Long-QT syndrome

Pathophysiological effects of SARS-CoV-2 infection on the cardiovascular system and its clinical manifestations-a mini review

Coronavirus disease 2019 (COVID-19) is a viral infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). COVID-19 may have a mild presentation, with few symptoms, or progress to a severe condition, characterized by generalized inflammation, systemic microvascular involvement, coagulopathy, and pulmonary and cardiovascular complications. Men present with more severe symptoms than women, especially men who are older and who present with comorbidities such as hypertension, diabetes mellitus, and a history of atherosclerotic diseases. Owing to its association with endothelial dysfunction, inflammation, thrombosis, and microvascular obstruction, SARS-CoV-2 infection can cause lesions in several organs, including the myocardium and the coronary arterial bed, which can result in clinical manifestations involving the cardiovascular system. In this mini review, we summarize the effects of SARS-CoV-2 infection on the cardiovascular system in both children and adults and characterize the various clinical manifestations associated with this disease.

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

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

Hypocalcemia-Induced QT Interval Prolongation

An 87-year-old man with a history of transcatheter aortic valve replacement, pulmonary hypertension, diastolic dysfunction with preserved systolic function, and myelofibrosis had a 12-lead ECG showed a prolonged QT interval of 508 ms with heart-rate correction placing it in the 99th percentile of the population. Reduction in the dose of furosemide and calcium supplementation increased serum calcium and shortened the QT interval. This case provides an opportunity to examine newer concepts for the understanding of the mechanisms by which hypocalcemia might induce QT prolongation. Hypocalcemia likely produces corrected QT interval prolongation primarily through a calcium-dependent inactivation (CDI) mechanism on the L-type calcium channel (LTCC). Lower extracellular calcium leads to a decreased ICaL, subsequently causing intracellular calcium to take longer to reach the critical threshold to induce CDI of the LTCC. The resulting prolonged repolarization of the ventricular myocyte can lead to early after-depolarizations and ensuing life-threatening ventricular arrhythmias. Genetic polymorphisms in Ca2+-binding protein calmodulin which can prolong QT, underscore the role for disturbances of intracellular myocardial calcium handling in arrhythmogenesis. Hypocalcemia is an under-recognized cause of QT prolongation and should be taken into careful consideration in patients presenting with incidental findings of a prolonged QT interval.

Electrocardiographic manifestations of COVID-19: Effect on cardiac activation and repolarization

BACKGROUND

Prolonged QT intervals are reported in patients with COVID-19. Additionally, virus particles in heart tissue and abnormal troponin levels have been reported. Consequently, we hypothesize that cardiac electrophysiologic abnormalities may be associated with COVID-19.

METHODS

This is a retrospective study between March 15^th, 2020 and May 30^th, 2020 of 828 patients with COVID-19 and baseline ECG. Corrected QT (QTc) and QRS intervals were measured from ECGs performed prior to intervention or administration of QT prolonging drugs. QTc and QRS intervals were evaluated as a function of disease severity (patients admitted versus discharged; inpatients admitted to medical unit vs ICU) and cardiac involvement (troponin elevation >0.03 ng/ml, elevated B-natriuretic peptide (BNP) or NT pro-BNP >500 pg/ml). Multivariable analysis was used to test for significance. Odds ratios for predictors of disease severity and mortality were generated.

FINDINGS

Baseline QTc of inpatients was prolonged compared to patients discharged (450.1±30.2 versus 423.4±21.7  msec, p<0.0001) and relative to a control group of patients with influenza (p=0.006). Inpatients with abnormal cardiac biomarkers had prolonged QTc and QRS compared to those with normal levels (troponin - QTc: 460.9±34.6 versus 445.3±26.6  msec, p<0.0001, QRS: 98.7±24.6 vs 90.5±16.9  msec, p<0.0001; BNP - QTc: 465.9±33.0 versus 446.0±26.2  msec, p<0.0001, QRS: 103.6±25.3 versus 90.6±17.6 msec, p<0.0001). Findings were confirmed with multivariable analysis (all p<0.05). QTc prolongation independently predicted mortality (8.3% increase in mortality for every 10  msec increase in QTc; OR 1.083, CI [1.002, 1.171], p=0.04).

INTERPRETATION

QRS and QTc intervals are early markers for COVID-19 disease progression and mortality. ECG, a readily accessible tool, identifies cardiac involvement and may be used to predict disease course.

FUNDING

St. Francis Foundation.

Using Medicare Data to Assess the Proarrhythmic Risk of Non-Cardiac Treatment Drugs that Prolong the QT Interval in Older Adults: An Observational Cohort Study

Introduction

Serious cardiac arrhythmias caused by QT-prolonging drugs are difficult to predict based on physiological measurement and pre-approval clinical trials. Post-marketing surveillance and monitoring are important to generate safety data.

Objectives

To assess whether an observational study using Medicare claims data can detect the arrhythmogenic risk of QT-prolonging drugs.

Methods

We identified 17 QT-prolonging drugs with known risk of torsades des pointes (TdP) that were not used to treat cardiac arrhythmias. Amoxicillin and four serotonin-norepinephrine reuptake inhibitors (SNRIs) were used as controls. De-identified claims data of 1.2 million Medicare beneficiaries were accessed. Two separate Cox regressions were done for short-term and chronic-use drugs. The primary outcome was a composite of ventricular arrhythmias and/or sudden death, identified by ICD diagnostic codes. We explored the independent effect of each study drug on the outcomes. Other covariates included patient demographics, comorbidities, and known risk factors for drug-induced cardiac arrhythmia.

Results

We were able to detect increased risk in 14 of 17 study drugs (82.3%), and none of the control drugs. Among the fluoroquinolones, ciprofloxacin was the safest. Azithromycin and clarithromycin were relatively safe compared to erythromycin. Compared to SNRIs, both citalopram and escitalopram had increased risk, more so with escitalopram than citalopram. Comorbidities associated with increased risk included ischemic heart disease, electrolyte imbalance, bradycardia, acute myocardial infarction, heart failure, and chronic kidney and liver disease.

Conclusion

Medicare data can be utilized for post-marketing surveillance and monitoring of the proarrhythmic risk of QT-prolonging drugs in older adults.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40801-021-00230-1.

Drug Development and the Use of Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Disease Modeling and Drug Toxicity Screening

: Over the years, numerous groups have employed human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) as a superb human-compatible model for investigating the function and dysfunction of cardiomyocytes, drug screening and toxicity, disease modeling and for the development of novel drugs for heart diseases. In this review, we discuss the broad use of iPSC-CMs for drug development and disease modeling, in two related themes. In the first theme-drug development, adverse drug reactions, mechanisms of cardiotoxicity and the need for efficient drug screening protocols-we discuss the critical need to screen old and new drugs, the process of drug development, marketing and Adverse Drug reactions (ADRs), drug-induced cardiotoxicity, safety screening during drug development, drug development and patient-specific effect and different mechanisms of ADRs. In the second theme-using iPSC-CMs for disease modeling and developing novel drugs for heart diseases-we discuss the rationale for using iPSC-CMs and modeling acquired and inherited heart diseases with iPSC-CMs.

Update on Brugada Syndrome 2019

Brugada syndrome (BrS) was first described in 1992 as an aberrant pattern of ST segment elevation in right precordial leads with a high incidence of sudden cardiac death (SCD) in patients with structurally normal heart. It represents 4% ∼ 12% of all SCD and 20% of SCD in patients with structurally normal heart. The extremely wide genetic heterogeneity of BrS and other inherited cardiac disorders makes this new area of genetic arrhytmology a fascinating one. This review shows the state of art in diagnosis, management, and treatment of BrS focusing all the aspects regarding genetics and Preimplant Genetic Diagnosis (PGD) of embryos, overlapping syndromes, risk stratification, familial screening, and future perspectives. Moreover the review analyzes key points like electrocardiogram (ECG) criteria, the role of electrophysiological study (the role of ventricular programmed stimulation and the need of universal accepted protocol) and the importance of a correct risk stratification to clarify when implantable cardioverter defibrillator or a close follow-up is needed. In recent years, cardiovascular studies have been focused on personalized risk assessment and to determine the most optimal therapy for an individual. The BrS syndrome has also benefited of these advances although there remain several key points to be elucidated. We will review the present knowledge, progress made, and future research directions on BrS.

Gene Patents in Canada: Is There a New Legal Landscape?

In 2016, the Children's Hospital of Eastern Ontario (CHEO) announced the settlement of its patent lawsuit against US-based Transgenomic, Inc. At issue in the case was CHEO's ability to test for gene mutations associated with long QT syndrome (LQTS) that are described in Transgenomic's patents. CHEO challenged the patents as invalid, and Transgenomic ultimately agreed to license them on a royalty-free basis to CHEO and other healthcare institutions for LQTS testing and research. While widely celebrated in the media, the ethical rhetoric surrounding the settlement has at times obscured the practical and legal context in which it was made and will operate. Here, we provide a nuanced account of the events surrounding the settlement and its implications for research and clinical care. Although the settlement is remarkable for the transparency of its terms and its inclusion of a license intended to benefit unaffiliated test providers, we conclude that another significant implication of the settlement may be its elimination of the opportunity to clarify an increasingly confused area of Canadian law against a backdrop of continued international controversy surrounding the patenting of genes and gene-based diagnostic and therapeutic methods.

Human Induced Pluripotent Stem Cell (hiPSC)-Derived Cells to Assess Drug Cardiotoxicity: Opportunities and Problems

Billions of US dollars are invested every year by the pharmaceutical industry in drug development, with the aim of introducing new drugs that are effective and have minimal side effects. Thirty percent of in-pipeline drugs are excluded in an early phase of preclinical and clinical screening owing to cardiovascular safety concerns, and several lead molecules that pass the early safety screening make it to market but are later withdrawn owing to severe cardiac side effects. Although the current drug safety screening methodologies can identify some cardiotoxic drug candidates, they cannot accurately represent the human heart in many aspects, including genomics, transcriptomics, and patient- or population-specific cardiotoxicity. Despite some limitations, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a powerful and evolving technology that has been shown to recapitulate many attributes of human cardiomyocytes and their drug responses. In this review, we discuss the potential impact of the inclusion of the hiPSC-CM platform in premarket candidate drug screening.

A mutation in the CACNA1C gene leads to early repolarization syndrome with incomplete penetrance: A Chinese family study

Background

Early repolarization syndrome (ERS) may be a near-Mendelian or an oligogenic disease; however, no direct evidence has been provided to support this theory.

Methods and results

We described a large Chinese family with nocturnal sudden cardiac death induced by ERS in most of the young male adults. One missense mutation (p.Q1916R) was found in the major subunit of the L-type calcium channel gene CACNA1C by the direct sequencing of candidate genes. A concomitant gain-of-function variant in the sodium channel gene SCN5A (p.R1193Q) was found to rescue the phenotype of the female CACNA1C-Q1916R mutation carriers, which led to the incomplete penetrance. The functional studies, via the exogenous expression approach, revealed that the CACNA1C-Q1916R mutation led to a decreasing L-type calcium current and the protein expression defect. The decreased calcium current produced by the mutant channel was improved by isoproterenol but exacerbated by testosterone. The effects of CACNA1C-Q1916R mutation and testosterone on cellular electrophysiology were further confirmed by the human ventricular action potential simulation.

Conclusions

Our results demonstrated that the loss-of-function CACNA1C-Q1916R mutation contributed to ERS-related sudden cardiac death, and the phenotypic incomplete penetrance was modified by the SCN5A-R1193Q variant and sex. These findings suggest that phenotypes of ERS are modified by multiple genetic factors, which supports the theory that ERS may be an oligogenic disease.

High incidence of functional ion-channel abnormalities in a consecutive Long QT cohort with novel missense genetic variants of unknown significance

The Long QT syndrome (LQTS) is a disorder characterized by a prolongation of the QT interval and a propensity to ventricular tachyarrhythmias, which may lead to syncope, cardiac arrest, or sudden death. Our objective was to (1) determine the incidence of variants with unknown significance (VUS) in a cohort of consecutive LQTS patients and (2) to determine the percentage of those with novel missense VUS that have demonstrable functional channel abnormalities from a single referral center. We performed genetic screening of candidate genes in 39 probands with a diagnosis of LQTS to identify mutations and variants. Seven variants of unknown significance were identified, six were missense variants and one was a splice site variant. We investigated the six novel missense VUS in five patients; three missense variants in KCNQ1 (L236R, W379R, Y522S) and three missense variants in KCNH2 (R35W, S620G, V491I). We employed two-electrode voltage-clamp experiments in Xenopus laevis oocytes and confocal imaging to characterize the novel missense mutations functionally. We revealed electrophysiological and trafficking loss-of-function phenotypes. This report emphasizes the frequency of adverse channel function in patients with LQTS and the importance of heterologous studies to define channel function.

Are ECG monitoring recommendations before prescription of QT-prolonging drugs applied in daily practice? The example of haloperidol

PURPOSE

Monitoring of the QT duration by electrocardiography (ECG) prior to treatment is frequently recommended in the label of QT-prolonging drugs. It is, however, unknown how often general practitioners in daily clinical practice are adhering to these risk-minimization measures. We assessed the frequency of ECG measurements in patients where haloperidol was initiated in primary care.

METHODS

Patients (≥18 years) with a first prescription of haloperidol in the UK Clinical Practice Research Datalink (2009-2013) were included. The proportion of ECGs made was determined in two blocks of 4 weeks: during the exposure period when haloperidol was initiated, and during the control period, 1 year before. Conditional logistic regression analysis was applied to calculate the relative risk of having an ECG in the exposure period compared with the control period. Subgroup analyses were performed to assess the proportion of ECG measurements in patients with one or more additional risk factors for QT prolongation.

RESULTS

In total, 3420 patients were prescribed haloperidol during the exposure period, and 1.8% of them had an ECG at treatment initiation, compared with 0.8% during the control period (relative risk [RR] 2.4 [1.5-3.8]). Of the patients with additional risk factors for QT prolongation, 1.9% of the patients had an ECG at initiation of the prescription, compared with 1.0% during the control period (RR 2.1 [1.2-3.5]).

CONCLUSIONS

Compliance with recommendations to perform an electrocardiogram when starting a new QT-prolonging drug is extremely low, when haloperidol is taken as an example.

QT interval heterogeneities induced through local epicardial warming/cooling. An experimental study

INTRODUCTION AND OBJECTIVES

Abnormal QT interval durations and dispersions have been associated with increased risk of ventricular arrhythmias. The present study examines the possible arrhythmogenic effect of inducing QT interval variations through local epicardial cooling and warming.

METHODS

In 10 isolated rabbit hearts, the temperatures of epicardial regions of the left ventricle were modified in a stepwise manner (from 22°C to 42°C) with simultaneous electrogram recording in these regions and in others of the same ventricle. QT and activation-recovery intervals were determined during sinus rhythm, whereas conduction velocity and ventricular arrhythmia induction were determined during programmed stimulation.

RESULTS

In the area modified from baseline temperature (37°C), the QT (standard deviation) was prolonged with maximum hypothermia (195 [47] vs 149 [12] ms; P<.05) and shortened with hyperthermia (143 [18] vs 152 [27] ms; P<.05). The same behavior was displayed for the activation-recovery interval. The conduction velocity decreased with hypothermia and increased with hyperthermia. No changes were seen in the other unmodified area. Repetitive responses were seen in 5 experiments, but no relationship was found between their occurrence and hypothermia or hyperthermia (P>.34).

CONCLUSIONS

In the experimental model employed, local variations in the epicardial temperature modulate the QT interval, activation-recovery interval, and conduction velocity. Induction of heterogeneities did not promote ventricular arrhythmia occurrence.

Prolonged QT Syndrome in a 27-Year-Old Female Presenting as a Cardiac Arrest after Elective Surgery

Cardiac arrest is a true medical emergency and clinicians should base the management on American Heart Association advanced cardiac life support algorithm. The potential triggers of cardiac arrest should be sought. We present a case of a 27-year-old female who developed cardiac arrest and was later found to have congenital long QT syndrome. The patient's outcome was favorable. Discussion of the key management options will be discussed in the text.

Octreotide-induced long QT syndrome in a child with congenital hyperinsulinemia and a novel missense mutation (p.Met115Val) in the ABCC8 gene

BACKGROUND/AIMS

Congenital hyperinsulinism (CHI) denotes an inappropriate secretion of insulin from pancreatic β-cells in the presence of a low blood glucose level due to various genetic causes. Diazoxide is the first-line medical treatment for CHI. In case of failure, a somatostatin analogue called octreotide is used. A prolonged QT interval is an unusual side effect of octreotide which can be lethal if unrecognized.

CASE PRESENTATION

We report on a 35-day-old infant who was diagnosed with CHI on the 3rd day of his life and underwent pancreatectomy due to failure of medical treatment at 8 months. His genetic analysis revealed a compound heterozygosity for a novel missense mutation (p.Met115Val) and a nonsense mutation (p.Trp1339X) in the ABCC8 gene. Furthermore, at the 6th month of follow-up, a long QT (0.49 s) was determined by ECG examination, which was normalized following discontinuation of octreotide treatment after pancreatectomy. Thus, the long QT was considered to be secondary to octreotide medication.

CONCLUSION

We recommend ECG monitoring before and during octreotide treatment in order to recognize a prolonged QT interval and to prevent related complications in cases with congenital hyperinsulinemia.

Roles of PKC Isoforms in PMA-Induced Modulation of the hERG Channel (Kv11.1)

Protein kinases C (PKC) modulate the activity of the Kv11.1 ion channel current (hERG). However, the differential effects of specific PKC subtypes on the biophysics of the channel are unknown. The pharmaceutical tools to selectively modulate PKC subtypes are not membrane permeable and must be added directly to the intracellular solution in electrophysiology studies. Here, the PatchXpress electrophysiology robot was used to voltage clamp up to 16 cells simultaneously yet asynchronously across individual Sealchip chambers. The precision afforded by repeats of automation procedures minimized the experimental errors typical of these assays. Eight well-known PKC selective peptidomimmetics and general synthetic modulators were used to modulate the protein-protein interactions between hERG and the major PKC subtypes. We identified a specific role for the PKCε inhibitory peptidomimmetics in decreasing PKC-induced hERG τ activation (80%) and half-maximum activation voltage (90%) at steady state; a specific PKCε activator exhibited the opposite effect. Disruption of PKCβ, PKCα, and PKCη interactions also showed significant effects albeit of lower magnitudes. The effect of PKCδ inhibitor was only marginal. A significant correlation was observed between the shifts in τ activation and half-maximum voltage at steady state (R(2)= 0.85). Peak current amplitudes and time constant of deactivation remained unaffected in all conditions.

Modeling heart disease in a dish: from somatic cells to disease-relevant cardiomyocytes

A scientific milestone that has tremendously impacted the cardiac research field has been the discovery and establishment of human-induced pluripotent stem cells (hiPSC). Key to this discovery has been uncovering a viable path in generating human patient and disease-specific cardiac cells to dynamically model and study human cardiac diseases in an in vitro setting. Recent studies have demonstrated that hiPSC-derived cardiomyocytes can be used to model and recapitulate various known disease features in hearts of patient donors harboring genetic-based cardiac diseases. Experimental drugs have also been tested in this setting and shown to alleviate disease phenotypes in hiPSC-derived cardiomyocytes, further paving the way for therapeutic interventions for cardiac disease. Here, we review state-of-the-art methods to generate high-quality hiPSC and differentiate them towards cardiomyocytes as well as the full range of genetic-based cardiac diseases, which have been modeled using hiPSC. We also provide future perspectives on exploiting the potential of hiPSC to compliment existing studies and gain new insights into the mechanisms underlying cardiac disease.

Sudden cardiac death in young athletes: preparticipation screening for underlying cardiovascular abnormalities and approaches to prevention

The study of sudden cardiac death (SCD) in athletes has received more interest in the medical and lay press over the past few years. Professional athletes represent ideals of fitness and health, and the sudden death of prominent athletes can come as a shock. Underlying occult cardiovascular disorders are the most common cause of SCD in athletes. Unfortunately, because these disorders rarely present clinically, their initial manifestation is often a fatal event. Due to this, much attention has turned to both primary and secondary prevention. Primary prevention includes preparticipation screening and secondary prevention includes having automatic external defibrillators available at sporting events. This article summarizes the most common causes of athletic-related cardiac arrest and evaluates the screening methods used to screen for these conditions. The general sentiment is that we need to more effectively identify athletes who are at risk for SCD, but how to do so using an efficient screening system and in a cost-effective manner have not been determined.

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.

Cardiac arrhythmias in adult patients with asthma

OBJECTIVE

The pathogenesis of cardiac arrhythmias in asthma patients has not been fully elucidated. Adverse drug effects, particularly those of β2-mimetics, may play a role. The aim of this study was to determine whether asthma is associated with the risk of cardiac arrhythmias and electrocardiographic characteristics of arrhythmogenicity (ECG) and to explore the role of β2-mimetics.

METHODS

A cross-sectional study was conducted among 158 adult patients with a diagnosis of asthma and 6303 participants without asthma from the cohort of the Utrecht Health Project-an ongoing, longitudinal, primary care-based study. All patients underwent extensive examinations, including resting 12-lead electrocardiogram (ECG) and pulmonary function tests. The primary outcome was "any arrhythmia on the ECG" (including tachycardia, bradycardia, premature ventricular contraction (PVC), and atrial fibrillation or flutter). Secondary outcomes were tachycardia, bradycardia, PVC, atrial fibrillation or flutter, mean heart rate, mean corrected QT (QTc) interval length, and prolonged QTc interval.

RESULTS

Tachycardia and PVCs were more prevalent in patients with asthma (3% and 4%, respectively) than those without asthma (0.6%, p < .001; 2%, p = .03, respectively). The prevalence of QTc interval prolongation was similar in participants with (2%) and without asthma (3%, odds ratio [OR]: 0.6 and 95% confidence interval [95% CI]: 0.2-2.0). In 74 asthma patients, who received β2-mimetics, tachycardia and PVCs were more common (OR: 12.4 [95% CI: 4.7-32.8] and 3.7 [95% CI: 1.3-10.5], respectively).

CONCLUSIONS

The adult patients with asthma more commonly show tachycardia and PVCs on the ECG than those without asthma. The patients with asthma received β2-mimetics; the risk of tachycardia and PVCs is even more pronounced.

Repeat long QT syndrome genetic testing of phenotype-positive cases: prevalence and etiology of detection misses

BACKGROUND

Approximately 75% of long QT syndrome (LQTS) has been explained genetically through research-based and, more recently, commercial genetic testing. While novel LQTS-susceptibility genes or mutations in unexplored regions of known genes underlie the genetic mechanism for some of the 25% "genotype-negative" remnant, it is likely that some cases represent false-negative test results owing to mutation detection failures.

OBJECTIVE

To determine the prevalence and etiology of false negatives that occurred with research-based mutational analysis involving denaturing high-performance liquid chromatography (DHPLC) followed by DNA sequencing (DHPLC-SEQ) in our previously published cohort of unrelated patients referred for LQTS genetic testing.

METHODS

Forty-four LQTS cases (29 men, average age 23 ± 15 years, average corrected QT interval 516 ± 56 ms) deemed genotype negative following DHPLC-SEQ were selected for repeat genetic testing using direct DNA sequencing.

RESULTS

LQTS-causing mutations were identified in 7 of 44 (16%) phenotype-positive/previously genotype-negative subjects, including 4 mutations in KCNQ1 (S225L, G568R, R591H, and R594Q), 2 in KCNH2 (H70R and G925R), and 1 in SCN5A (V411M). None of these variants were seen in more than 2600 reference alleles. Analysis of the misses revealed (1) normal DHPLC detection profile in 2, (2) allelic dropout in 2, (3) failure to correctly optimize DHPLC conditions in 1, and (4) failure to detect abnormal DHPLC signal in 2.

CONCLUSIONS

Repeat genetic testing using direct DNA sequencing may be warranted for LQTS phenotype-positive individuals who were pronounced genotype negative during the decade of research-based mutational analysis that involved intermediate mutation detection methods such as DHPLC.