Long QT Syndrome

T-wave morphology can distinguish healthy controls from LQTS patients

Long QT syndrome (LQTS) is an inherited disorder associated with prolongation of the QT/QTc interval on the surface electrocardiogram (ECG) and a markedly increased risk of sudden cardiac death due to cardiac arrhythmias. Up to 25% of genotype-positive LQTS patients have QT/QTc intervals in the normal range. These patients are, however, still at increased risk of life-threatening events compared to their genotype-negative siblings. Previous studies have shown that analysis of T-wave morphology may enhance discrimination between control and LQTS patients. In this study we tested the hypothesis that automated analysis of T-wave morphology from Holter ECG recordings could distinguish between control and LQTS patients with QTc values in the range 400-450 ms. Holter ECGs were obtained from the Telemetric and Holter ECG Warehouse (THEW) database. Frequency binned averaged ECG waveforms were obtained and extracted T-waves were fitted with a combination of 3 sigmoid functions (upslope, downslope and switch) or two 9th order polynomial functions (upslope and downslope). Neural network classifiers, based on parameters obtained from the sigmoid or polynomial fits to the 1 Hz and 1.3 Hz ECG waveforms, were able to achieve up to 92% discrimination between control and LQTS patients and 88% discrimination between LQTS1 and LQTS2 patients. When we analysed a subgroup of subjects with normal QT intervals (400-450 ms, 67 controls and 61 LQTS), T-wave morphology based parameters enabled 90% discrimination between control and LQTS patients, compared to only 71% when the groups were classified based on QTc alone. In summary, our Holter ECG analysis algorithms demonstrate the feasibility of using automated analysis of T-wave morphology to distinguish LQTS patients, even those with normal QTc, from healthy controls.

Drug-induced QT interval prolongation and torsades de pointes: Role of the pharmacist in risk assessment, prevention and management

Torsades de pointes (TdP) is a life-threatening arrhythmia associated with prolongation of the corrected QT (QTc) interval on the electrocardiogram. More than 100 drugs available in Canada, including widely used antibiotics, antidepressants, cardiovascular drugs and many others, may cause QTc interval prolongation and TdP. Risk factors for TdP include QTc interval >500 ms, increase in QTc interval ≥60 ms from the pretreatment value, advanced age, female sex, acute myocardial infarction, heart failure with reduced ejection fraction, hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, treatment with diuretics and elevated plasma concentrations of QTc interval-prolonging drugs due to drug interactions, inadequate dose adjustment of renally eliminated drugs in patients with kidney disease and rapid intravenous administration. Pharmacokinetic drug interactions associated with the highest risk of TdP include antifungal agents, macrolide antibiotics (except azithromycin) and drugs to treat human immunodeficiency virus interacting with amiodarone, disopyramide, dofetilide or pimozide. Other important pharmacokinetic interactions include antidepressants (bupropion, duloxetine, fluoxetine, paroxetine) interacting with flecainide, quinidine or thioridazine. Pharmacists play an important role in minimizing the risk of drug-induced QTc interval prolongation and TdP through knowledge of drugs that are associated with a known or possible risk of TdP, individualized assessment of risk of drug-induced QTc interval prolongation, awareness of drug interactions most likely to result in TdP and attention to dose reduction of renally eliminated QTc interval-prolonging drugs in patients with kidney disease. Treatment of hemodynamically stable TdP consists of discontinuation of the offending drug(s), correction of electrolyte abnormalities and administration of intravenous magnesium sulfate 1 to 2 g.

Recent advances in genetic testing and counseling for inherited arrhythmias

Inherited arrhythmias, such as cardiomyopathies and cardiac ion channelopathies, along with coronary heart disease (CHD) are three most common disorders that predispose adults to sudden cardiac death. In the last three decades, causal genes in inherited arrhythmias have been successfully identified. At the same time, it has become evident that the genetic architectures are more complex than previously known. Recent advancements in DNA sequencing technology (next generation sequencing) have enabled us to study such complex genetic traits.

This article discusses indications for genetic testing of patients with inherited arrhythmias. Further, it describes the benefits and challenges that we face in the era of next generation sequencing. Finally, it briefly discusses genetic counseling, in which a multidisciplinary approach is required due to the increased complexity of the genetic information related to inherited arrhythmias.

Ventricular repolarization measures for arrhythmic risk stratification

Ventricular repolarization is a complex electrical phenomenon which represents a crucial stage in electrical cardiac activity. It is expressed on the surface electrocardiogram by the interval between the start of the QRS complex and the end of the T wave or U wave (QT). Several physiological, pathological and iatrogenic factors can influence ventricular repolarization. It has been demonstrated that small perturbations in this process can be a potential trigger of malignant arrhythmias, therefore the analysis of ventricular repolarization represents an interesting tool to implement risk stratification of arrhythmic events in different clinical settings. The aim of this review is to critically revise the traditional methods of static analysis of ventricular repolarization as well as those for dynamic evaluation, their prognostic significance and the possible application in daily clinical practice.

Ventricular repolarization measures for arrhythmic risk stratification

Ventricular repolarization is a complex electrical phenomenon which represents a crucial stage in electrical cardiac activity. It is expressed on the surface electrocardiogram by the interval between the start of the QRS complex and the end of the T wave or U wave (QT). Several physiological, pathological and iatrogenic factors can influence ventricular repolarization. It has been demonstrated that small perturbations in this process can be a potential trigger of malignant arrhythmias, therefore the analysis of ventricular repolarization represents an interesting tool to implement risk stratification of arrhythmic events in different clinical settings. The aim of this review is to critically revise the traditional methods of static analysis of ventricular repolarization as well as those for dynamic evaluation, their prognostic significance and the possible application in daily clinical practice.

Association of Arrhythmia-Related Genetic Variants With Phenotypes Documented in Electronic Medical Records

IMPORTANCE

Large-scale DNA sequencing identifies incidental rare variants in established Mendelian disease genes, but the frequency of related clinical phenotypes in unselected patient populations is not well established. Phenotype data from electronic medical records (EMRs) may provide a resource to assess the clinical relevance of rare variants.

OBJECTIVE

To determine the clinical phenotypes from EMRs for individuals with variants designated as pathogenic by expert review in arrhythmia susceptibility genes.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study included 2022 individuals recruited for nonantiarrhythmic drug exposure phenotypes from October 5, 2012, to September 30, 2013, for the Electronic Medical Records and Genomics Network Pharmacogenomics project from 7 US academic medical centers. Variants in SCN5A and KCNH2, disease genes for long QT and Brugada syndromes, were assessed for potential pathogenicity by 3 laboratories with ion channel expertise and by comparison with the ClinVar database. Relevant phenotypes were determined from EMRs, with data available from 2002 (or earlier for some sites) through September 10, 2014.

EXPOSURES

One or more variants designated as pathogenic in SCN5A or KCNH2.

MAIN OUTCOMES AND MEASURES

Arrhythmia or electrocardiographic (ECG) phenotypes defined by International Classification of Diseases, Ninth Revision (ICD-9) codes, ECG data, and manual EMR review.

RESULTS

Among 2022 study participants (median age, 61 years [interquartile range, 56-65 years]; 1118 [55%] female; 1491 [74%] white), a total of 122 rare (minor allele frequency <0.5%) nonsynonymous and splice-site variants in 2 arrhythmia susceptibility genes were identified in 223 individuals (11% of the study cohort). Forty-two variants in 63 participants were designated potentially pathogenic by at least 1 laboratory or ClinVar, with low concordance across laboratories (Cohen κ = 0.26). An ICD-9 code for arrhythmia was found in 11 of 63 (17%) variant carriers vs 264 of 1959 (13%) of those without variants (difference, +4%; 95% CI, -5% to +13%; P = .35). In the 1270 (63%) with ECGs, corrected QT intervals were not different in variant carriers vs those without (median, 429 vs 439 milliseconds; difference, -10 milliseconds; 95% CI, -16 to +3 milliseconds; P = .17). After manual review, 22 of 63 participants (35%) with designated variants had any ECG or arrhythmia phenotype, and only 2 had corrected QT interval longer than 500 milliseconds.

CONCLUSIONS AND RELEVANCE

Among laboratories experienced in genetic testing for cardiac arrhythmia disorders, there was low concordance in designating SCN5A and KCNH2 variants as pathogenic. In an unselected population, the putatively pathogenic genetic variants were not associated with an abnormal phenotype. These findings raise questions about the implications of notifying patients of incidental genetic findings.

SUMOylation and Potassium Channels: Links to Epilepsy and Sudden Death

Neuronal potassium ion channels play an essential role in the generation of the action potential and excitability of neurons. The dysfunction of ion channel subunits can cause channelopathies, which are associated in some cases with sudden unexplained death in epilepsy SUDEP. The physiological roles of neuronal ion channels have been largely determined, but little is known about the molecular mechanisms underlying neurological channelopathies, especially the determinants of the channels' regulation. SUMO (small ubiquitin-like modifier) proteins covalently conjugate lysine residues in a large number of target proteins and modify their functions. SUMO modification (SUMOylation) has emerged as an important regulatory mechanism for protein stability, function, subcellular localization, and protein-protein interactions. Since SUMO was discovered almost 20 years ago, the biological contribution of SUMOylation has not fully understood. It is until recently that the physiological impacts of SUMOylation on the regulation of neuronal potassium ion channels have been investigated. It is well established that SUMOylation controls many aspects of nuclear function, but it is now clear that it is also a key determinant in the function of potassium channels, and SUMOylation has also been implicated in a wide range of channelopathies, including epilepsy and sudden death.

Electro-mechanical dysfunction in long QT syndrome: Role for arrhythmogenic risk prediction and modulation by sex and sex hormones

Long QT syndrome (LQTS) is a congenital arrhythmogenic channelopathy characterized by impaired cardiac repolarization. Increasing evidence supports the notion that LQTS is not purely an "electrical" disease but rather an "electro-mechanical" disease with regionally heterogeneously impaired electrical and mechanical cardiac function. In the first part, this article reviews current knowledge on electro-mechanical (dys)function in LQTS, clinical consequences of the observed electro-mechanical dysfunction, and potential underlying mechanisms. Since several novel imaging techniques - Strain Echocardiography (SE) and Magnetic Resonance Tissue Phase Mapping (TPM) - are applied in clinical and experimental settings to assess the (regional) mechanical function, advantages of these non-invasive techniques and their feasibility in the clinical routine are particularly highlighted. The second part provides novel insights into sex differences and sex hormone effects on electro-mechanical cardiac function in a transgenic LQT2 rabbit model. Here we demonstrate that female LQT2 rabbits exhibit a prolonged time to diastolic peak - as marker for contraction duration and early relaxation - compared to males. Chronic estradiol-treatment enhances these differences in time to diastolic peak even more and additionally increases the risk for ventricular arrhythmia. Importantly, time to diastolic peak is particularly prolonged in rabbits exhibiting ventricular arrhythmia - regardless of hormone treatment - contrasting with a lack of differences in QT duration between symptomatic and asymptomatic LQT2 rabbits. This indicates the potential added value of the assessment of mechanical dysfunction in future risk stratification of LQTS patients.

Cardiac and autonomic mechanisms contributing to SUDEP

Sudden unexpected death in epilepsy is likely caused by a cascade of events affecting the vegetative nervous system leading to cardiorespiratory failure and death. Multiple genetic, electrophysiological, neurochemical, and pharmacological cardiac alterations have been associated with epilepsy, which can affect autonomic regulation of the heart and predispose patients to sudden unexpected death in epilepsy. These cardiac and autonomic changes are more frequently seen in patients with longstanding and medication refractory epilepsy and may be a prerequisite for sudden unexpected death in epilepsy. Cardiac changes are also observed within the immediate periictal period in patients with and without preexisting cardiac pathology and could be the tipping point in the cascade of events compromising autonomic, respiratory, and cardiac function during an epileptic convulsion. Better understanding if and how these cardiac alterations can make a particular individual with epilepsy more susceptible to sudden unexpected death in epilepsy will hopefully lead us to more effective preventative strategies.

Device therapy in the setting of long QT syndrome

Congenital long QT syndrome (LQTS) is an inherited disorder of myocardial repolarization characterized by prolongation of the QT interval associated with life-threatening polymorphic ventricular tachycardia. The treatment of congenital LQTS involves antiadrenergic therapies: β-blockers and surgical left cardiac sympathetic denervation (LCSD) to decrease sympathetic input to the heart, cardiac pacing, and implantable cardioverter-defibrillator (ICDs). Although this article focuses on the role of device therapy for the treatment of LQTS, it also discusses the role of β-blockers and LCSD because they are concomitant with device therapy. After implantation, programming should be optimized to minimize the risk for inappropriate ICD therapies.

[Long QT syndrome. History, genetics, clinical symptoms, causes and therapy]

The long QT syndrome is caused by a change in cardiac repolarization due to functional ion channel defects. A differentiation is made between a congenital (cLQTS) and an acquired (aLQTS) form of the disease. The disease results in the name-giving prolongation of the QT interval in the electrocardiogram and represents a predisposition for cardiac arrhythmia and sudden cardiac death. This article summarizes the current knowledge on the history, pathophysiology, clinical symptoms and therapy of cLQTS and aLQTS. This knowledge of pathophysiological features of the symptoms allows the underlying anesthesiological approach for individualized perioperative concepts for patients suffering from LQTS to be derived.

Genetic screening in sudden cardiac death in the young can save future lives

Background

Autopsy of sudden cardiac death (SCD) in the young shows a structurally and histologically normal heart in about one third of cases. Sudden death in these cases is believed to be attributed in a high percentage to inherited arrhythmogenic diseases. The purpose of this study was to investigate the value of performing post-mortem genetic analysis for autopsy-negative sudden unexplained death (SUD) in 1 to 35 year olds.

Methods and results

From January 2009 to December 2011, samples from 15 cases suffering SUD were referred to the Department of Clinical Genetics, Umeå University Hospital, Sweden, for molecular genetic evaluation. PCR and bidirectional Sanger sequencing of genes important for long QT syndrome (LQTS), short QT syndrome (SQTS), Brugada syndrome type 1 (BrS1), and catecholaminergic polymorphic ventricular tachycardia (CPVT) (KCNQ1, KCNH2, SCN5A, KCNE1, KCNE2, and RYR2) was performed. Multiplex ligation-dependent probe amplification (MLPA) was used to detect large deletions or duplications in the LQTS genes. Six pathogenic sequence variants (four LQTS and two CPVT) were discovered in 15 SUD cases (40 %). Ten first-degree family members were found to be mutation carriers (seven LQTS and three CPVT).

Conclusion

Cardiac ion channel genetic testing in autopsy-negative sudden death victims has a high diagnostic yield, with identification of the disease in 40 % of families. First-degree family members should be offered predictive testing, clinical evaluation, and treatment with the ultimate goal to prevent sudden death.

[Primary and secondary prophylactic ICD therapy in congenital electrical and structural cardiomyopathies]

Congenital electrical and structural cardiomyopathies are rare and associated with an increased risk for syncope and sudden cardiac death in the young. Due to the young age of the patients and the limited data available, risk stratification and especially ICD therapy are challenging. In this young patient collective, ICD therapy is associated with a high complication rate, which does not justify unreserved primary prophylactic ICD implantation. The aim of this review is to elucidate risk stratification and ICD therapy of various electrical and structural cardiomyopathies.

Cardiac QTc interval characteristics before and after hematopoietic stem cell transplantation: an analysis of 995 consecutive patients at a single center

Hematopoietic stem cell transplantation (HSCT) treats disorders affecting patients of all ages. We studied the rate-corrected cardiac QT interval (QTc) in 995 consecutive children and adults undergoing HSCT at the University of Minnesota. We sought to (1) describe QTc before and after HSCT; (2) describe the change in QTc after HSCT; (3) identify factors affecting QTc and its change; and (4) scrutinize an 'at risk' sub-cohort with a long QTc before HSCT. Pre HSCT: 952 (96%) patients had an evaluable electrocardiography (ECG); median QTc was 426 ms and depended upon disease necessitating transplant. Post HSCT: 506 (51%) patients had an evaluable ECG; median QTc was 441 ms. Intrapatient QTc change: 490 (49%) evaluable patients showed median QTc change (pre to post HSCT) of +16 ms (P<0.0001). At risk group: 68 patients were 'at risk' (long pre-HSCT QTc). In some, 'at-risk' status trended toward predictive of post-transplant nonrelapse mortality. QTc interval prolongation is evident in a large, diverse cohort undergoing HSCT at our institution. Prospective studies of this patient population may be warranted, particularly for 'at-risk' patients who demonstrate significant QTc prolongation both pre and post HSCT.

The Long QT Syndrome: A Review and Mortality Analysis

Objective .- To provide a recent review of literature pertinent to the assessment of life risk for individuals with a history of long QT syndrome (LQTS) and assess the mortality risk of a subset of these patients. Methods .- Standard comparative mortality techniques were employed to analyze relevant survival curves. Results .- Mortality risk in LQTS varies by age, sex, QTc interval length, genotype, and history of symptoms. A narrowly-defined subgroup of LQTS patients, those over age 20 with no history of syncope prior to age 20 and a QTc of less than 500ms, have an excess death rate of 0.5 - 2.0 per thousand per year. Conclusions .- Though the risk of sudden cardiac death in those with a history of long QT syndrome persists, there are subgroups of patients for whom the excess risk is lower than has been reported for this group of patients as a whole.

Congenital long QT syndromes: prevalence, pathophysiology and management

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

Hyper-SUMOylation of the Kv7 potassium channel diminishes the M-current leading to seizures and sudden death

Sudden unexplained death in epilepsy (SUDEP) is the most common cause of premature mortality in epilepsy and was linked to mutations in ion channels; however, genes within the channel protein interactome might also represent pathogenic candidates. Here we show that mice with partial deficiency of Sentrin/SUMO-specific protease 2 (SENP2) develop spontaneous seizures and sudden death. SENP2 is highly enriched in the hippocampus, often the focus of epileptic seizures. SENP2 deficiency results in hyper-SUMOylation of multiple potassium channels known to regulate neuronal excitability. We demonstrate that the depolarizing M-current conducted by Kv7 channel is significantly diminished in SENP2-deficient hippocampal CA3 neurons, primarily responsible for neuronal hyperexcitability. Following seizures, SENP2-deficient mice develop atrioventricular conduction blocks and cardiac asystole. Both seizures and cardiac conduction blocks can be prevented by retigabine, a Kv7 channel opener. Thus, we uncover a disease-causing role for hyper-SUMOylation in the nervous system and establish an animal model for SUDEP.

Translating advances in cardiogenetics into effective clinical practice

In this article we describe a qualitative research study in which we explored individuals' subjective experiences of both genetic testing and cardiogenetic disorders. Using a grounded theory approach, we coded and analyzed interview and focus group transcripts from 50 participants. We found that just under half of the participants who received their diagnosis during the study reported difficulty understanding information about both the purpose of genetic testing and their cardiac disease. A high level of anxiety about genetic testing and cardiac symptoms exacerbated individuals' cognitive confusion. Participants reported both positive and negative interactions with the medical community, depending on health care professionals' knowledge of cardiogenetic disorders. Overall, participants expressed a range of attitudes--positive, negative, and ambivalent--toward genetic testing. We conclude with a discussion of the barriers to achieving effective clinical care for genetic conditions and offer suggestions for improving collaborative decision making between physicians and patients.

The Therapeutic Potential of hERG1 K+ Channels for Treating Cancer and Cardiac Arrhythmias

hERG potassium channels present pharmacologists and medicinal chemists with a dilemma. On the one hand hERG is a major reason for drugs being withdrawn from the market because of drug induced long QT syndrome and the associated risk of inducing sudden cardiac death, and yet hERG blockers are still widely used in the clinic to treat cardiac arrhythmias. Moreover, in the last decade overwhelming evidence has been provided that hERG channels are aberrantly expressed in cancer cells and that they contribute to tumour cell proliferation, resistance to apoptosis, and neoangiogenesis. Here we provide an overview of the properties of hERG channels and their role in excitable cells of the heart and nervous system as well as in cancer. We consider the therapeutic potential of hERG, not only with regard to the negative impact due to drug induced long QT syndrome, but also its future potential as a treatment in the fight against cancer.

MicroRNAs in cardiac arrhythmia: DNA sequence variation of MiR-1 and MiR-133A in long QT syndrome

Long QT syndrome (LQTS) is a genetic cardiac condition associated with prolonged ventricular repolarization, primarily a result of perturbations in cardiac ion channels, which predisposes individuals to life-threatening arrhythmias. Using DNA screening and sequencing methods, over 700 different LQTS-causing mutations have been identified in 13 genes worldwide. Despite this, the genetic cause of 30-50% of LQTS is presently unknown. MicroRNAs (miRNAs) are small (∼ 22 nucleotides) noncoding RNAs which post-transcriptionally regulate gene expression by binding complementary sequences within messenger RNAs (mRNAs). The human genome encodes over 1800 miRNAs, which target about 60% of human genes. Consequently, miRNAs are likely to regulate many complex processes in the body, indeed aberrant expression of various miRNA species has been implicated in numerous disease states, including cardiovascular diseases. MiR-1 and MiR-133A are the most abundant miRNAs in the heart and have both been reported to regulate cardiac ion channels. We hypothesized that, as a consequence of their role in regulating cardiac ion channels, genetic variation in the genes which encode MiR-1 and MiR-133A might explain some cases of LQTS. Four miRNA genes (miR-1-1, miR-1-2, miR-133a-1 and miR-133a-2), which encode MiR-1 and MiR-133A, were sequenced in 125 LQTS probands. No genetic variants were identified in miR-1-1 or miR-133a-1; but in miR-1-2 we identified a single substitution (n.100A> G) and in miR-133a-2 we identified two substitutions (n.-19G> A and n.98C> T). None of the variants affect the mature miRNA products. Our findings indicate that sequence variants of miR-1-1, miR-1-2, miR-133a-1 and miR-133a-2 are not a cause of LQTS in this cohort.

Sports-Related Injuries and Deaths

Physical activity in children and adolescents should be strongly encouraged. While there is a very low risk of death associated with participation in athletics within this age group, the epidemic of childhood obesity and sedentary lifestyle must be combated to ensure the long-term health and quality of life of today’s youth. Sports-related deaths due to trauma are usually readily identified; others require careful examination, adjunctive testing, and/or the expertise of consultants. A thorough investigation of circumstances surrounding the death, review of the medical records, and autopsy is mandated in these cases.

Electrocardiographic screening for hypertrophic cardiomyopathy and long QT syndrome: the drivers of cost-effectiveness for the prevention of sudden cardiac death

It is universally recognized that the prevention of sudden cardiac death (SCD) in youth is an important public health initiative. The best approach remains uncertain. Many European and Asian countries support the use of electrocardiograms (ECGs). In the United States, this is highly controversial. Many debate its cost-effectiveness. We designed a comprehensive economic model of two of the most prevalent causes of SCD identifiable by ECG, hypertrophic cardiomyopathy (HCM) and long QT syndrome (LQTS), to determine the drivers of uncertainty in the estimate of cost-effectiveness. We compared the cost-effectiveness of screening with history and physical examination (H&P) plus ECG to the current United States standard, H&P alone, for the detection and treatment of HCM and LQTS. We used a Markov model on a theoretical cohort of healthy 12-year-olds over a 70-year time horizon from a societal perspective, employing extensive univariable and probabilistic sensitivity analyses, to determine drivers of costs and effectiveness. The incremental cost-effectiveness of adding ECGs to H&Ps was $41,400/life-year saved. The model was highly sensitive to the effect of identification and treatment of previously undiagnosed individuals with HCM; however, it was insensitive to many variables commonly assumed to be significant, including the costs of ECGs, echocardiograms, and genetic testing, as well as the sensitivity and specificity of ECGs. No LQTS-related parameters were significant. This study suggests that the key to determining the cost-effectiveness of ECG screening in the United States lies in developing a better understanding of disease progression in the previously undiagnosed HCM population.

Brief report: Emotional distress and recent stressful life events in long QT syndrome mutation carriers

To study emotional distress in symptomatic and asymptomatic long QT syndrome mutation carriers who had experienced a recent stressful life event. The participants were 209 symptomatic and 279 asymptomatic long QT syndrome mutation carriers. Emotional distress was assessed with the Cope questionnaire and stressful life events with the Social Readjustment Rating Scale. Symptomatic long QT syndrome mutation carriers with burdening recent stressful life events reported a higher emotional distress (β = 0.35, p < 0.001), while the asymptomatic did not show such difference (β = 0.13, p = 0.393). Symptomatic long QT syndrome mutation carriers who have experienced stressful life events recently report an increased emotional distress.

A phosphoinositide 3-kinase (PI3K)-serum- and glucocorticoid-inducible kinase 1 (SGK1) pathway promotes Kv7.1 channel surface expression by inhibiting Nedd4-2 protein

Epithelial cell polarization involves several kinase signaling cascades that eventually divide the surface membrane into an apical and a basolateral part. One kinase, which is activated during the polarization process, is phosphoinositide 3-kinase (PI3K). In MDCK cells, the basolateral potassium channel Kv7.1 requires PI3K activity for surface-expression during the polarization process. Here, we demonstrate that Kv7.1 surface expression requires tonic PI3K activity as PI3K inhibition triggers endocytosis of these channels in polarized MDCK. Pharmacological inhibition of SGK1 gave similar results as PI3K inhibition, whereas overexpression of constitutively active SGK1 overruled it, suggesting that SGK1 is the primary downstream target of PI3K in this process. Furthermore, knockdown of the ubiquitin ligase Nedd4-2 overruled PI3K inhibition, whereas a Nedd4-2 interaction-deficient Kv7.1 mutant was resistant to both PI3K and SGK1 inhibition. Altogether, these data suggest that a PI3K-SGK1 pathway stabilizes Kv7.1 surface expression by inhibiting Nedd4-2-dependent endocytosis and thereby demonstrates that Nedd4-2 is a key regulator of Kv7.1 localization and turnover in epithelial cells.

Long QT syndrome: a Korean single center study

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

LQTS in Northern BC: homozygosity for KCNQ1 V205M presents with a more severe cardiac phenotype but with minimal impact on auditory function

Long QT syndrome (LQTS), a rare congenital cardiac condition associated with life-threatening ventricular arrhythmias is characterized by a prolonged QT interval on electrocardiograph corrected for heart rate [corrected QT (QTc)]. LQTS has been historically categorized into the autosomal dominant Romano-Ward syndrome (RWS) and the autosomal recessive Jervell and Lange-Nielsen syndrome (JLNS). JLNS is associated with prelingual sensorineural deafness. Both types of LQTS can be caused by mutations in channel genes (e.g. KCNQ1) responsible for potassium homeostasis in cardiac myocytes and cochlea. Autosomal dominant mutations often cause the RWS phenotype and homozygous or compound heterozygous mutations contribute to JLNS. Two First Nations communities in northern British Columbia are affected disproportionately with LQTS largely due to the V205M mutation in KCNQ1, however, the pathology and phenotypic expression for those V205M homozygous has been unknown. Here, we show that four V205M homozygous individuals have a significantly higher 'peak' QTc, and a more severe cardiac phenotype compared with 41 V205M heterozygous carriers and 57 first to third degree relatives without mutations. Given the lack of prelingual deafness the homozygous V205M LQTS patients present with a phenotype more typical of RWS than JLNS.

Cardiomyocyte calcium cycling in a naturally occurring German shepherd dog model of inherited ventricular arrhythmia and sudden cardiac death

OBJECTIVE

To further characterize arrhythmic mechanisms in German shepherd dogs (GSDs) affected with inherited ventricular arrhythmias by evaluating intracellular calcium cycling and expression of calcium handling genes.

ANIMALS

Twenty five GSDs, 9 backcross dogs, and 6 normal mongrel dogs (controls) were studied. The GSDs and backcross dogs were from a research colony of inherited ventricular arrhythmias. The control research dogs were purchased.

METHODS

Action potentials (APs) and pseudo-electrocardiograms (ECG) were recorded from left ventricular (LV) wedge preparations of GSDs and normal dogs. Midmyocardial (Mid) LV cells from GSDs and normal mongrels were isolated by enzymatic digestion. Cells were either field stimulated or voltage clamped and calcium transients were measured by confocal microscopy using the indicator Fluo-3AM. Expression of calcium handling genes was measured by quantitative RT-PCR.

RESULTS

Mean calcium transient decay (tau) was not different between affected GSDs and control dogs, but striking cell-to-cell variability for tau was observed within affected GSDs and between affected GSDs and controls (P < 0.0001 each); within-dog variability accounted for 75% of total variability. Calcium sparks and afterdepolarizations occurred in GSD but not control cells. ATP2A2/SERCA2a expression was significantly reduced (P = 0.0063) in affected GSDs and inversely correlated (P = 0.0006) with severity of ventricular arrhythmias.

CONCLUSIONS

German shepherd dogs with inherited ventricular arrhythmias have electrophysiologic abnormalities in calcium cycling associated with reduced ATP2A2/SERCA2a expression. These animals provide a unique opportunity to study calcium remodeling at the genetic and molecular level in familial ventricular arrhythmias.

Family-based associations in measures of psychological distress and quality of life in a cardiac screening clinic for inheritable cardiac diseases: a cross-sectional study

BACKGROUND

Family-based cardiac screening programmes for persons at risk for genetic cardiac diseases are now recommended. However, the psychological wellbeing and health related quality of life (QoL) of such screened patients is poorly understood, especially in younger patients. We sought to examine wellbeing and QoL in a representative group of adults aged 16 and over in a dedicated family cardiac screening clinic.

METHODS

Prospective survey of consecutive consenting patients attending a cardiac screening clinic, over a 12 month period. Data were collected using two health measurement tools: the Short Form 12 (version 2) and the Hospital Anxiety and Depression Scale (HADS), along with baseline demographic and screening visit-related data. The HADS and SF-12v.2 outcomes were compared by age group. Associations with a higher HADS score were examined using logistic regression, with multi-level modelling used to account for the family-based structure of the data.

RESULTS

There was a study response rate of 86.6%, with n=334 patients providing valid HADS data (valid response rate 79.5%), and data on n=316 retained for analysis. One-fifth of patients were aged under 25 (n=61). Younger patients were less likely than older to describe significant depression on their HADS scale (p<0.0001), although there were overall no difference between the prevalence of a significant HADS score between the younger and older age groups (18.0% vs 20.0%, p=0.73). Significant positive associates of a higher HADS score were having lower educational attainment, being single or separated, and being closely related to the family proband. Between-family variance in anxiety and depression scores was greater than within-family variance.

CONCLUSIONS

High levels of anxiety were seen amongst patients attending a family-based cardiac screening clinic.Younger patients also had high rates of clinically significant anxiety. Higher levels of anxiety and depression tends to run in families, and this has implications for family screening and intervention programmes.

Cardiac channelopathies: genetic and molecular mechanisms

Channelopathies are diseases caused by dysfunctional ion channels, due to either genetic or acquired pathological factors. Inherited cardiac arrhythmic syndromes are among the most studied human disorders involving ion channels. Since seminal observations made in 1995, thousands of mutations have been found in many of the different genes that code for cardiac ion channel subunits and proteins that regulate the cardiac ion channels. The main phenotypes observed in patients carrying these mutations are congenital long QT syndrome (LQTS), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), short QT syndrome (SQTS) and variable types of conduction defects (CD). The goal of this review is to present an update of the main genetic and molecular mechanisms, as well as the associated phenotypes of cardiac channelopathies as of 2012.

Risk of life-threatening cardiac events among patients with long QT syndrome and multiple mutations

BACKGROUND

Patients with long QT syndrome (LQTS) who harbor multiple mutations (i.e. ≥ 2 mutations in ≥ 1 LQTS-susceptibility gene) may experience increased risk for life-threatening cardiac events.

OBJECTIVES

The present study was designed to compare the clinical course of LQTS patients with multiple mutations to those with a single mutation.

METHODS

The risk for life-threatening cardiac events (comprising aborted cardiac arrest, implantable defibrillator shock, or sudden cardiac death) from birth through age 40 years, by the presence of multiple vs. single mutations, was assessed among 403 patients from the LQTS Registry.

RESULTS

Patients with multiple mutations (n=57) exhibited a longer QTc at enrollment compared with those with a single mutation (mean ± SD: 506 ± 72 vs. 480 ± 56 msec, respectively; P=0.003) and had a higher rate of life threatening cardiac events during follow-up (23% vs. 11%, respectively; p=0.031). Consistently, multivariate analysis demonstrated that patients with multiple mutations had a 2.3-fold (P=0.015) increased risk for life threatening cardiac events as compared to patients with a single mutation. The presence of multiple mutations in a single LQTS gene was associated with a 3.2-fold increased risk for life threatening cardiac events (P=0.010) whereas the risk associated with multiple mutation status involving >1 LQTS gene was not significantly different from the risk associated with a single mutation (HR 1.7, P=0.26).

CONCLUSIONS

LQTS patients with multiple mutations have a greater risk for life-threatening cardiac events as compared to patients with a single mutation.

Founder mutations characterise the mutation panorama in 200 Swedish index cases referred for Long QT syndrome genetic testing

Background

Long QT syndrome (LQTS) is an inherited arrhythmic disorder characterised by prolongation of the QT interval on ECG, presence of syncope and sudden death. The symptoms in LQTS patients are highly variable, and genotype influences the clinical course. This study aims to report the spectrum of LQTS mutations in a Swedish cohort.

Methods

Between March 2006 and October 2009, two hundred, unrelated index cases were referred to the Department of Clinical Genetics, Umeå University Hospital, Sweden, for LQTS genetic testing. We scanned five of the LQTS-susceptibility genes (KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2) for mutations by DHPLC and/or sequencing. We applied MLPA to detect large deletions or duplications in the KCNQ1, KCNH2, SCN5A, KCNE1, and KCNE2 genes. Furthermore, the gene RYR2 was screened in 36 selected LQTS genotype-negative patients to detect cases with the clinically overlapping disease catecholaminergic polymorphic ventricular tachycardia (CPVT).

Results

In total, a disease-causing mutation was identified in 103 of the 200 (52%) index cases. Of these, altered exon copy numbers in the KCNH2 gene accounted for 2% of the mutations, whereas a RYR2 mutation accounted for 3% of the mutations. The genotype-positive cases stemmed from 64 distinct mutations, of which 28% were novel to this cohort. The majority of the distinct mutations were found in a single case (80%), whereas 20% of the mutations were observed more than once. Two founder mutations, KCNQ1 p.Y111C and KCNQ1 p.R518*, accounted for 25% of the genotype-positive index cases. Genetic cascade screening of 481 relatives to the 103 index cases with an identified mutation revealed 41% mutation carriers who were at risk of cardiac events such as syncope or sudden unexpected death.

Conclusion

In this cohort of Swedish index cases with suspected LQTS, a disease-causing mutation was identified in 52% of the referred patients. Copy number variations explained 2% of the mutations and 3 of 36 selected cases (8%) harboured a mutation in the RYR2 gene. The mutation panorama is characterised by founder mutations (25%), even so, this cohort increases the amount of known LQTS-associated mutations, as approximately one-third (28%) of the detected mutations were unique.

Congenital long and short QT syndromes

Congenital long and short QT syndromes are familial arrhythmias characterized by derangement of repolarization and a high risk of sudden cardiac death due to ventricular tachyarrhythmias. With growing understanding of these syndromes in both the medical and lay communities, diagnostic and therapeutic difficulties are increasingly faced by health care providers. Modern genomics has determined the mechanism of arrhythmia induction in these patients, resulting in specific medical therapies and improved risk stratification. This paper reviews the common presentations, genetic etiology, basic evaluation, risk stratification, and therapeutic approach for both syndromes. Particular attention is paid to the effect of the individual syndrome on the cardiac action potential and its correlate the surface 12 lead ECG. In conclusion, patients with long and short QT syndromes are at risk for sudden death, with accurate diagnosis, risk stratification, and resulting appropriate therapy favorably altering their outcome.

Congenital long-QT syndrome in Addison's disease: a novel association

This report describes a teenager found to have both Addision's disease and long-QT syndrome type 1. This association is unique, but congenital long-QT channelopathies have been associated with other endocrinopathies. It remains to be seen whether genetic investigation should be performed for all patients with long-QTc's and endocrinopathies.

Mortality of Inherited Arrhythmia Syndromes

Background—

For most arrhythmia syndromes, the risk of sudden cardiac death for asymptomatic mutation carriers is ill defined. Data on the natural history of these diseases, therefore, are essential. The family tree mortality ratio method offers the unique possibility to study the natural history at a time when the disease was not known and patients received no treatment.

Methods and Results—

In 6 inherited arrhythmia syndromes caused by specific mutations, we analyzed all-cause mortality with the family tree mortality ratio method (main outcome measure, standardized mortality ratio [SMR]). In long-QT syndrome (LQTS) type 1, severely increased mortality risk during all years of childhood was observed (1–19 years), in particular during the first 10 years of life (SMR, 2.9; 95% CI, 1.5–5.1). In LQTS type 2, we observed increasing SMRs starting from age 15 years, which just reached significance between age 30 and 39 (SMR, 4.0; 95% CI, 1.1–10.0). In LQTS type 3, the SMR was increased between age 15 and 19 years (SMR, 5.8; 95% CI, 1.2–16.9). In the SCN5A overlap syndrome, excess mortality was observed between age 10 and 59 years, with a peak between 20 and 39 years (SMR, 3.8; 95% CI, 2.5–5.7). In catecholaminergic polymorphic ventricular tachycardia, excess mortality was restricted to ages 20 to 39 years (SMR, 3.0; 95% CI, 1.3–6.0). In Brugada syndrome, excess mortality was observed between age 40 and 59 (SMR, 1.79; 95% CI, 1.2–2.4), particularly in men.

Conclusions—

We identified age ranges during which the mortality risk manifests in an unselected and untreated population, which can guide screening in these families.

Age-and sex-dependent mRNA expression of KCNQ1 and HERG in patients with long QT syndrome type 1 and 2

INTRODUCTION

The main goal of this study was to examine the patient age and sex dependent expression of KCNQ1 and HERG genes that encode potassium channels responsible for the occurrence of long QT syndrome (LQTS).

MATERIAL AND METHODS

The study enrolled 43 families whose members suffered from LQTS type 1 (LQTS1) or 2 (LQTS2) or were healthy. The study attempted to prove that β-actin is a good endogenous control when determining the expression of the studied genes. Examination of gene expression was achieved with quantitative real-time PCR (QRT-PCR). Expression of the investigated genes was inferred from the analysis of the number of mRNA copies per 1 μg total RNA isolated from whole blood.

RESULTS

Significantly lower KCNQ1 and KCNH2 mRNA levels in healthy females than healthy males were observed (p = 0.032; p = 0.02). In male patients both transcripts were expressed at a lower level (p = 0.0084; p = 0.035). The comparison of transcriptional activity of KCNQ1 and KCNH2 in healthy adults and children revealed higher KCNQ1 and lower KCNH2 mRNA levels in healthy adults (p = 0.033; p = 0.04), higher KCNQ1 and lower KCNH2 mRNA levels in adult patients below 55 years old than in adults over 55 years old (p=0.036; p = 0.044), and significantly higher KCNQ1 and lower KCNH2 mRNA levels in adult patients (over 55 years) than in paediatric patients (below 15 years) (p=0.047; p = 0.08).

CONCLUSIONS

The results support the hypothesis that KCNQ1 and HERG gene expression is influenced by age and gender in human patients with long QT syndrome and in healthy subjects.

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

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