How do sex hormones modify arrhythmogenesis in long QT syndrome? Sex hormone effects on arrhythmogenic substrate and triggered activity

[Cardiac channelopathies in the context of hereditary arrhythmia syndromes]

Genetic arrhythmia disorders are rare diseases; however, they are a common cause of sudden cardiac death in children, adolescents, and young adults. In principle, a distinction can be made between channelopathies and cardiomyopathies in the context of genetic diseases. This paper focuses on the channelopathies long and short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia (CPVT). Early diagnosis of these diseases is essential, as drug therapy, behavioral measures, and if necessary, implantation of a cardioverter defibrillator can significantly improve the prognosis and quality of life of patients. This paper highlights the pathophysiological and genetic basis of these channelopathies, describes their clinical manifestations, and comments on the principles of diagnosis, risk stratification and therapy.

Sex-related similarities and differences in responses to heart failure therapies

Although sex-related differences in the epidemiology, risk factors, clinical characteristics and outcomes of heart failure are well known, investigations in the past decade have shed light on an often overlooked aspect of heart failure: the influence of sex on treatment response. Sex-related differences in anatomy, physiology, pharmacokinetics, pharmacodynamics and psychosocial factors might influence the response to pharmacological agents, device therapy and cardiac rehabilitation in patients with heart failure. In this Review, we discuss the similarities between men and women in their response to heart failure therapies, as well as the sex-related differences in treatment benefits, dose-response relationships, and tolerability and safety of guideline-directed medical therapy, device therapy and cardiac rehabilitation. We provide insights into the unique challenges faced by men and women with heart failure, highlight potential avenues for tailored therapeutic approaches and call for sex-specific evaluation of treatment efficacy and safety in future research.

The electromechanical window for arrhythmia-risk assessment

The electromechanical window (EMW) is calculated by subtracting the repolarization duration from a mechanical reference representing contraction duration in the same heartbeat (eg, aortic valve closure during echocardiography with simultaneous electrocardiography). Here we review the current knowledge on the role of the EMW as an independent parameter for ventricular arrhythmia-risk stratification. We (1) provide a standardized approach to echocardiographic EMW assessment, (2) define relevant cutoff values for both abnormal EMW negativity and positivity, (3) discuss pathophysiological underpinnings of EMW negativity, and (4) outline the potential future role of cardiac electromechanical relations in patients with proarrhythmic conditions.

Ventricular Tachycardia Due to Triggered Activity: Role of Early and Delayed Afterdepolarizations

Most forms of sustained ventricular tachycardia (VT) are caused by re-entry, resulting from altered myocardial conduction and refractoriness secondary to underlying structural heart disease. In contrast, VT caused by triggered activity (TA) is unrelated to an abnormal structural substrate and is often caused by molecular defects affecting ion channel function or regulation of intracellular calcium cycling. This review summarizes the cellular and molecular bases underlying TA and exemplifies their clinical relevance with selective representative scenarios. The underlying basis of TA caused by delayed afterdepolarizations is related to sarcoplasmic reticulum calcium overload, calcium waves, and diastolic sarcoplasmic reticulum calcium leak. Clinical examples of TA caused by delayed afterdepolarizations include sustained right and left ventricular outflow tract tachycardia and catecholaminergic polymorphic VT. The other form of afterpotentials, early afterdepolarizations, are systolic events and inscribe early afterdepolarizations during phase 2 or phase 3 of the action potential. The fundamental defect is a decrease in repolarization reserve with associated increases in late plateau inward currents. Malignant ventricular arrhythmias in the long QT syndromes are initiated by early afterdepolarization-mediated TA. An understanding of the molecular and cellular bases of these arrhythmias has resulted in generally effective pharmacologic-based therapies, but these are nonspecific agents that have off-target effects. Therapeutic efficacy may need to be augmented with an implantable defibrillator. Next-generation therapies will include novel agents that rescue arrhythmogenic abnormalities in cellular signaling pathways and gene therapy approaches that transfer or edit pathogenic gene variants or silence mutant messenger ribonucleic acid.

Practical solutions for including sex as a biological variable (SABV) in preclinical neuropsychopharmacological research

Recently, many funding agencies have released guidelines on the importance of considering sex as a biological variable (SABV) as an experimental factor, aiming to address sex differences and avoid possible sex biases to enhance the reproducibility and translational relevance of preclinical research. In neuroscience and pharmacology, the female sex is often omitted from experimental designs, with researchers generalizing male-driven outcomes to both sexes, risking a biased or limited understanding of disease mechanisms and thus potentially ineffective therapeutics. Herein, we describe key methodological aspects that should be considered when sex is factored into in vitro and in vivo experiments and provide practical knowledge for researchers to incorporate SABV into preclinical research. Both age and sex significantly influence biological and behavioral processes due to critical changes at different timepoints of development for males and females and due to hormonal fluctuations across the rodent lifespan. We show that including both sexes does not require larger sample sizes, and even if sex is included as an independent variable in the study design, a moderate increase in sample size is sufficient. Moreover, the importance of tracking hormone levels in both sexes and the differentiation between sex differences and sex-related strategy in behaviors are explained. Finally, the lack of robust data on how biological sex influences the pharmacokinetic (PK), pharmacodynamic (PD), or toxicological effects of various preclinically administered drugs to animals due to the exclusion of female animals is discussed, and methodological strategies to enhance the rigor and translational relevance of preclinical research are proposed.

Gender and race-related disparities in the management of ventricular arrhythmias

Modern studies have revealed gender and race-related disparities in the management and outcomes of cardiac arrhythmias, but few studies have focused on outcomes for ventricular arrhythmias (VAs) such as ventricular tachycardia (VT) or ventricular fibrillation (VF). The aim of this article is to review relevant studies and identify outcome differences in the management of VA among Black and female patients. We found that female patients typically present younger for VA, are more likely to have recurrent VA after catheter ablation, are less likely to be prescribed antiarrhythmic medication, and are less likely to receive primary prevention ICD placement as compared to male patients. Additionally, female patients appear to derive similar overall mortality benefit from primary prevention ICD placement as compared to male patients, but they may have an increased risk of acute post-procedural complications. We also found that Black patients presenting with VA are less likely to undergo catheter ablation, receive appropriate primary prevention ICD placement, and have significantly higher risk-adjusted 1-year mortality rates after hospital discharge as compared to White patients. Black female patients appear to have the worst outcomes out of any demographic subgroup.

New drug discovery of cardiac anti-arrhythmic drugs: insights in animal models

Cardiac rhythm regulated by micro-macroscopic structures of heart. Pacemaker abnormalities or disruptions in electrical conduction, lead to arrhythmic disorders may be benign, typical, threatening, ultimately fatal, occurs in clinical practice, patients on digitalis, anaesthesia or acute myocardial infarction. Both traditional and genetic animal models are: In-vitro: Isolated ventricular Myocytes, Guinea pig papillary muscles, Patch-Clamp Experiments, Porcine Atrial Myocytes, Guinea pig ventricular myocytes, Guinea pig papillary muscle: action potential and refractory period, Langendorff technique, Arrhythmia by acetylcholine or potassium. Acquired arrhythmia disorders: Transverse Aortic Constriction, Myocardial Ischemia, Complete Heart Block and AV Node Ablation, Chronic Tachypacing, Inflammation, Metabolic and Drug-Induced Arrhythmia. In-Vivo: Chemically induced arrhythmia: Aconitine antagonism, Digoxin-induced arrhythmia, Strophanthin/ouabain-induced arrhythmia, Adrenaline-induced arrhythmia, and Calcium-induced arrhythmia. Electrically induced arrhythmia: Ventricular fibrillation electrical threshold, Arrhythmia through programmed electrical stimulation, sudden coronary death in dogs, Exercise ventricular fibrillation. Genetic Arrhythmia: Channelopathies, Calcium Release Deficiency Syndrome, Long QT Syndrome, Short QT Syndrome, Brugada Syndrome. Genetic with Structural Heart Disease: Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia, Dilated Cardiomyopathy, Hypertrophic Cardiomyopathy, Atrial Fibrillation, Sick Sinus Syndrome, Atrioventricular Block, Preexcitation Syndrome. Arrhythmia in Pluripotent Stem Cell Cardiomyocytes. Conclusion: Both traditional and genetic, experimental models of cardiac arrhythmias' characteristics and significance help in development of new antiarrhythmic drugs.

25 years of basic and translational science in EP Europace: novel insights into arrhythmia mechanisms and therapeutic strategies

In the last 25 years, EP Europace has published more than 300 basic and translational science articles covering different arrhythmia types (ranging from atrial fibrillation to ventricular tachyarrhythmias), different diseases predisposing to arrhythmia formation (such as genetic arrhythmia disorders and heart failure), and different interventional and pharmacological anti-arrhythmic treatment strategies (ranging from pacing and defibrillation to different ablation approaches and novel drug-therapies). These studies have been conducted in cellular models, small and large animal models, and in the last couple of years increasingly in silico using computational approaches. In sum, these articles have contributed substantially to our pathophysiological understanding of arrhythmia mechanisms and treatment options; many of which have made their way into clinical applications. This review discusses a representative selection of EP Europace manuscripts covering the topics of pacing and ablation, atrial fibrillation, heart failure and pro-arrhythmic ventricular remodelling, ion channel (dys)function and pharmacology, inherited arrhythmia syndromes, and arrhythmogenic cardiomyopathies, highlighting some of the advances of the past 25 years. Given the increasingly recognized complexity and multidisciplinary nature of arrhythmogenesis and continued technological developments, basic and translational electrophysiological research is key advancing the field. EP Europace aims to further increase its contribution to the discovery of arrhythmia mechanisms and the implementation of mechanism-based precision therapy approaches in arrhythmia management.

Sex Related Differences in Electrocardiography

Since its implementation into the clinical medicine by Willem Einthoven electrocardiography had become one of crucial diagnostic method in cardiology. In spite of this fact effects of gender differences on parameters of electrocardiographic recordings started to be studied only recently. Sex related differences in physiological ECG are only minimal in childhood but there are developing during adolescence reflecting rapidly evolving differences particularly in hormonal secretion and activity of an autonomic nervous system. The heart rate is approximately 7 % higher in women than in men, PQ and QRS intervals are longer in men while QT interval is longer in women. The ST segment in females is flatter but generally the sex-related differences in ST-T waveform patterns are relatively very small with higher level of ST segment and taller T wave in men. The effects of sex-related differences, including sex hormones, on cardiac cell injury and death and their influence in determining rhythmogenesis and action potential configuration and conduction play an important role in clinics. Women have a higher prevalence of sick sinus syndrome, inappropriate sinus tachycardia, atrioventricular nodal reentry tachycardia, idiopathic right ventricular tachycardia, and arrhythmic events in the long QT syndrome. In contrast, men have a higher prevalence of atrioventricular block, carotid sinus syndrome, atrial fibrillation, supraventricular tachycardia due to accessory pathways, Wolff-Parkinson-White syndrome, reentrant ventricular tachycardia, ventricular fibrillation and sudden death, and the Brugada syndrome.

Long-QT mutations in KCNE1 modulate the 17β-estradiol response of Kv7.1/KCNE1

Estradiol (17[Formula: see text]-E2) is implicated in higher arrhythmia risk of women with congenital or acquired long-QT syndrome (LQTS) compared to men. However, the underlying mechanisms remain poorly understood, and little is known about the impact of LQTS-associated mutations. We show that 17[Formula: see text]-E2 inhibits the human cardiac Kv7.1/KCNE1 channel expressed in Xenopus oocytes. We find that the 17[Formula: see text]-E2 effect depends on the Kv7.1 to KCNE1 stoichiometry, and we reveal a critical function of the KCNE1 carboxyl terminus for the effect. LQTS-associated mutations in the KCNE1 carboxyl terminus show a range of responses to 17[Formula: see text]-E2, from a wild-type like response to impaired or abolished response. Together, this study increases our understanding of the mechanistic basis for 17[Formula: see text]-E2 inhibition of Kv7.1/KCNE1 and demonstrates mutation-dependent responses to 17[Formula: see text]-E2. These findings suggest that the 17[Formula: see text]-E2 effect on Kv7.1/KCNE1 might contribute to the higher arrhythmia risk of women, particularly in carriers with specific LQTS-associated mutations.

Injectable Contraceptive, Depo-Provera, Produces Erratic Beating Patterns in Patient-Specific Induced Pluripotent Stem Cell-derived Cardiomyocytes with Type 2 Long QT Syndrome

BACKGROUND

Long QT syndrome type 2 (LQT2) is caused by pathogenic variants in KCNH2. LQT2 may manifest as QT prolongation on an ECG and present with arrhythmic syncope/seizures, sudden cardiac arrest/death. Oral progestin-based contraceptives may increase the risk of LQT2-triggered cardiac events in women. We previously reported on a LQT2 woman with recurrent cardiac events temporally related and attributed to the progestin-based contraceptive, medroxyprogesterone acetate ("Depo-Provera", Depo).

OBJECTIVE

To evaluate the arrhythmic-risk of Depo in a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model of LQT2.

METHODS

An iPSC-CM line was generated from a 40-year-old female with p.G1006Afs*49-KCNH2. A CRISPR/Cas9 gene-edited/variant-corrected, isogenic control (IC) iPSC-CM line was generated. FluoVolt was used to measure the action potential duration (APD) following treatment with 10 μM Depo. Erratic beating patterns characterized as alternating spike amplitudes, alternans, or early after depolarization-like phenomena were assessed using multi-electrode array (MEA) following 10 μM Depo, 1 μM isoproterenol (ISO), or combined Depo + ISO treatment.

RESULTS

Depo treatment shortened the APD-90 of the G1006Afs*49 iPSC-CMs from 394±10 ms to 303±10 ms (p<0.0001). Combined Depo and ISO treatment increased the percent of electrodes displaying erratic beating in G1006Afs*49 iPSC-CMs [baseline 18±5% vs. Depo + ISO 54±5% (p<0.0001)] but not in IC iPSC-CMs [baseline 0±0% vs. Depo + ISO 10±3% (p=0.9659)].

CONCLUSION

This cell study provides a potential mechanism for the patient's clinically documented Depo-associated episodes of recurrent ventricular fibrillation. This in-vitro data should prompt a large-scale clinical assessment of Depo's potential pro-arrhythmic effect in women with LQT2.

Sex-related differences in incidence, phenotype and risk of sudden cardiac death in inherited arrhythmia syndromes

Inherited Arrhythmia Syndromes (IAS) including long QT and Brugada Syndrome, are characterized by life-threatening arrhythmias in the absence of apparent structural heart disease and are caused by pathogenic variants in genes encoding cardiac ion channels or associated proteins. Studies of large pedigrees of families affected by IAS have demonstrated incomplete penetrance and variable expressivity. Biological sex is one of several factors that have been recognized to modulate disease severity in IAS. There is a growing body of evidence linking sex hormones to the susceptibility to arrhythmias, yet, many sex-specific disease aspects remain underrecognized as female sex and women with IAS are underinvestigated and findings from male-predominant cohorts are often generalized to both sexes with minimal to no consideration of relevant sex-associated differences in prevalence, disease manifestations and outcome. In this review, we highlight current knowledge of sex-related biological differences in normal cardiac electrophysiology and sex-associated factors that influence IAS phenotypes.

Sex and racial disparities in catheter ablation

Sex and racial disparities in the presentation, diagnosis, and management of cardiac arrhythmias are recognized. Sex-specific differences in electrophysiological parameters are well known and are predominantly related to differences in ion channel expression and the influence of sex hormones. However, the relationship between hormonal or racial influence and arrhythmia mechanisms, presentation, and management needs to be better defined. Women and racial and ethnic groups are less likely to undergo catheter ablation procedures for treatment of cardiac arrhythmias. Underrepresentation of women and racial/ethnic groups in clinical trials has resulted in significant knowledge gaps. Whether sex and racial disparities in arrhythmia management reflect barriers in access to care, physician bias, patient values, and preferences or other factors requires further study.

Hardware-Mappable Cellular Neural Networks for Distributed Wavefront Detection in Next-Generation Cardiac Implants

Artificial intelligence algorithms are being adopted to analyze medical data, promising faster interpretation to support doctors' diagnostics. The next frontier is to bring these powerful algorithms to implantable medical devices. Herein, a closed-loop solution is proposed, where a cellular neural network is used to detect abnormal wavefronts and wavebrakes in cardiac signals recorded in human tissue is trained to achieve >96% accuracy, >92% precision, >99% specificity, and >93% sensitivity, when floating point precision weights are assumed. Unfortunately, the current hardware technologies for floating point precision are too bulky or energy intensive for compact standalone applications in medical implants. Emerging device technologies, such as memristors, can provide the compact and energy-efficient hardware fabric to support these efforts and can be reliably embedded with existing sensor and actuator platforms in implantable devices. A distributed design that considers the hardware limitations in terms of overhead and limited bit precision is also discussed. The proposed distributed solution can be easily adapted to other medical technologies that require compact and efficient computing, like wearable devices and lab-on-chip platforms.

Animal Models to Study Cardiac Arrhythmias

Cardiac arrhythmias are a significant cause of morbidity and mortality worldwide, accounting for 10% to 15% of all deaths. Although most arrhythmias are due to acquired heart disease, inherited channelopathies and cardiomyopathies disproportionately affect children and young adults. Arrhythmogenesis is complex, involving anatomic structure, ion channels and regulatory proteins, and the interplay between cells in the conduction system, cardiomyocytes, fibroblasts, and the immune system. Animal models of arrhythmia are powerful tools for studying not only molecular and cellular mechanism of arrhythmogenesis but also more complex mechanisms at the whole heart level, and for testing therapeutic interventions. This review summarizes basic and clinical arrhythmia mechanisms followed by an in-depth review of published animal models of genetic and acquired arrhythmia disorders.

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.

Integrated Pharmacogenetics Analysis of the Three Fangjis Decoctions for Treating Arrhythmias Based on Molecular Network Patterns

Aim: To explore the diverse target distribution and variable mechanisms of different fangjis prescriptions when treating arrhythmias based on the systems pharmacology.

Methods: The active ingredients and their corresponding targets were acquired from the three fangjis [Zhigancao Tang (ZT), Guizhigancao Longgumuli Tang (GLT), and Huanglian E'jiao Tang (HET)] and the arrhythmia-related genes were identified based on comprehensive database screening. Networks were constructed between the fangjis and arrhythmia and used to define arrhythmia modules. Common and differential gene targets were identified within the arrhythmia network modules and the cover rate (CR) matrix was applied to compare the contributions of the fangjis to the network and modules. Comparative pharmacogenetics analyses were then conducted to define the arrhythmia-related signaling pathways regulated by the fangjis prescriptions. Finally, the divergence and convergence points of the arrhythmia pathways were deciphered based on databases and the published literature.

Results: A total of 187, 105, and 68 active ingredients and 1,139, 1,195, and 811 corresponding gene targets of the three fangjis were obtained and 102 arrhythmia-related genes were acquired. An arrhythmia network was constructed and subdivided into 4 modules. For the target distribution analysis, 65.4% of genes were regulated by the three fangjis within the arrhythmia network. ZT and GLT were more similar to each other, mainly regulated by module two, whereas HET was divided among all the modules. From the perspective of signal transduction, calcium-related pathways [calcium, cyclic guanosine 3′,5′-monophosphate (cGMP)-PKG, and cyclic adenosine 3′,5′-monophosphate (cAMP)] and endocrine system-related pathways (oxytocin signaling pathway and renin secretion pathways) were associated with all the three fangjis prescriptions. Nevertheless, heterogeneity existed between the biological processes and pathway distribution among the three prescriptions. GLT and HET were particularly inclined toward the conditions involving abnormal hormone secretion, whereas ZT tended toward renin-angiotensin-aldosterone system (RAAS) disorders. However, calcium signaling-related pathways prominently feature in the pharmacological activities of the decoctions. Experimental validation indicated that ZT, GLT, and HET significantly shortened the duration of ventricular arrhythmia (VA) and downregulated the expression of CALM2 and interleukin-6 (IL-6) messenger RNAs (mRNAs); GLT and HET downregulated the expression of CALM1 and NOS3 mRNAs; HET downregulated the expression of CRP mRNA.

Conclusion: Comparing the various distributions of the three fangjis, pathways provide evidence with respect to precise applications toward individualized arrhythmia treatments.

OUP accepted manuscript

Current exercise recommendations make it difficult for long QT syndrome (LQTS) patients to adopt a physically active and/or athletic lifestyle. The purpose of this review is to summarize the current evidence, identify knowledge gaps, and discuss research perspectives in the field of exercise and LQTS. The first aim is to document the influence of exercise training, exercise stress, and postural change interventions on ventricular repolarization in LQTS patients, while the second aim is to describe electrophysiological measurements used to study the above. Studies examining the effects of exercise on congenital or acquired LQTS in human subjects of all ages were included. Systematic searches were performed on 1 October 2021, through PubMed (NLM), Ovid Medline, Ovid All EBM Reviews, Ovid Embase, and ISI Web of Science, and limited to articles written in English or French. A total of 1986 LQTS patients and 2560 controls were included in the 49 studies. Studies were mainly case-control studies (n = 41) and examined exercise stress and/or postural change interventions (n = 48). One study used a 3-month exercise training program. Results suggest that LQTS patients have subtype-specific repolarization responses to sympathetic stress. Measurement methods and quality were found to be very heterogeneous, which makes inter-study comparisons difficult. In the absence of randomized controlled trials, the current recommendations may have long-term risks for LQTS patients who are discouraged from performing physical activity, rendering its associated health benefits out of range. Future research should focus on discovering the most appropriate levels of exercise training that promote ventricular repolarization normalization in LQTS.

Why Is Only Type 1 Electrocardiogram Diagnostic of Brugada Syndrome? Mechanistic Insights From Computer Modeling

BACKGROUND

Three types of characteristic ST-segment elevation are associated with Brugada syndrome but only type 1 is diagnostic. Why only type 1 ECG is diagnostic remains unanswered.

METHODS

Computer simulations were performed in single cells, 1-dimensional cables, and 2-dimensional tissues to investigate the effects of the peak and late components of the transient outward potassium current (Ito), sodium current, and L-type calcium current (ICa,L) as well as other potassium currents on the genesis of ECG morphologies and phase 2 reentry (P2R).

RESULTS

Although a sufficiently large peak Ito was required to result in the type 1 ECG pattern and P2R, increasing the late component of Ito converted type 1 ECG to type 2 ECG and suppressed P2R. Increasing the peak Ito promoted spiral wave breakup, potentiating the transition from tachycardia to fibrillation, but increasing the late Ito prevented spiral wave breakup by flattening the action potential duration restitution and preventing P2R. A sufficiently large ICa,L conductance was needed for P2R to occur, but once above the critical conductance, blocking ICa,L promoted P2R. However, selectively blocking the window and late components of ICa,L suppressed P2R, countering the effect of the late Ito. Blocking either the peak or late components of sodium current promoted P2R, with the late sodium current blockade having the larger effect. As expected, increasing other potassium currents potentiated P2R, with ATP-sensitive potassium current exhibiting a larger effect than rapid and slow component of the delayed rectifier potassium current.

CONCLUSIONS

The peak Ito promotes type 1 ECG and P2R, whereas the late Ito converts type 1 ECG to type 2 ECG and suppresses P2R. Blocking the peak ICa,L and either the peak or the late sodium current promotes P2R, whereas blocking the window and late ICa,L suppresses P2R. These results provide important insights into the mechanisms of arrhythmogenesis and potential therapeutic targets for treatment of Brugada syndrome. Graphic Abstract: A graphic abstract is available for this article.

Risk of sports-related sudden cardiac death in women

Sudden cardiac death (SCD) is a tragic incident accountable for up to 50% of deaths from cardiovascular disease. Sports-related SCD (SrSCD) is a phenomenon which has previously been associated with both competitive and recreational sport activities. SrSCD has been found to occur 5-33-fold less frequently in women than in men, and the sex difference persists despite a rapid increase in female participation in sports. Establishing the reasons behind this difference could pinpoint targets for improved prevention of SrSCD. Therefore, this review summarizes existing knowledge on epidemiology, characteristics, and causes of SrSCD in females, and elaborates on proposed mechanisms behind the sex differences. Although literature concerning the aetiology of SrSCD in females is limited, proposed mechanisms include sex-specific variations in hormones, blood pressure, autonomic tone, and the presentation of acute coronary syndromes. Consequently, these biological differences impact the degree of cardiac hypertrophy, dilation, right ventricular remodelling, myocardial fibrosis, and coronary atherosclerosis, and thereby the occurrence of ventricular arrhythmias in male and female athletes associated with short- and long-term exercise. Finally, cardiac examinations such as electrocardiograms and echocardiography are useful tools allowing easy differentiation between physiological and pathological cardiac adaptations following exercise in women. However, as a significant proportion of SrSCD causes in women are non-structural or unexplained after autopsy, channelopathies may play an important role, encouraging attention to prodromal symptoms and family history. These findings will aid in the identification of females at high risk of SrSCD and development of targeted prevention for female sport participants.

Arrhythmia in Cardiomyopathy: Sex and Gender Differences

PURPOSE OF REVIEW

There is emerging evidence for important sex differences in cardiac arrhythmias. In this up-to-date review, we summarise the differences in incidence, aetiology, treatment and prevention of ventricular arrhythmias (VAs) and sudden cardiac death (SCD) in women versus men, in the context of ischaemic and nonischaemic cardiomyopathies.

RECENT FINDINGS

The incidence of ventricular tachyarrhythmia and SCD is significantly lower in women than in men with ischaemic cardiomyopathy, whereas sex differences in nonischaemic cardiomyopathy are less clear. Women who receive a primary prevention implantable cardioverter-defibrillator (ICD) are less likely to receive appropriate activations, compared to men; however, such findings are limited by under-representation of women. Women with ischaemic cardiomyopathy have significantly lower incidence of VA and SCD compared to men and may not derive the same benefit from a primary prevention ICD. However, further clinical ICD studies are needed that ensure adequate female participation, in order to examine sex differences in outcomes in both ischaemic and nonischaemic cardiomyopathies.

Revealing the Influences of Sex Hormones and Sex Differences in Atrial Fibrillation and Vascular Cognitive Impairment

The impacts of sex differences on the biology of various organ systems and the influences of sex hormones on modulating health and disease have become increasingly relevant in clinical and biomedical research. A growing body of evidence has recently suggested fundamental sex differences in cardiovascular and cognitive function, including anatomy, pathophysiology, incidence and age of disease onset, symptoms affecting disease diagnosis, disease severity, progression, and treatment responses and outcomes. Atrial fibrillation (AF) is currently recognized as the most prevalent sustained arrhythmia and might contribute to the pathogenesis and progression of vascular cognitive impairment (VCI), including a range of cognitive deficits, from mild cognitive impairment to dementia. In this review, we describe sex-based differences and sex hormone functions in the physiology of the brain and vasculature and the pathophysiology of disorders therein, with special emphasis on AF and VCI. Deciphering how sex hormones and their receptor signaling (estrogen and androgen receptors) potentially impact on sex differences could help to reveal disease links between AF and VCI and identify therapeutic targets that may lead to potentially novel therapeutic interventions early in the disease course of AF and VCI.

Recurrent Pregnancy Loss and Concealed Long-QT Syndrome

Background

Recurrent pregnancy loss affects 1% to 2% of couples attempting childbirth. A large fraction of all cases remains idiopathic, which warrants research into monogenic causes of this distressing disorder.

Methods and Results

We investigated a nonconsanguineous Estonian family who had experienced 5 live births, intersected by 3 early pregnancy losses, and 6 fetal deaths, 3 of which occurred during the second trimester. No fetal malformations were described at the autopsies performed in 3 of 6 cases of fetal death. Parental and fetal chromosomal abnormalities (including submicroscopic) and maternal risk factors were excluded. Material for genetic testing was available from 4 miscarried cases (gestational weeks 11, 14, 17, and 18). Exome sequencing in 3 pregnancy losses and the mother identified no rare variants explicitly shared by the miscarried conceptuses. However, the mother and 2 pregnancy losses carried a heterozygous nonsynonymous variant, resulting in p.Val173Asp (rs199472695) in the ion channel gene KCNQ1. It is expressed not only in heart, where mutations cause type 1 long‐QT syndrome, but also in other tissues, including uterus. The p.Val173Asp variant has been previously identified in a patient with type 1 long‐QT syndrome, but not reported in the Genome Aggregation Database. With heterologous expression in CHO cells, our in vitro electrophysiologic studies indicated that the mutant slowly activating voltage‐gated K+ channel (I_Ks) is dysfunctional. It showed reduced total activating and deactivating currents (P<0.01), with dramatically positive shift of voltage dependence of activation by ≈10 mV (P<0.05).

Conclusions

The current study uncovered concealed maternal type 1 long‐QT syndrome as a potential novel cause behind recurrent fetal loss.

Sex Disparities in Sudden Cardiac Death

The overall incidence of sudden cardiac death is considerably lower among women than men, reflecting significant and often under-recognized sex differences. Women are older at time of sudden cardiac death, less likely to have a prior cardiac diagnosis, and less likely to have coronary artery disease identified on postmortem examination. They are more likely to experience their death at home, during sleep, and less likely witnessed. Women are also more likely to present in pulseless electrical activity or systole rather than ventricular fibrillation or ventricular tachycardia. Conversely, women are less likely to receive bystander cardiopulmonary resuscitation or receive cardiac intervention post-arrest. Underpinning sex disparities in sudden cardiac death is a paucity of women recruited to clinical trials, coupled with an overall lack of prespecified sex-disaggregated evidence. Thus, predominantly male-derived data form the basis of clinical guidelines. This review outlines the critical sex differences concerning epidemiology, cause, risk factors, prevention, and outcomes. We propose 4 broad areas of importance to consider: physiological, personal, community, and professional factors.

Sex differences in the origin of Purkinje ectopy-initiated idiopathic ventricular fibrillation

BACKGROUND

Purkinje ectopics (PurkEs) are major triggers of idiopathic ventricular fibrillation (VF). Identifying clinical factors associated with specific PurkE characteristics could yield insights into the mechanisms of Purkinje-mediated arrhythmogenicity.

OBJECTIVE

The purpose of this study was to examine the associations of clinical, environmental, and genetic factors with PurkE origin in patients with PurkE-initiated idiopathic VF.

METHODS

Consecutive patients with PurkE-initiated idiopathic VF from 4 arrhythmia referral centers were included. We evaluated demographic characteristics, medical history, clinical circumstances associated with index VF events, and electrophysiological characteristics of PurkEs. An electrophysiology study was performed in most patients to confirm the Purkinje origin.

RESULTS

Eighty-three patients were included (mean age 38 ± 14 years; 44 [53%] women), of whom 32 had a history of syncope. Forty-four patients had VF at rest. PurkEs originated from the right ventricle (RV) in 41 patients (49%), from the left ventricle (LV) in 36 (44%), and from both ventricles in 6 (7%). Seasonal and circadian distributions of VF episodes were similar according to PurkE origin. The clinical characteristics of patients with RV vs LV PurkE origins were similar, except for sex. RV PurkEs were more frequent in men than in women (76% vs 24%), whereas LV and biventricular PurkEs were more frequent in women (81% vs 19% and 83% vs 17%, respectively) (P < .0001).

CONCLUSION

PurkEs triggering idiopathic VF originate dominantly from the RV in men and from the LV or both ventricles in women, adding to other sex-related arrhythmias such as Brugada syndrome or long QT syndrome. Sex-based factors influencing Purkinje arrhythmogenicity warrant investigation.

Development of a Patient-Specific p.D85N-Potassium Voltage-Gated Channel Subfamily E Member 1-Induced Pluripotent Stem Cell-Derived Cardiomyocyte Model for Drug-Induced Long QT Syndrome

BACKGROUND

Prior epidemiological studies demonstrated that the p.D85N-Potassium voltage-gated channel subfamily E member 1 (KCNE1) common variant reduces repolarization reserve and predisposes to drug-induced QT prolongation/torsades de pointes. We sought to develop a cellular model for drug-induced long QT syndrome using a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM).

METHODS

p.D85N-KCNE1 iPSCs were generated from a 23-year-old female with an exaggerated heart rate-corrected QT interval response to metoclopramide (ΔQTc of 160 ms). Clustered regularly interspaced short palindromic repeats-associated 9 technology was used to generate gene-corrected isogenic iPSCs. Field potential duration and action potential duration (APD) were measured from iPSC-CMs.

RESULTS

At baseline, p.D85N-KCNE1 iPSC-CMs displayed significantly longer field potential duration (281±15 ms, n=13 versus 223±8.6 ms, n=14, P<0.01) and action potential duration at 90% repolarization (APD90; 579±22 ms, n=24 versus 465±33 ms, n=26, P<0.01) than isogenic-control iPSC-CMs. Dofetilide at a concentration of 2 nM increased significantly field potential duration (379±20 ms, n=13, P<0.01) and APD90 (666±11 ms, n=46, P<0.01) in p.D85N-KCNE1 iPSC-CMs but not in isogenic-control. The effect of dofetilide on APD90 (616±54 ms, n=7 versus 526±54 ms, n=10, P<0.05) was confirmed by Patch-clamp. Interestingly, treatment of p.D85N-KCNE1 iPSC-CMs with estrogen at a concentration of 1 nM exaggerated further dofetilide-induced APD90 prolongation (696±9 ms, n=81, P<0.01) and caused more early afterdepolarizations (11.7%) compared with isogenic control (APD90: 618±8 ms, n=115 and early afterdepolarizations: 2.6%, P<0.05).

CONCLUSIONS

This iPSC-CM study provides further evidence that the p.D85N-KCNE1 common variant in combination with environmental factors such as QT prolonging drugs and female sex is proarrhythmic.

Protein Kinases Mediate Anti-Inflammatory Effects of Cannabidiol and Estradiol Against High Glucose in Cardiac Sodium Channels

Background: Cardiovascular anomalies are predisposing factors for diabetes-induced morbidity and mortality. Recently, we showed that high glucose induces changes in the biophysical properties of the cardiac voltage-gated sodium channel (Nav1.5) that could be strongly correlated to diabetes-induced arrhythmia. However, the mechanisms underlying hyperglycemia-induced inflammation, and how inflammation provokes cardiac arrhythmia, are not well understood. We hypothesized that inflammation could mediate the high glucose-induced biophyscial changes on Nav1.5 through protein phosphorylation by protein kinases A and C. We also hypothesized that this signaling pathway is, at least partly, involved in the cardiprotective effects of cannabidiol (CBD) and 17β-estradiol (E₂).

Methods and Results: To test these ideas, we used Chinese hamster ovarian (CHO) cells transiently co-transfected with cDNA encoding human Nav1.5 α-subunit under control, a cocktail of inflammatory mediators or 100 mM glucose conditions (for 24 h). We used electrophysiological experiments and action potential modeling. Inflammatory mediators, similar to 100 mM glucose, right shifted the voltage dependence of conductance and steady-state fast inactivation and increased persistent current leading to computational prolongation of action potential (hyperexcitability) which could result in long QT3 arrhythmia. We also used human iCell cardiomyocytes derived from inducible pluripotent stem cells (iPSC-CMs) as a physiologically relevant system, and they replicated the effects produced by inflammatory mediators observed in CHO cells. In addition, activators of PK-A or PK-C replicated the inflammation-induced gating changes of Nav1.5. Inhibitors of PK-A or PK-C, CBD or E₂ mitigated all the potentially deleterious effects provoked by high glucose/inflammation.

Conclusion: These findings suggest that PK-A and PK-C may mediate the anti-inflammatory effects of CBD and E₂ against high glucose-induced arrhythmia. CBD, via Nav1.5, may be a cardioprotective therapeutic approach in diabetic postmenopausal population.

Transgenic rabbit models for cardiac disease research

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

Sex-Related Differences in Cardiac Channelopathies: Implications for Clinical Practice

Sex-related differences in prevalence, clinical presentation, and outcome of cardiac channelopathies are increasingly recognized, despite their autosomal transmission and hence equal genetic predisposition among sexes. In congenital long-QT syndrome, adult women carry a greater risk for Torsades de pointes and sudden cardiac death than do men. In contrast, Brugada syndrome is observed predominantly in adult men, with a considerably higher risk of arrhythmic sudden cardiac death in adult men than in women. In both conditions, the risk for arrhythmias varies with age. Sex-associated differences appear less evident in other cardiac channelopathies, likely a reflection of their rare(r) occurrence and our limited knowledge. In several cardiac channelopathies, sex-specific predictors of outcome have been identified. Together with genetic and environmental factors, sex hormones contribute to the sex-related disparities in cardiac channelopathies through modulation of the expression and function of cardiac ion channels. Despite these insights, essential knowledge gaps exist in the mechanistic understanding of these differences, warranting further investigation. Precise application of the available knowledge may improve the individualized care of patients with cardiac channelopathies. Promoting the reporting of sex-related phenotype and outcome parameters in clinical and experimental studies and advancing research on cardiac channelopathy animal models should translate into improved patient outcomes. This review provides a critical digest of the current evidence for sex-related differences in cardiac channelopathies and emphasizes their clinical implications and remaining gaps requiring further research.

Characteristics of Cardiac Memory in Patients with Implanted Cardioverter-defibrillators: The Cardiac Memory with Implantable Cardioverter-defibrillator (CAMI) Study

This study sought to determine factors associated with cardiac memory (CM) in patients with implantable cardioverter-defibrillators (ICDs). Patients with structural heart disease [n = 20; mean age: 72.6 ± 11.6 years; 80% male; mean left ventricular ejection fraction (LVEF): 31.7 ± 7.6%; history of myocardial infarction in 75% and nonsustained ventricular tachycardia (NSVT) in 85%] and preserved atrioventricular conduction received dual-chamber ICDs for primary (80%) or secondary (20%) prevention. Standard 12-lead electrocardiograms were recorded in AAI and DDD modes before and after seven days of right ventricular (RV) pacing in DDD mode with a short atrioventricular delay. The direction (azimuth and elevation) and magnitude of spatial QRS, T, and spatial ventricular gradient vectors were measured before and after seven days of RV pacing. CM was quantified as the degree of alignment between QRS_DDD-7 and T_AAI-7 vectors (QRS_DDD-7 –T_AAI-7 angle). Circular statistics and mixed models with a random slope and intercept were adjusted for changes in cardiac activation, LVEF, known risk factors, and the use of medications known to affect CM occurring on days 1 through 7. The QRS_DDD-7–T_AAI-7 angle strongly correlated (circular r = −0.972; p < 0.0001) with a T_AAI-7–T_DDD-7 angle. In the mixed models, CM-T azimuth changes [+132° (95% confidence interval (CI): 80°–184°); p < 0.0001] were counteracted by the history of MI [−180° (95% CI: −320° to −40°); p = 0.011] and female sex [−162° (95% CI: −268° to −55°); p = 0.003]. A CM-T area increase [+15 (95% CI: 6–24) mV*ms; p < 0.0001] was amplified by NSVT history [+27 (95% CI: 4–46) mV*ms; p = 0.007]. These findings suggest that preexistent electrical remodeling affects CM in response to RV pacing, that CM exhibits saturation behavior, and that women reach CM saturation more easily than men.

Three-Week-Old Rabbit Ventricular Cardiomyocytes as a Novel System to Study Cardiac Excitation and EC Coupling

Cardiac arrhythmias significantly contribute to cardiovascular morbidity and mortality. The rabbit heart serves as an accepted model system for studying cardiac cell excitation and arrhythmogenicity. Accordingly, primary cultures of adult rabbit ventricular cardiomyocytes serve as a preferable model to study molecular mechanisms of human cardiac excitation. However, the use of adult rabbit cardiomyocytes is often regarded as excessively costly. Therefore, we developed and characterized a novel low-cost rabbit cardiomyocyte model, namely, 3-week-old ventricular cardiomyocytes (3wRbCMs). Ventricular myocytes were isolated from whole ventricles of 3-week-old New Zealand White rabbits of both sexes by standard enzymatic techniques. Using wheat germ agglutinin, we found a clear T-tubule structure in acutely isolated 3wRbCMs. Cells were adenovirally infected (multiplicity of infection of 10) to express Green Fluorescent Protein (GFP) and cultured for 48 h. The cells showed action potential duration (APD90 = 253 ± 24 ms) and calcium transients similar to adult rabbit cardiomyocytes. Freshly isolated and 48-h-old-cultured cells expressed critical ion channel proteins: calcium voltage-gated channel subunit alpha1 C (Ca_vα1c), sodium voltage-gated channel alpha subunit 5 (Nav1.5), potassium voltage-gated channel subfamily D member 3 (Kv4.3), and subfamily A member 4 (Kv1.4), and also subfamily H member 2 (RERG. Kv11.1), KvLQT1 (K7.1) protein and inward-rectifier potassium channel (Kir2.1). The cells displayed an appropriate electrophysiological phenotype, including fast sodium current (I _Na), transient outward potassium current (I _to), L-type calcium channel peak current (I _Ca,L), rapid and slow components of the delayed rectifier potassium current (I _Kr and I _Ks), and inward rectifier (I _K1). Although expression of the channel proteins and some currents decreased during the 48 h of culturing, we conclude that 3wRbCMs are a new, low-cost alternative to the adult-rabbit-cardiomyocytes system, which allows the investigation of molecular mechanisms of cardiac excitation on morphological, biochemical, genetic, physiological, and biophysical levels.

Exercise-induced electrocardiographic changes after treadmill exercise testing in healthy children: A comprehensive study

Background:

Aims and Objectives:

Materials and Methods:

Results:

Conclusion:

Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior

Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.

Does Sex Modify an Association of Electrophysiological Substrate with Sudden Cardiac Death? The Atherosclerosis Risk in Communities (ARIC) Study

Background

Sex is a well-recognized risk factor for sudden cardiac death (SCD). We hypothesized that sex modifies the association of electrophysiological (EP) substrate with SCD.

Objective

The purpose of this study was to determine whether there are sex differences in electrocardiographic (ECG) measures and whether sex modifies the association of ECG measures of EP substrate with SCD.

Methods

Participants from the Atherosclerosis Risk in Communities study with analyzable ECGs (n = 14,725; age 54.2 ± 5.8 years; 55% female; 74% white) were included. EP substrate was characterized by heart rate, QRS, QTc, Cornell voltage, spatial ventricular gradient (SVG), and sum absolute QRST integral (SAI QRST) ECG metrics. Two competing outcomes were adjudicated: SCD and non-SCD. Interaction of ECG metrics with sex was studied in Cox proportional hazards and Fine-Gray competing risk models. Model 1 was adjusted for prevalent cardiovascular disease (CVD) and risk factors. Time-updated model 2 was additionally adjusted for incident nonfatal CVD. Relative hazard ratio (RHR) and relative subhazard ratio with 95% confidence interval (CI) for SCD and non-SCD risk for women relative to men were calculated. Model 1 was adjusted for prevalent CVD and risk factors. Time-updated model 2 was additionally adjusted for incident nonfatal CVD.

Results

Over median follow-up of 24.4 years, there were 530 SCDs (incidence 1.72; 95% CI 1.58–1.88 per 1000 person-years). Women compared to men experienced a greater risk of SCD associated with Cornell voltage (RHR 1.18; 95% CI 1.06–1.32; P = .003), SAI QRST (RHR 1.16; 95% CI 1.04–1.30; P = .007), and SVG magnitude (RHR 1.24; 95% CI 1.05–1.45; P = .009), independently from incident CVD.

Conclusion

In women, the global EP substrate is associated with up to 24% greater risk of SCD than in men, suggesting differences in underlying mechanisms and the need for sex-specific SCD risk stratification.

Transgenic Rabbit Models in Proarrhythmia Research

Drug-induced proarrhythmia constitutes a potentially lethal side effect of various drugs. Most often, this proarrhythmia is mechanistically linked to the drug's potential to interact with repolarizing cardiac ion channels causing a prolongation of the QT interval in the ECG. Despite sophisticated screening approaches during drug development, reliable prediction of proarrhythmia remains very challenging. Although drug-induced long-QT-related proarrhythmia is often favored by conditions or diseases that impair the individual's repolarization reserve, most cellular, tissue, and whole animal model systems used for drug safety screening are based on normal, healthy models. In recent years, several transgenic rabbit models for different types of long QT syndromes (LQTS) with differences in the extent of impairment in repolarization reserve have been generated. These might be useful for screening/prediction of a drug's potential for long-QT-related proarrhythmia, particularly as different repolarizing cardiac ion channels are impaired in the different models. In this review, we summarize the electrophysiological characteristics of the available transgenic LQTS rabbit models, and the pharmacological proof-of-principle studies that have been performed with these models—highlighting the advantages and disadvantages of LQTS models for proarrhythmia research. In the end, we give an outlook on potential future directions and novel models.

Mothers with long QT syndrome are at increased risk for fetal death: findings from a multicenter international study

BACKGROUND

Most fetal deaths are unexplained. Long QT syndrome is a genetic disorder of cardiac ion channels. Affected individuals, including fetuses, are predisposed to sudden death. We sought to determine the risk of fetal death in familial long QT syndrome, in which the mother or father carries the long QT syndrome genotype. In addition, we assessed whether risk differed if the long QT syndrome genotype was inherited from the mother or father.

OBJECTIVE

This was a retrospective review of pregnancies in families with the 3 most common heterozygous pathogenic long QT syndrome genotypes in KCNQ1 (LQT1), KCNH2 (LQT2), or SCN5A (LQT3), which occur in approximately 1 in 2000 individuals. The purpose of our study was to compare pregnancy and birth outcomes in familial long QT syndrome with the normal population and between maternal and paternal carriers of the long QT syndrome genotype. We hypothesized that fetal death before (miscarriage) and after (stillbirths) 20 weeks gestation would be increased in familial long QT syndrome compared with the normal population and that the parent of origin would not affect birth outcomes.

STUDY DESIGN

Our study was a multicenter observational case series of 148 pregnancies from 103 families (80 mothers, 23 fathers) with familial long QT syndrome (60 with LQT1, 29 with LQT2, 14 with LQT3) who were recruited from 11 international centers with expertise in hereditary heart rhythm diseases, pediatric and/or adult electrophysiology, and high-risk pregnancies. Clinical databases from these sites were reviewed for long QT syndrome that occurred in men or women of childbearing age (18-40 years). Pregnancy outcomes (livebirth, stillbirth, and miscarriage), birthweights, and gestational age at delivery were compared among long QT syndrome genotypes and between maternal vs paternal long QT syndrome-affected status with the use of logistic regression analysis.

RESULTS

Most offspring (80%; 118/148) were liveborn at term; 66% of offspring (73/110) had long QT syndrome. Newborn infants of mothers with long QT syndrome were delivered earlier and, when the data were controlled for gestational age, weighed less than newborn infants of long QT syndrome fathers. Fetal arrhythmias were observed rarely, but stillbirths (fetal death at >20 weeks gestation) were 8 times more frequent in long QT syndrome (4% vs approximately 0.5%); miscarriages (fetal death at ≤20 weeks gestation) were 2 times that of the general population (16% vs 8%). The likelihood of fetal death was significantly greater with maternal vs paternal long QT syndrome (24.4% vs 3.4%; P=.036). Only 10% of all fetal deaths underwent postmortem long QT syndrome testing; 2 of 3 cases were positive for the family long QT syndrome genotype.

CONCLUSION

This is the first report to demonstrate that mothers with long QT syndrome are at increased risk of fetal death and to uncover a previously unreported cause of stillbirth. Our results suggest that maternal effects of long QT syndrome channelopathy may cause placental or myometrial dysfunction that confers increased susceptibility to fetal death and growth restriction in newborn survivors, regardless of long QT syndrome status.

Selected Sex Related Differences in Pathophysiology of Cardiovascular System

The annual incidence of cardiovascular diseases is age-dependently increasing both in men and women, however, the prevalence is higher in men until midlife. The higher incidence of cardiovascular disease in men than in women of similar age, and the menopause-associated increase in cardiovascular disease in women, has led to speculation that gender-related differences in sex hormones might have a key role in the development and evolution of cardiovascular disease. There are several suggested pathways in which gender and sex hormones can affect human cardiovascular system to produce original sexually different pathophysiology between women and men. Sex steroid hormones and their receptors are critical determinants of cardiovascular gender differences. Also arterial blood pressure is typically lower in women than in men what could be explained particularly by greater synthesis of nitric oxide (NO) in women. Female cardiomyocytes have a greater survival advantage when challenged with oxidative stress, suggesting that female hormones may play an important role in antioxidative protection of myocardium. It was also demonstrated in animal models that combination of XX chromosomes versus an XY chromosomes enhances sex differences in higher HDL cholesterol. Women were found to have reduced sympathetic activity (reflected by lower total peripheral resistance) and pulmonary artery pressure and enhanced parasympathetic activity relative to men. Similarly, men were found to have higher plasma norepinephrine levels than women. Regarding differences between the sexes in electrophysiology of the heart, two principle mechanisms have been proposed to explain them: hormonal effects on the expression or function of ion channels or, conversely, differences in autonomic tone. To improve diagnosis and treatment of cardiovascular diseases, greater focus on understanding the molecular and cellular physiology of the sex steroid hormones and their receptors in the cardiovascular system will be required.

Risk Stratification of Type 2 Long-QT Syndrome Mutation Carriers With Normal QTc Interval: The Value of Sex, T-Wave Morphology, and Mutation Type

BACKGROUND

Long-QT (LQT) syndrome mutation carriers have higher risk of cardiac events than unaffected family members even in the absence of QTc prolongation. Changes in T-wave morphology may reflect penetrance of LQT syndrome mutations. We aimed to assess whether T-wave morphology may improve risk stratification of LQT2 mutation carriers with normal QTc interval.

METHODS

LQT2 mutation carriers with QTc <460 ms in men and <470 ms in women (n=154) were compared with unaffected family members (n=1007). Baseline ECGs recorded at age ≥18 years underwent blinded assessment. Flat, notched, or negative T waves in leads II or V₅ were considered abnormal. Cox regression analysis was performed to assess the association between T-wave morphology, the presence of mutations in the pore region of KCNH2, and the risk of cardiac events defined as syncope, aborted cardiac arrest, defibrillator therapy, or sudden cardiac death. Sex-specific associations were estimated using interactions terms.

RESULTS

LQT2 female carriers with abnormal T-wave morphology had significantly higher risk of cardiac events compared with LQT2 female carriers with normal T waves (hazard ratio, 3.31; 95% confidence interval, 1.68-6.52; P=0.001), whereas this association was not significant in men. LQT2 men with pore location of mutations have significantly higher risk of cardiac events than those with nonpore mutations (hazard ratio, 6.01; 95% confidence interval, 1.50-24.08; P=0.011), whereas no such association was found in women.

CONCLUSIONS

The risk of cardiac events in LQT2 carriers with normal QTc is associated with abnormal T-wave morphology in women and pore location of mutation in men. The findings further indicate sex-specific differences in phenotype and genotype relationship in LQT2 patients.

Changes in left ventricular repolarization after short-term testosterone replacement therapy in hypogonadal males

BACKGROUND AND AIM

Evidences suggest that androgen deficiency is associated with sudden cardiac death (SCD). Our purpose was to analyse some electrocardiographic (ECG) markers of repolarization phase in hypogonadal patients either at baseline or after testosterone replacement therapy (TRT).

PATIENTS AND METHODS

Baseline and after 6 months of testosterone replacement therapy, 14 hypogonadal patients and 10 age-matched controls underwent a short-term ECG recordings at rest and immediately after a maximal exercise test. The following ECG parameters have been collected: QTe (the interval between the q wave the end of T wave), QTp (the interval between the q wave and the peak of T wave), and Te (the interval between the peak and the end of T wave).

RESULTS

At baseline, in the hypogonadal patients, corrected QTe and QTp values were longer at rest than in the controls at rest (p < 0.05), whereas, during the recovery phase, only the QTp remained significantly longer (p < 0.05). After TRT, hypogonadal patients showed an improvement only in Te (p < 0.05). Conversely, any difference between hypogonadal patients and control subjects was found with respect to the markers of temporal dispersion of repolarization phases, except for a worse QTp → Te coherence (p = 0.001) obtained during the recovery phase.

CONCLUSIONS

In conclusion, at rest, hypogonadal patients suffer from a stable increase in the myocardial repolarization phase without an increase in its temporal dispersion and, hence, the SCD risk seems to be low.

Acquired Long QT Syndrome and Electrophysiology of Torsade de Pointes

Congenital long QT syndrome (LQTS) has been the most investigated cardiac ion channelopathy. Although congenital LQTS remains the domain of cardiologists, cardiac electrophysiologists and specialised centres, the much more frequently acquired LQTS is the domain of physicians and other members of healthcare teams required to make therapeutic decisions. This paper reviews the electrophysiological mechanisms of acquired LQTS, its ECG characteristics, clinical presentation, and management. The paper concludes with a comprehensive review of the electrophysiological mechanisms of torsade de pointes.

Cardiac arrhythmias secondary to hormone therapy in trans women

Introduction: With greater social acceptance and the evolution of transgender medicine as a specialty, more trans women are seeking hormone therapy (HT). Several studies have identified an increase in cardiovascular disease in trans women, however no studies have investigated the incidence of arrhythmias. Using two cases from the authors' clinic as examples, we propose that hormone therapy in trans women may increase the risk of cardiac arrhythmias. Areas covered: A literature search of sex hormones and cardiac arrhythmias was conducted. Using sex hormone studies completed in cis individuals and animal models we identified several similarities to trans women on HT. In cis men, low levels of testosterone are associated with increased rates of atrial fibrillation and right ventricular outflow tract arrhythmias. The role of estradiol remains less clear but there is evidence to suggest that the administration of exogenous estrogen may increase the rates of cardiac arrhythmias in cis women. Expert opinion: Research in the field of transgender medicine is expanding. As more trans women initiate HT, we will have a larger database from which to collect information regarding the benefits and risks of treatment, including the potential side effect of arrhythmias.