A new oral therapy for long QT syndrome

Congenital Long QT Syndrome in Children and Adolescents: A General Overview

Congenital long QT syndrome (LQTS) represents a disorder of myocardial repolarization characterized by a prolongation of QTc interval on ECG, which can degenerate into fast polymorphic ventricular arrhythmias. The typical symptoms of LQTS are syncope and palpitations, mainly triggered by adrenergic stimuli, but it can also manifest with cardiac arrest. At least 17 genotypes have been associated with LQTS, with a specific genotype-phenotype relationship described for the three most common subtypes (LQTS1, -2, and -3). β-Blockers are the first-line therapy for LQTS, even if the choice of the appropriate patients needing to be treated may be challenging. In specific cases, interventional measures, such as an implantable cardioverter-defibrillator (ICD) or left cardiac sympathetic denervation (LCSD), are useful. The aim of this review is to highlight the current state-of-the-art knowledge on LQTS, providing an updated picture of possible diagnostic algorithms and therapeutic management.

Predictors for prolonged qt intervals in acute antipsychotic poisoned patients

Background

Acute antipsychotic poisoning is correlated to a high prevalence of qt interval prolongation.

Aim

This study aimed to evaluate early qt interval prolongation predictors in acute antipsychotic-poisoned patients.

Methodology

This prospective cohort study enrolled 70 symptomatic patients with acute antipsychotic poisoning. Sociodemographic data, toxicological, clinical, investigation, and outcomes were collected and analyzed. The estimation of the corrected qt interval (QTc) was performed using Bazett's method. Primary outcome was normal or abnormal length of QTc interval. Secondary outcomes included duration of hospital stay, complete recovery and mortality. The corrected qt interval was analyzed by univariate and multivariate logistic regression analysis.

Results

Patients were divided into groups A (normal QTc interval up to 440 msec; 58.6% of cases) and B (prolonged QTc interval ≥ 440 msec; 41.4% of cases). Patients in group B had significantly high incidences of quetiapine intake, bradycardia, hypotension, hypokalemia, and long duration of hospital stay. By multivariate analysis, quetiapine [Odd's ratio (OR): 39.674; Confidence Interval (C.I:3.426-459.476)], bradycardia [OR: 22.664; C.I (2.534-202.690)], and hypotension [OR: 16.263; (C.I: 2.168-122.009)] were significantly correlated with prolonged QTc interval.

Conclusion

In acute antipsychotic poisoning, quetiapine, bradycardia, and hypotension are early clinical predictors for prolonged QTc interval.

Management of patients with an electrical storm or clustered ventricular arrhythmias: a clinical consensus statement of the European Heart Rhythm Association of the ESC-endorsed by the Asia-Pacific Heart Rhythm Society, Heart Rhythm Society, and Latin-American Heart Rhythm Society

Electrical storm (ES) is a state of electrical instability, manifesting as recurrent ventricular arrhythmias (VAs) over a short period of time (three or more episodes of sustained VA within 24 h, separated by at least 5 min, requiring termination by an intervention). The clinical presentation can vary, but ES is usually a cardiac emergency. Electrical storm mainly affects patients with structural or primary electrical heart disease, often with an implantable cardioverter-defibrillator (ICD). Management of ES requires a multi-faceted approach and the involvement of multi-disciplinary teams, but despite advanced treatment and often invasive procedures, it is associated with high morbidity and mortality. With an ageing population, longer survival of heart failure patients, and an increasing number of patients with ICD, the incidence of ES is expected to increase. This European Heart Rhythm Association clinical consensus statement focuses on pathophysiology, clinical presentation, diagnostic evaluation, and acute and long-term management of patients presenting with ES or clustered VA.

Personalized Care in Long QT Syndrome: Better Management, More Sports, and Fewer Devices

Long QT Syndrome (LQTS) is a potentially life-threatening yet highly treatable inherited cardiac channelopathy. When evaluating these patients, it is important to consider patient-specific as well as genotype-specific factors in order to adequately encompass the many nuances to care that exist in its management. The tendency to follow a "one-size-fits-all" approach needs to be replaced by treatment strategies that embrace the unique considerations of the individual patient in the context of their genotype. Herein, the authors aim to review the spectrum of LQTS, including the considerations when tailoring a personalized, genotype-tailored treatment program for a patient's LQTS.

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.

Congenital Long QT Syndrome

Congenital long QT syndrome (LQTS) encompasses a group of heritable conditions that are associated with cardiac repolarization dysfunction. Since its initial description in 1957, our understanding of LQTS has increased dramatically. The prevalence of LQTS is estimated to be ∼1:2,000, with a slight female predominance. The diagnosis of LQTS is based on clinical, electrocardiogram, and genetic factors. Risk stratification of patients with LQTS aims to identify those who are at increased risk of cardiac arrest or sudden cardiac death. Factors including age, sex, QTc interval, and genetic background all contribute to current risk stratification paradigms. The management of LQTS involves conservative measures such as the avoidance of QT-prolonging drugs, pharmacologic measures with nonselective β-blockers, and interventional approaches such as device therapy or left cardiac sympathetic denervation. In general, most forms of exercise are considered safe in adequately treated patients, and implantable cardioverter-defibrillator therapy is reserved for those at the highest risk. This review summarizes our current understanding of LQTS and provides clinicians with a practical approach to diagnosis and management.

Effect of moderate potassium-elevating treatment in long QT syndrome: the TriQarr Potassium Study

Background

In long QT syndrome (LQTS), beta blockers prevent arrhythmias. As a supplement, means to increase potassium has been suggested. We set to investigate the effect of moderate potassium elevation on cardiac repolarisation.

Methods

Patients with LQTS with a disease-causing KCNQ1 or KCNH2 variant were included. In addition to usual beta-blocker treatment, patients were prescribed (1) 50 mg spironolactone (low dose) or (2) 100 mg spironolactone and 3 g potassium chloride per day (high dose+). Electrocardiographic measures were obtained at baseline and after 7 days of treatment.

Results

Twenty patients were enrolled (10 low dose and 10 high dose+). One patient was excluded due to severe influenza-like symptoms, and 5 of 19 patients completing the study had mild side effects. Plasma potassium in low dose did not increase in response to treatment (4.26±0.22 to 4.05±0.19 mmol/L, p=0.07). Also, no change was observed in resting QTcF (QT interval corrected using Fridericia's formula) before versus after treatment (478±7 vs 479±7 ms, p=0.9). In high dose+, potassium increased significantly from 4.08±0.29 to 4.48±0.54 mmol/L (p=0.001). However, no difference in QTcF was observed comparing before (472±8 ms) versus after (469±8 ms) (p=0.66) high dose+ treatment. No patients developed hyperkalaemia.

Conclusion

In patients with LQTS, high dose+ treatment increased plasma potassium by 0.4 mmol/L without cases of hyperkalaemia. However, the potassium increase did not shorten the QT interval and several patients had side effects. Considering the QT interval as a proxy for arrhythmic risk, our data do not support that potassium-elevating treatment has a role as antiarrhythmic prophylaxis in patients with LQTS with normal-range potassium levels.

Trial registration number

NCT03291145.

Congenital Long QT Syndrome: A Clinician's Guide

Congenital long QT syndrome (LQTS) is a familial cardiac ion channelopathy first described over sixty years ago. It is characterised by prolonged ventricular repolarization (long QT on ECG), ventricular arrhythmias and associated syncope or sudden cardiac death. As the most closely studied cardiac channelopathy, over the decades we have gained a deep appreciation of the complex genetic model of LQTS. Variability in genetic expression and incomplete penetrance leads to a heterogenous phenotype that can be challenging to clinically classify. In recent times, progress has been made in diagnostic method, risk stratification and treatment options. This review has been written as a guide for the general cardiologist to understand the basic pathophysiology, diagnosis, and management priorities for the most encountered LQTS subtypes: LQT1, LQT2 and LQT3. This article is protected by copyright. All rights reserved.

Diagnosis, management and therapeutic strategies for congenital long QT syndrome

Congenital long QT syndrome (LQTS) is characterised by heart rate corrected QT interval prolongation and life-threatening arrhythmias, leading to syncope and sudden death. Variations in genes encoding for cardiac ion channels, accessory ion channel subunits or proteins modulating the function of the ion channel have been identified as disease-causing mutations in up to 75% of all LQTS cases. Based on the underlying genetic defect, LQTS has been subdivided into different subtypes. Growing insights into the genetic background and pathophysiology of LQTS has led to the identification of genotype–phenotype relationships for the most common genetic subtypes, the recognition of genetic and non-genetic modifiers of phenotype, optimisation of risk stratification algorithms and the discovery of gene-specific therapies in LQTS. Nevertheless, despite these great advancements in the LQTS field, large gaps in knowledge still exist. For example, up to 25% of LQTS cases still remain genotype elusive, which hampers proper identification of family members at risk, and it is still largely unknown what determines the large variability in disease severity, where even within one family an identical mutation causes malignant arrhythmias in some carriers, while in other carriers, the disease is clinically silent. In this review, we summarise the current evidence available on the diagnosis, clinical management and therapeutic strategies in LQTS. We also discuss new scientific developments and areas of research, which are expected to increase our understanding of the complex genetic architecture in genotype-negative patients, lead to improved risk stratification in asymptomatic mutation carriers and more targeted (gene-specific and even mutation-specific) therapies.

Drug-induced organ injury in coronavirus disease 2019 pharmacotherapy: Mechanisms and challenges in differential diagnosis and potential protective strategies

The world is currently facing an unprecedented pandemic caused by a newly recognized and highly pathogenic coronavirus disease 2019 (COVID‐19; induced by SARS‐CoV‐2 virus), which is a severe and ongoing threat to global public health. Since COVID‐19 was officially declared a pandemic by the World Health Organization in March 2020, several drug regimens have rapidly undergone clinical trials for the management of COVID‐19. However, one of the major issues is drug‐induced organ injury, which is a prominent clinical challenge. Unfortunately, most drugs used against COVID‐19 are associated with adverse effects in different organs, such as the kidney, heart, and liver. These side effects are dangerous and, in some cases, they can be lethal. More importantly, organ injury is also a clinical manifestation of COVID‐19 infection. These adverse reactions are increasingly recognized as outcomes of COVID‐19 infection. Therefore, the differential diagnosis of drug‐induced adverse effects from COVID‐19‐induced organ injury is a clinical complication. This review highlights the importance of drug‐induced organ injury, its known mechanisms, and the potential therapeutic strategies in COVID‐19 pharmacotherapy. We review the potential strategies for the differential diagnosis of drug‐induced organ injury. This information can facilitate the development of therapeutic strategies, not only against COVID‐19 but also for future outbreaks of other emerging infectious diseases.

Adverse drug events are well‐known and common clinical problems in COVID‐19 patients.

The differential diagnosis of adverse drug effects and disease‐induced organ injury is a clinical challenge.

Obtaining a detailed history and biochemical analysis of blood‐based biomarkers from the patients as soon as they are admitted is critical for differential diagnosis of drug or disease‐induced organ injury.

Pharmacological activation of IKr in models of long QT Type 2 risks overcorrection of repolarization

AIMS

Current treatment for congenital long QT syndrome Type 2 (cLQTS2), an electrical disorder that increases the risk of life-threatening cardiac arrhythmias, is aimed at reducing the incidence of arrhythmia triggers (beta-blockers) or terminating the arrhythmia after onset (implantable cardioverter-defibrillator). An alternative strategy is to target the underlying disease mechanism, which is reduced rapid delayed rectifier current (IKr) passed by Kv11.1 channels. Small molecule activators of Kv11.1 have been identified but the extent to which these can restore normal cardiac signalling in cLQTS2 backgrounds remains unclear. Here, we examined the ability of ICA-105574, an activator of Kv11.1 that impairs transition to the inactivated state, to restore function to heterozygous Kv11.1 channels containing either inactivation enhanced (T618S, N633S) or expression deficient (A422T) mutations.

METHODS AND RESULTS

ICA-105574 effectively restored Kv11.1 current from heterozygous inactivation enhanced or expression defective mutant channels in heterologous expression systems. In a human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model of cLQTS2 containing the expression defective Kv11.1 mutant A422T, cardiac repolarization, estimated from the duration of calcium transients in isolated cells and the rate corrected field potential duration (FPDc) in culture monolayers of cells, was significantly prolonged. The Kv11.1 activator ICA-105574 was able to reverse the prolonged repolarization in a concentration-dependent manner. However, at higher doses, ICA-105574 produced a shortening of the FPDc compared to controls. In vitro and in silico analysis suggests that this overcorrection occurs as a result of a temporal redistribution of the peak IKr to much earlier in the plateau phase of the action potential, which results in early repolarization.

CONCLUSION

Kv11.1 activators, which target the primary disease mechanism, provide a possible treatment option for cLQTS2, with the caveat that there may be a risk of overcorrection that could itself be pro-arrhythmic.

Effect of QT interval prolongation on cardiac arrest following liver transplantation and derivation of a risk index

Liver transplantation (LT) has a 4-fold higher risk of periprocedural cardiac arrest and ventricular arrhythmias (CA/VAs) compared with other noncardiac surgeries. Prolongation of the corrected QT interval (QTc) is common in patients with liver cirrhosis. Whether it is associated with an increased risk of CA/VAs following LT is unclear. Rates of 30-day CA/VAs post-LT were assessed in consecutive adults undergoing LT between 2010 and 2017. Pretransplant QTc was measured by a cardiologist blinded to clinical outcomes. Among 408 patients included, CA/VAs occurred in 26 patients (6.4%). QTc was significantly longer in CA/VA patients (475 ± 34 vs 450 ± 34 ms, P < .001). Optimal QTc cut-off for prediction of CA/VAs was ≥480 ms. After adjustment, QTc ≥480 ms remained the strongest predictor for the occurrence of CA/VAs (odds ratio [OR] 5.2, 95% confidence interval [CI] 2.2-12.6). A point-based cardiac arrest risk index (CARI) was derived with the bootstrap method for yielding optimism-corrected coefficients (2 points: QTc ≥480, 1 point: Model for End-Stage Liver Disease [MELD] ≥30, 1 point: age ≥65, and 1 point: male). CARI score ≥3 demonstrated moderate discrimination (c-statistic 0.79, optimism-corrected c-statistic 0.77) with appropriate calibration. QTc ≥480 ms was associated with a 5-fold increase in the risk of CA/VAs. The CARI score may identify patients at higher risk of these events. Whether heightened perioperative cardiac surveillance, avoidance of QT prolonging medications, or beta blockers could mitigate the risk of CA/VAs in this population merits further study.

Update on long QT syndrome

Long QT syndrome (LQTS) is an inherited disorder characterized by a prolonged QT interval in the 12-lead electrocardiogram and increased risk of malignant arrhythmias in patients with a structurally normal heart. Since its first description in the 1950s, advances in molecular genetics have greatly improved our understanding of the cause and mechanisms of this disease. Sixteen genes linked to LQTS have been described and genetic testing had become an integral part of the diagnosis and risk stratification. This article provides an updated review of the genetic basis, diagnosis, and clinical management of LQTS.

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.

An Overview of Diagnosis and Management Strategies for Long QT Syndrome

Significant clinical, research, genetic, and therapeutic advances in the diagnosis and management of long QT syndrome (LQTS) have made the treatment of this channelopathy one of the most exciting and enlightening bench-to-bed success stories in the field of cardiology. Cascade screening identifies affected family members, and pre-symptomatic therapy saves lives. Here, we present a case of LQTS in a child and a review of the diagnostic and treatment strategies that have been introduced to date in the modern era.

Molecular Pathophysiology of Congenital Long QT Syndrome

Ion channels represent the molecular entities that give rise to the cardiac action potential, the fundamental cellular electrical event in the heart. The concerted function of these channels leads to normal cyclical excitation and resultant contraction of cardiac muscle. Research into cardiac ion channel regulation and mutations that underlie disease pathogenesis has greatly enhanced our knowledge of the causes and clinical management of cardiac arrhythmia. Here we review the molecular determinants, pathogenesis, and pharmacology of congenital Long QT Syndrome. We examine mechanisms of dysfunction associated with three critical cardiac currents that comprise the majority of congenital Long QT Syndrome cases: 1) IKs, the slow delayed rectifier current; 2) IKr, the rapid delayed rectifier current; and 3) INa, the voltage-dependent sodium current. Less common subtypes of congenital Long QT Syndrome affect other cardiac ionic currents that contribute to the dynamic nature of cardiac electrophysiology. Through the study of mutations that cause congenital Long QT Syndrome, the scientific community has advanced understanding of ion channel structure-function relationships, physiology, and pharmacological response to clinically employed and experimental pharmacological agents. Our understanding of congenital Long QT Syndrome continues to evolve rapidly and with great benefits: genotype-driven clinical management of the disease has improved patient care as precision medicine becomes even more a reality.

T-Wave Morphology Analysis in Congenital Long QT Syndrome Discriminates Patients From Healthy Individuals

OBJECTIVES

This study aims to assess the capability of T-wave analysis to: 1) identify genotype-positive long QT syndrome (LQTS) patients; 2) identify LQTS patients with borderline or normal QTc interval (≤460 ms); and 3) classify LQTS subtype.

BACKGROUND

LQTS often presents with a nondiagnostic electrocardiogram (ECG). T-wave abnormalities may be the only marker of this potentially lethal arrhythmia syndrome.

METHODS

ECGs taken at rest in 108 patients (43 with LQTS1, 20 with LQTS2, and 45 control subjects) were evaluated for T-wave flatness, asymmetry, and notching, which produces a morphology combination score (MCS) of the 3 features (MCS = 1.6 × flatness + asymmetry + notch) using QT Guard Plus Software (GE Healthcare, Milwaukee, Wisconsin). To assess for heterogeneity of repolarization, the principal component analysis ratio 2 (PCA-2) was calculated.

RESULTS

Mean QTc intervals were 486 ± 50 ms (LQTS1), 479 ± 36 ms (LQTS2), and 418 ± 24 ms (control subjects) (p < 0.05). MCS and PCA-2 differed between LQTS patients and control subjects (MCS: 117.8 ± 57.4 vs. 71.9 ± 16.2; p < 0.001; PCA-2: 20.2 ± 10.4% vs. 14.6 ± 5.5%; p < 0.001), LQTS1 and LQTS2 patients (MCS: 96.3 ± 28.7 vs. 164 ± 75.2; p < 0.001; PCA-2: 17.8 ± 8.3% vs. 25 ± 12.6%; p < 0.001), and between LQTS patients with borderline or normal QTc intervals (n = 17) and control subjects (MCS: 105.7 ± 49.9 vs. 71.9 ± 16.2; p < 0.001; PCA-2: 18.1 ± 7.2% vs. 14.6 ± 5.5%; p < 0.001). T-wave metrics were consistent across multiple ECGs from individual patients based on the average intraclass correlation coefficient (MCS: 0.96; PCA-2: 0.86).

CONCLUSIONS

Automated T-wave morphology analysis accurately discriminates patients with pathogenic LQTS mutations from control subjects and between the 2 most common LQTS subtypes. Mutation carriers without baseline QTc prolongation were also identified. This may be a useful tool for screening families of LQTS patients, particularly when the QTc interval is subthreshold and genetic testing is unavailable.

Management of Patients with Long QT Syndrome

Long QT syndrome (LQTS) is a rare cardiac channelopathy associated with syncope and sudden death due to torsades de pointes and ventricular fibrillation. Syncope and sudden death are frequently associated with physical and emotional stress. Management of patients with LQTS consists of life-style modification, β-blockers, left cardiac sympathetic denervation (LCSD), and implantable cardioverter-defibrillator (ICD) implantation. Prohibition of competitive exercise and avoidance of QT-prolonging drugs are important issues in life-style modification. Although β-blockers are the primary treatment modality for patients with LQTS, these drugs are not completely effective in some patients. Lifelong ICD implantation in young and active patients is associated with significant complications. LCSD is a relatively simple and highly effective surgical procedure. However, LCSD is rarely used.

Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias

Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.

Elderly Onset Celiac Disease: A Narrative Review

Celiac sprue is a chronic disease, which usually occurs in children and young adults. However, it can develop in any age group, and the prevalence is increasing even in the elderly population. The atypical patterns of clinical presentation in this age group sometimes can cause a delay in diagnosis. Given the lower sensitivity and specificity of serological tests in the aged population, clinical suspect often arises in the presence of complications (autoimmune disorders, fractures, and finally, malignancy) and must be supported by endoscopic and imaging tools. In this review, we highlight the incidence and prevalence of celiac disease in the elderly, the patterns of clinical presentation, diagnosis, and the most frequent complications, with the aim of increasing awareness and reducing the diagnostic delay of celiac disease even in the elderly population.

Influence of steroid hormones on ventricular repolarization

QT interval prolongation, corrected for heart rate (QTc), either spontaneous or drug-induced, is associated with an increased risk of torsades de pointes and sudden death. Women have longer QTc than men and are at higher risk of torsades de pointes, particularly during post-partum and the follicular phase. Men with peripheral hypogonadism have longer QTc than healthy controls. The role of the main sex steroid hormones has been extensively studied with inconsistent findings. Overall, estradiol is considered to promote QTc lengthening while progesterone and testosterone shorten QTc. New findings suggest more complex regulation of QTc by sex steroid hormones involving gonadotropins (i.e. follicle-stimulating hormone), the relative concentrations of sex steroid hormones (which depends on gender, i.e., progesterone/estradiol ratio in women). Aldosterone, another structurally related steroid hormone, can also prolong ventricular repolarization in both sex. Better understanding of pathophysiological hormonal processes which may lead to increased susceptibility of women (and possibly hypogonadic men) to drug-induced arrhythmia may foster preventive treatments (e.g. progesterone in women). Exogenous hormonal intake might offer new therapeutic opportunities or, alternatively, increase the risk of torsades de pointes. Some exogenous sex steroids may also have paradoxical effects on ventricular repolarization. Lastly, variations of QTc in women linked to the menstrual cycle and sex hormone fluctuations are generally ignored in regulatory thorough QT studies. Investigators and regulatory agencies promoting inclusion of women in thorough QT studies should be aware of this source of variability especially when studying drugs over several days of administration.

Update on the Diagnosis and Management of Familial Long QT Syndrome

This update was reviewed by the CSANZ Continuing Education and Recertification Committee and ratified by the CSANZ board in August 2015. Since the CSANZ 2011 guidelines, adjunctive clinical tests have proven useful in the diagnosis of LQTS and are discussed in this update. Understanding of the diagnostic and risk stratifying role of LQTS genetics is also discussed. At least 14 LQTS genes are now thought to be responsible for the disease. High-risk individuals may have multiple mutations, large gene rearrangements, C-loop mutations in KCNQ1, transmembrane mutations in KCNH2, or have certain gene modifiers present, particularly NOS1AP polymorphisms. In regards to treatment, nadolol is preferred, particularly for long QT type 2, and short acting metoprolol should not be used. Thoracoscopic left cardiac sympathectomy is valuable in those who cannot adhere to beta blocker therapy, particularly in long QT type 1. Indications for ICD therapies have been refined; and a primary indication for ICD in post-pubertal females with long QT type 2 and a very long QT interval is emerging.

Common Genotypes of Long QT Syndrome in China and the Role of ECG Prediction

OBJECTIVES

Genetic testing, a gold standard for long QT syndrome (LQTS) diagnosis, is time-consuming and costly when all the 15 candidate genes are screened. Since genotype-specific ECG patterns are present in most LQT1-3 mutation carriers, we tested the utility of ECG-guided genotyping in a large cohort of Chinese LQTS patients.

METHODS AND RESULTS

We enrolled 230 patients (26 ± 17 years, 66% female) with a clinical diagnosis of LQTS. Genotypes were predicted as LQT1-3 based on the presence of ECG patterns typical for each genotype in 200 patients (85 LQT1, 110 LQT2 and 5 LQT3). Family-based genotype prediction was also conducted if gene-specific ECG patterns were found in other affected family members. Mutational screening identified 104 mutations (44% novel), i.e. 46 KCNQ1, 54 KCNH2 and 4 SCN5A mutations. The overall predictive accuracy of ECG-guided genotyping was 79% (157/200) and 79% (67/85), 78% (86/110) and 80% (4/5) for LQT1, LQT2 and LQT3, respectively. The predictive accuracy was 98% (42/43) when family-based ECG assessment was performed.

CONCLUSIONS

From this large-scale genotyping study, we found that LQT2 is the most common genotype among the Chinese. Family-based ECG-guided genotyping is highly accurate. ECG-guided genotyping is time- and cost-effective. We therefore recommend it as an optimal approach for the genetic diagnosis of LQTS.

Genetics of inherited primary arrhythmia disorders

A sudden unexplained death is felt to be due to a primary arrhythmic disorder when no structural heart disease is found on autopsy, and there is no preceding documentation of heart disease. In these cases, death is presumed to be secondary to a lethal and potentially heritable abnormality of cardiac ion channel function. These channelopathies include congenital long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, and short QT syndrome. In certain cases, genetic testing may have an important role in supporting a diagnosis of a primary arrhythmia disorder, and can also provide prognostic information, but by far the greatest strength of genetic testing lies in the screening of family members, who may be at risk. The purpose of this review is to describe the basic genetic and molecular pathophysiology of the primary inherited arrhythmia disorders, and to outline a rational approach to genetic testing, management, and family screening.

Unveiling specific triggers and precipitating factors for fatal cardiac events in inherited arrhythmia syndromes

Patients with inherited arrhythmia syndromes, such as long QT syndrome, Brugada syndrome, early repolarization syndrome, catecholaminergic polymorphic ventricular tachycardia, and their latent forms, are at risk for fatal arrhythmias. These diseases are typically associated with genetic mutations that perturb cardiac ionic currents. The analysis of cardiac events by genotype-phenotype correlation studies has revealed that fatal arrhythmias in some genotypes are triggered by physical or emotional stress, and those in the others are more likely to occur during sleep or at rest. Thus, the risk stratification and management of affected patients differ strikingly according to the genetic variant of the inherited arrhythmia syndrome. Risk stratification may be further refined by considering the precipitating factors, such as drugs, bradycardia, electrolyte disturbances, fever, and cardiac memory. Moreover, an increasing number of studies imply that the susceptibility of fatal arrhythmias in patients with acute coronary syndrome or takotsubo cardiomyopathy is at least partly ascribed to the genetic variants causing inherited arrhythmia syndromes. In this article, we review the recent advances in the understanding of the molecular genetics and genotype-phenotype correlations in inherited arrhythmia syndromes and consider the triggers and precipitating factors for fatal arrhythmias in these disorders. Further studies to explore the triggers and precipitating factors specific to the genotypes and diseases are needed for better clinical management.

Congenital long QT syndromes: prevalence, pathophysiology and management

Long QT syndrome is a genetic disorder associated with life threatening ventricular arrhythmias and sudden death. This inherited arrhythmic disorder exhibits genetic heterogeneity, incomplete penetrance, and variable expressivity. During the past two decades there have been major advancements in understanding the genotype-phenotype correlations in LQTS. This genotype-phenotype relationship can lead to improved management of LQTS. However, development of genotype-specific or mutation-specific management strategies is very challenging. This review describes the pathophysiology of LQTS, genotype-phenotype correlations, and focuses on the management of LQTS. In general, the treatment of LQTS consists of lifestyle modifications, medical therapy with beta-blockers, device and surgical therapy. We further summarize current data on the efficacy of pharmacological treatment options for the three most prevalent LQTS variants including beta-blockers in LQT1, LQT2 and LQT3, sodium channel blockers and ranolazine for LQT3, potassium supplementation and spironolactone for LQT2, and possibly sex hormone-based therapy for LQT2.

Suppression of the hERG potassium channel response to premature stimulation by reduction in extracellular potassium concentration

Potassium channels encoded by human ether‐à‐go‐go‐related gene (hERG) mediate the cardiac rapid delayed rectifier K⁺ current (I_Kr), which participates in ventricular repolarization and has a protective role against unwanted premature stimuli late in repolarization and early in diastole. Ionic current carried by hERG channels (I_hERG) is known to exhibit a paradoxical dependence on external potassium concentration ([K⁺]_e), but effects of acute [K⁺]_e changes on the response of I_hERG to premature stimulation have not been characterized. Whole‐cell patch‐clamp measurements of hERG current were made at 37°C from hERG channels expressed in HEK293 cells. Under conventional voltage‐clamp, both wild‐type (WT) and S624A pore‐mutant I_hERG during depolarization to +20 mV and subsequent repolarization to −40 mV were decreased when superfusate [K⁺]_e was decreased from 4 to 1 mmol/L. When [K⁺]_e was increased from 4 to 10 mmol/L, pulse current was increased and tail I_hERG was decreased. Increasing [K⁺]_e produced a +10 mV shift in voltage‐dependent inactivation of WT I_hERG and slowed inactivation time course, while lowering [K⁺]_e from 4 to 1 mmol/L produced little change in inactivation voltage dependence, but accelerated inactivation time course. Under action potential (AP) voltage‐clamp, lowering [K⁺]_e reduced the amplitude of I_hERG during the AP and suppressed the maximal I_hERG response to premature stimuli. Raising [K⁺]_e increased I_hERG early during the AP and augmented the I_hERG response to premature stimuli. Our results are suggestive that during hypokalemia not only is the contribution of I_Kr to ventricular repolarization reduced but its ability to protect against unwanted premature stimuli also becomes impaired.

hERG potassium channels are important for ventricular repolarization and for protecting the ventricles of the heart from unwanted premature stimuli. This study shows that, in addition to reducing the contribution of hERG channel current to ventricular repolarization, hypokalemia impairs the protective response of hERG to premature stimulation.

The effects of six antipsychotic agents on QTc--an attempt to mimic clinical trial through simulation including variability in the population

BACKGROUND

Many drugs (belonging to different chemical groups) have the potential for QT interval prolongation associated with ionic channel blockade in the cardiomyocyte membrane. Due to the fact that this phenomenon is linked to a higher risk of TdP, the ability to predict its scale is one of the most important outcomes of cardiotoxicity assessment of new agents.

METHODS

With use of the Cardiac Safety Simulator (CSS), the effect of six antipsychotic drugs was predicted in silico. Separate simulations were carried out for each studied population taking the drug. The aim of this study was to predict both the mean values of delta QTc and the results range. To be able to observe individual variability after drug administration, each patient was randomly assigned to the individual drug concentration. Also, appropriate diversity in heart rate, plasma electrolytes concentrations, morphometric parameters of ventricular myocytes, and one common hERG polymorphism frequency in population were added.

RESULTS

Analyzing the results of simulation with Student's t-test, in five of six cases, there were no statistically significant differences between observed and predicted mean values. The diversity of results in all populations studied, however, was not fully reconstructed.

DISCUSSION

The model was able to accurately reproduce the average effect of the drug on the length when the phenomenon is associated purely with blocking of ionic channels. Nevertheless, the problem of variability in the population and its effect on the QT interval requires further study.

Genotype-specific risk stratification and management of patients with long QT syndrome

Long QT syndrome (LQTS) is an inherited disorder associated with life-threatening ventricular arrhythmias. An understanding of the relationship between the genotype and phenotype characteristics of LQTS can lead to improved risk stratification and management of this hereditary arrhythmogenic disorder. Risk stratification in LQTS relies on combined assessment of clinical, electrocardiographic, and mutations-specific factors. Studies have shown that there are genotype-specific risk factors for arrhythmic events including age, gender, resting heart rate, QT corrected for heart rate, prior syncope, the postpartum period, menopause, mutation location, type of mutation, the biophysical function of the mutation, and response to beta-blockers. Importantly, genotype-specific therapeutic options have been suggested. Lifestyle changes are recommended according to the prevalent trigger for cardiac events. Beta-blockers confer greater benefit among patients with LQT1 with the greatest benefit among those with cytoplasmic loops mutations; specific beta-blocker agents may provide greater protection than other agents in specific LQTS genotypes. Potassium supplementation and sex hormone-based therapy may protect patients with LQT2. Sodium channel blockers such as mexiletine, flecainide, and ranolazine could be treatment options in LQT3.

In vitro-in vivo extrapolation of drug-induced proarrhythmia predictions at the population level

Drug cardiotoxicity is a serious issue for patients, regulators, pharmaceutical companies and health service payers because they are all affected by its consequences. Despite the wide range of data they generate, existing approaches for cardiac safety testing might not be adequate and sufficiently cost-effective, probably as a result of the complexity of the problem. For this reason, translational tools (based on biophysically detailed, mathematical models) allowing for in vitro-in vivo extrapolation are gaining increasing interest. This current review describes approaches that can be used for cardiac safety assessment at the population level, by accounting for various sources of variability including kinetics of the compound of interest.

Current pharmacogenomic studies on hERG potassium channels

Genetic polymorphisms in human ether-a-go-go-related gene (hERG) potassium channels are associated with many complex diseases and sensitivity to channel-related drugs. Genotypes may underlie different sensitivities to the same drug, and different drugs selectively repair the functional deficits caused by individual mutations. In fact, not all drugs that block hERG function have adverse effects as previously thought. This suggests that the severe adverse reactions observed clinically may only occur in subjects with a particular genotype, but to others may be safe. Similarly, a drug that is ineffective in one population may be both safe and effective in another. Therefore, detecting polymorphisms in KCNH2 encoding hERG1 is of great significance in guiding the prevention and treatment of related diseases, re-evaluating drug safety, and individualizing treatment. This article reviews current pharmacogenomic studies on hERG potassium channels to provide a reference for developing individualized treatments and evaluating their safety.

Genetics of cardiac electrical disease

Few tragedies compare to the sudden death of a family member. Sadly, this may represent the first sign of a familial vulnerability to such events. One common cause is an inherited cardiac arrhythmia syndrome. Sufferers are prone to premature sudden cardiac death due to altered ion channel function in the heart. Typical causes include Brugada syndrome, long QT syndrome, short QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and the newly recognized early repolarization syndrome. Our knowledge of the genetic underpinnings of each of these disorders has increased markedly in recent years. Genetic screening is now a routine part of clinical care and promises more accurate diagnosis and efficient family screening. This review summarizes the diagnosis and management of each of the listed syndromes in the context of currently available genetic testing.

Drug-Induced Long QT Syndrome - Clinical and Analytical Aspects for Medical Examiners

The long QT syndrome may occur due to genetic aberrations of cardiac transcellular ionic transporters, but also occurs secondary to a wide range of therapeutic and illicit drugs. This review will outline how the interaction of the blockade of the cardiac ion channels with drugs may lead to death from the long QT syndrome. Toxicology laboratories have a role, although somewhat limited, in supporting the investigation of sudden adult death and the contribution to the etiology of the long QT syndrome.

Mechanisms, risk factors, and management of acquired long QT syndrome: a comprehensive review

Long QT syndrome is characterized by prolongation of the corrected QT (QTc) interval on the surface electrocardiogram and is associated with precipitation of torsade de pointes (TdP), a polymorphic ventricular tachycardia that may cause sudden death. Acquired long QT syndrome describes pathologic excessive prolongation of the QT interval, upon exposure to an environmental stressor, with reversion back to normal following removal of the stressor. The most common environmental stressor in acquired long QT syndrome is drug therapy. Acquired long QT syndrome is an important issue for clinicians and a significant public health problem concerning the large number of drugs with this adverse effect with a potentially fatal outcome, the large number of patients exposed to these drugs, and our inability to predict the risk for a given individual. In this paper, we focus on mechanisms underlying QT prolongation, risk factors for torsades de pointes and describe the short- and long-term treatment of acquired long QT syndrome.

Potassium-channel mutations and cardiac arrhythmias--diagnosis and therapy

The coordinated generation and propagation of action potentials within cardiomyocytes creates the intrinsic electrical stimuli that are responsible for maintaining the electromechanical pump function of the human heart. The synchronous opening and closing of cardiac Na(+), Ca(2+), and K(+) channels corresponds with the activation and inactivation of inward depolarizing (Na(+) and Ca(2+)) and outward repolarizing (K(+)) currents that underlie the various phases of the cardiac action potential (resting, depolarization, plateau, and repolarization). Inherited mutations in pore-forming α subunits and accessory β subunits of cardiac K(+) channels can perturb the atrial and ventricular action potential and cause various cardiac arrhythmia syndromes, including long QT syndrome, short QT syndrome, Brugada syndrome, and familial atrial fibrillation. In this Review, we summarize the current understanding of the molecular and cellular mechanisms that underlie K(+)-channel-mediated arrhythmia syndromes. We also describe translational advances that have led to the emerging role of genetic testing and genotype-specific therapy in the diagnosis and clinical management of individuals who harbor pathogenic mutations in genes that encode α or β subunits of cardiac K(+) channels.

Differential conditions for early after-depolarizations and triggered activity in cardiomyocytes derived from transgenic LQT1 and LQT2 rabbits

Early after-depolarization (EAD), or abnormal depolarization during the plateau phase of action potentials, is a hallmark of long-QT syndrome (LQTS). More than 13 genes have been identified as responsible for LQTS, and elevated risks for EADs may depend on genotypes, such as exercise in LQT1 vs. sudden arousal in LQT2 patients. We investigated mechanisms underlying different high-risk conditions that trigger EADs using transgenic rabbit models of LQT1 and LQT2, which lack I(Ks) and I(Kr) (slow and fast components of delayed rectifying K(+) current), respectively. Single-cell patch-clamp studies show that prolongation of action potential duration (APD) can be further enhanced by lowering extracellular potassium concentration ([K(+)](o)) from 5.4 to 3.6 mm. However, only LQT2 myocytes developed spontaneous EADs following perfusion with lower [K(+)](o), while there was no EAD formation in littermate control (LMC) or LQT1 myocytes, although APDs were also prolonged in LMC myocytes and LQT1 myocytes. Isoprenaline (ISO) prolonged APDs and triggered EADs in LQT1 myocytes in the presence of lower [K(+)](o). In contrast, continuous ISO perfusion diminished APD prolongation and reduced the incidence of EADs in LQT2 myocytes. These different effects of ISO on LQT1 and LQT2 were verified by optical mapping of the whole heart, suggesting that ISO-induced EADs are genotype specific. Further voltage-clamp studies revealed that ISO increases L-type calcium current (I(Ca)) faster than I(Ks) (time constant 9.2 s for I(Ca) and 43.6 s for I(Ks)), and computer simulation demonstrated a high-risk window of EADs in LQT2 during ISO perfusion owing to mismatch in the time courses of I(Ca) and I(Ks), which may explain why a sympathetic surge rather than high sympathetic tone can be an effective trigger of EADs in LQT2 perfused hearts. In summary, EAD formation is genotype specific, such that EADs can be elicited in LQT2 myocytes simply by lowering [K(+)](o), while LQT1 myocytes require sympathetic stimulation. Slower activation of I(Ks) than of I(Ca) by ISO may explain why different sympathetic modes, i.e. sympathetic surge vs. high sympathetic tone, are associated with polymorphic ventricular tachycardia in LQTS patients.