments revealed that the R219H mutation opens up a pathway directly through the voltage sensitive domain (VSD) of Nav1.5 channels. We hypothesized that such a proton leak through the VSD caused by the R219H mutation may be responsible for the clinical phenotypes observed in our index patient. We unraveled the underlying mechanism responsible for the association of SCN5A and DCM. Indeed, the data shows the presence of a gating pore or omega current that is responsible of the observed abnormal ionic homeostasis, absent in control hiPS-CM. Action potential recordings showed abnormal electrical activities in both atrial and ventricular hiPS-CM. Myocytes stemmed from the index patient exhibited dilatation. Single cardiomyocytes contractility probed using atomic force microscopy revealed a higher frequency of contractility with reduced force compared to control myocytes. This could be attributed to the observed contractile protein dysfunction uncovered using immunofluorescence. Overall, the results support the hypothesis that the Nav1.5/R219H mutation creates a proton leak. This leak then causes electrical, structural and contractile disturbances that may explain the related cardiac arrhythmias associated with myocytes dilatation. We concluded that gating pore current, a novel cardiac channelopathy is directly related to the association of SCN5A and DCM. We suggest that this aberrant leak current should be investigated to characterize similar SCN5A mutations with similar clinical phenotypes.

Abstract 16529: Molecular and Functional Characterization of an Ultra Rare Frame-shift Mutation in CALR-encoded Calreticulin as a Probable Long QT Syndrome-susceptibility Variant

Introduction: Long QT syndrome (LQTS) is the most common, autosomal dominant, sudden death predisposing cardiac channelopathy. Although 17 LQTS genes have been discovered, 20% of LQTS remains genetically elusive. Whole exome sequencing (WES) followed by a strategic, knowledge-based variant filtration approach may elucidate novel LQTS-susceptibility genes. Methods: A LQTS family with multiple sudden deaths was referred for genetic evaluation. The index case was a 21-year-old male who died suddenly but had a pre-mortem ECG with marked QT prolongation. The decedent’s mother also showed QT prolongation. Only paraffin embedded tissue (PET) was available from the decedent, so the mother’s DNA was analyzed by WES. Following WES, variants were filtered using Ingenuity Variant Analysis (IVA) software. Only non-synonymous variants with a quality score >20, read-depth >10, and absent in ExAC were considered. Further filtration was performed using IVA’s biological context pathway analysis set to capture genes most likely related to LQTS. Electrophysiological studies were performed on the variant with highest probability of pathogenicity. Results: Following WES and variant filtration, only a CALR frame-shift variant (R376fs/10) remained as a probable LQTS mutation. No radical CALR variants reside in ExAC’s 60,000+ exomes. The mutation was confirmed in the decedent’s PET-derived DNA. CALR-encoded calreticulin (CRT) is a Ca2+ binding chaperone of the endoplasmic reticulum. Both knockout and over-expression of CRT exert extreme effects on the murine cardiac system, including sudden death. Recently, CRT has been linked with altered L-type calcium (LTCC) ion channel activity. Wild-type (WT)-CALR reduced Cav1.2 peak current density by 43.1%. In contrast, CALR-R376fs/10 mutation reversed this Cav1.2 inhibition and caused a net gain-of-function of Cav1.2 channel current compared with CALR-WT co-expression (64.2% increase). No pathogenic variants in CALR were identified in 25 additional, unrelated, genetically elusive LQTS cases. Conclusion: Mutations in CALR-encoded calreticulin may be a rare cause of autosomal dominant LQTS precipitated in part by an accentuation of the LTCC, thereby potentially mimicking CACNA1C-mediated LQTS.

Implantable defibrillators versus medical therapy for cardiac channelopathies.

Sudden cardiac death is a significant cause of mortality in both the US and globally. However, 5% to 15% of people with sudden cardiac death have no structural abnormalities, and most of these events are attributed to underlying cardiac ion channelopathies. Rates of cardiac ion channelopathy diagnosis are increasing. However, the optimal treatment for such people is poorly understood and current guidelines rely primarily on expert opinion. To compare the effect of implantable cardioverter defibrillators (ICD) with antiarrhythmic drugs or usual care in reducing the risk of all-cause mortality, fatal and non-fatal cardiovascular events, and adverse events in people with cardiac ion channelopathies. We searched the Cochrane Central Register of Controlled Trials (CENTRAL, 2015, Issue 6), EMBASE, MEDLINE, Conference Proceedings Citation Index - Science (CPCI-S), ClinicalTrials.gov, and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) in July 2015. We applied no language restrictions. We included all randomized controlled trials of people aged 18 years and older with ion channelopathies, including congenital long QT syndrome, congenital short QT syndrome, Brugada syndrome, or catecholaminergic polymorphic ventricular tachycardia. Participants must have been randomized to ICD implantation and compared to antiarrhythmic drug therapy or usual care. Two authors independently selected studies for inclusion and extracted the data. We included all-cause mortality, fatal and non-fatal cardiovascular events, and adverse events for our primary outcome analyses and non-fatal cardiovascular events, rates of inappropriate ICD firing, quality of life, and cost for our secondary outcome analyses. We calculated risk ratios (RR) and associated 95% confidence intervals (CIs) for dichotomous outcomes, both for independent and pooled study analyses. From the 468 references identified after removing duplicates, we found two trials comprising 86 participants that met our inclusion criteria. Both trials included participants with Brugada syndrome who were randomized to ICD versus β-blocker therapy for secondary prevention for sudden cardiac death. Both studies were small, were performed by the same investigators, and exhibited a high risk of bias across multiple domains. In the group randomized to ICD therapy, there was a nine-fold lower risk of mortality compared with people randomized to medical therapy (0% with ICD versus 18% with medical therapy; RR 0.11, 95% CI 0.01 to 0.83; 2 trials, 86 participants). There was low quality evidence of a difference in the rates of combined fatal and non-fatal cardiovascular events, and the results were imprecise (26% with ICD versus 18% with medical therapy; RR 1.49, 95% CI 0.66 to 3.34; 2 trials, 86 participants). The rates of adverse events were higher in the ICD group, but these results were imprecise (28% with ICD versus 10% with medical therapy; RR 2.44, 95% CI 0.92 to 6.44; 2 trials, 86 participants). For secondary outcomes, the risk of non-fatal cardiovascular events was higher in the ICD group, but these results were imprecise and were driven entirely by appropriate ICD-termination of cardiac arrhythmias (26% with ICD versus 0% with medical therapy; RR 11.4, 95% CI 1.57 to 83.3; 2 trials, 86 participants). Approximately 25% of the ICD group experienced inappropriate ICD firing, all of which was corrected by device reprogramming. No data were available for quality of life or cost. We considered the quality of evidence low using the GRADE methodology, due to study limitations and imprecision of effects. Among people with Brugada syndrome who have survived a prior episode of sudden cardiac death, ICD therapy appeared to reduce mortality when compared to β-blocker therapy, but the true magnitude may be substantially different from the estimate of the effect because of study limitations and imprecision. Due to the large magnitude of effect, it is unlikely that there will be additional studies evaluating the role of ICDs for secondary prevention in this population. Further studies are necessary to determine the optimal treatment, if any, to prevent an initial episode of sudden cardiac death in people with cardiac ion channelopathies.

Exploring the Discussion of Risk of Sudden Cardiac Death.

Sudden arrhythmic death syndrome (SADS), where death is secondary to cardiac arrhythmia, is associated with several cardiac ion channelopathies, including long QT syndrome and Brugada syndrome, as well as cardiomyopathies such as hypertrophic cardiomyopathy and dilated cardiomyopathy. Many of these conditions often present in childhood or adolescence. This study investigates how diagnoses of cardiac diseases associated with SADS are communicated within families. A questionnaire was distributed through cardiac disease-focused support groups and organizations. Data from 114 parents who have a child with a SADS condition were used for analysis. Based on the responses, parents explained the risk of SADS in a straightforward manner and related the risk to the importance of compliance with the prescribed treatment. Participants also found it difficult to determine and enforce lifestyle modifications, manage individuals' emotional reactions, convey the seriousness of the information without scaring their children, and discuss the risk of SADS during these conversations. Concerns regarding disease progression, length and quality of life, and treatment failures were also expressed. Healthcare providers, the Internet, other affected people, visual aids, and personal experience were all reported to be helpful for facilitating these discussions. Services and resources requested by participants included children's support groups, a counselor or psychologist, and child-oriented materials. Increased understanding of how families discuss children's diagnosis of SADS conditions will equip healthcare providers with the information to address parental concerns and help facilitate meaningful and informative discussions within families.

Inherited ion channel diseases: a brief review.

Ion channelopathies are diseases caused by dysfunctional ion channels that may lead to sudden death. These diseases can be either acquired or inherited. The main phenotypes observed in patients carrying these heritable arrhythmia syndromes are congenital long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome. In the recent years, tremendous progress has been made in the recognition, mechanisms, and treatment of these diseases. The goal of this review is to provide an overview of the main phenotypes, genetic underpinnings, risk stratification, and treatment options for these so-called cardiac ion channelopathies.

Combined gating and trafficking defect in Kv11.1 manifests as a malignant long QT syndrome phenotype in a large Danish p.F29L founder family

Background. Congenital long QT syndrome (LQTS) is a hereditary cardiac channelopathy characterized by delayed ventricular repolarization, syncope, torsades de pointes and sudden cardiac death. Thirty-three members of five apparently ‘unrelated’ Danish families carry the KCNH2:c.87C> A; p.F29L founder mutation. Methods and Results. Linkage disequilibrium mapping with microsatellites around KCNH2 enabled us to estimate the age of the founder mutation to be approximately 22 generations, corresponding to around 550 years. Neighbouring-Joining analysis disclosed one early and three later nodes. The median QTc time of the carriers was 490 ms (range: 415–589 ms) and no difference was seen between the different branches of the family. The mutation is malignant with a penetrance of 73%. Ten F29L carriers received implantable defibrillators (ICDs) (median age at implant 20 years), and of those four individuals experienced eight appropriate shocks. Patch-clamp analysis in HEK 293 cells, performed at 34°C disclosed a loss-of-function phenotype with fast deactivation, reduced steady-state inactivation current density and a positive voltage shift in inactivation. Western blotting of HEK 293 cells transfected with KCNH2:WT and KCNH2:c.87C> A revealed a reduced fraction of fully glycosylated hERG:p.F29L suggesting that this mutation results in defective trafficking. Conclusion. The altered channel gating kinetics in combination with defective trafficking of mutated channels is expected to result in reduced repolarizing current density and, thus, a LQTS phenotype.

The prevalence and significance of a short QT interval in 18 825 low-risk individuals including athletes

ObjectivesThe short QT syndrome is a cardiac channelopathy characterised by accelerated repolarisation which manifests as a short QT interval on the ECG. The definition of a short QT interval is...

Role of pharmacotherapy in cardiac ion channelopathies.

In the last decade, there have been considerable advances in the understanding of the pathophysiology of malignant ventricular tachyarrhythmias (VT) and sudden cardiac death (SCD). Over 80% of SCD occurs in patients with organic heart disease. However, approximately 10%-15% of SCD occurs in the presence of structurally normal heart, and the majority of these patients are young. In this group of patients, changes in genes encoding cardiac ion channels produce modifications of the function of the channel resulting in an electrophysiological substrate of VT and SCD. Collectively, these disorders are referred to as cardiac ion channelopathies. The four major syndromes in this group are: the long QT syndrome (LQTS), the Brugada syndrome (BrS), the short QT syndrome (SQTS), and the catecholaminergic polymorphic ventricular tachycardia (CPVT). Each of these syndromes includes multiple subtypes with different and sometimes complex cardiac ion channel genetic abnormalities. Many are associated with other somatic and neurological abnormalities besides the risk of VT and SCD. The current management of cardiac ion channelopathies can be summarized as follows: (1) in symptomatic patients, the implantable cardioverter defibrillator (ICD) is the only viable option; (2) in asymptomatic patients, risk stratification is necessary, followed by either the ICD, pharmacotherapy, or a combination of both. A genotype-specific approach to pharmacotherapy requires a thorough understanding of the molecular-cellular basis of arrhythmogenesis in cardiac ion channelopathies as well as the specific drug profile.

Faulty cardiac repolarization reserve in alternating hemiplegia of childhood broadens the phenotype.

Alternating hemiplegia of childhood is a rare disorder caused by de novo mutations in the ATP1A3 gene, expressed in neurons and cardiomyocytes. As affected individuals may survive into adulthood, we use the term 'alternating hemiplegia'. The disorder is characterized by early-onset, recurrent, often alternating, hemiplegic episodes; seizures and non-paroxysmal neurological features also occur. Dysautonomia may occur during hemiplegia or in isolation. Premature mortality can occur in this patient group and is not fully explained. Preventable cardiorespiratory arrest from underlying cardiac dysrhythmia may be a cause. We analysed ECG recordings of 52 patients with alternating hemiplegia from nine countries: all had whole-exome, whole-genome, or direct Sanger sequencing of ATP1A3. Data on autonomic dysfunction, cardiac symptoms, medication, and family history of cardiac disease or sudden death were collected. All had 12-lead electrocardiogram recordings available for cardiac axis, cardiac interval, repolarization pattern, and J-point analysis. Where available, historical and prolonged single-lead electrocardiogram recordings during electrocardiogram-videotelemetry were analysed. Half the cohort (26/52) had resting 12-lead electrocardiogram abnormalities: 25/26 had repolarization (T wave) abnormalities. These abnormalities were significantly more common in people with alternating hemiplegia than in an age-matched disease control group of 52 people with epilepsy. The average corrected QT interval was significantly shorter in people with alternating hemiplegia than in the disease control group. J wave or J-point changes were seen in six people with alternating hemiplegia. Over half the affected cohort (28/52) had intraventricular conduction delay, or incomplete right bundle branch block, a much higher proportion than in the normal population or disease control cohort (P = 0.0164). Abnormalities in alternating hemiplegia were more common in those ≥16 years old, compared with those <16 (P = 0.0095), even with a specific mutation (p.D801N; P = 0.045). Dynamic, beat-to-beat or electrocardiogram-to-electrocardiogram, changes were noted, suggesting the prevalence of abnormalities was underestimated. Electrocardiogram changes occurred independently of seizures or plegic episodes. Electrocardiogram abnormalities are common in alternating hemiplegia, have characteristics reflecting those of inherited cardiac channelopathies and most likely amount to impaired repolarization reserve. The dynamic electrocardiogram and neurological features point to periodic systemic decompensation in ATP1A3-expressing organs. Cardiac dysfunction may account for some of the unexplained premature mortality of alternating hemiplegia. Systematic cardiac investigation is warranted in alternating hemiplegia of childhood, as cardiac arrhythmic morbidity and mortality are potentially preventable.

Identification and Functional Characterization of a Novel CACNA1C-Mediated Cardiac Disorder Characterized by Prolonged QT Intervals With Hypertrophic Cardiomyopathy, Congenital Heart Defects, and Sudden Cardiac Death.

A portion of sudden cardiac deaths can be attributed to structural heart diseases, such as hypertrophic cardiomyopathy (HCM) or cardiac channelopathies such as long-QT syndrome (LQTS); however, the underlying molecular mechanisms are distinct. Here, we identify a novel CACNA1C missense mutation with mixed loss-of-function/gain-of-function responsible for a complex phenotype of LQTS, HCM, sudden cardiac death, and congenital heart defects. Whole exome sequencing in combination with Ingenuity variant analysis was completed on 3 affected individuals and 1 unaffected individual from a large pedigree with concomitant LQTS, HCM, and congenital heart defects and identified a novel CACNA1C mutation, p.Arg518Cys, as the most likely candidate mutation. Mutational analysis of exon 12 of CACNA1C was completed on 5 additional patients with a similar phenotype of LQTS plus a personal or family history of HCM-like phenotypes and identified 2 additional pedigrees with mutations at the same position, p.Arg518Cys/His. Whole cell patch clamp technique was used to assess the electrophysiological effects of the identified mutations in CaV1.2 and revealed a complex phenotype, including loss of current density and inactivation in combination with increased window and late current. Through whole exome sequencing and expanded cohort screening, we identified a novel genetic substrate p.Arg518Cys/His-CACNA1C, in patients with a complex phenotype including LQTS, HCM, and congenital heart defects annotated as cardiac-only Timothy syndrome. Our electrophysiological studies, identification of mutations at the same amino acid position in multiple pedigrees, and cosegregation with disease in these pedigrees provide evidence that p.Arg518Cys/His is the pathogenic substrate for the observed phenotype.

Sudden Cardiac Death and Disorders of the QT Interval: Anesthetic Implications and Focus on Perioperative Management.

ONG QT SYNDROME (LQTS) and short QT syndrome SODIUM CHANNEL PATHOPHYSIOLOGY AND LQTS/SQTS L(SQTS) are genetic cardiac ion channelopathies that occur in the general population and have a well-documented association with sudden cardiac death both in children and adults. Sudden cardiac death usually is caused by sustained ventricular tachycardia, including ventricular fibrillation. The published incidence averages about 5 to 10 deaths per 10,000 population. In the United States, sudden cardiac death is responsible for about 300,000 to 450,000 deaths per year. The ion channelopathies are a heterogenous group of inherited multisystem disorders that include Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and arrhythmogenic right ventricular cardiomyopathy. These conditions have 3 features in common: (1) a structurally normal heart, (2) genetic basis, and (3) predisposition to lethal arrhythmias. They are being recognized with increased frequency in the perioperative period, and guidelines for the management of patients with these complex arrhythmias are lacking. This review addresses the perioperative issues associated with LQTS and SQTS, with a focus on evidence-based management.

Targeted next generation sequencing application in cardiac channelopathies: Analysis of a cohort of autopsy-negative sudden unexplained deaths

Genetic testing for cardiac channelopathies in sudden unexplained death (SUD) has developed substantially over the last years. The Next Generation Sequencing (NGS) technology provides an unprecedented opportunity to screen for genetic variations underlying arrhythmogenic genes in a short period of time at a low cost.The present study aimed to perform genetic testing with NGS technologies on the Ion Torrent Personal Genome Machine™ (Ion PGM™) sequencer, in targeting a total of 23 genes reported to be associated with inherited cardiac channelopathies in order to identify the possible cause of death in a cohort of post-mortem cases.The molecular analyses focused on 16 cases of SUD, aged less than 35 years old. In all cases, the cause of death could not be determined after a rigorous autopsy associated with histopathological and toxicological analyses according to the guidelines of the Association for European Cardiovascular Pathology. DNA was extracted from fresh frozen tissue.An average of 200 variants was identified per case. However, after the prioritization process using a new scoring program (VaRank) and after the conjunction of clinical data and molecular findings, four “likely pathogenic” variants (including two undescribed variants), were identified in three cases (18.75%) of our cohort in the genes KCNH2, ANK2, SCN5A and RYR2. One case, who died during psychiatric hospitalization after administration of a QT prolonging drug, showed a double “likely pathogenic” variant in Long QT genes (ANK2 and SCN5A) which may have predisposed to drug-induced cardiac arrhythmias.Our study illustrates that the NGS approach based on AmpliSeq™ libraries and Ion Torrent PGM™ sequencing may be an efficient approach, integrated to post-mortem examination. Given the massive amount of information generated by NGS, a rigorous filtration strategy of variants coupled with multidisciplinary collaboration is crucial to determine the potential pathogenic role of identified variants in the cause of death.

Genetic purgatory and the cardiac channelopathies: Exposing the variants of uncertain/unknown significance issue

AbstractMerriam-Webster’s online dictionary defines purgatory as “an intermediate state after death for expiatory purification” or more specifically as “a place or state of punishment wherein according to Roman Catholic doctrine the souls of those who die in God׳s grace may make satisfaction for past sins and so become fit for heaven.” Alternatively, it is defined as “a place or state of temporary suffering or misery.” Either way, purgatory is a place where you are stuck, and you don’t want to be stuck there. It is in this context that the term genetic purgatory is introduced. Genetic purgatory is a place where the genetic test–ordering physician and patients and their families are stuck when a variant of uncertain/unknown significance (VUS) has been elucidated. It is in this dark place where suffering and misery are occurring because of unenlightened handling of a VUS, which includes using the VUS for predictive genetic testing and making radical treatment recommendations based on the presence or absence of a so-called maybe mutation. Before one can escape from this miserable place, one must first recognize that one is stuck there. Hence, the purpose of this review article is to fully expose the VUS issue as it relates to the cardiac channelopathies and make the cardiologists/geneticists/genetic counselors who order such genetic tests believers in genetic purgatory. Only then can one meaningfully attempt to get out of that place and seek to promote a VUS to disease-causative mutation status or demote it to an utterly innocuous and irrelevant variant.

Obstructive Sleep Apnea in Patients with Congenital Long QT Syndrome: Implications for Increased Risk of Sudden Cardiac Death.

Congenital long QT syndrome (LQTS) is a familial arrhythmogenic cardiac channelopathy characterized by prolonged ventricular repolarization and increased risk of torsades de pointes-mediated syncope, seizures, and sudden cardiac death (SCD). QT prolongation corrected for heart rate (QTc) is an important diagnostic and prognostic feature in LQTS. Obstructive sleep apnea (OSA) has been increasingly implicated in the pathogenesis of cardiovascular disease, including arrhythmias and SCD. We tested the hypothesis that the presence of concomitant OSA in patients with LQTS is associated with increased QT intervals, both during sleep and while awake. Polysomnography with simultaneous overnight 12-lead electrocardiography (ECG) was recorded in 54 patients with congenital LQTS and 67 control subjects. OSA was diagnosed as apnea-hypopnea index (AHI) ≥ 5 events/h for adults and AHI > 1 event/h for children. RR and QT intervals were measured from the 12-lead surface ECG. QTc was determined by the Bazett formula. Respiratory disturbance index, AHI, and arousal index were significantly increased in patients with LQTS and with OSA compared to those without OSA and control subjects. QTc during different sleep stages and while awake was also significantly increased in patients with LQTS and OSA compared to those without OSA. Severity of OSA in patients with LQTS was directly associated with the degree of QTc. The presence and severity of obstructive sleep apnea (OSA) in patients with congenital long QT syndrome (LQTS) is associated with increased QT prolongation corrected for heart rate, which is an important biomarker of sudden cardiac death (SCD). Treatment of OSA in LQTS patients may reduce QT prolongation, thus reducing the risk of LQT-triggered SCD.

Cardiac channelopathies – A too frequently trivialized problem?

Cardiac channelopathies – A too frequently trivialized problem?

A note on the prevalence of cardiac ion channelopathies in the sudden infant death syndrome

In the December 2014 issue of Europace , Wong and Behr1 published a review on the role of undiagnosed inherited cardiac conditions in sudden unexplained death in infants and children, which I read with great interest. In their Table 1, Wong and Behr1 provide the reader with data on the frequency of mutations in ion channel-related genes in cases of sudden infant death syndrome (SIDS). For example, a frequency of 1.0% is listed for mutations in the KCNQ1 gene, with reference to three studies on cohorts of SIDS cases (their references 30–32, which I cannot repeat here because of the restrictions …

SCN4A variants and Brugada syndrome: phenotypic and genotypic overlap between cardiac and skeletal muscle sodium channelopathies.

SCN5A mutations involving the α-subunit of the cardiac voltage-gated muscle sodium channel (NaV1.5) result in different cardiac channelopathies with an autosomal-dominant inheritance such as Brugada syndrome. On the other hand, mutations in SCN4A encoding the α-subunit of the skeletal voltage-gated sodium channel (NaV1.4) cause non-dystrophic myotonia and/or periodic paralysis. In this study, we investigated whether cardiac arrhythmias or channelopathies such as Brugada syndrome can be part of the clinical phenotype associated with SCN4A variants and whether patients with Brugada syndrome present with non-dystrophic myotonia or periodic paralysis and related gene mutations. We therefore screened seven families with different SCN4A variants and non-dystrophic myotonia phenotypes for Brugada syndrome and performed a neurological, neurophysiological and genetic work-up in 107 Brugada families. In the families with an SCN4A-associated non-dystrophic myotonia, three patients had a clinical diagnosis of Brugada syndrome, whereas we found a remarkably high prevalence of myotonic features involving different genes in the families with Brugada syndrome. One Brugada family carried an SCN4A variant that is predicted to probably affect function, one family suffered from a not genetically confirmed non-dystrophic myotonia, one family was diagnosed with myotonic dystrophy (DMPK gene) and one family had a Thomsen disease myotonia congenita (CLCN1 variant that affects function). Our findings and data suggest a possible involvement of SCN4A variants in the pathophysiological mechanism underlying the development of a spontaneous or drug-induced type 1 electrocardiographic pattern and the occurrence of malignant arrhythmias in some patients with Brugada syndrome.

Clinical presentation and course of long QT syndrome in Thai children

BackgroundCongenital long QT syndrome (LQTS) is a genetically transmitted cardiac channelopathy that can lead to lethal arrhythmia and sudden cardiac death in healthy young people. The clinical characteristics of LQTS are variable and depend on the subtype of long QT syndrome, which differ among populations. This single hospital-based case review study examined the clinical presentation of long QT syndrome and the outcomes of its treatment in 20 Thai children at King Chulalongkorn Memorial Hospital in Bangkok, Thailand. MethodsInpatient and outpatient records of children (aged 0–14 years) diagnosed with long QT syndrome from January 1, 1998, to September 30, 2013, were retrospectively reviewed. Presentation at diagnosis, treatments, and clinical courses were collected and analyzed. In the 20 subjects, total Schwartz scores totaled 5.2±0.9 points, and mean age at diagnosis was 7.6±4.4 years (range, 1 day–13.8 years). The patients were assigned to one of 3 groups based on trigger events: 50% of patients had events at rest (sleep or at rest), 35% experienced adrenergic-mediated events (e.g., stress, exercise, startle), and 15% were asymptomatic. Excluding the 3 patients who died at first presentation, 100% of patients received a beta blocker, and 47.1% were treated with an automatic implantable cardioverter-defibrillator (AICD). ResultsAt follow-up (median=959 days; range, 1–4170 days), 4 patients (20%) were known to have died, 3 of whom died shortly after the diagnosis. Among patients who survived the initial event, 52.9% (9 of 17) experienced cardiac events (appropriate AICD shock, death, and/or syncope) during the follow-up period. The mean duration from diagnosis to cardiac event was 1420±759 days (range, 497–2499 days). ConclusionsAll 20 patients with LQTS were mostly symptomatic at presentation. Owing to the geographical region and ethnicity of the Thai population, we conclude that the ratio of patients who develop cardiac symptoms at rest or during sleep might be higher than in other Asian countries.