Congenital Long QT Syndrome

The Clinical and Electrocardiographic Phenotype of Patients with Genotype Negative Long QT Syndrome

BACKGROUND

Long QT syndrome (LQTS) is a genetic heart disease that increases the risk for ventricular arrhythmias and sudden cardia arrest. Despite advances in genetic testing, a small subset of LQTS patients remain genetically elusive.

OBJECTIVE

To determine the prevalence and clinical characteristics of patients with a phenotype of LQTS but genotype negative.

METHODS

This study aimed to identify phenotype-positive, genotype-negative LQTS patients seen at Mayo Clinic (2000 - 2024). Retrospective data included demographics, clinical evaluations, ECGs, and genetic results. Diagnosis adhered to established criteria, and genotype-negative LQTS was defined by the absence of pathogenic variants despite clinical presentation.

RESULTS

The study included 1,829 patients with LQTS. From these, 1,706 (93%) had pathogenic or likely pathogenic variants and 95 patients (5%) had upgraded clinically variants of uncertain significance, leaving 32 (1.7%) with negative genetic tests. Among the genotype-negative patients, 17 underwent next-generation sequencing, identifying a genetic cause in 6 cases (0.3% of the total). The mean age at diagnosis for the remaining 26 patients was 25 ± 15 years, 76% being female and an average initial QTc of 498 ± 41 ms. Fourteen patients (53%) experienced cardiac events prior to diagnosis, and 11 (44%) received an implantable cardioverter-defibrillator (ICD). The mean follow-up period was 8 ± 7 years.

CONCLUSION

Genotype-negative LQTS accounted for <2% of our cohort, highlighting diagnostic and management challenges. Comprehensive clinical evaluation and advanced genetic testing remain essential for accurate diagnosis and care.

Gene therapy for cardiac arrhythmias

Cardiovascular diseases are the leading cause of death globally, with cardiac arrhythmias contributing substantially to this burden. Gene therapy, which directly targets the underlying disease pathobiology, offers an appealing treatment strategy for cardiac arrhythmias owing to its potential as a one-time, curative solution. Over the past two decades, substantial efforts have been made to develop new gene therapy approaches that overcome the limitations of conventional treatments. In this Review, we describe the rationale for gene therapy to treat cardiac arrhythmias; discuss advantages and disadvantages of gene silencing, gene replacement, gene suppression-and-replacement and gene editing technologies; summarize vector modalities and delivery approaches used in the field; present examples of gene therapy strategies used for atrial and ventricular arrhythmias; and highlight the current challenges and limitations in the gene therapy field.

Cardiac Channelopathies: Clinical Diagnosis and Promising Therapeutics

Cardiac channelopathies, also known as primary electrical heart diseases, are inherited genetic abnormalities of cardiomyocyte electrical behavior. Notable for their absence of structural heart diseases, they include a diverse group of diseases such as long QT syndrome, short QT syndrome, Brugada syndrome, early repolarization syndrome, catecholaminergic polymorphic ventricular tachycardia, and idiopathic ventricular fibrillation, and carry the risk of malignant arrhythmias leading to sudden cardiac death. The genetic and molecular foundations of these diseases are diverse and complex, with evolving research highlighting the multifactorial nature of their pathophysiology and the intricate interplay of various genes in the manifestation of arrhythmias. While advances in diagnostic techniques, such as genetic testing and electrophysiological studies, have improved the identification and management of these conditions, the relationship between specific genetic mutations and sudden cardiac death remains incompletely understood. This review provides an overview of the molecular and genetic mechanisms underlying those inherited arrhythmias, exploring both well-established and emerging data. Additionally, it discusses current diagnostic approaches and management strategies, aiming to enhance the understanding of these conditions and contribute to better sudden cardiac death prevention.

Clinical characteristics and gene analysis of long QT syndrome in 15 children

Objective

To elucidate the genetic and clinical characteristics of children diagnosed with long QT syndrome (LQTS) at our institution.

Study design

This was a retrospective study. Clinical data and gene detection results of 15 cases diagnosed with congenital LQTS at our center from January 1, 2018 to December 30, 2023 were collected and analyzed using independent sample t-test and Levene's test for equality of variances.

Results

The 15 LQTS cases included 7 females and 8 males. The mean age of onset for females (11.83 ± 3.48 years) was later than that for males (8.06 ± 2.50 years), and the mean QTc value for females (564.57 ± 20.72 ms) was higher than that for males (502. 25 ± 48.62 ms), both differences were statistically significant (P < 0.05). Intense exercise and psychological stress are the most common predisposing factors in these cases. Gene mutations were found in 14 of the 15 cases and most mutations (13/14) were inherited from parents. According to the mutation sites, the most common mutation type was missense mutations (11/15). One genetically exclusive case with a Schwartz score of 4 was clinically diagnosed with LQTS after excluding other diseases.

Conclusions

In this cohort, age of onset and QTc value are different between male and female. The most common primary symptom of LQTS is syncope. Most LQTS patients have a mutated gene inherited from their parents, and the most common pathogenic gene is KCNQ1.

Clinical, Electrical, and Mechanical Parameters in Potassium Channel-Mediated Congenital Long QT Syndrome

Background: Congenital long QT syndrome (LQTS) is a rare cardiac disorder caused by repolarization abnormalities in the myocardium that predisposes to ventricular arrhythmias and sudden cardiac death. Potassium channel-mediated LQT1 and LQT2 are the most common types of channelopathy. Recently, LQTS has been acknowledged as an electromechanical disease. Methods: A total of 87 genotyped LQT1/LQT2 patients underwent cardiac evaluation. A comparison between LQT1 and LQT2 electrical and mechanical parameters was performed. Results: LQT2 patients had worse electrical parameters at rest: a longer QTc interval (p = 0.007), a longer Tpe in lead V2 (p = 0.028) and in lead V5 (p < 0.001), and a higher Tpe/QT ratio in lead V2 (p = 0.011) and in lead V5 (p = 0.005). Tpe and Tpe/QT remained significantly higher in the LQT2 group after brisk standing. Tpe was longer in LQT2 patients compared with LQT1 patients during peak exercise (p = 0.007) and almost all recovery periods in lead V2 during EST. The mid-cavity myocardium mean radial contraction duration (CD) was longer in LQT2 patients (p = 0.02). LQT2 patients had a longer mean radial CD in mid-septal (p = 0.015), mid-inferior (p = 0.034), and mid-posterior (p = 0.044) segments. Conclusions: Potassium channel-mediated LQTS has different effects on cardiac electromechanics with a more pronounced impact on LQT2 patients. Tpe was more prominent in the LQT2 cohort, not only at rest and brisk standing but also during EST exercise and at recovery phases. The altered mean radial CD in the mid-cavity myocardium was also specific for LQT2 patients.

Induced Pluripotent Stem Cells in Congenital Long QT Syndrome: Research Progress and Clinical Applications

Congenital long QT syndrome (LQTS) is a potentially life-threatening hereditary arrhythmia characterized by a prolonged QT interval on electrocardiogram (ECG) due to delayed ventricular repolarization. This condition predisposes individuals to severe arrhythmic events, including ventricular tachycardia and sudden cardiac death. Traditional approaches to LQTS research and treatment are limited by an incomplete understanding of its gene-specific pathophysiology, variable clinical presentation, and the challenges associated with developing effective, personalized therapies. Recent advances in human induced pluripotent stem cell (iPSC) technology have opened new avenues for elucidating LQTS mechanisms and testing therapeutic strategies. By generating cardiomyocytes from patient-specific iPSCs (iPSC-CMs), it is now possible to recreate the patient's genetic context and study LQTS in a controlled environment. This comprehensive review describes how iPSC technology deepens our understanding of LQTS and accelerates the development of tailored treatments, as well as ongoing challenges such as incomplete cell maturation and cellular heterogeneity.

Exploring the mechanisms of sex-specific proarrhythmia in long QT syndrome through computational modeling

Females exhibit longer QT intervals and a higher risk of long QT syndrome (LQTS) associated arrhythmogenesis compared with males. Although several studies suggest these sex disparities result from the effect of sex hormones on cardiac ion channels, the underlying mechanisms remain incompletely understood. This research investigates the arrhythmogenic effects, sex-specific risk, and mechanisms associated with LQTS linked to either to loss-of-function of the rapidly activating delayed rectifier K+ current (IKr), or gain-of-function of the L-type Ca2+ current (ICaL). We primarily used the Tomek-Rodriguez (ToR-ORd) model of human ventricular cardiomyocytes and incorporated sex-specific parameterizations based on previous studies. The O'Hara-Rudy and Grandi-Bers models were used to demonstrate model-independence of the findings. We used a populations-of-models approach to assess early afterdepolarization (EAD) susceptibility in control and LQTS male and female groups. All female models had consistently longer action potentials and were more prone to EADs than male models. In the ToR-ORd model, IKr loss-of-function led to EADs in 65.8% of females versus 22.8% of males. ICaL gain-of-function led to EADs in 66.2% of females but only 3.6% of males. Using logistic regression analysis, we identified key ionic predictors of EAD susceptibility, with maximal conductance of the L-type Ca2+ current (GCaL) and maximal transport rate of the Na+/Ca2+ exchanger (GNCX) consistently emerging as positively and maximal conductance of the rapidly activating delayed rectifier K+ current (GKr) as negatively associated to EADs across both sexes and LQTS types. Notably, higher GNCX but lower GKr in female versus male cardiomyocytes could explain heightened female EAD risk. Our studies explore the ionic traits that favor (or confer resilience against) EADs with potential implications for personalized treatments. NEW & NOTEWORTHY We explored sex disparities in long QT syndrome (LQTS) using sex-specific human ventricular cardiomyocyte models. We showed that females exhibit greater susceptibility to early afterdepolarizations (EADs) than males, and identified key ionic predictors of EAD risk, including increases in the voltage-gated L-type Ca2+ current and electrogenic Na+/Ca2+ exchanger, and downregulation of the rapidly activating delayed rectifier K+ current. These findings offer new insights into sex-specific mechanisms underlying arrhythmogenesis in LQTS, with potential implications for personalized treatments.

Risk Stratification of QTc Prolongation in Critically Ill Patients Receiving Antipsychotics for the Management of Delirium Symptoms

BackgroundPatients experiencing significant agitation or perceptual disturbances related to delirium in an intensive care setting may benefit from short-term treatment with an antipsychotic medication. Some antipsychotic medications may prolong the QTc interval, which increases the risk of potentially fatal ventricular arrhythmias. In this targeted review, we describe the evidence regarding the relationships between antipsychotic medications and QTc prolongation and practical methods for monitoring the QTc interval and mitigating arrhythmia risk.MethodsSearches of PubMed and Cochrane Library were performed to identify studies, published before February 2023, investigating the relationships between antipsychotic medications and QTc prolongation or arrhythmias.ResultsMost antipsychotic medications commonly used for the management of delirium symptoms (eg, intravenous haloperidol, olanzapine, quetiapine) cause a moderate degree of QTc prolongation. Among other antipsychotics, those most likely to cause QTc prolongation are iloperidone and ziprasidone, while aripiprazole and lurasidone appear to have minimal risk for QTc prolongation. Genetic vulnerabilities, female sex, older age, pre-existing cardiovascular disease, electrolyte abnormalities, and non-psychiatric medications also increase the risk of QTc prolongation. For individuals at risk of QTc prolongation, it is essential to measure the QTc interval accurately and consistently and consider medication adjustments if needed.ConclusionsAntipsychotic medications are one of many risk factors for QTc prolongation. When managing agitation related to delirium, it is imperative to assess an individual patient's risk for QTc prolongation and to choose a medication and monitoring strategy commensurate to the risks. In intensive care settings, we recommend regular ECG monitoring, using a linear regression formula to correct for heart rate. If substantial QTc prolongation (eg, QTc > 500 msec) is present, a change in pharmacologic treatment can be considered, though a particular medication may still be warranted if the risks of discontinuation (eg, extreme agitation, removal of invasive monitoring devices) outweigh the risks of arrhythmias.AimsThis review aims to summarize the current literature on relationships between antipsychotic medications and QTc prolongation and to make practical clinical recommendations towards the approach of antipsychotic medication use for the management of delirium-related agitation and perceptual disturbances in intensive care settings.

Out-of-Hospital Cardiac Arrest in Apparently Healthy, Young Adults

Importance

Out-of-hospital cardiac arrest incidence in apparently healthy adults younger than 40 years ranges from 4 to 14 per 100 000 person-years worldwide. Of an estimated 350 000 to 450 000 total annual out-of-hospital cardiac arrests in the US, approximately 10% survive.

Observations

Among young adults who have had cardiac arrest outside of a hospital, approximately 60% die before reaching a hospital (presumed sudden cardiac death), approximately 40% survive to hospitalization (resuscitated sudden cardiac arrest), and 9% to 16% survive to hospital discharge (sudden cardiac arrest survivor), of whom approximately 90% have a good neurological status (Cerebral Performance Category 1 or 2). Autopsy-based studies demonstrate that 55% to 69% of young adults with presumed sudden cardiac death have underlying cardiac causes, including sudden arrhythmic death syndrome (normal heart by autopsy, most common in athletes) and structural heart disease such as coronary artery disease. Among young adults, noncardiac causes of cardiac arrest outside of a hospital may include drug overdose, pulmonary embolism, subarachnoid hemorrhage, seizure, anaphylaxis, and infection. More than half of young adults with presumed sudden cardiac death had identifiable cardiovascular risk factors such as hypertension and diabetes. Genetic cardiac disease such as long QT syndrome or dilated cardiomyopathy may be found in 2% to 22% of young adult survivors of cardiac arrest outside of the hospital, which is a lower yield than for nonsurvivors (13%-34%) with autopsy-confirmed sudden cardiac death. Persons resuscitated from sudden cardiac arrest should undergo evaluation with a basic metabolic profile and serum troponin; urine toxicology test; electrocardiogram; chest x-ray; head-to-pelvis computed tomography; and bedside ultrasound to assess for pericardial tamponade, aortic dissection, or hemorrhage. Underlying reversible causes, such as ST elevation myocardial infarction, coronary anomaly, and illicit drug or medication overdose (including QT-prolonging medicines) should be treated. If an initial evaluation does not reveal the cause of an out-of-hospital cardiac arrest, transthoracic echocardiography should be performed to screen for structural heart disease (eg, unsuspected cardiomyopathy) or valvular disease (eg, mitral valve prolapse) that can precipitate sudden cardiac death. Defibrillator implant is indicated for young adult sudden cardiac arrest survivors with nonreversible cardiac causes including structural heart disease and arrhythmia syndromes.

Conclusions and Relevance

Cardiac arrest in apparently healthy adults younger than 40 years may be due to inherited or acquired cardiac disease or noncardiac causes. Among young adults who have had cardiac arrest outside of a hospital, only 9% to 16% survive to hospital discharge. Sudden cardiac arrest survivors require comprehensive evaluation for underlying causes of cardiac arrest and cardiac defibrillator should be implanted in those with nonreversible cardiac causes of out-of-hospital cardiac arrest.

Asthma and the risk of cardiac events among patients with long QT syndrome after age 40

Background

Limited data exist on the impact of asthma on long QT syndrome (LQTS) in middle-aged and older adults.

Objective

This study aimed to examine the association between asthma, β2-agonist treatment, and cardiac events (CEs) in LQTS patients over 40 years of age.

Methods

The risk of CEs (comprising syncope, aborted cardiac arrest, implantable cardioverter-defibrillator shock, or sudden cardiac death) from age 40 through 75 years, by the presence of asthma with and without treatment with a β2-agonist inhaler, was assessed among 1020 LQTS patients from the Rochester LQTS Registry.

Results

Among 1020 LQTS patients, 162 (16%) had asthma by age 40 years or subsequent follow-up, with 63% treated with a β2-agonist inhaler. Patients with asthma vs no asthma had a higher cumulative rate of CEs from age 40 through 75 years (44% vs 26%, P < .001). Consistently, multivariate analysis showed that asthma was associated with a 2-fold (hazard ratio 1.97, P = .001) increased risk of CEs. Subgroup analysis showed that the association of asthma with CEs was consistent within risk subsets of LQTS patients, including QTc duration, syncope prior to age 40 years, β-blocker use, sex, and LQTS genotype (all P values for risk subset-by-asthma interaction >.10). Asthma patients with LQTS who were treated with a β2-agonist inhaler did not show an increased risk compared with those who were not treated (hazard ratio 1.02, P = .963).

Conclusion

The presence of asthma is associated with increased risk of CEs among middle-aged and older patients with LQTS regardless of baseline risk factors or treatment with a β2-agonist inhaler.

Ion channel traffic jams: the significance of trafficking deficiency in long QT syndrome

A well-balanced ion channel trafficking machinery is paramount for the normal electromechanical function of the heart. Ion channel variants and many drugs can alter the cardiac action potential and lead to arrhythmias by interfering with mechanisms like ion channel synthesis, trafficking, gating, permeation, and recycling. A case in point is the Long QT syndrome (LQTS), a highly arrhythmogenic disease characterized by an abnormally prolonged QT interval on ECG produced by variants and drugs that interfere with the action potential. Disruption of ion channel trafficking is one of the main sources of LQTS. We review some molecular pathways and mechanisms involved in cardiac ion channel trafficking. We highlight the importance of channelosomes and other macromolecular complexes in helping to maintain normal cardiac electrical function, and the defects that prolong the QT interval as a consequence of variants or the effect of drugs. We examine the concept of "interactome mapping" and illustrate by example the multiple protein-protein interactions an ion channel may undergo throughout its lifetime. We also comment on how mapping the interactomes of the different cardiac ion channels may help advance research into LQTS and other cardiac diseases. Finally, we discuss how using human induced pluripotent stem cell technology to model ion channel trafficking and its defects may help accelerate drug discovery toward preventing life-threatening arrhythmias. Advancements in understanding ion channel trafficking and channelosome complexities are needed to find novel therapeutic targets, predict drug interactions, and enhance the overall management and treatment of LQTS patients.

Gene therapy for cardiac diseases: methods, challenges, and future directions

Gene therapy is advancing at an unprecedented pace, and the recent success of clinical trials reinforces optimism and trust among the scientific community. Recently, the cardiac gene therapy pipeline, which had progressed more slowly than in other fields, has begun to advance, overcoming biological and technical challenges, particularly in treating genetic heart pathologies. The primary rationale behind the focus on monogenic cardiac diseases is the well-defined molecular mechanisms driving their phenotypes, directly linked to the pathogenicity of single genetic mutations. This aspect makes these conditions a remarkable example of 'genetically druggable' diseases. Unfortunately, current treatments for these life-threatening disorders are few and often poorly effective, underscoring the need to develop therapies to modulate or correct their molecular substrates. In this review we examine the latest advancements in cardiac gene therapy, discussing the pros and cons of different molecular approaches and delivery vectors, with a focus on their therapeutic application in cardiac inherited diseases. Additionally, we highlight the key factors that may enhance clinical translation, drawing insights from previous trials and the current prospects of cardiac gene therapy.

Cardiac safety of antipsychotic medications in pediatric and adolescent population: a systematic review and pathways for future research

Understanding the cardiac risks of antipsychotic use is crucial for clinicians managing psychiatric conditions in children and adolescents. However, the effects on the QT interval in pediatric populations have been poorly investigated. We performed a systematic review to provide clinicians an updated source on the effects of antipsychotic medications on QTc and guide drug's choice. A literature search on the PubMed and Scopus databases was conducted from April 22, 1989, to May 28, 2023, for all studies investigating the effects of antipsychotic medications on the QTc interval in patients aged 0-18 years. A total of 10 articles including 523 patients and 7 different antipsychotic drugs met our search criteria. Among the included articles were three randomized clinical trials, five controlled trials without randomization or prospective comparative cohort trials, and two retrospective cohort studies. Clinical data emerging from these studies were classified according to the Oxford Centre for Evidence-Based Medicine. Risperidone and aripiprazole showed minimal to no significant QTc prolongation, whereas quetiapine, olanzapine, and ziprasidone showed variable effects on QTc. Haloperidol did not demonstrate significant QTc prolongation. In a prospective comparative cohort trial, pimozide exhibited significant QTc prolongation in a cohort with Tourette syndrome.

CONCLUSION

Only 10 studies have carefully addressed the effect of antipsychotic medications on QTc among pediatric patients, underscoring the need for further research. Personalized risk assessment and regular cardiac monitoring should be integrated into clinical management of pediatric and adolescent patients receiving antipsychotics to facilitate early detection of repolarization abnormalities and potential intervention.

WHAT IS KNOWN

• QT interval prolongation is a reported side effect of antipsychotics among adults especially with first-generation antipsychotics and parenteral infusion. • Understanding the effect of antipsychotics on QT is essential for clinical monitoring and avoidance of complications.

WHAT IS NEW

• Risperidone and aripiprazole were the most studied antipsychotics in pediatric patients and showed minimal QT prolongation. • The absence of a standardized protocol for assessing the effects on the QT interval makes comparisons between studies challenging and emphasizes the need for further research.

The Yield of Genetic Testing and Putative Genetic Factors of Disease Heterogeneity in Long QT Syndrome Patients

Genetic overdiagnosis of long QT syndrome (LQTS) becomes a critical concern due to the high clinical significance of DNA diagnosis. Current guidelines for LQTS genetic testing recommend a limited scope and strict referral based on the Schwartz score. Nevertheless, LQTS may be underdiagnosed in patients with borderline phenotypes. We aimed to evaluate the total yield of rare variants in cardiac genes in LQTS patients. The cohort of 82 patients with LQTS referral diagnosis underwent phenotyping, Schwartz score counting, and exome sequencing. We assessed known LQTS genes for diagnostics, as per guidelines, and a broader set of genes for research. Diagnostic testing yield reached 75% in index patients; all causal variants were found in KCNQ1, KCNH2, and SCN5A genes. Research testing of 248 heart-related genes achieved a 50% yield of molecular diagnosis in patients with a low Schwartz score (<3.5). In patients with LQTS-causing variants, each additional rare variant in heart-related genes added 0.94 points to the Schwartz score (p value = 0.04), reflecting the more severe disease in such patients than in those with causal variants but without additional findings. We conclude that the current LQTS genetic diagnosis framework is highly specific but may lack sensitivity for patients with a Schwartz score <3.5. Improving referral criteria for these patients could enhance DNA diagnosis. Also, our results suggest that additional variants in cardiac genes may affect the severity of the disease in the carriers of LQTS-causing variants, which may aid in identifying new modifier genes.

Cardiac channelopathies in pediatrics: a genetic update

Cardiac channelopathies are a group of inherited syndromes that can cause malignant arrhythmias and sudden cardiac death, particularly in the pediatric population. Today, a 12-lead electrocardiogram is the most effective tool to diagnose these diseases. Incomplete penetrance and variable expressivity are hallmarks of these syndromes. Some of these malignant entities may remain hidden and only a trigger such as exercise, emotions or fever can unmask the electrical pattern to diagnose the disease. Sudden cardiac death may be the first manifestation of any of these syndromes. The use of complementary tests that allow early diagnosis is strongly recommended, among which we find: pharmacological provocations, exercise tests, and genetic analysis. Genetic testing makes it possible to unravel the origin of the disease, and also identify family members who carry the harmful genetic defect and are therefore at risk. One of the main challenges in this area is the large number of genetic variants of uncertain significance, which prevent effective translation into clinical practice. Early identification of the pediatric population at risk and adequate risk stratification are crucial to adopting personalized preventive measures that reduce the risk of lethal episodes in this population. What is Known: • In the pediatric population, malignant arrhythmias leading to sudden cardiac death are mainly caused by inherited syndromes. • A conclusive genetic diagnosis unravels the origin of the syndrome and allows cascade screening to identify relatives carrying the genetic alteration. What is New: • The use of sequencing technologies allows a broad genetic analysis, helping to unravel new genetic alterations causing inherited arrhythmogenic syndromes. • A periodic reanalysis of genetic variants that currently have an ambiguous role will help discern those that are truly pathogenic.

Clinical presentation and genetic characterization of early-onset atrial fibrillation in patients affected by long QT syndrome: A single-center experience

INTRODUCTION

Early-onset atrial fibrillation (AF) has already been observed in approximately 2% of patients with genetically proven long QT syndrome (LQTS). This frequency is higher than population-based estimates of early-onset AF. However, the concomitant expression of AF in LQTS is likely underestimated. The purpose of this study was to examine the clinical presentation, genetic background, and outcomes of a cohort of patients with LQTS and early-onset AF referred to a single tertiary center.

METHODS

Twenty-seven patients diagnosed with congenital LQTS were included in the study based on the documentation of early-onset (age ≤50 years) clinical or subclinical AF episodes in all available medical records, including standard electrocardiograms, wearable monitor or cardiac implantable electronic devices.

RESULTS

Seventeen patients experienced clinical AF during the follow-up period. Subclinical AF was detected in 10 patients through insertable or wearable cardiac monitors. In our series, the mean heart rate during AF episodes was found to be relatively low despite the patients' young age and the low or minimal effective doses of beta-blockers used for QTc interval control. All patients exhibiting LQTS and early-onset AF were genotype positive, carrying mutations in the KCNQ1 (66%), KCNH2, KCNE1, and SCN5A genes. Notably, most of these patients carried the same p.(R231C) mutation in the KCNQ1 gene (59%) and were from the same families, suggesting concurrent expression of familial AF and LQTS.

CONCLUSION

LQTS patients are prone to developing clinical and subclinical AF, even at a younger age. The occurrence of early-onset AF in the LQTS population could be more frequent than previously assumed. AF should be considered as a potential dysrhythmia related to LQTS. Our study emphasizes the importance of carefully researching clinical and/or subclinical episodes of AF through strict heart rhythm monitoring in the LQTS population.

2024 HRS expert consensus statement on arrhythmias in the athlete: Evaluation, treatment, and return to play

Youth and adult participation in sports continues to increase, and athletes may be diagnosed with potentially arrhythmogenic cardiac conditions. This international multidisciplinary document is intended to guide electrophysiologists, sports cardiologists, and associated health care team members in the diagnosis, treatment, and management of arrhythmic conditions in the athlete with the goal of facilitating return to sport and avoiding the harm caused by restriction. Expert, disease-specific risk assessment in the context of athlete symptoms and diagnoses is emphasized throughout the document. After appropriate risk assessment, management of arrhythmias geared toward return to play when possible is addressed. Other topics include shared decision-making and emergency action planning. The goal of this document is to provide evidence-based recommendations impacting all areas in the care of athletes with arrhythmic conditions. Areas in need of further study are also discussed.

Idiopathic Prolonged Long QT Interval Leading to Sudden Cardiac Arrest in an Adolescent

Sudden cardiac arrest (SCA) can be caused by inherited and acquired conditions and can lead to sudden cardiac death. There are many causes and risk factors for SCA such as QTc prolongation which can be inherited or acquired. Potential causes of acquired QTc prolongation include medications, electrolyte abnormalities, etc. Genetic causes are less common and look at channelopathies involved in the cardiac action potential that interferes with the repolarization, causing a prolonged ventricular contraction reflected in the QTc interval. Before determining that the cause of an SCA is due to a QTc prolonged interval, a full cardiac workup needs to be done to eliminate other anatomical causes of SCA. This case report elicits an interesting clinical scenario in which a previously healthy 20-year-old male experiences SCA while playing basketball. The patient was resuscitated at the scene. After defibrillation, intubation, various imaging studies, and a subcutaneous implantable cardioverter-defibrillator (ICD) placement, the patient was diagnosed with long QTc syndrome and underwent genetic testing which was later found to be negative. Hence, understanding the causes of SCA in young patients can be important in avoiding dreadful and life-threatening situations and providing information to the patient and family members.

Brazilian Guideline for Exercise Testing in Children and Adolescents - 2024

CLASSES OF RECOMMENDATION

LEVELS OF EVIDENCE

Detection of distant relatedness in biobanks to identify undiagnosed cases of Mendelian disease as applied to Long QT syndrome

Rare genetic diseases are typically studied in referral populations, resulting in underdiagnosis and biased assessment of penetrance and phenotype. To address this, we develop a generalizable method of genotype inference based on distant relatedness and deploy this to identify undiagnosed Type 5 Long QT Syndrome (LQT5) rare variant carriers in a non-referral population. We identify 9 LQT5 families referred to a single specialty clinic, each carrying p.Asp76Asn, the most common LQT5 variant. We uncover recent common ancestry and a single shared haplotype among probands. Application to a non-referral population of 69,819 BioVU biobank subjects identifies 22 additional subjects sharing this haplotype, which we confirm to carry p.Asp76Asn. Referral and non-referral carriers have prolonged QT interval corrected for heart rate (QTc) compared to controls, and, among carriers, the QTc polygenic score is independently associated with QTc prolongation. Thus, our innovative analysis of shared chromosomal segments identifies undiagnosed cases of genetic disease and refines the understanding of LQT5 penetrance and phenotype.

Multimodal fusion learning for long QT syndrome pathogenic genotypes in a racially diverse population

Congenital long QT syndrome (LQTS) diagnosis is complicated by limited genetic testing at scale, low prevalence, and normal QT corrected interval in patients with high-risk genotypes. We developed a deep learning approach combining electrocardiogram (ECG) waveform and electronic health record data to assess whether patients had pathogenic variants causing LQTS. We defined patients with high-risk genotypes as having ≥1 pathogenic variant in one of the LQTS-susceptibility genes. We trained the model using data from United Kingdom Biobank (UKBB) and then fine-tuned in a racially/ethnically diverse cohort using Mount Sinai BioMe Biobank. Following group-stratified 5-fold splitting, the fine-tuned model achieved area under the precision-recall curve of 0.29 (95% confidence interval [CI] 0.28-0.29) and area under the receiver operating curve of 0.83 (0.82-0.83) on independent testing data from BioMe. Multimodal fusion learning has promise to identify individuals with pathogenic genetic mutations to enable patient prioritization for further work up.

From genes to clinical management: A comprehensive review of long QT syndrome pathogenesis and treatment

Background

Long QT syndrome (LQTS) is a rare cardiac disorder characterized by prolonged ventricular repolarization and increased risk of ventricular arrhythmias. This review summarizes current knowledge of LQTS pathogenesis and treatment strategies.

Objectives

The purpose of this study was to provide an in-depth understanding of LQTS genetic and molecular mechanisms, discuss clinical presentation and diagnosis, evaluate treatment options, and highlight future research directions.

Methods

A systematic search of PubMed, Embase, and Cochrane Library databases was conducted to identify relevant studies published up to April 2024.

Results

LQTS involves mutations in ion channel-related genes encoding cardiac ion channels, regulatory proteins, and other associated factors, leading to altered cellular electrophysiology. Acquired causes can also contribute. Diagnosis relies on clinical history, electrocardiographic findings, and genetic testing. Treatment strategies include lifestyle modifications, β-blockers, potassium channel openers, device therapy, and surgical interventions.

Conclusion

Advances in understanding LQTS have improved diagnosis and personalized treatment approaches. Challenges remain in risk stratification and management of certain patient subgroups. Future research should focus on developing novel pharmacological agents, refining device technologies, and conducting large-scale clinical trials. Increased awareness and education are crucial for early detection and appropriate management of LQTS.

Frontiers in premature beats research: a bibliometric analysis

Background

This study aimed to assess the scientific results and activities of premature beats research from a global perspective.

Methods

Publications related to premature beats published between 2003 and 2024 were identified and selected from the Web of Science core collection. VOSviewer was used to conduct co-authorship, co-citation, and co-occurrence analyses of the authors, organizations, countries/regions, references, sources, cited authors, and keywords.

Results

In total, 5,283 publications on the topic of premature beats were identified from the Web of Science core collection. The number of publications on this topic has steadily grown since 2003. Fred Morady, Frank Bogun and Krit Jongnarangsin were the top three researchers with the strongest total link strengths. The University of Washington, Johns Hopkins University, and the University of Minnesota are the top three organizations with the strongest total link strengths. The United States has made the greatest contributions to the field of premature beats. Haïssaguerre, M et al.'s publication in The New England Journal of Medicine in 1998 entitled "Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins" is the most cited reference. The most cited references come from the journal named Circulation. Haïssaguerre, M has the highest number of citations. The keywords for all current publications can be divided into four categories: "mortality rate," "risk and prevention," "mechanism," and "classification and treatment."

Conclusions

This bibliometric study provides insights into the current status and research trends in premature beats over more than 20 years. Future research will focus on an in-depth exploration of the nature of premature beats, especially ventricular premature beats, mastering the development law of premature beats, and optimizing existing detection methods.

ST segment and T wave abnormalities: A narrative review

INTRODUCTION

The electrocardiogram (ECG) is a valuable tool for interpreting ventricular repolarization. This article aims to broaden the diagnostic scope beyond the conventional ischemia-centric approach, integrating an understanding of pathophisiological influences on ST-T wave changes.

METHODS

A review was conducted on the physiological underpinnings of ventricular repolarization and the pathophisiological processes that can change ECG patterns. The research encompassed primary repolarization abnormalities due to uniform variations in ventricular action potential, secondary changes from electrical or mechanical alterations, and non-ischemic conditions influencing ST-T segments.

RESULTS

Primary T waves are characterized by symmetrical waves with broad bases and variable QT intervals, indicative of direct myocardial action potential modifications due to ischemia, electrolyte imbalances, and channelopathies. Secondary T waves are asymmetric and often unassociated with significant QT interval changes, suggesting depolarization alterations or changes in cardiac geometry and contractility.

CONCLUSION

We advocate for a unified ECG analysis, recognizing primary and secondary ST-T changes, and their clinical implications. Our proposed analytical framework enhances the clinician's ability to discern a wide array of cardiac conditions, extending diagnostic accuracy beyond myocardial ischemia.

Sudden Cardiac Death, Post-Mortem Investigation: A Proposing Panel of First Line and Second Line Genetic Tests

Investigating the causes of Sudden cardiac death (SCD) is always difficult; in fact, genetic cardiac conditions associated with SCD could be "silent" even during autopsy investigation. In these cases, it is important to exclude other aetiology and assist to ask for genetic investigations. Herein, the purpose of this review is to collect the most-implicated genes in SCD and generate a panel with indications for first line and second line investigations. A systematic review of genetic disorders that may cause SCD in the general population was carried out according to the Preferred Reporting Item for Systematic Review (PRISMA) standards. We subsequently listed the genes that may be tested in the case of sudden cardiac death when the autopsy results are negative or with no evidence of acquired cardiac conditions. To make genetic tests more specific and efficient, it is useful and demanded to corroborate autopsy findings with the molecular investigation as evident in the panel proposed. The genes for first line investigations are HCM, MYBPC3, MYH7, TNNT2, TNNI3, while in case of DCM, the most implicated genes are LMNA and TTN, and in second line for these CDM, ACTN2, TPM1, C1QPB could be investigated. In cases of ACM/ARVC, the molecular investigation includes DSP, DSG2, DSC2, RYR2, PKP2. The channelopathies are associated with the following genes: SCN5A, KCNQ1, KCNH2, KCNE1, RYR2. Our work underlines the importance of genetic tests in forensic medicine and clinical pathology; moreover, it could be helpful not only to assist the pathologists to reach a diagnosis, but also to prevent other cases of SCD in the family of the descendant and to standardise the type of analysis performed in similar cases worldwide.

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.

Impacts of gene variants on drug effects-the foundation of genotype-guided pharmacologic therapy for long QT syndrome and short QT syndrome

The clinical significance of optimal pharmacotherapy for inherited arrhythmias such as short QT syndrome (SQTS) and long QT syndrome (LQTS) has been increasingly recognised. The advancement of gene technology has opened up new possibilities for identifying genetic variations and investigating the pathophysiological roles and mechanisms of genetic arrhythmias. Numerous variants in various genes have been proven to be causative in genetic arrhythmias. Studies have demonstrated that the effectiveness of certain drugs is specific to the patient or genotype, indicating the important role of gene-variants in drug response. This review aims to summarize the reported data on the impact of different gene-variants on drug response in SQTS and LQTS, as well as discuss the potential mechanisms by which gene-variants alter drug response. These findings may provide valuable information for future studies on the influence of gene variants on drug efficacy and the development of genotype-guided or precision treatment for these diseases.

Use of portable single-lead electrocardiogram device as an alternative for QTc monitoring in critically ill patients

PURPOSE

Acquired QT prolongation is frequent and leads to a higher mortality rate in critically ill patients. KardiaMobile 1L® (KM1L) is a portable, user-friendly single lead, mobile alternative to conventional 12-lead electrocardiogram (12-L ECG) that could be more readily available, potentially facilitating more frequent QTc assessments in intensive care units (ICU); however, there is currently no evidence to validate this potential use.

METHODS

We conducted a prospective diagnostic test study comparing QT interval measurement using KM1L with conventional 12-L ECG ordered for any reason in patients admitted to an ICU. We compared the mean difference using a paired t-test, agreement using Bland-Altman analysis, and Lin's concordance coefficient, numerical precision (proportion of QT measurements with <10 ms difference between KM1L and conventional 12-L ECG), and clinical precision (concordance for adequate discrimination of prolonged QTc).

RESULTS

We included 114 patients (61.4% men, 60% cardiovascular etiology of hospitalization) with 131 12-L ECG traces. We found no statistical difference between corrected QT measurements (427 ms vs. 428 ms, p = .308). Lin's concordance coefficient was 0.848 (95% CI 0.801-0.894, p = .001). Clinical precision was excellent in males and substantial in females (Kappa 0.837 and 0.781, respectively). Numerical precision was lower in patients with vasoactive drugs (-13.99 ms), QT-prolonging drugs (13.84 ms), antiarrhythmic drugs (-12.87 ms), and a heart rate (HR) difference of ≥5 beats per minute (bpm) between devices (-11.26 ms).

CONCLUSION

Our study validates the clinical viability of KM1L, a single-lead mobile ECG device, for identifying prolonged QT intervals in ICU patients. Caution is warranted in patients with certain medical conditions that may affect numerical precision.

Opioids-Induced Long QT Syndrome: A Challenge to Cardiac Health

The challenge posed by opioid overdose has become a significant concern for health systems due to the complexities associated with drug prohibition, widespread clinical use, and potential abuse. In response, healthcare professionals have primarily concentrated on mitigating the hallucinogenic and respiratory depressant consequences of opioid overdose to minimize associated risks. However, it is crucial to acknowledge that most opioids possess the capacity to prolong the QT interval, particularly in cases of overdose, thereby potentially resulting in severe ventricular arrhythmias and even sudden death if timely intervention is not implemented. Consequently, alongside addressing the typical adverse effects of opioids, it is imperative to consider their cardiotoxicity. To enhance comprehension of the correlation between opioids and arrhythmias, identify potential targets for prompt intervention, and mitigate the hazards associated with clinical utilization, an exploration of the interaction between drugs and ion channels, as well as their underlying mechanisms, becomes indispensable. This review primarily concentrates on elucidating the impact of opioid drugs on diverse ion channels, investigating recent advancements in this domain, and attaining a deeper understanding of the mechanisms underlying the prolongation of the QT interval by opioid drugs, along with potential interventions.

Catheter Ablation for Channelopathies: When Is Less More?

Ventricular fibrillation (VF) is a common cause of sudden cardiac death in patients with channelopathies, particularly in the young population. Although pharmacological treatment, cardiac sympathectomy, and implantable cardioverter defibrillators (ICD) have been the mainstay in the management of VF in patients with channelopathies, they are associated with significant adverse effects and complications, leading to poor quality of life. Given these drawbacks, catheter ablation has been proposed as a therapeutic option for patients with channelopathies. Advances in imaging techniques and modern mapping technologies have enabled increased precision in identifying arrhythmia triggers and substrate modification. This has aided our understanding of the underlying pathophysiology of ventricular arrhythmias in channelopathies, highlighting the roles of the Purkinje network and the epicardial right ventricular outflow tract in arrhythmogenesis. This review explores the role of catheter ablation in managing the most common channelopathies (Brugada syndrome, congenital long QT syndrome, short QT syndrome, and catecholaminergic polymorphic ventricular tachycardia). While the initial results for ablation in Brugada syndrome are promising, the long-term efficacy and durability of ablation in different channelopathies require further investigation. Given the genetic and phenotypic heterogeneity of channelopathies, future studies are needed to show whether catheter ablation in patients with channelopathies is associated with a reduction in VF, and psychological distress stemming from recurrent ICD shocks, particularly relative to other available therapeutic options (e.g., quinidine in high-risk Brugada patients).

Ablation of the epicardial substrate in patients with long-QT syndrome at risk of sudden death

Sudden cardiac death remains a critical public health concern globally, affecting millions annually. Recent advances in cardiac arrhythmia mapping have demonstrated that the ventricular epicardial region has a critical arrhythmogenic role in some inherited cardiogenetic diseases. Among these, long-QT syndrome (LQTS) exposes patients to the risk of life-threatening arrhythmic events. Despite advancements, there is a need for more effective therapeutic strategies. A recent study has uncovered a noteworthy connection between LQTS and epicardial structural abnormalities, challenging the traditional view of LQTS as purely an electrical disorder. High-density mapping revealed electroanatomic abnormalities in the right ventricular epicardium, presenting a potential target for catheter ablation, to finally suppress ventricular fibrillation recurrences in high-risk LQTS patients.

Artificial Intelligence in Diagnosis of Long QT Syndrome: A Review of Current State, Challenges, and Future Perspectives

Long QT syndrome (LQTS) is a potentially life-threatening cardiac repolarization disorder characterized by an increased risk of fatal arrhythmias. Accurate and timely diagnosis is essential for risk stratification and appropriate management. However, traditional diagnostic approaches have limitations, necessitating more objective and efficient tools. Artificial intelligence (AI) offers promising solutions by enhancing the accuracy and efficiency of electrocardiography (ECG) interpretation. The AI algorithms can process ECG data more rapidly than human experts, providing real-time analysis and prompt identification of individuals at risk, and reducing interobserver variability. By analyzing large volumes of ECG data, AI algorithms can extract meaningful features that may not be apparent to the human eye. Advancements in AI-driven corrected QT interval monitoring using mobile ECG devices, such as smartwatches, offer a valuable and convenient tool for identifying individuals at risk of LQTS-related complications, which is particularly applicable during pandemic conditions, such as COVID-19. Integration of AI into clinical practice poses a number of challenges. Bias in data gathering and patient privacy concerns are important considerations that must be addressed. Safeguarding patient privacy and ensuring data protection are crucial for maintaining trust in AI-driven systems. In addition, the interpretability of AI algorithms is a concern because understanding the decision-making process is essential for clinicians to trust and confidently use these tools. Future perspectives in this field may involve the integration of AI into diagnostic protocols, through genetic subtype classifications on the basis of ECG data. Moreover, explainable AI techniques aim to uncover ECG features associated with LQTS diagnosis, suggesting new insights into LQTS pathophysiology.

Comparison of the effects of propofol and alfaxalone on the electrocardiogram of dogs, with particular reference to QT interval

Cardiac electrical activity is often altered by administration of anesthetic drugs. While the effects of propofol in this regard have previously been described in dogs, to date, there are no reports of the effect of alfaxalone. This study investigated the impact of both propofol and alfaxalone on the ECG of 60 dogs, after premedication with acepromazine and methadone. Heart rate increased significantly in both groups. The PR and QRS intervals were significantly increased following propofol while with alfaxalone the QRS duration was significantly increased and ST segment depression was observed. The QT and JT interval were significantly shorter following induction with alfaxalone, but, when corrected (c) for heart rate, QTc and JTc in both groups were significantly greater following induction. When comparing the magnitude of change between groups, the change in RR interval was greater in the alfaxalone group. The change in both QT and JT intervals were significantly greater following alfaxalone, but when QTc and JTc intervals were compared, there were no significant differences between the two drugs. The similarly increased QTc produced by both drugs may suggest comparable proarrhythmic effects.

Repotrectinib in a Patient With NTRK Fusion-Positive Pancreatic Carcinoma and Congenital Long QT Syndrome

Repotrectinib in a patient with NTRK fusion-positive pancreatic carcinoma and congenital long QT syndrome.

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

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

Provocation testing in congenital long QT syndrome: A practical guide

Congenital long QT syndrome (LQTS) is a hereditary cardiac channelopathy with an estimated prevalence of 1 in 2500. A prolonged resting QT interval corrected for heart rate (QTc interval) remains a key diagnostic component; however, the QTc value may be normal in up to 40% of patients with genotype-positive LQTS and borderline in a further 30%. Provocation of QTc prolongation and T-wave changes may be pivotal to unmasking the diagnosis and useful in predicting genotype. LQTS provocation testing involves assessment of repolarization during and after exercise, in response to changes in heart rate or autonomic tone, with patients with LQTS exhibiting a maladaptive repolarization response. We review the utility and strengths and limitations of 4 forms of provocation testing-stand-up test, exercise stress test, epinephrine challenge, and mental stress test-in diagnosing LQTS and provide some practical guidance for performing provocation testing. Ultimately, exercise testing, when feasible, is the most useful form of provocation testing when considering diagnostic sensitivity and specificity.

Action potential morphology affects T-wave symmetry (simulation study)

BACKGROUND

Assessing T-wave symmetry in addition to QT subintervals measurements can provide novel independent data about ventricular repolarization abnormalities linked with arrhythmogenesis. However, the causes of the changes of T-wave symmetry are not completely understood. In silico studies showed that the more symmetrical T-waves were associated with shorter action potential duration (APD) and larger dispersion of ventricular repolarization (DOR). The aim of present simulation was to study the association between T-wave symmetry and action potential (AP) shape.

METHODS

ECGs were simulated using a cellular automata model shaped as a ventricular wall segment, and two biophysically-detailed models of ventricular AP - the rabbit and the human. The symmetry ratio (SR) was calculated as a T-wave onset-peak to peak-end area ratio. The individual and combined effects of APD, DOR and AP shape on SR were simulated. To study the effect of AP shape, different APs from triangulated to rectangular were simulated.

RESULTS

The simulations showed that AP shape along with APD and DOR contributes much to T-wave symmetry. APs with a flat phase 3 (triangulated) produced asymmetrical T-waves (SR ≥ 1.5) in all simulations, except the shortest APD range. APs with a rapid phase 3 (rectangular) were associated with more symmetrical T-waves (SR ≤ =1) both at the short and the long APDs.

CONCLUSION

SR marker in combination with the standard ECG parameters (QT interval, Tpeak-Tend interval) may be useful to identify the proarrhythmic triangulated AP shape.

Unlocking the Potential of Left Cardiac Sympathetic Denervation: A Scoping Review of a Promising Approach for Long QT Syndrome

Left cardiac sympathetic denervation (LCSD) has emerged as an alternative therapy for individuals diagnosed with long QT syndrome (LQTS), a genetic disorder characterized by abnormal electrical activity in the heart and sudden cardiac death (SCD). This review examines the history and rationale behind LCSD in LQTS treatment, as well as the procedure, its efficacy, and indications along with the adverse effects that may be associated with it. LQTS presents with prolonged QT intervals on an electrocardiogram and can manifest as seizures, fainting, and SCD. Beta-blockers are the primary treatment for LQTS but some patients do not respond well to these medications or experience side effects. Additionally, implantable cardioverter-defibrillators (ICDs) are not always effective in preventing arrhythmias and can lead to complications. LCSD might offer an alternative approach by disrupting sympathetic activity in the heart. In humans, LCSD reduces the release of norepinephrine, normalizes the QT interval, and decreases the likelihood of life-threatening heart rhythms. The procedure does not impair heart rate or cardiac function due to the compensatory effects of the right cardiac sympathetic nerves. The surgical procedure for LCSD involves the removal of the lower half of the stellate ganglion and thoracic ganglia. Complete denervation is essential for optimal outcomes, while incomplete procedures are considered unacceptable. Traditional and minimally invasive approaches, such as video-assisted thoracic surgery (VATS), are available, with VATS offering shorter hospital stays and fewer complications. In conclusion, LCSD provides a viable treatment option for individuals with LQTS who do not respond well to beta-blockers or require additional protection beyond medication or ICDs. Further research and clinical experience are needed to enhance its acceptance and implementation in routine practice.

Implantable Devices in Genetic Heart Disease: Disease-Specific Device Selection and Programming

Diagnosis and risk stratification of rare genetic heart diseases remains clinically challenging. In many cases, there are few data and insufficient numbers to support randomized controlled trials. While implantable cardioverter defibrillator (ICD) use is vital to protect higher-risk individuals from life-threatening ventricular arrhythmias, low-risk individuals also require protection from unnecessary ICDs and their associated complications. Once an ICD has been implanted, appropriate device programming is essential to ensure maximal protection while balancing the risks of inappropriate therapy.

Polypharmacy, Gender Disparities, and Ethnic and Racial Predispositions in Long QT Syndrome: An In-Depth Review

Long QT syndrome (LQTS) is a complex disorder of cardiac electrophysiology. It is characterized by delayed myocardial polarization leading to QT prolongation and alterations on the ST segment and T wave visible on electrocardiogram (ECG). Syncope is a common manifestation, and torsade de pointes (TdP) can lead to sudden cardiac death. Three major LQTS genes (KCI31, KCNH2, and SCN5) lead to most of the cases of LQTS. Lifestyle modifications, beta blockers, and implantable cardioverter defibrillator (ICD) placement are the main treatments for LQTS. Polypharmacy, including QT-prolonging drugs, has been shown to worsen LQTS. The impact on potassium channels and the human ether-a-go-go-related gene (hERG) is the mechanism behind the QT interval prolongation caused by these medications. There is an increased incidence of LQTS among African-American men and women as compared to Caucasians. Women with LQTS tend to have a higher mortality rate from the condition, especially during menstruation and shortly after giving birth. Genetic testing is reserved to those patientswho exhibit either a strong clinical index of suspicion or experience persistent QT prolongation despite their lack of symptoms. Knowing the genetics, racial, and gender discrepancies can help improve patient management and a better comprehension on each case. Proper understanding of how ion channels function and their interaction with medications will lead to a better comprehension and to develop effective forms to treat those patients.

Novel combinations of variations in KCNQ1 were associated with patients with long QT syndrome or Jervell and Lange-Nielsen syndrome

OBJECTIVES

Long QT syndrome (LQTS) is one of the primary causes of sudden cardiac death (SCD) in youth. Studies have identified mutations in ion channel genes as key players in the pathogenesis of LQTS. However, the specific etiology in individual families remains unknown.

METHODS

Three unrelated Chinese pedigrees diagnosed with LQTS or Jervell and Lange-Nielsen syndrome (JLNS) were recruited clinically. Whole exome sequencing (WES) was performed and further validated by multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing.

RESULTS

All of the probands in our study experienced syncope episodes and featured typically prolonged QTc-intervals. Two probands also presented with congenital hearing loss and iron-deficiency anemia and thus were diagnosed with JLNS. A total of five different variants in KCNQ1, encoding a subunit of the voltage-gated potassium channel, were identified in 3 probands. The heterozygous variants, KCNQ1 c.749T > C was responsible for LQTS in Case 1, transmitting in an autosomal dominant pattern. Two patterns of compound heterozygous variants were responsible for JLNS, including a large deletion causing loss of the exon 16 and missense variant c.1663 C > T in Case 2, and splicing variant c.605-2 A > G and frame-shift variant c.1265del in Case 3. To our knowledge, the compound heterozygous mutations containing a large deletion and missense variant were first reported in patients with JLNS.

CONCLUSION

Our study expanded the LQTS genetic spectrum, thus favoring disease screening and diagnosis, personalized treatment, and genetic consultation.

The value of the 12-lead electrocardiogram in the prediction of sudden cardiac death

Sudden cardiac death (SCD) can be caused by several clinical conditions, overt or misconceived, which recognize different pathophysiologies determining the development of fatal arrhythmic events. In the various forms of structural heart disease such as ischaemic heart disease, cardiomyopathies (e.g. hypertrophic cardiomyopathy, dilated cardiomyopathy, and arrhythmogenic cardiomyopathy), channelopathies (e.g. long-QT syndrome, congenital short QT, Brugada syndrome, early repolarization (ER) syndrome, and idiopathic ventricular fibrillation) but also in the apparently healthy subject, the 12-lead electrocardiogram (ECG) has proved, over the years, to be a reliable and readily available method for stratifying the risk of adverse arrhythmic events and consequently SCD. Several electrocardiographic markers have been shown to be associated with adverse outcomes in different types of patients. Although with different sensitivity and specificity in each clinical condition, depolarization abnormalities, such as QRS fragmentation, Q waves, QRS duration, left posterior fascicular block, low QRS voltage, and left ventricular hypertrophy and similarly repolarization abnormalities as ER pattern, T wave alternans, QT interval, and QT dispersion, have shown significant efficacy in predicting SCD. Despite the advancement of techniques especially in the field of imaging, the correct interpretation of the 12-lead ECG remains, therefore, an effective tool for assessing the possible prognostic outcome in terms of arrhythmic risk and SCD in different types of patients.

Detection of distant familial relatedness in biobanks for identification of undiagnosed carriers of a Mendelian disease variant: application to Long QT syndrome

Importance

The diagnosis and study of rare genetic disease is often limited to referral populations, leading to underdiagnosis and a biased assessment of penetrance and phenotype.

Objective

To develop a generalizable method of genotype inference based on distant relatedness and to deploy this to identify undiagnosed Type 5 Long QT Syndrome (LQT5) rare variant carriers in a non-referral population.

Participants

We identified 9 LQT5 probands and 3 first-degree relatives referred to a single Genetic Arrhythmia clinic, each carrying D76N (p.Asp76Asn), the most common variant implicated in LQT5. The non-referral population consisted of 69,879 ancestry-matched subjects in BioVU, a large biobank that links electronic health records to dense array data. Participants were enrolled from 2007-2022. Data analysis was performed in 2022.

Exposures

We developed and applied a novel approach to genotype inference (Distant Relatedness for Identification and Variant Evaluation, or DRIVE) to identify shared, identical-by-descent (IBD) large chromosomal segments in array data.

Main Outcomes and Measures

We sought to establish genetic relatedness among the probands and to use genomic segments underlying D76N to identify other potential carriers in BioVU. We then further studied the role of D76N in LQT5 pathogenesis.

Results

Genetic reconstruction of pedigrees and distant relatedness detection among clinic probands using DRIVE revealed shared recent common ancestry and identified a single long shared haplotype. Interrogation of the non-referral population in BioVU identified a further 23 subjects sharing this haplotype, and sequencing confirmed D76N carrier status in 22, all previously undiagnosed with LQT5. The QTc was prolonged in D76N carriers compared to BioVU controls, with 40% penetrance of QTc ≥ 480 msec. Among D76N carriers, a QTc polygenic score was additively associated with QTc prolongation.

Conclusions and Relevance

Detection of IBD shared chromosomal segments around D76N enabled identification of distantly related and previously undiagnosed rare-variant carriers, demonstrated the contribution of polygenic risk to monogenic disease penetrance, and further established LQT5 as a primary arrhythmia disorder. Analysis of shared chromosomal regions spanning disease-causing mutations can identify undiagnosed cases of genetic diseases.

Modeling incomplete penetrance in long QT syndrome type 3 through ion channel heterogeneity: an in silico population study

Many cardiac diseases are characterized by an increased late sodium current, including heart failure, hypertrophic cardiomyopathy, and inherited long QT syndrome type 3 (LQT3). The late sodium current in LQT3 is caused by a gain-of-function mutation in the voltage-gated sodium channel Nav1.5. Despite a well-defined genetic cause of LQT3, treatment remains inconsistent because of incomplete penetrance of the mutation and variability of antiarrhythmic efficacy. Here, we investigate the relationship between LQT3-associated mutation incomplete penetrance and variability in ion channel expression, simulating a population of 1,000 individuals with the O'Hara-Rudy model of the human ventricular myocyte. We first simulate healthy electrical activity (i.e., in the absence of a mutation) and then incorporate heterozygous expression for three LQT3-associated mutations (Y1795C, I1768V, and ΔKPQ), to directly compare the effects of each mutation on individuals across a diverse population. For all mutations, we find that susceptibility, defined by either the presence of an early afterdepolarization (EAD) or prolonged action potential duration (APD), primarily depends on the balance between the conductance of IKr and INa, for which individuals with a higher IKr-to-INa ratio are less susceptible. Furthermore, we find distinct differences across the population, observing individuals susceptible to zero, one, two, or all three mutations. Individuals tend to be less susceptible with an appropriate balance of repolarizing currents, typically via increased IKs or IK1. Interestingly, the more critical repolarizing current is mutation specific. We conclude that the balance between key currents plays a significant role in mutant-specific presentation of the disease phenotype in LQT3.NEW & NOTEWORTHY An in silico population approach investigates the relationship between variability in ion channel expression and gain-of-function mutations in the voltage-gated sodium channel associated with the congenital disorder long QT syndrome type 3 (LQT3). We find that ion channel variability can contribute to incomplete penetrance of the mutation, with mutant-specific differences in ion channel conductances leading to susceptibility to proarrhythmic action potential duration prolongation or early afterdepolarizations.

Acute exposure to low-dose bisphenol A delays cardiac repolarization in female canine heart - Implication for proarrhythmic toxicity in large animals

Bisphenol A (BPA) is a common environmental chemical with a range of potential adverse health effects. The impact of environmentally-relevant low dose of BPA on the electrical properties of the hearts of large animals (e.g., dog, human) is poorly defined. Perturbation of cardiac electrical properties is a key arrhythmogenic mechanism. In particular, delay of ventricular repolarization and prolongation of the QT interval of the electrocardiogram is a marker for the risk of malignant arrhythmias. We examined the acute effect of 10-9 M BPA on the electrical properties of female canine ventricular myocytes and tissues. BPA rapidly delayed action potential repolarization and prolonged action potential duration (APD). The dose response curve of BPA on APD was nonmonotonic. BPA rapidly inhibited the IKr K+ current and ICaL Ca2+ current. Computational modeling indicated that the effect of BPA on APD can be accounted for by its suppression of IKr. At the tissue level, BPA acutely prolonged the QT interval in 4 left ventricular wedges. ERβ signaling contributed to the acute effects of BPA on ventricular repolarization. Our results demonstrate that BPA has QT prolongation liability in female canine hearts. These findings have implication for the potential proarrhythmic cardiac toxicity of BPA in large animals.