Efficacy and safety of flecainide for ventricular arrhythmias in patients with Andersen-Tawil syndrome with KCNJ2 mutations

Bidirectional Ventricular Tachycardia and Prominent U Waves: Look at Fingers and Muscles and Use Flecainide

We present a case of bidirectional ventricular tachycardia in a 15-year-old boy asymptomatic for arrhythmias, whose major complaint was muscle weakness. At our first evaluation he was receiving sotalol for his ventricular arrhythmias. In addition to bidirectional tachycardia, electrocardiogram during sinus rhythm showed prominent U waves and prolonged QT-U interval. These electrocardiographic signs, along with the evidence of clinodactyly and mild hypertelorism, led us to the diagnosis of Andersen-Tawil syndrome, confirmed by genetic analysis that revealed a "de novo" missense mutation of KCNJ2 gene. Monotherapy with flecainide was rapidly effective and almost eliminated ventricular arrhythmias. After a 4-year follow-up there were no adverse events, flecainide has been well tolerated without significant modification of the QRS or repolarization, and ventricular arrhythmias have not been relapsed to date. The case highlights the importance of a correct clinical diagnosis, which is crucial for the optimal selection of the most appropriate drug therapy, which is expected not to be harmful, before being beneficial.

Precision medicine for long QT syndrome: patient-specific iPSCs take the lead

Long QT syndrome (LQTS) is a detrimental arrhythmia syndrome mainly caused by dysregulated expression or aberrant function of ion channels. The major clinical symptoms of ventricular arrhythmia, palpitations and syncope vary among LQTS subtypes. Susceptibility to malignant arrhythmia is a result of delayed repolarisation of the cardiomyocyte action potential (AP). There are 17 distinct subtypes of LQTS linked to 15 autosomal dominant genes with monogenic mutations. However, due to the presence of modifier genes, the identical mutation may result in completely different clinical manifestations in different carriers. In this review, we describe the roles of various ion channels in orchestrating APs and discuss molecular aetiologies of various types of LQTS. We highlight the usage of patient-specific induced pluripotent stem cell (iPSC) models in characterising fundamental mechanisms associated with LQTS. To mitigate the outcomes of LQTS, treatment strategies are initially focused on small molecules targeting ion channel activities. Next-generation treatments will reap the benefits from development of LQTS patient-specific iPSC platform, which is bolstered by the state-of-the-art technologies including whole-genome sequencing, CRISPR genome editing and machine learning. Deep phenotyping and high-throughput drug testing using LQTS patient-specific cardiomyocytes herald the upcoming precision medicine in LQTS.

Bidirectional Ventricular Tachycardia in a Young Female: A Case of Andersen-Tawil Syndrome

Bidirectional ventricular tachycardia (VT) is a rare ventricular dysrhythmia with a limited differential diagnosis that includes digitalis toxicity, catecholaminergic polymorphic VT, aconite poisoning, and genetic channelopathy syndromes, specifically, Andersen-Tawil syndrome (ATS). We present a case of a young female with palpitations found to have bidirectional VT on cardiac event monitor and strong family history of cardiac dysrhythmias. Her physical examination findings included minor dysmorphic features of mandibular hypoplasia, hypertelorism, and clinodactyly. The patient was clinically diagnosed with ATS and started on a beta-blocker for control of ectopy. A second Holter review demonstrated markedly decreased burden of ventricular ectopy compared to the initial monitoring. She was referred for genetic testing, which revealed a KCNJ2 mutation. Bidirectional VT is an uncommon ventricular dysrhythmia that has a limited differential diagnosis, one of which is ATS-a rare genetic disorder that results from mutations in the KCNJ2 gene. The condition is frequently associated with developmental, skeletal, and cardiac abnormalities. Although there are no strong recommendations that exist for treatment of ventricular dysrhythmias associated with this genetic disorder, we demonstrate a case of clinical improvement in a patient with ATS by using the beta-blocker metoprolol succinate. Furthermore, we propose that ATS patients may not need exercise restrictions as overall ventricular ectopy burden decreased with exercise and there was no prolongation of the QT interval. This patient will continue to follow up in our clinic to reassess symptom burden and for continued monitoring for the development of any new features.

Case report: Mexiletine suppresses ventricular arrhythmias in Andersen-Tawil syndrome

It is arduous to determine clinical solutions for Andersen-Tawil syndrome (ATS) in patients intolerant of β-blocker. Here, we present the case of a 7-year-old boy with periodic paralysis and dysmorphic features who experienced syncope four times during exercise. His ECG revealed enlarged U waves and QU-prolongation associated with ATS-specific U wave patterns, frequent PVCs, and non-sustained bidirectional or polymorphic ventricular tachycardia. The genetic test showed a de novo missense R218W mutation of KCNJ2. With the diagnosis of ATS and intolerance of β-blocker, the patient was prescribed oral medications of mexiletine 450 mg/day without severe adverse effects. The repeat ECG showed decreased PVC burden from 38 to 3% and absence of ventricular tachycardia. He remained symptom-free during over 2 years of outpatient follow-up. This case demonstrates a new anti-arrhythmic therapy with mexiletine for prevention of life-threatening cardiac events in patients with ATS who are intolerant of β-blocker treatment.

Tetramisole is a new IK1 channel agonist and exerts IK1 -dependent cardioprotective effects in rats

Cardiac ischemia, hypoxia, arrhythmias, and heart failure share the common electrophysiological changes featured by the elevation of intracellular Ca2+ (Ca2+ overload) and inhibition of the inward rectifier potassium (IK1 ) channel. IK1 channel agonists have been considered a new type of anti-arrhythmia and cardioprotective agents. We predicted using a drug repurposing strategy that tetramisole (Tet), a known anthelminthic agent, was a new IK1 channel agonist. The present study aimed to experimentally identify the above prediction and further demonstrate that Tet has cardioprotective effects. Results of the whole-cell patch clamp technique showed that Tet at 1-100 μmol/L enhanced IK1 current, hyperpolarized resting potential (RP), and shortened action potential duration (APD) in isolated rat cardiomyocytes, while without effects on other ion channels or transporters. In adult Sprague-Dawley (SD) rats in vivo, Tet showed anti-arrhythmia and anticardiac remodeling effects, respectively, in the coronary ligation-induced myocardial infarction model and isoproterenol (Iso, i.p., 3 mg/kg/day, 10 days) infusion-induced cardiac remodeling model. Tet also showed anticardiomyocyte remodeling effect in Iso (1 μmol/L) infused adult rat ventricular myocytes or cultured H9c2 (2-1) cardiomyocytes. Tet at 0.54 mg/kg in vivo or 30 μmol/L in vitro showed promising protections on acute ischemic arrhythmias, myocardial hypertrophy, and fibrosis. Molecular docking was performed and identified the selective binding of Tet with Kir2.1. The cardioprotection of Tet was associated with the facilitation of IK1 channel forward trafficking, deactivation of PKA signaling, and inhibition of intracellular calcium overload. Enhancing IK1 may play dual roles in anti-arrhythmia and antiventricular remodeling mediated by restoration of Ca2+ homeostasis.

Molecular stratification of arrhythmogenic mechanisms in the Andersen Tawil Syndrome

Andersen Tawil Syndrome (ATS) is a rare inheritable disease associated with loss-of-function mutations in KCNJ2, the gene coding the strong inward rectifier potassium channel Kir2.1, which forms an essential membrane protein controlling cardiac excitability. ATS is usually marked by a triad of periodic paralysis, life-threatening cardiac arrhythmias and dysmorphic features, but its expression is variable and not all patients with a phenotype linked to ATS have a known genetic alteration. The mechanisms underlying this arrhythmogenic syndrome are poorly understood. Knowing such mechanisms would be essential to distinguish ATS from other channelopathies with overlapping phenotypes and to develop individualized therapies. For example, the recently suggested role of Kir2.1 as a countercurrent to sarcoplasmic calcium reuptake might explain the arrhythmogenic mechanisms of ATS and its overlap with catecholaminergic polymorphic ventricular tachycardia (CPVT). Here we summarize current knowledge on the mechanisms of arrhythmias leading to sudden cardiac death in ATS. We first provide an overview of the syndrome and its pathophysiology, from the patient´s bedside to the protein, and discuss the role of essential regulators and interactors that could play a role in cases of ATS. The review highlights novel ideas related to some post-translational channel interactions with partner proteins that might help define the molecular bases of the arrhythmia phenotype. We then propose a new all-embracing classification of the currently known ATS loss-of-function mutations according to their position in the Kir2.1 channel structure and their functional implications. We also discuss specific ATS pathogenic variants, their clinical manifestations and treatment stratification. The goal is to provide a deeper mechanistic understanding of the syndrome toward the development of novel targets and personalized treatment strategies.

Management of ventricular arrhythmias in heart failure: Current perspectives

Congestive heart failure (HF) is a progressive affliction defined as the inability of the heart to sufficiently maintain blood flow. Ventricular arrhythmias (VAs) are common in patients with HF, and conversely, advanced HF promotes the risk of VAs. Management of VA in HF requires a systematic, multimodality approach that comprises optimization of medical therapy and use of implantable cardioverter-defibrillator and/or device combined with cardiac resynchronization therapy. Catheter ablation is one of the most important strategies with the potential to abolish or decrease the number of recurrences of VA in this population. It can be a curative strategy in arrhythmia-induced cardiomyopathy and may even save lives in cases of an electrical storm. Additionally, modulation of the autonomic nervous system and stereotactic radiotherapy have been introduced as novel methods to control refractory VAs. In patients with end-stage HF and refractory VAs, an institution of the mechanical circulatory support device and cardiac transplant may be considered. This review aims to provide an overview of current evidence regarding management strategies of VAs in HF with an emphasis on interventional treatment.

Flecainide in Ventricular Arrhythmias: From Old Myths to New Perspectives

Flecainide is an IC antiarrhythmic drug (AAD) that received in 1984 Food and Drug Administration approval for the treatment of sustained ventricular tachycardia (VT) and subsequently for rhythm control of atrial fibrillation (AF). Currently, flecainide is mainly employed for sinus rhythm maintenance in AF and the treatment of idiopathic ventricular arrhythmias (IVA) in absence of ischaemic and structural heart disease on the basis of CAST data. Recent studies enrolling patients with different structural heart diseases demonstrated good effectiveness and safety profile of flecainide. The purpose of this review is to assess current evidence for appropriate and safe use of flecainide, 30 years after CAST data, in the light of new diagnostic and therapeutic tools in the field of ischaemic and non-ischaemic heart disease.

Association analysis of SNPs in GRHL3, FAF1, and KCNJ2 with NSCPO sub-phenotypes in Han Chinese

OBJECTIVES

Non-syndromic cleft palate only (NSCPO) is a common congenital deformity with complex etiologies. GRHL3, FAF1, and KCNJ2 have been reported to be involved in the pathogenesis of NSCPO. Up till now, there have been no replication studies based on large Han Chinese. Therefore, this study aimed to investigate associations between GRHL3, FAF1, KCNJ2, and NSCPO sub-phenotypes patients in Han Chinese.

MATERIALS AND METHODS

Firstly, we selected 2 SNPs based on previous literatures: FAF1 (rs3827730) and GRHL3 (rs41268753). Also, we selected 8 tagSNPs in GRHL3 (rs557811, rs609352, rs10903078, rs6659209, rs12401714, rs12568599, rs3887581, rs12024148) and 2 tagSNPs in KCNJ2 (rs75855040 and rs236514). Afterward, we evaluated these SNPs among 1668 NSCPO patients and 1811 normal controls from Han Chinese. Following data were analyzed by PLINK and Haploview program.

RESULTS

Association analysis under additive model showed that allele A at rs12568599 in GRHL3 gene is significantly associated with NSCPO (p = 0.0034, OR = 1.38 and 95%CI: 1.11-1.72) and its sub-phenotype incomplete cleft palate (ICP) (p = 0.0039, OR = 1.4 and 95%CI: 1.11-1.75), and it could increase the risk of both NSCPO and ICP.

CONCLUSIONS

This study firstly found that rs12568599 in GRHL3 is associated with NSCPO and ICP in Han Chinese, indicating that sub-phenotypes of NSCPO have different etiologies.

Towards Mutation-Specific Precision Medicine in Atypical Clinical Phenotypes of Inherited Arrhythmia Syndromes

Most causal genes for inherited arrhythmia syndromes (IASs) encode cardiac ion channel-related proteins. Genotype-phenotype studies and functional analyses of mutant genes, using heterologous expression systems and animal models, have revealed the pathophysiology of IASs and enabled, in part, the establishment of causal gene-specific precision medicine. Additionally, the utilization of induced pluripotent stem cell (iPSC) technology have provided further insights into the pathophysiology of IASs and novel promising therapeutic strategies, especially in long QT syndrome. It is now known that there are atypical clinical phenotypes of IASs associated with specific mutations that have unique electrophysiological properties, which raises a possibility of mutation-specific precision medicine. In particular, patients with Brugada syndrome harboring an SCN5A R1632C mutation exhibit exercise-induced cardiac events, which may be caused by a marked activity-dependent loss of R1632C-Nav1.5 availability due to a marked delay of recovery from inactivation. This suggests that the use of isoproterenol should be avoided. Conversely, the efficacy of β-blocker needs to be examined. Patients harboring a KCND3 V392I mutation exhibit both cardiac (early repolarization syndrome and paroxysmal atrial fibrillation) and cerebral (epilepsy) phenotypes, which may be associated with a unique mixed electrophysiological property of V392I-Kv4.3. Since the epileptic phenotype appears to manifest prior to cardiac events in this mutation carrier, identifying KCND3 mutations in patients with epilepsy and providing optimal therapy will help prevent sudden unexpected death in epilepsy. Further studies using the iPSC technology may provide novel insights into the pathophysiology of atypical clinical phenotypes of IASs and the development of mutation-specific precision medicine.

Every face tells a story-unravelling a case of bidirectional ventricular tachycardia

Bidirectional ventricular tachycardia is a rare form of tachycardia. We hereby report a case of bidirectional ventricular tachycardia in an 8-year-old boy wherein careful clinical exami-nation led to the diagnosis of Andersen Tawil syndrome. The case also demonstrates the efficacy of flecainide in managing bidirectional ventricular tachycardia in the setting of Andersen Tawil syndrome.

Compound heterozygous mutations in KCNJ2 and KCNH2 in a patient with severe Andersen-Tawil syndrome

Andersen-Tawil syndrome (ATS) is a rare channelopathy, sometimes referred to as long QT syndrome type 7. ATS is an autosomal dominant disease predominantly caused by mutations in the KCNJ2 gene. Patients with ATS present with episodes of muscle weakness, arrythmias, including prolonged QT intervals, and various skeletal abnormalities. Unlike other channelopathies, ATS has a relatively mild clinical course and low risk of sudden cardiac death. In this study, we describe a female patient with typical symptoms of ATS with the addition of unusually severe arrhythmias. Extensive DNA testing was performed to find the possible cause of this unique presentation. In addition to a known mutation in KCNJ2, the patient carried a variant in KCNH2 The combination of genetic variants may lead to the severe clinical manifestation of ATS. Additional genetic information allowed accurate genetic counselling to be provided to the patient.

"Electrifying dysmorphology": Potassium channelopathies causing dysmorphic syndromes

Potassium channels are a heterogeneous group of membrane-bound proteins, whose functions support a diverse range of biological processes. Genetic disorders arising from mutations in potassium channels are classically recognized by symptoms arising from acute channel dysfunction, such as periodic paralysis, ataxia, seizures, or cardiac conduction abnormalities, often in a patient with otherwise normal examination findings. In this chapter, we review a distinct subgroup of rare potassium channelopathies whose presentations are instead suggestive of a developmental disorder, with features including intellectual disability, craniofacial dysmorphism or other physical anomalies. Known conditions within this subgroup are: Andersen-Tawil syndrome, Birk-Barel syndrome, Cantú syndrome, Keppen-Lubinsky syndrome, Temple-Baraitser syndrome, Zimmerman-Laband syndrome and a very similar disorder called Bauer-Tartaglia or FHEIG syndrome. Ion channelopathies are unlikely to be routinely considered in the differential diagnosis of children presenting with developmental concerns, and so detailed description and photographs of the clinical phenotype are provided to aid recognition. For several of these disorders, functional characterization of the genetic mutations responsible has led to identification of candidate therapies, including drugs already commonly used for other indications, which adds further impetus to their prompt recognition. Together, these cases illustrate the potential for mechanistic insights gained from genetic diagnosis to drive translational work toward targeted, disease-modifying therapies for rare disorders.

Multivariate analysis of TU wave complex on electrocardiogram in Andersen-Tawil syndrome with KCNJ2 mutations

BACKGROUND

The exact differences between the TU wave complex of ATS1 and that of healthy individuals remain to be investigated. We sought to characterize the TU wave complex of Andersen-Tawil syndrome type 1 (ATS1) using high frequency electrocardiogram (ECG) data.

METHODS

Electrocardiograms were recorded as time series data with a 2 kHz frequency ECG amplifier in 13 patients with ATS1 (positive for KCNJ2 mutation, ATS1 group) and age-matched healthy individuals (control group). Conventional ECG parameters were measured, and principal component analysis (PCA) and independent component analysis (ICA) were applied to the TU wave complex.

RESULTS

Time from T peak (Tp) to U peak (Up), time from bottom (B) to Up, and time from B to U end (BUe, U duration) (0.232 ± 0.018 vs. 0.165 ± 0.017, p < .0001), where B is the lowest point between T and U waves, were all longer in the ATS1 group than the control group. Multivariate logistic regression analysis revealed that BUe could completely differentiate the two groups. PCA ratios in the ATS1 group were significantly larger than the control group (26.5 ± 12.3 vs. 10.4 ± 6.2, p = .0005). ICA revealed 1 or 2 U-wave-specific independent components (ICs) that exclusively comprise the U wave in ATS1, whereas U waves in the control group were composed of some ICs that also comprised T waves.

CONCLUSIONS

U-wave-related temporal parameters, particularly BUe, and the existence of U-wave-specific ICs, extracted in the ICA, are useful for differentiation of U waves in ATS1 from those in healthy individuals.

Usefulness of the intravenous flecainide challenge test before oral flecainide treatment in a patient with Andersen-Tawil syndrome

Andersen-Tawil syndrome (ATS) is an inherited disorder characterised by the triad of ventricular arrhythmias (VAs), periodic paralysis and dysmorphic features. A 31-year-old woman diagnosed with ATS caused by a KCNJ2 mutation (p.R228ins) was urgently admitted to our hospital following an episode of syncope during exercise. Electrocardiography revealed frequent premature ventricular complexes and non-sustained ventricular tachycardias (VTs) with pleomorphic QRS patterns. During the intravenous flecainide test (30 mg), the frequent VAs were inhibited completely. After oral flecainide (100 mg) was started, VAs, except for a brief bigeminy, were suppressed during the exercise test. On 24-hour Holter recordings, the VAs decreased from 50 133 to 13 363 beats/day (-73%). Sustained VT and syncope were not observed during a 3-year follow-up period. Intravenous flecainide challenge test may be useful in predicting the efficacy of oral flecainide treatment for patients with ATS.

Recent understanding of clinical sequencing and gene-based risk stratification in inherited primary arrhythmia syndrome

Inherited primary arrhythmia syndromes (IPAS) may result in ventricular tachycardia or ventricular fibrillation by some genetic disorders, leading to sudden cardiac death. IPAS are also called "channelopathies" since many of these are caused by an abnormality in myocardial ion channels. Congenital long-QT syndrome (LQTS) is the most well documented IPAS, which may be seen in 0.1% of the general population. More than 15 disease-causing genes have been identified in almost 70% of LQTS patients and genetic testing is well applied to not only clinical diagnosis but also risk stratification and gene-based therapeutic strategy for each person with LQTS. Thus, in LQTS, gene-based personalized medicine can be realized. Unlike the LQTS, genetic testing for the Brugada syndrome (BrS) is still controversial since only 20% of patients can be identified with the causing gene mutations, most of which are in SCN5A. Furthermore, even in the SCN5A mutation-positive carriers, their phenotypes are not completely consistent with BrS, but may cause other IPAS including LQTS, cardiac conduction defect, sick sinus syndrome, and dilated cardiomyopathy. On the other hand, a recent Japanese BrS registry demonstrated that the pore-region mutations in SCN5A are significantly associated with a risk of lethal cardiac events. Furthermore, a genome-wide association study revealed that a common variant in SCN10A or HEY2 in addition to SCN5A is associated with BrS, thus, BrS may not be a monogenic Mendelian disease but probably an oligogenic disease. The purpose of this review is to describe the basic genetic and pathophysiological findings of the IPAS, particularly LQTS and Brugada syndrome, and to outline a rational approach to genetic testing, management, and family screening.

Long QT Syndrome: Genetics and Future Perspective

Long QT syndrome (LQTS) is an inherited primary arrhythmia syndrome that may present with malignant arrhythmia and, rarely, risk of sudden death. The clinical symptoms include palpitations, syncope, and anoxic seizures secondary to ventricular arrhythmia, classically torsade de pointes. This predisposition to malignant arrhythmia is from a cardiac ion channelopathy that results in delayed repolarization of the cardiomyocyte action potential. The QT interval on the surface electrocardiogram is a summation of the individual cellular ventricular action potential durations, and hence is a surrogate marker of the abnormal cellular membrane repolarization. Severely affected phenotypes administered current standard of care therapies may not be fully protected from the occurrence of cardiac arrhythmias. There are 17 different subtypes of LQTS associated with monogenic mutations of 15 autosomal dominant genes. It is now possible to model the various LQTS phenotypes through the generation of patient-specific induced pluripotent stem cell-derived cardiomyocytes. RNA interference can silence or suppress the expression of mutant genes. Thus, RNA interference can be a potential therapeutic intervention that may be employed in LQTS to knock out mutant mRNAs which code for the defective proteins. CRISPR/Cas9 is a genome editing technology that offers great potential in elucidating gene function and a potential therapeutic strategy for monogenic disease. Further studies are required to determine whether CRISPR/Cas9 can be employed as an efficacious and safe rescue of the LQTS phenotype. Current progress has raised opportunities to generate in vitro human cardiomyocyte models for drug screening and to explore gene therapy through genome editing.

The Safety and Effectiveness of Flecainide in Children in the Current Era

This retrospective study sought to determine the safety and effectiveness of flecainide in children with normal hearts and those with congenital heart disease (CHD) or cardiomyopathy (CMO). Baseline and follow-up data at two pediatric cardiology sites were queried (2000-2015); a total of 175 patients (20 with CHD and two with CMO) receiving flecainide were assessed. When comparing patients with CHD to those with normal hearts, patients with CHD were younger at diagnosis (median age 19 days; IQR 3-157.5 days vs normal heart patients median age 21 days; IQR 7-172 days, p = 0.4) and severe cardiac dysfunction was more prevalent (30% in CHD patients vs 8% in normal heart patients, p = 0.009). Treatment duration did not differ between the two groups (CHD patients median duration 52 weeks; IQR 27-91.5 weeks vs normal heart patients median duration 55 weeks; IQR 32-156 weeks, p = 0.5). Cardiac dysfunction resulting in flecainide discontinuation occurred in two patients (1%), one with CHD and one without. Three patients experienced proarrhythmia (2%) and there were no cardiac arrests during follow-up. There was one death in this cohort in a patient with severe CHD and an RSV infection (<1%). Arrhythmia control did not differ between the groups (90% in CHD patients vs 77% in normal heart patients, p = 0.2). Flecainide was well tolerated in this cohort, with fewer than 3% discontinuing medication due to flecainide-associated adverse events. Contrary to adult studies, there was no difference in the incidence of adverse events between patients with normal hearts and patients with CHD. Flecainide is a safe and effective antiarrhythmic medication, even for children with underlying CHD.

Review of the Diagnosis and Treatment of Periodic Paralysis

Periodic paralyses (PPs) are rare neuromuscular disorders caused by mutations in skeletal muscle sodium, calcium, and potassium channel genes. PPs include hypokalemic paralysis, hyperkalemic paralysis, and Andersen‐Tawil syndrome. Common features of PP include autosomal dominant inheritance, onset typically in the first or second decades, episodic attacks of flaccid weakness, which are often triggered by diet or rest after exercise. Diagnosis is based on the characteristic clinic presentation then confirmed by genetic testing. In the absence of an identified genetic mutation, documented low or high potassium levels during attacks or a decrement on long exercise testing support diagnosis. The treatment approach should include both management of acute attacks and prevention of attacks. Treatments include behavioral interventions directed at avoidance of triggers, modification of potassium levels, diuretics, and carbonic anhydrase inhibitors. Muscle Nerve57: 522–530, 2018

Andersen-Tawil syndrome: Clinical presentation and predictors of symptomatic arrhythmias - Possible role of polymorphisms K897T in KCNH2 and H558R in SCN5A gene

BACKGROUND

Andersen-Tawil syndrome (ATS) is rare channelopathy caused by KCNJ2 mutation and probably KCNJ5. It is characterized by arrhythmias, neurological symptoms, and dysmorphic features. The present study retrospectively examined the characteristics of 11 unrelated families with ATS.

METHODS

This study consisted of 11 probands positive for KCNJ2 variants and 33 family members (mean age 30.0±17.3 years, female n=31). Additional genetic screening of 3 LQTS genes (KCNQ1, KCNH2, SCN5A) was performed in 9 families. Predictors of arrhythmias [premature ventricular beats>2000/24h, biventricular and polymorphic ventricular tachycardia (VT)], syncope, and/or cardiac arrest (CA) were evaluated.

RESULTS

In KCNJ2 mutation carriers vs non-carriers (n=25 vs n=19) significant differences were observed in U-wave manifestations in V2-V4, T_peak-T_end duration, QTUc duration (p<0.0001), dysmorphic features, and neurological symptoms. Compared to asymptomatic carriers (n=9), in those with arrhythmias and/or syncope and/or CA (n=16) micrognathia (p=0.004), periodic paralysis (p=0.019), palpitation (p=0.005), U-wave n V2-V4 (p=0.049) were more frequent; QTU (p=0.045) and T_peak-T_end (p=0.014) were also longer (n=9). In the subgroup of carriers with syncope and/or cardiac arrest (n=10, 90% women), K897T-KCNH2 polymorphism (p=0.02), periodic paralysis (p=0.004), muscle weakness (p=0.04), palpitations (p=0.04), arrhythmias (biventricular VT, p=0.003; polymorphic VT, p=0.009) were observed more frequently. T_peak-T_end duration was longer (p=0.007) and the percentage of patients with premature ventricular contraction >2000/24h was higher (p=0.005).

CONCLUSION

A higher risk of arrhythmia, syncope, and/or CA is associated with the presence of micrognathia, periodic paralysis, and prolonged T_peak-T_end time. Our findings suggest that K897T may contribute to the occurrence of syncope.

Beyond the Electrocardiogram: Mutations in Cardiac Ion Channel Genes Underlie Nonarrhythmic Phenotypes

Cardiac ion channelopathies are an important cause of sudden death in the young and include long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, idiopathic ventricular fibrillation, and short QT syndrome. Genes that encode ion channels have been implicated in all of these conditions, leading to the widespread implementation of genetic testing for suspected channelopathies. Over the past half-century, researchers have also identified systemic pathologies that extend beyond the arrhythmic phenotype in patients with ion channel gene mutations, including deafness, epilepsy, cardiomyopathy, periodic paralysis, and congenital heart disease. A coexisting phenotype, such as cardiomyopathy, can influence evaluation and management. However, prior to recent molecular advances, our understanding and recognition of these overlapping phenotypes were poor. This review highlights the systemic and structural heart manifestations of the cardiac ion channelopathies, including their phenotypic spectrum and molecular basis.

Exercise-induced Ventricular Tachycardia/Ventricular Fibrillation in the Normal Heart: Risk Stratification and Management

Exercise-induced ventricular tachycardia (VT) rarely occurs in the absence of organic heart disease. Idiopathic monomorphic VT has an excellent prognosis. The main aspect of the risk stratification process is recognizing subtle forms of organic heart disease, particularly arrhythmogenic right ventricular cardiomyopathy. Exercise-induced polymorphic VT is potentially malignant. Exercise-induced polymorphic VT has also been seen in mitral valve prolapse. Some patients with stable coronary disease, and even healthy athletes, sometimes have short bursts of polymorphic VT during exercise tests but these arrhythmias are usually not reproducible during repeated testing and have unknown long-term clinical significance.