Endocannabinoids enhance hKV7.1/KCNE1 channel function and shorten the cardiac action potential and QT interval

BACKGROUND

Genotype-positive patients who suffer from the cardiac channelopathy Long QT Syndrome (LQTS) may display a spectrum of clinical phenotypes, with often unknown causes. Therefore, there is a need to identify factors influencing disease severity to move towards an individualized clinical management of LQTS. One possible factor influencing the disease phenotype is the endocannabinoid system, which has emerged as a modulator of cardiovascular function. In this study, we aim to elucidate whether endocannabinoids target the cardiac voltage-gated potassium channel K_V7.1/KCNE1, which is the most frequently mutated ion channel in LQTS.

METHODS

We used two-electrode voltage clamp, molecular dynamics simulations and the E4031 drug-induced LQT2 model of ex-vivo guinea pig hearts.

FINDINGS

We found a set of endocannabinoids that facilitate channel activation, seen as a shifted voltage-dependence of channel opening and increased overall current amplitude and conductance. We propose that negatively charged endocannabinoids interact with known lipid binding sites at positively charged amino acids on the channel, providing structural insights into why only specific endocannabinoids modulate K_V7.1/KCNE1. Using the endocannabinoid ARA-S as a prototype, we show that the effect is not dependent on the KCNE1 subunit or the phosphorylation state of the channel. In guinea pig hearts, ARA-S was found to reverse the E4031-prolonged action potential duration and QT interval.

INTERPRETATION

We consider the endocannabinoids as an interesting class of hK_V7.1/KCNE1 channel modulators with putative protective effects in LQTS contexts.

FUNDING

ERC (No. 850622), Canadian Institutes of Health Research, Canada Research Chairs and Compute Canada, Swedish National Infrastructure for Computing.

Continuous Bayesian variant interpretation accounts for incomplete penetrance among Mendelian cardiac channelopathies

PURPOSE

The congenital Long QT Syndrome (LQTS) and Brugada Syndrome (BrS) are Mendelian autosomal dominant diseases that frequently precipitate fatal cardiac arrhythmias. Incomplete penetrance is a barrier to clinical management of heterozygotes harboring variants in the major implicated disease genes KCNQ1, KCNH2, and SCN5A. We apply and evaluate a Bayesian penetrance estimation strategy that accounts for this phenomenon.

METHODS

We generated Bayesian penetrance models for KCNQ1-LQT1 and SCN5A-LQT3 using variant-specific features and clinical data from the literature, international arrhythmia genetic centers, and population controls. We analyzed the distribution of posterior penetrance estimates across 4 genotype-phenotype relationships and compared continuous estimates with ClinVar annotations. Posterior estimates were mapped onto protein structure.

RESULTS

Bayesian penetrance estimates of KCNQ1-LQT1 and SCN5A-LQT3 are empirically equivalent to 10 and 5 clinically phenotype heterozygotes, respectively. Posterior penetrance estimates were bimodal for KCNQ1-LQT1 and KCNH2-LQT2, with a higher fraction of missense variants with high penetrance among KCNQ1 variants. There was a wide distribution of variant penetrance estimates among identical ClinVar categories. Structural mapping revealed heterogeneity among "hot spot" regions and featured high penetrance estimates for KCNQ1 variants in contact with calmodulin and the S6 domain.

CONCLUSIONS

Bayesian penetrance estimates provide a continuous framework for variant interpretation.

General anesthesia using propofol infusion for implantation of an implantable cardioverter defibrillator in a pediatric patient with Andersen-Tawil syndrome: a case report

Andersen-Tawil syndrome (ATS) is a rare genetic disease characterized by a triad of episodic flaccid muscle weakness, ventricular arrhythmias, and physical anomalies. ATS patients have various cardiac arrhythmias that can cause sudden death. Implantation of an implantable cardioverter-defibrillator (ICD) is required when life-threatening cardiac arrhythmias do not respond to medical treatment. An 11-year-old girl underwent surgery for an ICD implantation. For general anesthesia in ATS patients, anesthesiologists should focus on the potentially difficult airway, serious cardiac arrhythmias, such as ventricular tachycardia (VT), and delayed recovery from neuromuscular blockade. We followed the difficult airway algorithm, avoided drugs that can precipitate QT prolongation and fatal cardiac arrhythmias, and tried to maintain normoxia, normocarbia, normothermia, normoglycemia, and pain control for prevention of sympathetic stimulation. We report the successful application of general anesthesia for ICD implantation in a pediatric patient with ATS and recurrent VT.

Exploring the role of Islam on the lived experience of patients with Long QT Syndrome in Saudi Arabia

Genetic services are rapidly growing in the Arab world leading to increasing number of patients being diagnosed with genetic disorders. Islam is the only/major religion of the local population in these countries. Muslim patients integrate religion in virtually every aspect of their lives, and it is vital to understand the role of Islam on their coping and decision-making in the context of genetic counseling. This will help provide patients with the most appropriate services aligned to their religious beliefs and will improve outcomes. Increasing numbers of patients are being diagnosed with Long QT syndrome in Saudi Arabia. Using semi-structured interviews, this study explored the role of Islam on the lived experience of 13 Saudi participants diagnosed with autosomal dominant Long QT syndrome (3/13) or who are carriers of Jervell and Lange-Nielsen syndrome (10/13). The interviews investigated how they made sense of living with the condition in light of their religion/spirituality. The data were analyzed using interpretative phenomenological analysis and produced four superordinate themes: 1) Common belief and idiosyncratic interpretation; 2) Using religion to justify positive reframing of current illnesses; 3) Interplay between belief in medicine and in religion; and 4) Complex impact of diagnosis on religiosity. The results show that the participants' idiosyncratic interpretations of the religious principles, not the principles themselves, had an important influence on their coping, medical decision-making, perceptions regarding the cause of their disease, and compliance with medical advice. A novel insight of the current study is that the personal understanding and interpretation of medical information played the greatest role in the decision-making process, and not the religious beliefs. Thus, it is important for health professionals to give patients' information in a manner that is clear and detailed in order for them to facilitate an informed decision, and to ensure that they fully understand the implications.

Independent validation and clinical implications of the risk prediction model for long QT syndrome (1-2-3-LQTS-Risk)

AIMS

Risk stratification of patients with long QT syndrome (LQTS) represents a difficult task. In 2018, we proposed a granular estimate of the baseline 5-year risk of life-threatening arrhythmias (LAE) for patients with LQTS, based on the genotype (long QT syndrome Type 1, long QT syndrome Type 2, and long QT syndrome Type 3) and the duration of the QTc interval. We sought to externally validate a novel risk score model (1-2-3-LQTS-Risk model) in a geographically diverse cohort from the USA and to evaluate its performance and assess potential clinical implication of this novel model.

METHODS AND RESULTS

The prognostic model (1-2-3-LQTS-Risk model) was derived using data from a prospective, single-centre longitudinal cohort study published in 2018 (discovery cohort) and was validated using an independent cohort of 1689 patients enrolled in the International LQTS Registry (Rochester NY, USA). The validation study revealed a C-index of 0.69 [95% confidence interval (CI): 0.61-0.77] in the validation cohort, when compared with C-index of 0.79 (95% CI: 0.70-0.88) in the discovery cohort. Adopting a 5-year risk ≥5%, as suggested by the ROC curve analysis as the most balanced threshold for implantable cardioverter-defibrillator (ICD) implantation, would result in a number needed to treat (NNT) of nine (NNT = 9; 95% CI: 6.3-13.6).

CONCLUSION

The 1-2-3-LQTS-Risk model, the first validated 5-year risk score model for patients with LQTS, can be used to aid clinicians to identify patients at the highest risk of LAE who could benefit most from an ICD implant and avoid unnecessary implants.

Transgenic rabbit models for cardiac disease research

To study the pathophysiology of human cardiac diseases and to develop novel treatment strategies, complex interactions of cardiac cells on cellular, tissue and on level of the whole heart need to be considered. As in vitro cell-based models do not depict the complexity of the human heart, animal models are used to obtain insights that can be translated to human diseases. Mice are the most commonly used animals in cardiac research. However, differences in electrophysiological and mechanical cardiac function and a different composition of electrical and contractile proteins limit the transferability of the knowledge gained. Moreover, the small heart size and fast heart rate are major disadvantages. In contrast to rodents, electrophysiological, mechanical and structural cardiac characteristics of rabbits resemble the human heart more closely, making them particularly suitable as an animal model for cardiac disease research. In this review, various methodological approaches for the generation of transgenic rabbits for cardiac disease research, such as pronuclear microinjection, the sleeping beauty transposon system and novel genome-editing methods (ZFN and CRISPR/Cas9)will be discussed. In the second section, we will introduce the different currently available transgenic rabbit models for monogenic cardiac diseases (such as long QT syndrome, short-QT syndrome and hypertrophic cardiomyopathy) in detail, especially in regard to their utility to increase the understanding of pathophysiological disease mechanisms and novel treatment options.

Long-term follow-up of a patient with type 2 Timothy syndrome and the partial efficacy of mexiletine

We report a detailed case of type 2 TS due to a p.(Gly402Ser) mutation in exon 8 of the CACNA1C gene. The patient shows a marked prolongation of repolarization with a mean QTc of 540 ms. He shows no structural heart disease, syndactyly, or cranio-facial abnormalities. However, he shows developmental delays, without autism, and dental abnormalities. The cardiac phenotype is very severe, with a resuscitated cardiac arrest at 2.5 years of age, followed by 26 appropriate shocks during nine years of follow-up. Adding mexiletine to nadolol resulted in a reduction of the QTc and a slight decrease in the number of appropriate shocks.

[Congenital long QT syndrome]

Congenital long QT syndrome (LQTS) represents a group of heart diseases of genetic origin characterized by prolongation of the QT interval and an abnormal T wave on the electrocardiogram (ECG). They can have a dominant or recessive expression, the latter associated with sensorineural deafness. In both cases, its clinical presentation is associated with recurrent syncope and sudden death as a consequence of ventricular tachycardia, specifically Torsades de Pointes. Currently they are classified according to the specific genetic defect, being able to compromise around 16 genes and almost 2000 mutations. It should be suspected in individuals with related symptoms, electrocardiographic findings, and family history. Management is based on the reduction or elimination of symptoms, and concomitantly the prevention of sudden death (SD), in those children with congenital deafness, the management requires the application of the otolaryngologist specialist's own measures. The cardiovascular management implies the modification of lifestyles, mainly the prohibition of competitive sports, including swimming, avoiding exposure to loud sounds or triggers. The medications used include beta-blockers, and more rarely flecainide, ranozaline, and verapamil; invasive management consists of the implantation of a cardioverter defibrillator or even left sympathetic denervation, each with its own risks and benefits. In any of the cases, we must avoid the circumstances that increase the QT interval, as well as carry out the appropriate analysis of the benefits and risks of each possible invasive measure.

Ranolazine as an Alternative Therapy to Flecainide for SCN5A V411M Long QT Syndrome Type 3 Patients

The prolongation of the QT interval represents the main feature of the long QT syndrome (LQTS), a life-threatening genetic disease. The heterozygous SCN5A V411M mutation of the human sodium channel leads to a LQTS type 3 with severe proarrhythmic effects due to an increase in the late component of the sodium current (INaL). The two sodium blockers flecainide and ranolazine are equally recommended by the current 2015 ESC guidelines to treat patients with LQTS type 3 and persistently prolonged QT intervals. However, awareness of pro-arrhythmic effects of flecainide in LQTS type 3 patients arose upon the study of the SCN5A E1784K mutation. Regarding SCN5A V411M individuals, flecainide showed good results albeit in a reduced number of patients and no evidence supporting the use of ranolazine has ever been released. Therefore, we ought to compare the effect of ranolazine and flecainide in a SCN5A V411M model using an in-silico modeling and simulation approach. We collected clinical data of four patients. Then, we fitted four Markovian models of the human sodium current (INa) to experimental and clinical data. Two of them correspond to the wild type and the heterozygous SCN5A V411M scenarios, and the other two mimic the effects of flecainide and ranolazine on INa. Next, we inserted them into three isolated cell action potential (AP) models for endocardial, midmyocardial and epicardial cells and in a one-dimensional tissue model. The SCN5A V411M mutation produced a 15.9% APD90 prolongation in the isolated endocardial cell model, which corresponded to a 14.3% of the QT interval prolongation in a one-dimensional strand model, in keeping with clinical observations. Although with different underlying mechanisms, flecainide and ranolazine partially countered this prolongation at the isolated endocardial model by reducing the APD90 by 8.7 and 4.3%, and the QT interval by 7.2 and 3.2%, respectively. While flecainide specifically targeted the mutation-induced increase in peak INaL, ranolazine reduced it during the entire AP. Our simulations also suggest that ranolazine could prevent early afterdepolarizations triggered by the SCN5A V411M mutation during bradycardia, as flecainide. We conclude that ranolazine could be used to treat SCN5A V411M patients, specifically when flecainide is contraindicated.

Frequency of Long QT in Patients with SARS-CoV-2 Infection Treated with Hydroxychloroquine: A Meta-analysis

Introduction Hydroxychloroquine (HCQ) has been proposed as a SARS-CoV-2 treatment but the frequency of long QT (LQT) during use is unknown.

Objective To conduct a meta-analysis of the frequency of LQT in patients with SARS-CoV-2 infection treated with HCQ.

Data Sources PubMed, EMBASE, Google Scholar, the Cochrane Database of Systematic Reviews and preprint servers (medRxiv, Research Square) were searched for studies published between December 2019 and June 30, 2020.

Methods Effect statistics were pooled using random effects. The quality of observational studies and randomized controlled trials was appraised with STROBE and the Cochrane Risk of Bias Assessment tools, respectively.

Outcomes Critical LQT was defined as: (1) maximum QT corrected (QTc)≥500 ms (if QRS<120 ms) or QTc≥550 ms (if QRS≥120 ms), and (2) QTc increase ≥60 ms.

Results In the 28 studies included (n=9124), the frequency of LQT during HCQ treatment was 6.7% (95% confidence interval [CI]: 3.7-10.2). In 20 studies (n=7825), patients were also taking other QT-prolonging drugs. The frequency of LQT in the other 8 studies (n=1299) was 1.7% (95% CI: 0.3-3.9). Twenty studies (n=6869) reported HCQ discontinuation due to LQT, with a frequency of 3.7% (95% CI: 1.5-6.6). The frequency of ventricular arrhythmias during HCQ treatment was 1.68% (127/7539) and that of arrhythmogenic death was 0.69% (39/5648). Torsades de Pointes occurred in 0.06% (3/5066). Patients aged >60 years were at highest risk of HCQ-associated LQT (P<0.001).

Conclusions HCQ-associated cardiotoxicity in SARS-CoV-2 patients is uncommon but requires ECG monitoring, particularly in those aged >60 years and/or taking other QT-prolonging drugs.

Electrophysiological characterization of the modified hERGT potassium channel used to obtain the first cryo-EM hERG structure

The voltage-gated hERG (human-Ether-à-go-go Related Gene) K+ channel plays a fundamental role in cardiac action potential repolarization. Loss-of-function mutations or pharmacological inhibition of hERG leads to long QT syndrome, whilst gain-of-function mutations lead to short QT syndrome. A recent open channel cryo-EM structure of hERG represents a significant advance in the ability to interrogate hERG channel structure-function. In order to suppress protein aggregation, a truncated channel construct of hERG (hERGT ) was used to obtain this structure. In hERGT cytoplasmic domain residues 141 to 350 and 871 to 1,005 were removed from the full-length channel protein. There are limited data on the electrophysiological properties of hERGT channels. Therefore, this study was undertaken to determine how hERGT influences channel function at physiological temperature. Whole-cell measurements of hERG current (IhERG ) were made at 37°C from HEK 293 cells expressing wild-type (WT) or hERGT channels. With a standard +20 mV activating command protocol, neither end-pulse nor tail IhERG density significantly differed between WT and hERGT . However, the IhERG deactivation rate was significantly slower for hERGT . Half-maximal activation voltage (V0.5 ) was positively shifted for hERGT by ~+8 mV (p < .05 versus WT), without significant change to the activation relation slope factor. Neither the voltage dependence of inactivation, nor time course of development of inactivation significantly differed between WT and hERGT , but recovery of IhERG from inactivation was accelerated for hERGT (p < .05 versus WT). Steady-state "window" current was positively shifted for hERGT with a modest increase in the window current peak. Under action potential (AP) voltage clamp, hERGT IhERG showed modestly increased current throughout the AP plateau phase with a significant increase in current integral during the AP. The observed consequences for hERGT IhERG of deletion of the two cytoplasmic regions may reflect changes to electrostatic interactions influencing the voltage sensor domain.

Autonomic and Cardiac Repolarization Lability in Long QT Syndrome Patients

OBJECTIVE

Long QT-Syndrome (LQTS) patients are at risk of arrhythmias and seizures. We investigated whether autonomic and cardiac repolarization measures differed based on LQTS genotypes, and in LQTS patients with vs. without arrhythmias and seizures.

METHODS

We used 24-h ECGs from LQTS1 (n = 87), LQTS2 (n = 50), and LQTS genotype negative patients (LQTS^(-), n = 16). Patients were stratified by LQTS genotype, and arrhythmias/seizures. Heart rate variability (HRV) and QT variability index (QTVI) measures were compared between groups during specific physiological states (minimum, middle, & maximum sympathovagal balance, LF/HF). Results were further tested using logistic regression for each ECG measure, and all HRV measures in a single multivariate model.

RESULTS

Across multiple physiological states, total autonomic (SDNN) and vagal (RMSSD, pNN50) function were lower and repolarization dynamics (QTVI) were elevated in LQTS⁽⁺⁾, LQTS1, and LQTS2, compared to LQTS^(-). Many measures remained significant in the regression models. Multivariate modeling demonstrated that SDNN, RMSSD, and pNN50 were independent markers of LQTS⁽⁺⁾ vs. LQTS^(-), and SDNN and pNN50 were markers for LQTS1 vs. LQTS^(-). During sympathovagal balance (middle LF/HF), RMSSD and pNN50 distinguished LQTS1 vs. LQTS2. LQTS1 patients with arrhythmias had lower total (SDNN) and vagal (RMSSD and pNN50) autonomic function, and SDNN remained significant in the models. In contrast, ECG measures did not differ in LQTS2 patients with vs. without arrhythmias, and LQTS1 and LQTS2 with vs. without seizures.

CONCLUSION

Autonomic (HRV) and cardiac repolarization (QTVI) ECG measures differ based on LQTS genotype and history of arrhythmias in LQTS1. SDNN, RMSSD, and pNN50 were each independent markers for LQTS genotype.

Concealed congenital long QT syndrome during velopharyngeal dysfunction correction: a case report

The congenital long QT syndrome (LQTS) is an inherited cardiac disorder characterized by increased QT intervals and a tendency to experience ventricular tachycardia, which can cause fainting, heart failure, or sudden death. A 4-year-old female patient undergoing velopharyngeal correction surgery under general anesthesia suddenly developed Torsades de pointes. Although the patient spontaneously resolved to sinus rhythm without treatment, subsequent QT prolongation persisted. Here, we report a case of concealed LQTS with a literature review.

Polyunsaturated fatty acid analogues differentially affect cardiac NaV, CaV, and KV channels through unique mechanisms

The cardiac ventricular action potential depends on several voltage-gated ion channels, including Na_V, Ca_V, and K_V channels. Mutations in these channels can cause Long QT Syndrome (LQTS) which increases the risk for ventricular fibrillation and sudden cardiac death. Polyunsaturated fatty acids (PUFAs) have emerged as potential therapeutics for LQTS because they are modulators of voltage-gated ion channels. Here we demonstrate that PUFA analogues vary in their selectivity for human voltage-gated ion channels involved in the ventricular action potential. The effects of specific PUFA analogues range from selective for a specific ion channel to broadly modulating cardiac ion channels from all three families (Na_V, Ca_V, and K_V). In addition, a PUFA analogue selective for the cardiac I_Ks channel (Kv7.1/KCNE1) is effective in shortening the cardiac action potential in human-induced pluripotent stem cell-derived cardiomyocytes. Our data suggest that PUFA analogues could potentially be developed as therapeutics for LQTS and cardiac arrhythmia.

Syncope in a Child with Pulmonary Hypertension and Positive Gene Tests for Hereditary Hemorrhagic Telangiectasia and Long QT Syndrome

We present a 10-year-old boy with syncope who was found to have long-QT syndrome and severe Pulmonary Hypertension (PH) both in the absence of a secondary cause; to our knowledge, this is the first report with this unusual coexistence. His genetic tests were positive for hereditary hemorrhagic telangiectasia and Long QT Syndrome (LQTS) without any family history of PH or LQTS. We demonstrated that digital subtraction pulmonary angiography was more useful compared to CT angiogram to demonstrate pulmonary vascular changes which correlated with a noresponse to acute vasoreactivity testing during right heart catheterization. He has been stable for the last 2 years on Ambrisentan, Sildenafil, and Nadolol without recurrence of symptoms.

ω-6 and ω-9 polyunsaturated fatty acids with double bonds near the carboxyl head have the highest affinity and largest effects on the cardiac IK s potassium channel

Aim

The I_Ks channel is important for termination of the cardiac action potential. Hundreds of loss‐of‐function mutations in the I_Ks channel reduce the K⁺ current and, thereby, delay the repolarization of the action potential, causing Long QT Syndrome. Long QT predisposes individuals to Torsades de Pointes which can lead to ventricular fibrillation and sudden death. Polyunsaturated fatty acids (PUFAs) are potential therapeutics for Long QT Syndrome, as they affect I_Ks channels. However, it is unclear which properties of PUFAs are essential for their effects on I_Ks channels.

Methods

To understand how PUFAs influence I_Ks channel activity, we measured effects on I_Ks current by two‐electrode voltage clamp while changing different properties of the hydrocarbon tail.

Results

There was no, or weak, correlation between the tail length or number of double bonds in the tail and the effects on or apparent binding affinity for I_Ks channels. However, we found a strong correlation between the positions of the double bonds relative to the head group and effects on I_Ks channels.

Conclusion

Polyunsaturated fatty acids with double bonds closer to the head group had higher apparent affinity for I_Ks channels and increased I_Ks current more; shifting the bonds further away from the head group reduced apparent binding affinity for and effects on the I_Ks current. Interestingly, we found that ω‐6 and ω‐9 PUFAs, with the first double bond closer to the head group, left‐shifted the voltage dependence of activation the most. These results allow for informed design of new therapeutics targeting I_Ks channels in Long QT Syndrome.

Retrospective Genetic Analysis of 200 Cases of Sudden Infant Death Syndrome and Its Relationship with Long QT Syndrome in Korea

BACKGROUND

There has been a campaign by the National Education on Sleeping Habits and Living Environment, to reduce the incidence of sudden infant death syndrome (SIDS). However, more than 100 infants die suddenly and unexplainably before the age of 1 year in Korea. Long QT syndrome (LQTS), an inheritable cardiac disease, has been reported to likely be associated with up to 14% of SIDS cases. However, genetic studies of the association between SIDS and LQTS have not yet been conducted in Korea.

METHODS

We conducted genetic analysis using genomic DNA extracted from paraffin-embedded tissue blocks from 200 SIDS cases autopsied between 2005 and 2013. We analyzed the following genetic mutations associated with LQTS, KCNQ1, SCN5A, KCNE1, KCNE2, KCNJ2, and CAV3.

RESULTS

Of the 200 SIDS cases, 58% involved male infants (116 male and 84 female infants, respectively), the mean age was 140 days (median, 107 days; range, 24-270 days), and they were all of Asian-Korean ethnicity. SIDS IA category criteria comprised 45 cases (22.5%) while the rest were SIDS IB. Fifteen infants (7.5%) had R1193Q in SCN5A, of doubtful pathogenicity, and no pathogenic LQTS variants were observed.

CONCLUSION

This genetic investigation of LQTS in SIDS showed a low diagnostic yield. These findings suggest that LQTS molecular autopsy could be cautiously conducted in selected cases with family involvement to improve the available genetic counseling information. Meanwhile, a national SIDS registry should be established to document and evaluate the genetic risk of SIDS in Korea.

Cardiac Arrest with Clozapine and Olanzapine: Revealing Long QT Syndrome

The authors describe a rare case of "concealed" congenital Long QT Syndrome (LQTS) Type 3 in a patient with treatment resistant schizophrenia and no known personal or family history of cardiac disease. The patient in this Case Report had a hidden genetic condition revealed only following the essential administration of antipsychotics. As a result, this patient experienced an aborted cardiac arrest and a total of five episodes of ventricular tachycardia (VT) requiring cardioversion. Successful control of the VT occurred with an Automatic Internal Defibrillator (AID), judicious use of antipsychotic medications, and anti-arrhythmic medications. Risk factors for this rare anomaly include history of syncopy, unexplained ventricular arrhythmias, history of sudden cardiac death in a young family member, unusual reaction to initial dosages of medication known to prolong QTc which includes antipsychotics (particularly in combination). The work-up for those with risk factors would be a thorough family history of sudden cardiac death, baseline ECG, electrolytes, cardiology and electrophysiological consultation, and when indicated a genetic analysis for the Long QT Syndrome (LQTS). Monitoring includes ongoing patient assessment for symptoms, ECGs and electrolytes when indicated such as when medication and dosages are adjusted, AID interviewing, and cardiac and electrophysiological follow-up.

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.

Cardiac Delayed Rectifier Potassium Channels in Health and Disease

Cardiac delayed rectifier potassium channels conduct outward potassium currents during the plateau phase of action potentials and play pivotal roles in cardiac repolarization. These include IKs, IKr and the atrial specific IKur channels. In this article, we will review their molecular identities and biophysical properties. Mutations in the genes encoding delayed rectifiers lead to loss- or gain-of-function phenotypes, disrupt normal cardiac repolarization and result in various cardiac rhythm disorders, including congenital Long QT Syndrome, Short QT Syndrome and familial atrial fibrillation. We will also discuss the prospect of using delayed rectifier channels as therapeutic targets to manage cardiac arrhythmia.

Long QT syndrome: how effective therapy in a single patient favorably influenced the long-term clinical course and genetic understanding of this hereditary disorder

The story of the long QT syndrome involved a chance interaction that took place in 1957 when Dr. Moss was shown a unique series of ECGs with a prolonged QT interval in a young deaf boy whose recurrent syncope culminated in sudden death. Who could have predicted that this clinical experience would lead to innovative and effective new therapy for a patient with the long QT syndrome several years later and the subsequent formation of the International Long QT Registry? This Registry has stimulated interactions among and between patients and physicians and has enhanced collaborations involving clinical, genetic, and basic-science investigators. The net result has been a significant improvement in the diagnosis, treatment, and outcome of patients with the long QT syndrome and an overall advancement in the science of medicine - two of the many satisfactions that physicians can experience in the clinical practice of medicine.

Breath Holding Spells in Children with Long QT Syndrome

BACKGROUND

Long QT syndrome (LQTS) is a genetic heart rhythm disorder that may present with syncope, seizures, or sudden cardiac death. Breath holding spells (BHS) occur in 5% of all children and have been noted in children with LQTS anecdotally. The purpose of this study was to determine the frequency of BHS in children diagnosed with LQTS at ≤5 years of age.

DESIGN

A retrospective review was performed to identify children diagnosed with LQTS who were ≤5 years old at initial presentation to our LQTS clinic from August 1999 to November 2013. The mean length of follow-up was 6.4 ± 2.8 years. The electronic medical records were reviewed for clinical presentation of BHS, as well as LQTS-associated symptoms, diagnostic tests, and treatment.

RESULTS

The study cohort consisted of 115 children with LQTS (58% male; median age at diagnosis, 11 months [range, birth to 5 years]; mean corrected QT interval (QTc), 478 ± 60 milliseconds). At presentation, 80% of patients were asymptomatic. Genetic testing revealed type 1 LQTS (LQT1) in 48%. Overall, 5 of 115 patients (4.3%) had BHS (2 of 5 [40%] male, mean QTc: 492 ± 14 milliseconds, 4 [80%] with family history of LQTS). BHS were the presenting symptom in 1 of 23 symptomatic patients (4.3%). All BHS occurred in patients with LQT1 (P = .02).

CONCLUSIONS

Although BHS among children with LQTS are relatively rare and occur at similar frequency as the general population, they can be the presenting symptom for a heart rhythm disorder. Careful attention to BHS is important to distinguish an innocent BHS from a potential LQTS-triggered cardiac event so that proper treatment is initiated.

Sudden death associated with QT interval prolongation and KCNQ1 gene mutation in a family of English Springer Spaniels

Background

A 5‐year‐old, healthy English Springer Spaniel died suddenly 4 months after delivering a litter of 7 puppies. Within 4 months of the dam's death, 3 offspring also died suddenly.

Hypothesis

Abnormal cardiac repolarization, caused by an inherited long QT syndrome, is thought to be responsible for arrhythmias leading to sudden death in this family.

Animals

Four remaining dogs from the affected litter and 11 related dogs.

Methods

Physical examination and resting ECG were done on the littermates and 9 related dogs. Additional tests on some or all littermates included echocardiogram with Doppler, Holter monitoring, and routine serum biochemistry. Blood for DNA sequencing was obtained from all 15 dogs.

Results

Three of 4 littermates examined, but no other dogs, had prolonged QT intervals with unique T‐wave morphology. DNA sequencing of the KCNQ1 gene identified a heterozygous single base pair mutation, unique to these 3 dogs, which changes a conserved amino acid from threonine to lysine and is predicted to change protein structure.

Conclusions and Clinical Importance

This family represents the first documentation in dogs of spontaneous familial QT prolongation, which was associated with a KCNQ1 gene mutation and sudden death. Although the final rhythm could not be documented in these dogs, their phenotypic manifestations of QT interval prolongation and abnormal ECG restitution suggested increased risk for sudden arrhythmic death. The KCNQ1 gene mutation identified is speculated to impair the cardiac repolarizing current I_Ks, similar to KCNQ1 mutations causing long QT syndrome 1 in humans.

Never Out of the Woods: Onset of Events in Long QT Syndrome Late in Life Provoked by Atrial Arrhythmias

The assessment of risk in the asymptomatic patient with long QT syndrome can often be a challenging task, particularly when the available evidence is limited to relatively small retrospective registries, not to mention the need to consider the effect of individual patient factors which are often difficult to quantitate. We describe the relatively uncommon case of a man with a long-standing diagnosis of Long QT 2 syndrome who suffered his first cardiac event in his late 60's, likely precipitated by the development of paroxysmal atrial tachycardia. A brief review of the available literature on risk assessment in adults with genetically confirmed long QT syndrome who have remained asymptomatic late into adulthood will follow the case.

Arrhythmogenic KCNE gene variants: current knowledge and future challenges

There are twenty-five known inherited cardiac arrhythmia susceptibility genes, all of which encode either ion channel pore-forming subunits or proteins that regulate aspects of ion channel biology such as function, trafficking, and localization. The human KCNE gene family comprises five potassium channel regulatory subunits, sequence variants in each of which are associated with cardiac arrhythmias. KCNE gene products exhibit promiscuous partnering and in some cases ubiquitous expression, hampering efforts to unequivocally correlate each gene to specific native potassium currents. Likewise, deducing the molecular etiology of cardiac arrhythmias in individuals harboring rare KCNE gene variants, or more common KCNE polymorphisms, can be challenging. In this review we provide an update on putative arrhythmia-causing KCNE gene variants, and discuss current thinking and future challenges in the study of molecular mechanisms of KCNE-associated cardiac rhythm disturbances.

Long QT syndrome: a Korean single center study

The long QT syndrome (LQTS) is a rare hereditary disorder in which affected individuals have a possibility of ventricular tachyarrhythmia and sudden cardiac death. We investigated 62 LQTS (QTc ≥ 0.47 sec) and 19 family members whose genetic study revealed mutation of LQT gene. In the proband group, the modes of presentation were ECG abnormality (38.7%), aborted cardiac arrest (24.2%), and syncope or seizure (19.4%). Median age of initial symptom development was 10.5 yr. Genetic studies were performed in 61; and mutations were found in 40 cases (KCNQ1 in 19, KCNH2 in 10, SCN5A in 7, KCNJ2 in 3, and CACNA1C in 1). In the family group, the penetrance of LQT gene mutation was 57.9%. QTc was longer as patients had the history of syncope (P = 0.001), ventricular tachycardia (P = 0.017) and aborted arrest (P = 0.010). QTc longer than 0.508 sec could be a cut-off value for major cardiac events (sensitivity 0.806, specificity 0.600). Beta-blocker was frequently applied for treatment and had significant effects on reducing QTc (P = 0.007). Implantable cardioverter defibrillators were applied in 6 patients. Congenital LQTS is a potentially lethal disease. It shows various genetic mutations with low penetrance in Korean patients.

Single nucleotide deletion mutation of KCNH2 gene is responsible for LQT syndrome in a 3-generation Korean family

Long QT syndrome (LQTS) is characterized by the prolongation of the QT interval in ECG and manifests predisposition to life threatening arrhythmia which often leads to sudden cardiac death. We encountered a 3-generation family with 5 affected family members in which LQTS was inherited in autosomal dominant manner. The LQTS is considered an ion channel disorder in which the type and location of the genetic mutation determines to a large extent the expression of the clinical syndrome. Upon screening of the genomic sequences of cardiac potassium ion channel genes, we found a single nucleotide C deletion mutation in the exon 3 of KCNH2 gene that co-segregates with the LQTS in this family. This mutation presumably resulted in a frameshift mutation, P151fs+15X. This study added a new genetic cause to the pool of mutations that lead to defected potassium ion channels in the heart.

Epilepsy misdiagnosed as long QT syndrome: it can go both ways

Cardiogenic seizures are common and could be the sentinel event heralding the presence of congenital long QT syndrome (LQTS). Distinguishing a cardiogenic seizure from a neurogenic one is of the utmost importance. Herein, we present the case of a 12-year-old boy with recurrent episodes of syncope and seizures. Despite absence of QT prolongation on electrocardiogram, absence of documented arrhythmias, a negative LQTS genetic test, and recurrent episodes while on nadolol beta-blocker therapy, he was diagnosed with LQTS and implanted with an implantable cardioverter defibrillator (ICD). When syncope and seizure occurred with normal sinus rhythm documented on the ICD, he was referred to neurology, and an electroencephalogram was positive for numerous bursts of bilaterally synchronous generalized discharges. He was started on antiepileptic treatment after which his seizures resolved. His LQTS diagnosis was removed, beta-blocker therapy discontinued, and his ICD was explanted. He has been seizure-free for over 2 years.

Genetic Test for the Channelopaties: Useful or Less Than Useful for Patients? (Part II)

The advanced knowledge about genetic diseases and their mutations has widened the possibility to have a more precise and definitive diagnosis in many patients, but the use of genetic testing is still controversial. Actually, many cardiomyopathies show the availability of genetic testing. The clinical utility of this testing has been widely debated, but it is evident that the use of genetics must be put in a more organic diagnostic pathway that includes the evaluation of risks and benefits for the patient and his relatives, as well as the costs of the procedure. This review aims to clarify the role of genetic in clinics regarding Channelopaties, less frequent but equally important than other Cardiomyopathies because patients can often be asymptomatic until the first fatal manifestation.

Sudden cardiac arrest during anesthesia in a 30-month-old boy with syndactyly: a case of genetically proven Timothy syndrome

Timothy syndrome, long QT syndrome type 8, is highly malignant with ventricular tachyarrhythmia. A 30-month-old boy had sudden cardiac arrest during anesthesia induction before plastic surgery for bilateral cutaneous syndactyly. After successful resuscitation, prolonged QT interval (QTc, 0.58-0.60 sec) and T-wave alternans were found in his electrocardiogram. Starting β-blocker to prevent further tachycardia and collapse event, then there were no more arrhythmic events. The genes KCNQ1, KCNH2, KCNE1 and 2, and SCN5A were negative for long QT syndrome. The mutation p.Gly406Arg was confirmed in CACNA1C, which maintains L-type calcium channel depolarization in the heart and other systems.

Drugs to be avoided in patients with long QT syndrome: Focus on the anaesthesiological management

Long QT syndrome incidence is increasing in general population. A careful pre-, peri- and post-operative management is needed for patients with this syndrome because of the risk of Torsades de Pointes and malignant arrhythmias. The available data regarding prevention of lethal Torsades de Pointes during anesthesia in patients with long QT syndrome is scant and conflicting: only case reports and small case series with different outcomes have been published. Actually, there are no definitive guidelines on pre-, peri- and post-operative anesthetic management of congenital long QT syndrome. Our review focuses on anesthetic recommendations for patients diagnosed with congenital long QT syndrome furnishing some key points for preoperative optimization, intraoperative anesthetic agents and postoperative care plan, which could be the best for patients with c-long QT syndrome who undergo surgery.

Analysis of Relationship between Levofloxacin and Corrected QT Prolongation Using a Clinical Data Warehouse

Objective

The aim of this study was to examine whether or not levofloxacin has any relationship with QT prolongation in a real clinical setting by analyzing a clinical data warehouse of data collected from different hospital information systems.

Methods

Electronic prescription data and medical charts from 3 different hospitals spanning the past 9 years were reviewed, and a clinical data warehouse was constructed. Patients who were both administrated levofloxacin and given electrocardiograms (ECG) were selected. The correlations between various patient characteristics, concomitant drugs, corrected QT (QTc) prolongation, and the interval difference in QTc before and after levofloxacin administration were analyzed.

Results

A total of 2,176 patients from 3 different hospitals were included in the study. QTc prolongation was found in 364 patients (16.7%). The study revealed that age (OR 1.026, p < 0.001), gender (OR 0.676, p = 0.007), body temperature (OR 1.267, p = 0.024), and cigarette smoking (OR 1.641, p = 0.022) were related with QTc prolongation. After adjusting for related factors, 12 drugs concomitant with levofloxacin were associated with QTc prolongation. For patients who took ECGs before and after administration of levofloxacin during their hospitalization (n = 112), there was no significant difference in QTc prolongation.

Conclusions

The age, gender, body temperature, cigarette smoking and various concomitant drugs might be related with QTc prolongation. However, there was no definite causal relationship or interaction between levofloxacin and QTc prolongation. Alternative surveillance methods utilizing the massive accumulation of electronic medical data seem to be essential to adverse drug reaction surveillance in future.

Fever-triggered ventricular arrhythmias in Brugada syndrome and type 2 long-QT syndrome

The risk for lethal ventricular arrhythmias is increased in individuals who carry mutations in genes that encode cardiac ion channels. Loss-of-function mutations in SCN5A, the gene encoding the cardiac sodium channel, are linked to Brugada syndrome (BrS). Arrhythmias in BrS are often preceded by coved-type ST-segment elevation in the right-precordial leads V1 and V2. Loss-of-function mutations in KCNH2, the gene encoding the cardiac ion channel that is responsible for the rapidly activating delayed rectifying potassium current, are linked to long-QT syndrome type 2 (LQT-2). LQT-2 is characterised by delayed cardiac repolarisation and rate-corrected QT interval (QTc) prolongation. Here, we report that the risk for ventricular arrhythmias in BrS and LQT-2 is further increased during fever. Moreover, we demonstrate that fever may aggravate coved-type ST-segment elevation in BrS, and cause QTc lengthening in LQT-2. Finally, we describe molecular mechanisms that may underlie the proarrhythmic effects of fever in BrS and LQT-2. (Neth Heart J 2010;18:165-9.).

Fever accentuates transmural dispersion of repolarization and facilitates development of early afterdepolarizations and torsade de pointes under long-QT Conditions

BACKGROUND

The arrhythmogenic effects of hyperthermia have been highlighted in the Brugada syndrome but remain largely unexplored in other arrhythmic syndromes. The present study examines the effect of hyperthermia on transmural dispersion of action potential duration (TD-APD), early afterdepolarization (EAD) activity, and torsade de pointes (TdP) under long-QT conditions.

METHODS AND RESULTS

Standard and floating glass microelectrodes were used to record action potentials from epicardial, M cell, and endocardial regions of the arterially perfused left ventricle wedge, from tissue slices isolated from these regions, and from isolated Purkinje fibers. A transmural ECG was simultaneously recorded across the wedge. Under baseline conditions and in the presence of I(Ks) block (chromanol 293B), hyperthermia (39 degrees C to 40 degrees C) abbreviated APD in tissue slices from all 3 regions. In the presence of I(Kr) block (E-4031), hyperthermia prolonged APD and induced or augmented EADs in M cell and Purkinje preparations at pacing cycle lengths > or = 800 ms but abbreviated APD in epicardium and endocardium, resulting in a marked accentuation of TD-APD. Ryanodine prevented the hyperthermia- induced EAD. In perfused wedge preparations, hyperthermia abbreviated APD throughout both in the absence or presence of I(Kr) or I(Ks) block and did not induce EADs or TdP. Combined I(Kr) and I(Ks) block increased TD-APD and induced EADs (4/12) and spontaneous TdP (3/12) at 36 degrees C to 37 degrees C; hyperthermia (39 degrees C to 40 degrees C) further accentuated TD-APD and facilitated the development of EAD activity (9/12) and TdP (6/12).

CONCLUSIONS

Our findings suggest that hyperthermia can be associated with an increased arrhythmic risk when the repolarization reserve of the myocardium is compromised.

A simple approach discriminating cardio-safe drugs from toxic ones

More than 130 FDA-approved drugs have been identified for now to prolong the QT interval and possibly lead to sudden cardiac death. Due to their toxic effect, some of these drugs have been withdrawn from the pharmaceutical market. In this study, we have formulated few rules to assess the ability to prolong QT interval and thereby discriminate between cardiotoxic and -safe drugs. These rules have clearly determined that cardio-toxic drugs are more likely to obey Lipinski rule of 5 and Oprea lead-like rule. Moreover, the cardio-toxic drugs have been found to have in common values of -0.5 to 6.5 log P, 1-5 nitrogen atoms, up to 4 oxygen atoms, 5-27 hydrophobic atoms, and 15-53 single bonds. Matthews Correlation Coefficient with the value of 0.6 was also attained and nearly 96% of the cardio-toxic drugs were successfully covered. Thus, despite the simplicity of this methodology, we have obtained interesting and informative results. The proposed set of these simple rules could be employed to infer cardio-toxicity or -safety for current and potential drugs. The present study will have important impact on decision making in the fields of drug development, molecule screening in biological assays, and other applications as well.