The spectrum of symptoms and QT intervals in carriers of the gene for the long-QT syndrome

QTc Interval Prolongation as an Adverse Event of Azole Antifungal Drugs: Case Report and Literature Review

QTc prolongation and torsade de pointes (TdP) are significant adverse events linked to azole antifungals. Reports on QTc interval prolongation caused by these agents are limited. In this study, we report a case of a 77-year-old male with cardiovascular disease who experienced QTc prolongation and subsequent TdP while being treated with fluconazole for Candida albicans-induced knee arthritis. Additionally, a literature review was conducted on cases where QTc prolongation and TdP were triggered as adverse events of azole antifungal drugs. The case study detailed the patient's experience, whereas the literature review analyzed cases from May 1997 to February 2023, focusing on patient demographics, underlying diseases, antifungal regimens, concurrent medications, QTc changes, and outcomes. The review identified 16 cases, mainly in younger individuals (median age of 29) and women (75%). Fluconazole (63%) and voriconazole (37%) were the most common agents. Concurrent medications were present in 75% of cases, and TdP occurred in 81%. Management typically involved discontinuing or switching antifungals and correcting electrolytes, with all patients surviving. Risk assessment and concurrent medication review are essential before starting azole therapy. High-risk patients require careful electrocardiogram monitoring to prevent arrhythmias. Remote monitoring may enhance safety for patients with implanted devices. Further studies are needed to understand risk factors and management strategies.

T-wave morphology abnormalities in the STREAM stage 1 trial

BACKGROUND

Shorter regimens for drug-resistant tuberculosis (DR-TB) have non-inferior efficacy compared with longer regimens, but QT prolongation is a concern. T-wave morphology abnormalities may be a predictor of QT prolongation.

RESEARCH DESIGN AND METHODS

STREAM Stage 1 was a randomized controlled trial in rifampicin-resistant TB, comparing short and long regimens. All participants had regular ECGs. QT/QTcF prolongation (≥500 ms or increase in ≥60 ms from baseline) was more common on the short regimen which contained high-dose moxifloxacin and clofazimine. Blinded ECGs were selected from the baseline, early (weeks 1-4), and late (weeks 12-36) time points. T-wave morphology was categorized as normal or abnormal (notched, asymmetric, flat-wave, flat peak, or broad). Differences between groups were assessed using Chi-Square tests (paired/unpaired, as appropriate).

RESULTS

Two-hundred participants with available ECGs at relevant times were analyzed (QT prolongation group n = 82; non-prolongation group n = 118). At baseline, 23% (45/200) of participants displayed abnormal T-waves, increasing to 45% (90/200, p < 0.001) at the late time point. Abnormalities were more common in participants allocated the Short regimen (75/117, 64%) than the Long (14/38, 36.8%, p = 0.003); these occurred prior to QT/QTcF ≥500 ms in 53% of the participants (Long 2/5; Short 14/25).

CONCLUSIONS

T-wave abnormalities may help identify patients at risk of QT prolongation on DR-TB treatment.

TRIAL REGISTRATION

The trial is registered at ClinicalTrials.gov (CT.gov identifier: NCT02409290). Current Controlled Trial number, ISRCTN78372190.

Computational analysis of long QT syndrome type 2 and the therapeutic effects of KCNQ1 antibodies

Objective

Long QT interval syndrome (LQTS) is a highly dangerous cardiac disease that can lead to sudden cardiac death; however, its underlying mechanism remains largely unknown. This study is conceived to investigate the impact of two general genotypes of LQTS type 2, and also the therapeutic effects of an emerging immunology-based treatment named KCNQ1 antibody.

Methods

A multiscale virtual heart is developed, which contains multiple biological levels ranging from ion channels to a three-dimensional cardiac structure with realistic geometry. Critical biomarkers at different biological levels are monitored to investigate the remodeling of cardiac electrophysiology induced by mutations.

Results

Simulations revealed multiple important mechanisms that are hard to capture via conventional clinical techniques, including the augmented dispersion of repolarization, the increased vulnerability to arrhythmias, the impaired adaptability in tissue to high heart rates, and so on. An emerging KCNQ1 antibody-based therapy could rescue the prolonged QT interval but did not reduce the vulnerable window.

Conclusions

Tiny molecular alterations can lead to cardiac electrophysiological remodeling at multiple biological levels, which in turn contributes to higher susceptibility to lethal arrhythmias in long QT syndrome type 2 patients. The KCNQ1 antibody-based therapy has proarrhythmic risks notwithstanding its QT-rescuing effects.

Decreased vector magnitudes may help identify events in patients with Long QT syndrome

INTRODUCTION

All Long QT syndrome (LQTS) patients are at elevated risk for channelopathy-induced delayed myocardial repolarization and consequently potentially life-threatening cardiac events with 90% of initial cardiac events occurring between preteen and 40 years old. Utilizing ECG and derived vectorcardiographic parameters, including T wave Vector Magnitude (TwVM) measurement data, this study attempts to determine whether TwVM from baseline ECGs is effectively predictive of future cardiac events for genotype-positive LQTS patients.

METHODS

Verified carriers of established LQTS disease-causing genotypes were selected from University of Minnesota patient encounters between 2010 and 2020 for inclusion in this retrospective study. Baseline and predictive ECG and derived vectorcardiographic parameter evaluation, clinical data, and statistical analysis were compared between patients with and patients without cardiac events. First recorded ECG was at presentation to our hospital and final ECG is defined as ECG just prior to cardiac event (event defined below in Methods) or the most final documented ECG before cut-off year of 2020 for the event-free group.

RESULTS

Of 41 participants, 15 experienced cardiac events and 26 did not. While many baseline electrocardiographic parameter measurements did not show significant differences between patient groups, vectorcardiographic parameters at baseline, specifically the QRS vector magnitude (QRSVM) and azimuth of the spatial ventricular gradient, showed significance. Additionally, final vectorcardiographic parameters, particularly the QRSVM, TwVM, and azimuth of the spatial ventricular gradient showed significant differences between patient groups. Final T-wave frontal axis was significantly larger in those without cardiac events. Significant Kaplan-Meier curve separation between patient groups was noted based on a QRSVM of 1.43 mV or lower, with additional consideration to patient age, genotype, and beta blocker use.

CONCLUSION

This study shows evidence of ECG and derived vectorcardiographic parameters, including TwVM, being effective in early prediction of cardiac events in genotype-positive LQTS patients.

Diagnostic Accuracy of the Standing Test in Adults Suspected for Congenital Long-QT Syndrome

Background An elegant bedside provocation test has been shown to aid the diagnosis of long-QT syndrome (LQTS) in a retrospective cohort by evaluation of QT intervals and T-wave morphology changes resulting from the brief tachycardia provoked by standing. We aimed to prospectively determine the potential diagnostic value of the standing test for LQTS. Methods and Results In adults suspected for LQTS who had a standing test, the QT interval was assessed manually and automated. In addition, T-wave morphology changes were determined. A total of 167 controls and 131 genetically confirmed patients with LQTS were included. A prolonged heart rate-corrected QT interval (QTc) (men ≥430 ms, women ≥450 ms) at baseline before standing yielded a sensitivity of 61% (95% CI, 47-74) in men and 54% (95% CI, 42-66) in women, with a specificity of 90% (95% CI, 80-96) and 89% (95% CI, 81-95), respectively. In both men and women, QTc≥460 ms after standing increased sensitivity (89% [95% CI, 83-94]) but decreased specificity (49% [95% CI, 41-57]). Sensitivity further increased (P<0.01) when a prolonged baseline QTc was accompanied by a QTc≥460 ms after standing in both men (93% [95% CI, 84-98]) and women (90% [95% CI, 81-96]). However, the area under the curve did not improve. T-wave abnormalities after standing did not further increase the sensitivity or the area under the curve significantly. Conclusions Despite earlier retrospective studies, a baseline ECG and the standing test in a prospective evaluation displayed a different diagnostic profile for congenital LQTS but no unequivocal synergism or advantage. This suggests that there is markedly reduced penetrance and incomplete expression in genetically confirmed LQTS with retention of repolarization reserve in response to the brief tachycardia provoked by standing.

Targeted deep sequencing analyses of long QT syndrome in a Japanese population

Long QT syndrome (LQTS) is one of the most common inherited arrhythmias and multiple genes have been reported as causative. Presently, genetic diagnosis for LQTS patients is becoming widespread and contributing to implementation of therapies. However, causative genetic mutations cannot be detected in about 20% of patients. To elucidate additional genetic mutations in LQTS, we performed deep-sequencing of previously reported 15 causative and 85 candidate genes for this disorder in 556 Japanese LQTS patients. We performed in-silico filtering of the sequencing data and found 48 novel variants in 33 genes of 53 cases. These variants were predicted to be damaging to coding proteins or to alter the binding affinity of several transcription factors. Notably, we found that most of the LQTS-related variants in the RYR2 gene were in the large cytoplasmic domain of the N-terminus side. They might be useful for screening of LQTS patients who had no known genetic factors. In addition, when the mechanisms of these variants in the development of LQTS are revealed, it will be useful for early diagnosis, risk stratification, and selection of treatment.

Evolutionary Origins of Metabolic Reprogramming in Cancer

Metabolic changes that facilitate tumor growth are one of the hallmarks of cancer. These changes are not specific to tumors but also take place during the physiological growth of tissues. Indeed, the cellular and tissue mechanisms present in the tumor have their physiological counterpart in the repair of tissue lesions and wound healing. These molecular mechanisms have been acquired during metazoan evolution, first to eliminate the infection of the tissue injury, then to enter an effective regenerative phase. Cancer itself could be considered a phenomenon of antagonistic pleiotropy of the genes involved in effective tissue repair. Cancer and tissue repair are complex traits that share many intermediate phenotypes at the molecular, cellular, and tissue levels, and all of these are integrated within a Systems Biology structure. Complex traits are influenced by a multitude of common genes, each with a weak effect. This polygenic component of complex traits is mainly unknown and so makes up part of the missing heritability. Here, we try to integrate these different perspectives from the point of view of the metabolic changes observed in cancer.

The Pathological Mechanisms of Hearing Loss Caused by KCNQ1 and KCNQ4 Variants

Deafness-associated genes KCNQ1 (also associated with heart diseases) and KCNQ4 (only associated with hearing loss) encode the homotetrameric voltage-gated potassium ion channels Kv7.1 and Kv7.4, respectively. To date, over 700 KCNQ1 and over 70 KCNQ4 variants have been identified in patients. The vast majority of these variants are inherited dominantly, and their pathogenicity is often explained by dominant-negative inhibition or haploinsufficiency. Our recent study unexpectedly identified cell-death-inducing cytotoxicity in several Kv7.1 and Kv7.4 variants. Elucidation of this cytotoxicity mechanism and identification of its modifiers (drugs) have great potential for aiding the development of a novel pharmacological strategy against many pathogenic KCNQ variants. The purpose of this review is to disseminate this emerging pathological role of Kv7 variants and to underscore the importance of experimentally characterizing disease-associated variants.

Utility of Provocative Testing in the Diagnosis and Genotyping of Congenital Long QT Syndrome: A Systematic Review and Meta-Analysis

Background Diagnosis is particularly challenging in concealed or asymptomatic long QT syndrome (LQTS). Provocative testing, unmasking the characterization of LQTS, is a promising alternative method for the diagnosis of LQTS, but without uniform standards. Methods and Results A comprehensive search was conducted in PubMed, Embase, and the Cochrane Library through October 14, 2021. The fixed effects model was used to assess the effect of the provocative testing on QTc interval. A total of 22 studies with 1137 patients with LQTS were included. At baseline, QTc interval was 40 ms longer in patients with LQTS than in controls (mean difference [MD], 40.54 [95% CI, 37.43-43.65]; P<0.001). Compared with the control group, patients with LQTS had 28 ms longer ΔQTc upon standing (MD, 28.82 [95% CI, 23.05-34.58]; P<0.001), nearly 30 ms longer both at peak exercise (MD, 27.31 [95% CI, 21.51-33.11]; P<0.001) and recovery 4 to 5 minutes (MD, 29.85 [95% CI, 24.36-35.35]; P<0.001). With epinephrine infusion, QTc interval was prolonged both in controls and patients with QTS, most obviously in LQT1 (MD, 68.26 [95% CI, 58.91-77.60]; P<0.001) and LQT2 (MD, 60.17 [95% CI, 50.18-70.16]; P<0.001). Subgroup analysis showed QTc interval response to abrupt stand testing and exercise testing varied between LQT1, LQT2, and LQT3, named Type Ⅰ, Type Ⅱ, and Type Ⅲ. Conclusions QTc trend Type Ⅰ and Type Ⅲ during abrupt stand testing and exercise testing can be used to propose a prospective evaluation of LQT1 and LQT3, respectively. Type Ⅱ QTc trend combined epinephrine infusion testing could distinguish LQT2 from control. A preliminary diagnostic workflow was proposed but deserves further evaluation.

Genotype-Specific ECG-Based Risk Stratification Approaches in Patients With Long-QT Syndrome

Background

Congenital long-QT syndrome (LQTS) is a major cause of sudden cardiac death (SCD) in young individuals, calling for sophisticated risk assessment. Risk stratification, however, is challenging as the individual arrhythmic risk varies pronouncedly, even in individuals carrying the same variant.

Materials and Methods

In this study, we aimed to assess the association of different electrical parameters with the genotype and the symptoms in patients with LQTS. In addition to the heart-rate corrected QT interval (QTc), markers for regional electrical heterogeneity, such as QT dispersion (QT_max-QT_min in all ECG leads) and delta T_peak/end (T_peak/end V5 – T_peak/end V2), were assessed in the 12-lead ECG at rest and during exercise testing.

Results

QTc at rest was significantly longer in symptomatic than asymptomatic patients with LQT2 (493.4 ms ± 46.5 ms vs. 419.5 ms ± 28.6 ms, p = 0.004), but surprisingly not associated with symptoms in LQT1. In contrast, post-exercise QTc (minute 4 of recovery) was significantly longer in symptomatic than asymptomatic patients with LQT1 (486.5 ms ± 7.0 ms vs. 463.3 ms ± 16.3 ms, p = 0.04), while no such difference was observed in patients with LQT2. Enhanced delta T_peak/end and QT dispersion were only associated with symptoms in LQT1 (delta T_peak/end 19.0 ms ± 18.1 ms vs. −4.0 ms ± 4.4 ms, p = 0.02; QT-dispersion: 54.3 ms ± 10.2 ms vs. 31.4 ms ± 10.4 ms, p = 0.01), but not in LQT2. Delta T_peak/end was particularly discriminative after exercise, where all symptomatic patients with LQT1 had positive and all asymptomatic LQT1 patients had negative values (11.8 ± 7.9 ms vs. −7.5 ± 1.7 ms, p = 0.003).

Conclusion

Different electrical parameters can distinguish between symptomatic and asymptomatic patients in different genetic forms of LQTS. While the classical “QTc at rest” was only associated with symptoms in LQT2, post-exercise QTc helped distinguish between symptomatic and asymptomatic patients with LQT1. Enhanced regional electrical heterogeneity was only associated with symptoms in LQT1, but not in LQT2. Our findings indicate that genotype-specific risk stratification approaches based on electrical parameters could help to optimize risk assessment in LQTS.

Holter Recordings at Initial Assessment for Long QT Syndrome: Relationship to Genotype Status and Cardiac Events

Background: The relationship of Holter recordings of repolarization length to outcome in long QT syndrome (LQTS) is unknown. Methods: Holter recordings and initial 12 lead ECG QTc were related to outcome in 101 individuals with LQTS and 28 gene-negative relatives. Mean QTc (mQTc) and mean RTPc (R-wave to peak T-wave, mRTPc) using Bazett correction were measured, analyzing heart rates 40 to 120 bpm. Previously reported upper limit of normal (ULN) were: women and children (<15 years), mQTc 454, mRTPc 318 ms; men mQTc 446 ms, mRTPc 314 ms. Results: Measurements in LQTS patients were greatly prolonged; children and women mean mQTc 482 ms (range 406−558), mRTPc 351 ms (259−443); males > 15 years mQTc 469 ms (407−531), mRTPc 338 ms (288−388). Ten patients had cardiac arrest (CA), and 24 had arrhythmic syncope before or after the Holter. Holter values were more closely related to genotype status and symptoms than 12 lead QTc, e.g., sensitivity/specificity for genotype positive status, mRTPc > ULN (89%/86%); CA, mRTPc > 30 ms over ULN (48%/100%). Of 34 symptomatic (CA/syncope) patients, only 9 (26%) had 12 lead QTc > 500 ms, whereas 33/34 (94%) had an mRTPc or mQTc above ULN. In 10 with CA, all Holter measurements were > 15 ms above ULN, but only two had 12 lead QTc > 500 m. Conclusions: Holter average repolarization length, particularly mRTPc, reflects definite LQTS status and clinical risk better than the initial 12 lead QTc. Values below ULN indicate both a low risk of having LQTS and a low risk of cardiac events in the small percentage that do.

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.

shRNAs Targeting a Common KCNQ1 Variant Could Alleviate Long-QT1 Disease Severity by Inhibiting a Mutant Allele

Long-QT syndrome type 1 (LQT1) is caused by mutations in KCNQ1. Patients heterozygous for such a mutation co-assemble both mutant and wild-type KCNQ1-encoded subunits into tetrameric Kv7.1 potassium channels. Here, we investigated whether allele-specific inhibition of mutant KCNQ1 by targeting a common variant can shift the balance towards increased incorporation of the wild-type allele to alleviate the disease in human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs). We identified the single nucleotide polymorphisms (SNP) rs1057128 (G/A) in KCNQ1, with a heterozygosity of 27% in the European population. Next, we determined allele-specificity of short-hairpin RNAs (shRNAs) targeting either allele of this SNP in hiPSC-CMs that carry an LQT1 mutation. Our shRNAs downregulated 60% of the A allele and 40% of the G allele without affecting the non-targeted allele. Suppression of the mutant KCNQ1 allele by 60% decreased the occurrence of arrhythmic events in hiPSC-CMs measured by a voltage-sensitive reporter, while suppression of the wild-type allele increased the occurrence of arrhythmic events. Furthermore, computer simulations based on another LQT1 mutation revealed that 60% suppression of the mutant KCNQ1 allele shortens the prolonged action potential in an adult cardiomyocyte model. We conclude that allele-specific inhibition of a mutant KCNQ1 allele by targeting a common variant may alleviate the disease. This novel approach avoids the need to design shRNAs to target every single mutation and opens up the exciting possibility of treating multiple LQT1-causing mutations with only two shRNAs.

Hypernatremia and intercalated disc edema synergistically exacerbate long-QT syndrome type 3 phenotype

Cardiac voltage-gated sodium channel gain-of-function prolongs repolarization in the long-QT syndrome type 3 (LQT3). Previous studies suggest that narrowing the perinexus within the intercalated disc, leading to rapid sodium depletion, attenuates LQT3-associated action potential duration (APD) prolongation. However, it remains unknown whether extracellular sodium concentration modulates APD prolongation during sodium channel gain-of-function. We hypothesized that elevated extracellular sodium concentration and widened perinexus synergistically prolong APD in LQT3. LQT3 was induced with sea anemone toxin (ATXII) in Langendorff-perfused guinea pig hearts (n = 34). Sodium concentration was increased from 145 to 160 mM. Perinexal expansion was induced with mannitol or the sodium channel β1-subunit adhesion domain antagonist (βadp1). Epicardial ventricular action potentials were optically mapped. Individual and combined effects of varying clefts and sodium concentrations were simulated in a computational model. With ATXII, both mannitol and βadp1 significantly widened the perinexus and prolonged APD, respectively. The elevated sodium concentration alone significantly prolonged APD as well. Importantly, the combination of elevated sodium concentration and perinexal widening synergistically prolonged APD. Computational modeling results were consistent with animal experiments. Concurrently elevating extracellular sodium and increasing intercalated disc edema prolongs repolarization more than the individual interventions alone in LQT3. This synergistic effect suggests an important clinical implication that hypernatremia in the presence of cardiac edema can markedly increase LQT3-associated APD prolongation. Therefore, to our knowledge, this is the first study to provide evidence of a tractable and effective strategy to mitigate LQT3 phenotype by means of managing sodium levels and preventing cardiac edema in patients.NEW & NOTEWORTHY This is the first study to demonstrate that the long-QT syndrome type 3 (LQT3) phenotype can be exacerbated or concealed by regulating extracellular sodium concentrations and/or the intercalated disc separation. The animal experiments and computational modeling in the current study reveal a critically important clinical implication: sodium dysregulation in the presence of edema within the intercalated disc can markedly increase the risk of arrhythmia in LQT3. These findings strongly suggest that maintaining extracellular sodium within normal physiological limits may be an effective and inexpensive therapeutic option for patients with congenital or acquired sodium channel gain-of-function diseases.

American College of Rheumatology White Paper on Antimalarial Cardiac Toxicity

Hydroxychloroquine (HCQ) and chloroquine (CQ) are well-established medications used in treating systemic lupus erythematosus and rheumatoid arthritis, as well as skin conditions such as cutaneous lupus erythematosus. In rare cases, arrhythmias and conduction system abnormalities, as well as cardiomyopathy, have been reported in association with HCQ/CQ use. Recently, however, the corrected QT interval (QTc)-prolonging potential of these medications, and risk of torsade de pointes (TdP) in particular, have been highlighted in the setting of their experimental use for COVID-19 infection. This report was undertaken to summarize the current understanding of HCQ/CQ cardiac toxicity, describe QTc prolongation and TdP risks, and discuss areas of priority for future research. A working group of experts across rheumatology, cardiology, and dermatology performed a nonsystematic literature review and offered a consensus-based expert opinion. Current data clearly indicate that HCQ and CQ are invaluable medications in the management of rheumatic and dermatologic diseases, but they are associated with QTc prolongation by directly affecting cardiac repolarization. Prescribing clinicians should be cognizant of this small effect, especially in patients taking additional medications that prolong the QTc interval. Long-term use of HCQ/CQ may lead to a cardiomyopathy associated with arrhythmias and heart failure. Risk and benefit assessment should be considered prior to initiation of any medication, and both initial and ongoing risk-benefit assessments are important with regard to prescription of HCQ/CQ. While cardiac toxicity related to HCQ/CQ treatment of rheumatic diseases is rarely reported, it can be fatal. Awareness of the potential adverse cardiac effects of HCQ and CQ can increase the safe use of these medications. There is a clear need for additional research to allow better understanding of the cardiovascular risk and safety profile of these therapies used in the management of rheumatic and cutaneous diseases.

Cell death-inducing cytotoxicity in truncated KCNQ4 variants associated with DFNA2 hearing loss

KCNQ4 encodes the homotetrameric voltage-dependent potassium ion channel Kv7.4, and is the causative gene for autosomal dominant nonsyndromic sensorineural hearing loss, DFNA2. Dominant-negative inhibition accounts for the observed dominant inheritance of many DFNA2-associated KCNQ4 variants. In addition, haploinsufficiency has been presumed as the pathological mechanism for truncated Kv7.4 variants lacking the C-terminal tetramerization region, as they are unlikely to exert a dominant-negative inhibitory effect. Such truncated Kv7.4 variants should result in relatively mild hearing loss when heterozygous; however, this is not always the case. In this study, we characterized Kv7.4^Q71fs (c.211delC), Kv7.4^W242X (c.725G>A) and Kv7.4^A349fs (c.1044_1051del8) in heterologous expression systems and found that expression of these truncated Kv7.4 variants induced cell death. We also found similar cell death-inducing cytotoxic effects in truncated Kv7.1 (KCNQ1) variants, suggesting that the generality of our findings could account for the dominant inheritance of many, if not most, truncated Kv7 variants. Moreover, we found that the application of autophagy inducers can ameliorate the cytotoxicity, providing a novel insight for the development of alternative therapeutic strategies for Kv7.4 variants.

Summary: Expression of truncated KCNQ4 variants lacking the C-terminal tetramerization domain results in cell-death inducing cytotoxicity, providing novel insight into the development of alternative therapeutic strategies for DFNA2 hearing loss.

Rare Coding Variants Associated With Electrocardiographic Intervals Identify Monogenic Arrhythmia Susceptibility Genes: A Multi-Ancestry Analysis

BACKGROUND

Alterations in electrocardiographic (ECG) intervals are well-known markers for arrhythmia and sudden cardiac death (SCD) risk. While the genetics of arrhythmia syndromes have been studied, relations between electrocardiographic intervals and rare genetic variation at a population level are poorly understood.

METHODS

Using a discovery sample of 29 000 individuals with whole-genome sequencing from Trans-Omics in Precision Medicine and replication in nearly 100 000 with whole-exome sequencing from the UK Biobank and MyCode, we examined associations between low-frequency and rare coding variants with 5 routinely measured electrocardiographic traits (RR, P-wave, PR, and QRS intervals and corrected QT interval).

RESULTS

We found that rare variants associated with population-based electrocardiographic intervals identify established monogenic SCD genes (KCNQ1, KCNH2, and SCN5A), a controversial monogenic SCD gene (KCNE1), and novel genes (PAM and MFGE8) involved in cardiac conduction. Loss-of-function and pathogenic SCN5A variants, carried by 0.1% of individuals, were associated with a nearly 6-fold increased odds of the first-degree atrioventricular block (P=8.4×10^-5). Similar variants in KCNQ1 and KCNH2 (0.2% of individuals) were associated with a 23-fold increased odds of marked corrected QT interval prolongation (P=4×10^-25), a marker of SCD risk. Incomplete penetrance of such deleterious variation was common as over 70% of carriers had normal electrocardiographic intervals.

CONCLUSIONS

Our findings indicate that large-scale high-depth sequence data and electrocardiographic analysis identifies monogenic arrhythmia susceptibility genes and rare variants with large effects. Known pathogenic variation in conventional arrhythmia and SCD genes exhibited incomplete penetrance and accounted for only a small fraction of marked electrocardiographic interval prolongation.

Diagnostic accuracy of the response to the brief tachycardia provoked by standing in children suspected for long QT syndrome

Background

Adult long QT syndrome (LQTS) patients have inadequate corrected QT interval (QTc) shortening and an abnormal T-wave response to the sudden heart rate acceleration provoked by standing. In adults, this knowledge can be used to aid an LQTS diagnosis and, possibly, for risk stratification. However, data on the diagnostic value of the standing test in children are currently limited.

Objective

To determine the potential value of the standing test to aid LQTS diagnostics in children.

Methods

In a prospective cohort including children (≤18 years) who had a standing test, comprehensive analyses were performed including manual and automated QT interval assessments and determination of T-wave morphology changes.

Results

We included 47 LQTS children and 86 control children. At baseline, the QTc that identified LQTS children with a 90% sensitivity was 435 ms, which yielded a 65% specificity. A QTc ≥ 490 ms after standing only slightly increased sensitivity (91%, 95% confidence interval [CI]: 80%–98%) and slightly decreased specificity (58%, 95% CI: 47%–70%). Sensitivity increased slightly more when T-wave abnormalities were present (94%, 95% CI: 82%–99%; specificity 53%, 95% CI: 42%–65%). When a baseline QTc ≥ 440 ms was accompanied by a QTc ≥ 490 ms and T-wave abnormalities after standing, sensitivity further increased (96%, 95% CI: 85%–99%) at the expense of a further specificity decrease (41%, 95% CI: 30%–52%). Beat-to-beat analysis showed that 30 seconds after standing, LQTS children had a greater increase in heart rate compared to controls, which was more evidently present in LQTS boys and LQTS type 1 children.

Conclusion

In children, the standing test has limited additive diagnostic value for LQTS over a baseline electrocardiogram, while T-wave abnormalities after standing also have limited additional value. The standing test for LQTS should only be used with caution in children.

Long QT syndrome - Bench to bedside

Long QT syndrome (LQTS) is a cardiovascular disorder characterized by an abnormality in cardiac repolarization leading to a prolonged QT interval and T-wave irregularities on the surface electrocardiogram. It is commonly associated with syncope, seizures, susceptibility to torsades de pointes, and risk for sudden death. LQTS is a rare genetic disorder and a major preventable cause of sudden cardiac death in the young. The availability of therapy for this lethal disease emphasizes the importance of early and accurate diagnosis. Additionally, understanding of the molecular mechanisms underlying LQTS could help to optimize genotype-specific treatments to prevent deaths in LQTS patients. In this review, we briefly summarize current knowledge regarding molecular underpinning of LQTS, in particular focusing on LQT1, LQT2, and LQT3, and discuss novel strategies to study ion channel dysfunction and drug-specific therapies in LQT1, LQT2, and LQT3 syndromes.

Jervell and Lange-Nielsen syndrome with novel KCNQ1 and additional gene mutations

We encountered a boy with Jervell and Lange-Nielsen syndrome (JLNS) with compound heterozygous KCNQ1 mutations, maternal Trp248Phe and a novel paternal mutation, Leu347Arg. His father showed long QT (LQT) and arrhythmia. His mother was asymptomatic with no ECG abnormalities. The proband and his father had an additional mutation (SNTA1 Thr372Met), which is reportedly related to SIDS. These results suggest that multiple gene mutations influence the phenotype of KCNQ1 mutation-related arrhythmia.

A computational model of induced pluripotent stem-cell derived cardiomyocytes for high throughput risk stratification of KCNQ1 genetic variants

In the last decade, there has been tremendous progress in identifying genetic anomalies linked to clinical disease. New experimental platforms have connected genetic variants to mechanisms underlying disruption of cellular and organ behavior and the emergence of proarrhythmic cardiac phenotypes. The development of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) signifies an important advance in the study of genetic disease in a patient-specific context. However, considerable limitations of iPSC-CM technologies have not been addressed: 1) phenotypic variability in apparently identical genotype perturbations, 2) low-throughput electrophysiological measurements, and 3) an immature phenotype which may impact translation to adult cardiac response. We have developed a computational approach intended to address these problems. We applied our recent iPSC-CM computational model to predict the proarrhythmic risk of 40 KCNQ1 genetic variants. An I_Ks computational model was fit to experimental data for each mutation, and the impact of each mutation was simulated in a population of iPSC-CM models. Using a test set of 15 KCNQ1 mutations with known clinical long QT phenotypes, we developed a method to stratify the effects of KCNQ1 mutations based on proarrhythmic markers. We utilized this method to predict the severity of the remaining 25 KCNQ1 mutations with unknown clinical significance. Tremendous phenotypic variability was observed in the iPSC-CM model population following mutant perturbations. A key novelty is our reporting of the impact of individual KCNQ1 mutant models on adult ventricular cardiomyocyte electrophysiology, allowing for prediction of mutant impact across the continuum of aging. This serves as a first step toward translating predicted response in the iPSC-CM model to predicted response of the adult ventricular myocyte given the same genetic mutation. As a whole, this study presents a new computational framework that serves as a high throughput method to evaluate risk of genetic mutations based-on proarrhythmic behavior in phenotypically variable populations.

In the last decade, there has been tremendous progress in identifying genetic mutations linked to clinical diseases, such as cardiac arrhythmia. Many experimental platforms have been developed to study this link, including induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). IPSC-CMs are patient-derived cardiac cells which allow for the study of genetic variants within a patient-specific context. However, experimentally iPSC-CMs have certain limitations, including: (1) they exhibit variability in behavior within cells that are apparently genetically identical, and (2) they are immature compared to adult cardiac cells. In our study, we have developed a computational approach to model 40 genetic variants in the KCNQ1 gene and predict the proarrhythmic risk of each variant. To do this, we modeled the ionic current determined by KCNQ1, I_Ks, to fit experimental data for each mutation. We then simulated the impact of each mutation in a population of iPSC-CMs, incorporating variability across the population. We also simulated each variant in an adult cardiac cell model, providing a link between iPSC-CM response to mutants and adult cardiac cell response to the same mutants. Overall, this study provides a new computational framework to evaluate risk of genetic mutations based-on proarrhythmic behavior diverse populations of iPSC-CM models.

Is there a relationship between epicardial fat tissue thickness and Tp-Te/QT ratio in healthy individuals?

Introduction

Epicardial fat is a tissue that releases many proinflammatory and atherogenic mediators, with endocrine and paracrine effects on the heart. In this study, the implication of the EFT thickness (EFTt) on transmural dispersion of repolarisation (TDR) was analysed utilizing the T-wave peak to end interval (Tp-Te), the Tp-Te dispersion (Tp-Te (d)), and the Tp-Te/QT ratio.

Material and methods

One thousand seven hundred and thirteen subjects were enrolled in the research. The subjects were chosen to be healthy individuals, without any cardiovascular/systemic disorders or risk factors for atherosclerosis. Transthoracic echocardiography (TTE) was applied to all subjects, and EFTt was measured in both diastole and systole. The ECG measurements were taken from standard 12-lead surface ECG.

Results

Correlation analysis revealed that the EFTt is highly associated with the Tp-Te interval, Tp-Te/QT ratio, Tp-Te (d), increasing age, body mass index (BMI), body surface area (BSA), left ventricular (LV) mass, LV mass index, plasma glucose during fasting, triglycerides, and low-density lipoprotein cholesterol.

Conclusions

The study results showed that increased EFTt was associated with increased TDR values of Tp-Te, Tp-Te (d), and Tp-Te/QT ratio, even in the absence of other factors that could increase TDR and EFTt. Therefore, it can be stated that increased EFTt may cause an increase the risk for ventricular arrhythmia.

The relationship between atypical antipsychotics drugs, QT interval prolongation, and torsades de pointes: implications for clinical use

Introduction: Increased mortality has been observed in patients with mental health disorders. Specifically, exposure to antipsychotic medications conveys a greater than 2 fold risk of sudden death, thought to be mediated through effects on QT prolongation and risk of torsades de pointes.Areas covered: We review the association between antipsychotic drugs and sudden cardiac death, the physiologic basis for these associations, assessment of patients at risk, and strategies to minimize risk of sudden cardiac death.Expert opinion: Despite the prevalence of antipsychotic medication use for many decades, there remain considerable challenges in reducing the associated risk of sudden cardiac death. A structured algorithm that incorporates patient clinical factors and antipsychotic drug factors may improve risk assessment and reduce the risk of adverse cardiac events. Future advancements in genetics and artificial intelligence may allow for enhanced risk stratification and predicting response (efficacy and adverse effects) to therapy.

Critical assessment of secondary findings in genes linked to primary arrhythmia syndromes

As comprehensive sequencing technologies gain widespread use, questions about so-called secondary findings (SF) require urgent consideration. The American College of Medical Genetics and Genomics has recommended to report SF in 59 genes (ACMG SF v2.0) including four actionable genes associated with inherited primary arrhythmia syndromes (IPAS) such as catecholaminergic polymorphic ventricular tachycardia, long QT syndrome, and Brugada syndrome. Databases provide conflicting results for the purpose of identifying pathogenic variants in SF associated with IPAS at a level of sufficient evidence for clinical return. As IPAS account for a significant proportion of sudden cardiac deaths (SCD) in young and apparently healthy individuals, variant interpretation has a great impact on diagnosis and prevention of disease. Of 6381 individuals, 0.4% carry pathogenic variants in one of the four actionable genes related to IPAS: RYR2, KCNQ1, KCNH2, and SCN5A. Comparison of the databases ClinVar, Leiden Open-source Variant Database, and Human Gene Mutation Database showed impactful differences (0.2% to 1.3%) in variant interpretation improvable by expert-curation depending on database and classification system used. These data further highlight the need for international consensus regarding the variant interpretation, and subsequently management of SF in particular with regard to treatable arrhythmic disorders with increased risk of SCD.

Normative Heart-Rate Corrected Values for Repolarisation Length From Holter Recordings in Children and Adults

BACKGROUND

Normative values for heart-rate corrected repolarisation length are not available in children and are scarce in adults. We wished to define repeatability and normative values of Holter recording measurements of repolarisation length in healthy individuals using a commercially available system, and compare measurements with those from 12-lead electrocardiograms (ECGs).

METHODS

Twenty-four-hour (24-) Holter recordings were made on 99 Healthy volunteers: 52 children (7 months to 14 years) and 47 adults (≥15 yrs). Mean and peak values of QTc, and RTPc (R-wave to peak T-wave) were assessed. Bazett heart rate correction was employed for each measurement and only heart rates between 40 and 120 bpm were analysed. The end of the T-wave was defined from the zero-crossing point. QTc was also determined from 12-lead ECGs from the same population by manual measurement recording the longest QTc of leads 2 and V5. The tangent technique was used to define the end of the T-wave.

RESULTS

Interobserver repeatability: mean QTc ±15 ms (CI 3.5%), peak QTc ±25 ms (CI 4.5%), mean RTPc ±3 ms (CI 1%), peak RTPc ±44 ms (CI 11%). Mean values were very similar for <15 years and all females and were therefore amalgamated: mean (±2 SD); mean QTc 424 ms (394-454), mean RTPc 291ms (263-319). Values were lower in males ≥15 years; (mean QTc 408 ms (370-446), p<0.01; mean RTPc 274 ms (234-314), p<0.01. The highest mean QTc value was 467 ms in an adult female. QTc from 12-lead ECG: females <15 years 409 ms (384-434) males <15 years 408 ms (383-433), females ≥15 years 426 ms (401-451), males ≥15 years 385 ms (362-408).

CONCLUSIONS

Holter measurements of mean QTc and RTPc are highly repeatable. Males ≥15 years have shorter mean repolarisation length over 24 hours than males <15 years and all females. Mean QTc Holter values were on average 15-17 ms longer than QTc from 12-lead ECGs except in females >15 years.

Pre-Test Probability and Genes and Variants of Uncertain Significance in Familial Long QT Syndrome

The genetics underlying familial long QT syndrome (LQTS) are among the best characterised of all of the inherited heart conditions. Cohort and registry studies have demonstrated important genotype-phenotype correlations that are now essential in guiding clinical practice of patients with the most common three genotypes; KCNQ1 (LQT type 1), KCNH2 (LQT type 2) and SCN5A (LQT type 3). However, the growing number of genes-now more than 16-is confusing, and there is much doubt as to whether many actually cause LQTS at all. Furthermore, changes in sequencing techniques, evolving variant classification criteria and new scientific discoveries make all genes and variants subject to a continuous process of re-classification. This review discusses the nature of variant adjudication, the important concept of pre-test probability in interpreting a genetic result and how the nomenclature of LQTS is shifting in response to this new knowledge. It further discusses the role of deep phenotyping, the inclusion of evaluation of family members in interpreting a genetic test result, or even deciding if genetic testing should occur at all, and the role of specialist multidisciplinary teams to translate this continuously evolving knowledge into the best clinical advice, in partnership with referring cardiologists.

Quantitative T-wave morphology assessment from surface ECG is linked with cardiac events risk in genotype-positive KCNH2 mutation carriers with normal QTc values

INTRODUCTION

Long QT syndrome (LQTS) mutation carriers have elevated the risk of cardiac events even in the absence of QTc prolongation; however, mutation penetrance in patients with normal QTc may be reflected in abnormal T-wave shape, particularly in KCNH2 mutation carriers. We aimed to assess whether the magnitude of a three-dimensional T-wave vector (TwVM) will identify KCNH2-mutation carriers with normal QTc at risk for cardiac events.

METHODS

Adult LQT2 patients with QTc < 460 ms in men and <470 ms in women (n = 113, age 42 ± 16 years, 43% male) were compared with genotype-negative family members (n = 1007). The TwVM was calculated using T-wave amplitudes in leads V6, II, and V2 as the square root of (TV6²  + TII²  + (0.5*TV2)² ). Cox regression analysis adjusted for gender and time-dependent beta-blocker use was performed to assess cardiac event (CE) risk, defined as syncope, aborted cardiac arrest, implantable cardioverter-defibrillator therapy, or sudden death.

RESULTS

Dichotomized by median of 0.30 mV, lower TwVM was associated with elevated CE risk compared to those with high TwVM (HR = 2.95, 95% CI, 1.25-6.98, P = .014) and also remained significant after including sex and time-dependent beta-blocker usage in the Cox regression analysis (HR = 2.64, 95% CI, 1.64-4.24, P < .001). However, these associations were found only in women but not in men who had low event rates.

CONCLUSION

T-wave morphology quantified as repolarization vector magnitude using T-wave amplitudes retrieved from standard 12-lead electrocardiogram predicts cardiac events risk in LQT2 women and appears useful for risk stratification of KCNH2-mutation carriers without QTc prolongation.

Error-related brain activity as a transdiagnostic endophenotype for obsessive-compulsive disorder, anxiety and substance use disorder

BACKGROUND

Increased neural error-signals have been observed in obsessive-compulsive disorder (OCD), anxiety disorders, and inconsistently in depression. Reduced neural error-signals have been observed in substance use disorders (SUD). Thus, alterations in error-monitoring are proposed as a transdiagnostic endophenotype. To strengthen this notion, data from unaffected individuals with a family history for the respective disorders are needed.

METHODS

The error-related negativity (ERN) as a neural indicator of error-monitoring was measured during a flanker task from 117 OCD patients, 50 unaffected first-degree relatives of OCD patients, and 130 healthy comparison participants. Family history information indicated, that 76 healthy controls were free of a family history for psychopathology, whereas the remaining had first-degree relatives with depression (n = 28), anxiety (n = 27), and/or SUD (n = 27).

RESULTS

Increased ERN amplitudes were found in OCD patients and unaffected first-degree relatives of OCD patients. In addition, unaffected first-degree relatives of individuals with anxiety disorders were also characterized by increased ERN amplitudes, whereas relatives of individuals with SUD showed reduced amplitudes.

CONCLUSIONS

Alterations in neural error-signals in unaffected first-degree relatives with a family history of OCD, anxiety, or SUD support the utility of the ERN as a transdiagnostic endophenotype. Reduced neural error-signals may indicate vulnerability for under-controlled behavior and risk for substance use, whereas a harm- or error-avoidant response style and vulnerability for OCD and anxiety appears to be associated with increased ERN. This adds to findings suggesting a common neurobiological substrate across psychiatric disorders involving the anterior cingulate cortex and deficits in cognitive control.

Disease modeling of cardiac arrhythmias using human induced pluripotent stem cells

INTRODUCTION

Inherited arrhythmias are an uncommon, but malignant family of cardiac diseases that result from genetic abnormalities in the ion channels and/or structural proteins within cardiomyocytes. Given the inherent differences between species and the limited reproducibility of in vitro heterologous cell models, progress in understanding the mechanisms underlying these malignant diseases has always languished far behind the clinical science and need. The ability to study human induced pluripotent stem cells (iPSCs) derived cardiomyocytes promises to change this paradigm as patient cells have the potential to become testing platforms for disease phenotyping or therapeutic discovery.

AREAS COVERED

This review will outline methods developed to genetically reprogram adult cells into iPSCs, differentiate iPSCs into ex vivo models of adult cardiac tissue and iPSCs-based progress in exploring the mechanisms underlying pro-arrhythmic disease phenotypes.

EXPERT OPINION

Despite being discovered less than 15 years ago, several studies have successfully leveraged iPSCs-derived cardiomyocytes to study malignant arrhythmogenic diseases. These models promise to increase our understanding of the pathophysiology underlying these complex diseases and may identify personalized approaches to treatment.

Cardiac Channelopathies: Recognition, Treatment, Management

The discovery of the human genome has ushered in a new era of molecular testing, advancing our knowledge and ability to identify cardiac channelopathies. Genetic variations can affect the opening and closing of the potassium, sodium, and calcium channels, resulting in arrhythmias and sudden death. Cardiac arrhythmias caused by disorders of ion channels are known as cardiac channelopathies. Nurses are important members of many interdisciplinary teams and must have a general understanding of the pathophysiology of the most commonly encountered cardiac channelopathies, electrocardiogram characteristics, approaches to treatment, and care for patients and their families. This article provides an overview of cardiac channelopathies that nurses might encounter in an array of clinical and research settings, focusing on the clinically relevant features of long QT syndrome, short QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and arrhythmogenic right ventricular dysplasia/cardiomyopathy.

New formula for defining "normal" and "prolonged" QT in patients with bundle branch block

OBJECTIVES

To predict the QT interval in the presence of normal QRS for patients with left bundle branch block (LBBB).

BACKGROUND

There is no acceptable method for simple and reliable QT correction for patients with bundle branch block (BBB).

METHODS

We measured the QT interval in patients with new onset LBBB who had a recent electrocardiogram with narrow QRS for comparison. 48 patients who developed in-hospital LBBB were studied. Patients who had similar heart rate before and after LBBB were included. We used linear regression, the Bogossian method, and our new fixed QRS replacement method to evaluate the most reliable correction method.

RESULTS

JTc (QTc-QRS) interval was preserved before and after LBBB (328.9 ± 25.4 ms before LBBB vs. 327.3 ms post LBBB (p = 0.550). Mean predicted preLBBB QTc difference was 1.3 ms, -21.3 ms and 1.6 ms for the three methods respectively (p < 0.001 for Bogossian comparison with the other methods). Coefficients of correlation (R) between actual preLBBB QTc with predicted preLBBB QTc were 0.707, 0.683 and 0.665 respectively (p > 0.3 for R comparisons between all methods). The average absolute difference in preLBBB QTc was 15.5 ms and 16.7 ms for the regression and fixed-gender methods (p value between the two = 0.321) and 25.5 ms for the Bogossian method, which was found to be significantly underperforming.

CONCLUSIONS

In patients with LBBB, replacing of the QRS duration after deriving the QTc interval with a fixed value of 88 ms for female and 95 ms for male provides a simple and reliable method for predicting the QTc before the development of LBBB.

Ten-year experience in atenolol use and exercise evaluation in children with genetically proven long QT syndrome

Background

Due to its availability, atenolol is the primary beta-blocker used in Australia for children with long QT syndrome. There is limited data on long-term follow-up of its use.

Methods

A single-tertiary-center, retrospective, observational study investigating all children and adolescents who had genetically proven long QT syndrome type 1 (LQT1) and type 2 (LQT2) was conducted. Their pretreatment exercise tests were evaluated for QTc intervals into the recovery phase of exercise.

Results

Eighty six patients were identified (LQT1, 67, and LQT2, 19) from 2004 to 2014. The majority (86%) of patients were initially referred for family screening. Atenolol was administered at a mean dose of 1.58 ± 0.51 mg/kg/day. During the median follow-up period of 4.29 years, only one proband developed ventricular arrhythmia whilst taking atenolol, No patient had cardiac arrest or aborted cardiac arrest. With respect to side effects of atenolol, only two patients had intolerable side effects necessitating changes of medication. Evaluation of exercise tests (pretreatment) demonstrated that corrected QT (QTc) intervals at 2–3 min into the recovery phase of exercise were significantly prolonged for LQT1 patients. LQT1 patients with transmembrane mutation had longer QTc intervals than their C-terminus mutation counterparts, reaching statistical significance at 3 min into the recovery phase of exercise.

Conclusions

Atenolol is an effective treatment for genetically proven LQT1 and LQT2 children and adolescents, with good tolerability. In LQT1 patients, QTc intervals at 2–3 min into the recovery phase of exercise were significantly prolonged, particularly in patients with transmembrane mutations.

A New Formula for Estimating the True QT Interval in Left Bundle Branch Block

INTRODUCTION

QT prolongation is an independent risk factor for cardiac mortality. Left bundle branch block (LBBB) is more common in patients as they age. Widening of the QRS in LBBB causes false QT prolongation and thus makes true QT assessment difficult. We aimed to develop a simple formula to achieve a good estimate of the QT interval in the presence of LBBB.

METHODS AND RESULTS

To determine the effect of QRS duration on the QT interval, QRS and QT were measured in sinus rhythm and during right ventricular apical pacing in 62 patients (age 55 ± 11 years, 60% male) undergoing electrophysiology studies. A QT formula for LBBB (QT-LBBB) was derived based on the effect of increased QRSLBBB on QTLBBB . The predictive accuracy of the QT-LBBB formula was then tested in 22 patients (age 66 ± 13 years, 64% male) with intermittent LBBB with comparisons to prior QT formulae and JT index. On average, the net increase in QRSLBBB constituted 92% of the net increase in QTLBBB . A new formula, QT-LBBB = QTLBBB - (0.86 * QRSLBBB - 71), which takes the net increase in QRSLBBB into account, best predicted the QT interval with heart rate corrected QTc in the test set of LBBB ECGs when compared to the baseline value and prior formulae.

CONCLUSION

The QT-LBBB formula developed in this study best estimates the true QT interval in the presence of LBBB. It is simple and therefore can be easily utilized in clinical practice.

KCNQ1 p.L353L affects splicing and modifies the phenotype in a founder population with long QT syndrome type 1

Background

Variable expressivity and incomplete penetrance between individuals with identical long QT syndrome (LQTS) causative mutations largely remain unexplained. Founder populations provide a unique opportunity to explore modifying genetic effects. We examined the role of a novel synonymous KCNQ1 p.L353L variant on the splicing of exon 8 and on heart rate corrected QT interval (QTc) in a population known to have a pathogenic LQTS type 1 (LQTS1) causative mutation, p.V205M, in KCNQ1-encoded Kv7.1.

Methods

419 adults were genotyped for p.V205M, p.L353L and a previously described QTc modifier (KCNH2-p.K897T). Adjusted linear regression determined the effect of each variant on QTc, alone and in combination. In addition, peripheral blood RNA was extracted from three controls and three p.L353L-positive individuals. The mutant transcript levels were assessed via qPCR and normalised to overall KCNQ1 transcript levels to assess the effect on splicing.

Results

For women and men, respectively, p.L353L alone conferred a 10.0 (p=0.064) ms and 14.0 (p=0.014) ms increase in QTc and in men only a significant interaction effect in combination with the p.V205M (34.6 ms, p=0.003) resulting in a QTc of ∼500 ms. The mechanism of p.L353L's effect was attributed to approximately threefold increase in exon 8 exclusion resulting in ∼25% mutant transcripts of the total KCNQ1 transcript levels.

Conclusions

Our results provide the first evidence that synonymous variants outside the canonical splice sites in KCNQ1 can alter splicing and clinically impact phenotype. Through this mechanism, we identified that p.L353L can precipitate QT prolongation by itself and produce a clinically relevant interactive effect in conjunction with other LQTS variants.

Vectorcardiography identifies patients with electrocardiographically concealed long QT syndrome

BACKGROUND

Long QT syndrome (LQTS) and genotypic subtypes are associated with distinctive T-wave patterns, arrhythmogenic triggers, and corrected QT (QTc) interval risk associations. Twenty percent of patients with LQTS have normal QTc values, defined as electrographically concealed LQTS (ecLQTS). Vectorcardiography (VCG) has value for sudden cardiac death risk assessment.

OBJECTIVE

The purpose of this study was to determine the use of VCG to identify patients with ecLQTS.

METHODS

We performed a retrospective analysis in patients with ecLQTS with resting QTc values <440 ms. Computerized derivation of the spatial mean and peak QRS-T angles, QTpeak, Tpeak-Tend (angle between QRS and T-wave peak amplitudes in 3-dimensional space), and T-wave eigenvalues (TwEVs; amplitudes [in microvolts] for each of the first 4 TwEVs were derived from the 12-lead electrocardiogram) was performed. The results were compared with those for healthy controls. Intergenotype differences were analyzed.

RESULTS

Of 610 patients with LQTS, 169 patients (28%) had ecLQTS (86 (51%) men; mean age 22 ± 16 years; mean QTc interval 422 ± 14 ms). There were 519 healthy controls (44% men; mean age 19.8 ± 13.8 years) with a mean QTc interval of 426 ± 28 ms. Among VCG parameters, QTpeak and TwEVs significantly differentiated patients with ecLQTS from controls (P ≤ .01 for each) as well as differentiated KCNQ1-encoded type 1 LQTS (ecLQT1), KCNH2-encoded type 2 LQTS (ecLQT2), and SCN5A-encoded type 3 LQTS (ecLQT3) from controls (P < .01). ecLQT3 was differentiated from controls and ecLQT1 and ecLQT2 by the fourth TwEV (P < .01 for each). The fourth TwEV differentiated symptomatic patients with ecLQTS from asymptomatic patients with ecLQTS (P < .01).

CONCLUSION

ecLQTS can be distinguished from controls using QTpeak. ecLQT3 was best differentiated by the fourth TwEV. VCG may facilitate familial diagnostic anticipation of LQTS status before the completion of mutation-specific genetic testing even with normal resting QTc values.

International criteria for electrocardiographic interpretation in athletes: Consensus statement

Sudden cardiac death (SCD) is the leading cause of mortality in athletes during sport. A variety of mostly hereditary, structural or electrical cardiac disorders are associated with SCD in young athletes, the majority of which can be identified or suggested by abnormalities on a resting 12-lead electrocardiogram (ECG). Whether used for diagnostic or screening purposes, physicians responsible for the cardiovascular care of athletes should be knowledgeable and competent in ECG interpretation in athletes. However, in most countries a shortage of physician expertise limits wider application of the ECG in the care of the athlete. A critical need exists for physician education in modern ECG interpretation that distinguishes normal physiological adaptations in athletes from distinctly abnormal findings suggestive of underlying pathology. Since the original 2010 European Society of Cardiology recommendations for ECG interpretation in athletes, ECG standards have evolved quickly, advanced by a growing body of scientific data and investigations that both examine proposed criteria sets and establish new evidence to guide refinements. On 26-27 February 2015, an international group of experts in sports cardiology, inherited cardiac disease, and sports medicine convened in Seattle, Washington (USA), to update contemporary standards for ECG interpretation in athletes. The objective of the meeting was to define and revise ECG interpretation standards based on new and emerging research and to develop a clear guide to the proper evaluation of ECG abnormalities in athletes. This statement represents an international consensus for ECG interpretation in athletes and provides expert opinion-based recommendations linking specific ECG abnormalities and the secondary evaluation for conditions associated with SCD.

Value of the "Standing Test" in the Diagnosis and Evaluation of Beta-blocker Therapy Response in Long QT Syndrome

INTRODUCTION AND OBJECTIVES

Patients with congenital long QT syndrome (LQTS) have an abnormal QT adaptation to sudden changes in heart rate provoked by standing. The present study sought to evaluate the standing test in a cohort of LQTS patients and to assess if this QT maladaptation phenomenon is ameliorated by beta-blocker therapy.

METHODS

Electrographic assessments were performed at baseline and immediately after standing in 36 LQTS patients (6 LQT1 [17%], 20 LQT2 [56%], 3 LQT7 [8%], 7 unidentified-genotype patients [19%]) and 41 controls. The corrected QT interval (QTc) was measured at baseline (QTc_supine) and immediately after standing (QTc_standing); the QTc change from baseline (ΔQTc) was calculated as QTc_standing - QTc_supine. The test was repeated in 26 patients receiving beta-blocker therapy.

RESULTS

Both QTc_standing and ΔQTc were significantly higher in the LQTS group than in controls (QTc_standing, 528 ± 46ms vs 420 ± 15ms, P < .0001; ΔQTc, 78 ± 40ms vs 8 ± 13ms, P < .0001). No significant differences were noted between LQT1 and LQT2 patients. Typical ST-T wave patterns appeared after standing in LQTS patients. Receiver operating characteristic curves of QTc_standing and ΔQTc showed a significant increase in diagnostic value compared with the QTc_supine (area under the curve for both, 0.99 vs 0.85; P < .001). Beta-blockers attenuated the response to standing in LQTS patients (QTc_standing, 440 ± 32ms, P < .0001; ΔQTc, 14 ± 16ms, P < .0001).

CONCLUSIONS

Evaluation of the QTc after the simple maneuver of standing shows a high diagnostic performance and could be important for monitoring the effects of beta-blocker therapy in LQTS patients.

Neurological Complications of Cardiac Disease

This article focuses on the complex interactions between the cardiovascular and neurologic systems. Initially, we focus on neurological complications in children with congenital heart disease both secondary to the underlying cardiac disease and complications of interventions. We later discuss diagnosis and management of common syncope syndromes with emphasis on vasovagal syncope. We also review the diagnosis, classification, and management of children and adolescents with postural orthostatic tachycardia syndrome. Lastly, we discuss long QT syndrome and sudden unexpected death in epilepsy (SUDEP), reviewing advances in genetics and current knowledge of pathophysiology of these conditions. This article attempts to provide an overview of these disorders with focus on pathophysiology, advances in molecular genetics, and current medical interventions.

Long QTc Interval and Torsade de Pointes Caused by Fluconazole

Objective:

To describe a patient who developed torsade de pointes while being treated with fluconazole.

Case Summary:

A 33-year-old woman with a 5 year history of systemic lupus erythematosus was admitted to the intensive care unit because of respiratory insufficiency due to Candida albicans pneumonia. Therapy with intravenous fluconazole 200 mg/day, with dose later adjusted according to her renal function, was started. Prolongation of the QTc interval and torsade de pointes occurred. Initially, domperidone, which had been initiated the day before fluconazole, was suspected as the possible cause and was discontinued; ultimately, both drugs were discontinued. However, torsade de pointes recurred several weeks later when the patient was treated with fluconazole for a second time and disappeared again on withdrawal of the drug. According to the Naranjo probability scale, this adverse reaction was highly probable.

Discussion:

The risk of torsade de pointes does not correlate in a linear fashion with prolongation of the QTc interval, but an interval beyond 500 msec is considered a significant risk factor. Given that both fluconazole and domperidone are metabolized by the cytochrome P450 system, they may intensify each other's proarrhythmic effects, particularly in patients with concurrent renal dysfunction. These risks are of particular concern in patients whose baseline QTc interval is prolonged for any reason.

Conclusions:

From the case history, as well as use of the Naranjo scale, we concluded that fluconazole was the highly probable cause of the development of torsade de pointes in our patient.

Mutation analysis for the detection of long QT-syndrome (LQTS) associated SNPs

Congenital long QT-syndrome (LQTS) is an inherited cardiac arrhythmia, which is characterized by a prolonged QT interval which predisposes to sudden cardiac death due to ventricular arrhythmias. The altered functions are based on different mutations in LQTS-associated genes. In this study, we performed a mutation analysis for the detection of 125 LQTS-associated single nucleotide polymorphisms (SNPs) focused on the genes KCNQ1, KCNH2, and SCN5A by using the SNaPshot multiplex minisequencing technique. Furthermore, we investigated 152 autopsy-negative cases from younger adults and infants, as well as samples from patients with clinically suspicion for LQTS, in which we found two types of variations.