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Abstract Long‐QT syndrome (LQTS) is an arrhythmogenic disorder characterised by prolongation of the QT interval in the electrocardiogram, which can lead to sudden cardiac death. Pharmacological treatments are far from optimal for congenital forms of LQTS, while the acquired form, often triggered by drugs that (sometimes inadvertently) target the cardiac hERG channel, is still a challenge in drug development because of cardiotoxicity. Current experimental models in vitro fall short in predicting proarrhythmic properties of new drugs in humans. Here, we leveraged a series of isogenically matched, diseased and genetically engineered, human induced pluripotent stem cell‐derived cardiomyocytes (hiPSC‐CMs) from patients to test a novel hERG allosteric modulator for treating congenital LQTS, drug‐induced LQTS or a combination of the two. By slowing IKr deactivation and positively shifting IKr inactivation, the small molecule LUF7346 effectively rescued all of these conditions, demonstrating in a human system that allosteric modulation of hERG may be useful as an approach to treat inherited and drug‐induced LQTS. Furthermore, our study provides experimental support of the value of isogenic pairs of patient hiPSC‐CMs as platforms for testing drug sensitivities and performing safety pharmacology.

During the last years, attention and controversy have been present for the first commercially available equipment being used in Electrocardiographic Imaging (ECGI), a new cardiac diagnostic tool which opens up a new field of diagnostic possibilities. Previous knowledge and criteria of cardiologists using intracardiac Electrograms (EGM) should be revisited from the newly available spatial–temporal potentials, and digital signal processing should be readapted to this new data structure. Aiming to contribute to the usefulness of ECGI recordings in the current knowledge and methods of cardiac electrophysiology, we previously presented two results: First, spatial consistency can be observed even for very basic cardiac signal processing stages (such as baseline wander and low-pass filtering); second, useful bipolar EGMs can be obtained by a digital processing operator searching for the maximum amplitude and including a time delay. In addition, this work aims to demonstrate the functionality of ECGI for cardiac electrophysiology from a twofold view, namely, through the analysis of the EGM waveforms, and by studying the ventricular repolarization properties. The former is scrutinized in terms of the clustering properties of the unipolar an bipolar EGM waveforms, in control and myocardial infarction subjects, and the latter is analyzed using the properties of T-wave alternans (TWA) in control and in Long-QT syndrome (LQTS) example subjects. Clustered regions of the EGMs were spatially consistent and congruent with the presence of infarcted tissue in unipolar EGMs, and bipolar EGMs with adequate signal processing operators hold this consistency and yielded a larger, yet moderate, number of spatial–temporal regions. TWA was not present in control compared with an LQTS subject in terms of the estimated alternans amplitude from the unipolar EGMs, however, higher spatial–temporal variation was present in LQTS torso and epicardium measurements, which was consistent through three different methods of alternans estimation. We conclude that spatial–temporal analysis of EGMs in ECGI will pave the way towards enhanced usefulness in the clinical practice, so that atomic signal processing approach should be conveniently revisited to be able to deal with the great amount of information that ECGI conveys for the clinician.

Background Congenital long‐QT syndrome (LQTS) is a genetic disorder characterized by prolongation of the corrected QT interval (QTc) on an ECG. The aim of the present study was to estimate the prevalence of pathogenic and likely pathogenic sequence variants in patients who had at least 1 ECG with a QTc ≥500 ms. Methods and Results Telemark Hospital Trust is a community hospital within the Norwegian national health system, serving ≈173 000 inhabitants. We searched the ECG database at Telemark Hospital Trust, Norway, from January 2004 to December 2014, and identified 1531 patients with at least 1 ECG with a QTc ≥500 ms. At the time of inclusion in this study (2015), 766 patients were alive. A total of 733 patients were invited to participate, and 475 accepted. The 17 genes that have been reported to cause monogenic LQTS were sequenced among the patients. Pro‐QTc score was calculated for each patient. A molecular genetic cause of LQTS was detected in 31 (6.5%) of 475 patients. These patients had a lower pro‐QTc score than those without pathogenic or likely pathogenic variants (1.7±1.0 versus 2.8±1.6; P

Congenital long-QT syndrome (LQTS) is an inherited cardiac disorder characterized by the prolongation of ventricular repolarization, susceptibility to Torsades de Pointes (TdP), and a risk for sudden death. Various types of congenital LQTS exist, all due to specific defects in ion channel-related genes. Interestingly, almost all of the ion channels affected by the various types of LQTS gene mutations are also expressed in the human sinoatrial node (SAN). It is therefore not surprising that LQTS is frequently associated with a change in basal heart rate (HR). However, current data on how the LQTS-associated ion channel defects result in impaired human SAN pacemaker activity are limited. In this mini-review, we provide an overview of known LQTS mutations with effects on HR and the underlying changes in expression and kinetics of ion channels. Sinus bradycardia has been reported in relation to a large number of LQTS mutations. However, the occurrence of both QT prolongation and sinus bradycardia on a family basis is almost completely limited to LQTS types 3 and 4 (LQT3 and Ankyrin-B syndrome, respectively). Furthermore, a clear causative role of this sinus bradycardia in cardiac events seems reserved to mutations underlying LQT3.

Background: Torsades de pointes (TdP) is a life-threatening ventricular tachycardia occurring in long QT-syndrome patients. It usually develops when multiple QT-prolonging factors are concomitantly present, more frequently drugs and electrolyte imbalances. Since proton–pump inhibitors (PPIs)-associated hypomagnesemia is an increasingly recognized adverse event, PPIs were recently included in the list of drugs with conditional risk of TdP, despite only few cases of TdP in PPI users have been reported so far.Objectives: Aim of the present study is to evaluate whether PPI-induced hypomagnesemia actually has a significant clinical impact on the risk of TdP in the general population.Methods: Forty-eight unselected patients who experienced TdP were consecutively enrolled (2008-2017). Shortly after the first TdP episode, in those patients who did not receive magnesium sulfate and/or potassium or calcium replacement therapy, serum electrolytes were measured and their relationship with PPI usage analyzed.Results: Many patients (28/48, 58%) were under current PPI treatment when TdP occurred. Among TdP patients in whom serum electrolyte determinations were obtained before replacement therapy (27/48), those taking PPIs had significantly lower serum magnesium levels than those who did not. Hypomagnesemia occurred in ~40% of patients receiving PPIs (6/14), in all cases after an extended treatment (>2 weeks). In patients taking PPIs the mean QT-prolonging risk factor number was significantly higher than in those who did not, a difference which was mainly driven by lower magnesium levels.Conclusions: In unselected TdP patients, PPI-induced hypomagnesemia was common and significantly contributed to their cumulative arrhythmic risk. By providing clinical support to current recommendations, our data confirm that more awareness is needed when a PPI is prescribed, specifically as regards the risk of life-threatening arrhythmias.

Congenital long QT syndrome (LQTS) is associated with ventricular arrhythmia and an increased risk of sudden cardiac death in young people. However, it is extremely rare for an elderly man to experience ventricular fibrillation (VF) due to congenital LQTS as a first episode. We describe the case of an 84-year-old man who experienced syncope after urination. He had a medical history of hypertension and asthma, but no history of syncope. Electrocardiographic findings in 2017 showed QT prolongation (corrected QT = 505 ms). No medication that could induce QT prolongation was administered. Blood test results on admission showed no electrolyte abnormalities, and there were no abnormal findings on echocardiography. The second episode of loss of consciousness occurred during hospitalization, and electrocardiography revealed incessant torsade de pointes, caused by R-on-T with short-long-short (SLS) sequences due to bradyarrhythmia. Coronary angiography did not detect myocardial ischemia, and an implantable cardioverter-defibrillator was implanted for secondary prevention. Genetic testing revealed a mutation of the KCNH2 gene, indicating LQTS type 2. In summary, we report a rare case of prolonged QT interval with SLS sequences due to sick sinus syndrome triggering VF as the first attack in an elderly patient with LQTS type 2. < Learning objective: Physicians should be aware of the prolongation of QT as a cause of syncope in elderly patients and should pay attention to QT duration. Furthermore, patients with elderly-onset QT prolongation may have a genetic background associated with congenital long QT syndrome (LQTS); therefore, we should not hesitate to perform genetic testing in cases where LQTS is suspected in elderly patients.> [ABSTRACT FROM AUTHOR]

Diagnosis of inherited arrhythmia syndromes, including long-QT syndrome (LQTS), is challenging; however, early detection and initiation of therapies can reduce otherwise high rates of mortality. Two months following the birth of her first child a previously well 21-year-old female experienced four episodes of transient loss of consciousness (TLOC). The history was atypical for seizures but a video electroencephalogram (EEG) captured an episode with abnormal bifrontal epileptic discharge. She was commenced on levetiracetam. Within weeks of the birth of her second child she experienced five further episodes. During the subsequent hospital admission an electrocardiogram (ECG) recorded polymorphic ventricular tachycardia (VT) during a typical TLOC event. Other ECGs recorded a prolonged QT interval. A diagnosis of LQTS was made and TLOC episodes ceased on commencement of nadolol. The patient experienced 22 TLOC episodes before diagnosis - most likely from self-terminating VT. With widespread availability of effective treatments to reduce the risk of sudden cardiac death in such conditions, clinicians should always remember how the ECG is an essential investigation every time a patient presents with TLOC. [ABSTRACT FROM AUTHOR]

Background: Historically, individuals diagnosed with an inherited arrhythmia or cardiomyopathy have been advised to avoid participating in competitive sports. Consequently, these individuals may be more susceptible to weight gain and obesity. Methods: A retrospective longitudinal chart review was performed for a population of children with a genetic or clinical diagnosis of the long‐QT syndrome, catecholaminergic polymorphic ventricular tachycardia, hypertrophic cardiomyopathy, or arrhythmogenic right ventricular cardiomyopathy. We recorded the physical activity recommendation, postdiagnosis sports participation, and body mass index (BMI) over time. Results: A total of 109 charts were reviewed. Some level of physical activity restriction was documented for the majority of phenotype‐positive children (80%) but was less common for phenotype‐negative children (37%) (P < 0.001). Overall, 38% (n = 41) of the study population were reportedly participating in a moderate or high dynamic sports following their diagnosis. Nonetheless, the BMI did not differ over time based on physical activity restriction or sports participation, and the proportion of overweight and obese children at follow‐up was consistent with that seen in the Canadian pediatric population. Conclusion: Physical activity restriction was recommended for the majority of phenotype‐positive children with an inherited arrhythmia or cardiomyopathy. However, many children continue to participate in competitive sports. Children prescribed physical activity restriction appear to face similar concerns relating to obesity as other Canadian children. This study highlights the need to further assess the effectiveness of physical activity recommendations and its impact on the cardiovascular health. [ABSTRACT FROM AUTHOR]

In patients with Long-QT Syndrome (LQTS), mechanical abnormalities have been described. Recognition of these abnormalities could potentially be used in the diagnosis of LQTS, especially in the foetus where an ECG is not available and DNA-analysis is invasive. We aimed to develop and validate a marker for these mechanical abnormalities in children and to test its feasibility in foetuses as a proof of principle. We measured the myocardial contraction duration using colour Tissue Doppler Imaging (cTDI) in 41 LQTS children and age- and gender-matched controls. Children were chosen to develop and validate the measurement of the myocardial contraction duration, due to the availability of a simultaneously recorded ECG. Feasibility of this measurement in foetuses was tested in an additional pilot study among seven LQTS foetuses and eight controls. LQTS children had a longer myocardial contraction duration compared to controls, while there was no statistical difference in heart rate. Measuring the myocardial contraction duration in children had a high inter- and intra-observer validity and reliably correlated with the QT-interval. There was an area under the curve (AUC) of 0.71, and the optimal cut-off value showed an especially high specificity in diagnosing LQTS. Measuring the myocardial contraction duration was possible in all foetuses and had a high inter- and intra-observer validity (ICC = 0.71 and ICC = 0.88, respectively). LQTS foetuses seemed to have a longer myocardial contraction duration compared to controls. Therefore, a prolonged contraction duration may be a potential marker for the prenatal diagnosis of LQTS in the future. Further studies are required to support the measurement of the myocardial contraction duration as a diagnostic approach for foetal LQTS. [ABSTRACT FROM AUTHOR]

Abstract: Jervell‐Lange Nielsen syndrome (JLNS) with autosomal recessive inheritance is a congenital cardiovascular disorder characterized by prolongation of QT interval on the ECG and deafness. We have performed molecular investigation by haplotype analysis and DNA Sanger sequencing in 2 unrelated Iranian families with a history of syncope. Mutational screening of KCNQ1 gene revealed the novel homozygous frameshift mutation c.733‐734delGG (p.G245Rfs*39) in 2 obviously unrelated cases of JLNS which is probably a founder mutation in Iran. The novel mutation detected in this study is the first time reported among Iranian population and will be beneficial in the tribe and region‐specific cascade screening of LQTS in Iran. [ABSTRACT FROM AUTHOR]

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Abstract: Aims: A significant antiarrhythmic potential of ryanodine receptor inhibition was reported in experimental studies. The aim of the present study was to assess potential antiarrhythmic effects of dantrolene in an experimental whole‐heart model of drug‐induced long‐QT syndrome (LQTS). Methods: In 12 isolated rabbit hearts, long‐QT‐2‐syndrome was simulated by infusion of erythromycin (300 μM). Twelve rabbit hearts were treated with veratridine (0.5 μM) to mimic long‐QT‐3‐syndrome. Results: Monophasic action potentials and ECG showed a significant prolongation of QT‐interval (+71 ms, P < 0.01) and action potential duration (APD, +43 ms, P < 0.01) after infusion of erythromycin as compared with baseline. Similar results were obtained in veratridine‐treated hearts (QT‐interval: +43 ms, P < 0.01; APD: +36 ms, P < 0.01). Both erythromycin (+36 ms, P < 0.05) and veratridine (+38 ms) significantly increased dispersion of repolarization. Additional infusion of dantrolene (20 μM) did not significantly alter QT‐interval and APD but resulted in a significant reduction of dispersion of repolarization (erythromycin group: –33 ms, P < 0.05; veratridine group: –29 ms, P < 0.05). Lowering of potassium concentration resulted in the occurrence of early afterdepolarizations (EAD) and polymorphic ventricular tachycardia (VT) in 9 of 12 erythromycin‐treated hearts (175 episodes) and 8 of 12 veratridine‐treated hearts (66 episodes). Additional infusion of dantrolene significantly reduced occurrence of polymorphic VT and resulted in occurrence of EAD and polymorphic VT in 1 of 12 erythromycin‐treated hearts (18 episodes) and 1 of 12 veratridine‐treated hearts (3 episodes). Conclusion: Inhibition of the ryanodine receptor by dantrolene significantly reduced occurrence of polymorphic VT in drug‐induced LQTS. A significant reduction of spatial dispersion of repolarization represents a major antiarrhythmic mechanism. These results imply that dantrolene may represent a promising antiarrhythmic option in drug‐induced LQTS. [ABSTRACT FROM AUTHOR]

Abstract: Today, understanding the true risk of adverse events in long‐QT syndrome (LQTS) populations may be extremely complex and potentially dependent on many factors such as the affected gene, mutation location, degree of QTc prolongation, age, sex, and other yet unknown factors. In this context, risk stratification by genotype in LQTS patients has been extremely difficult, also during exercise practice, especially due to the lack of studies that would lead to a better understanding of the natural history of each mutation and its impact upon athletes. The creation of individualized guidelines for sport participation is a goal yet to be achieved not only due to the complexity of genotype effect on the phenotype in this patient population, but also due to penetrance in genotype‐positive patients. This article summarizes current knowledge and raises questions concerning the difficult relationship between exercise practice and LQTS. [ABSTRACT FROM AUTHOR]

The SCN5A gene encodes the pore-forming α-subunit of the ion channel that carries the cardiac fast sodium current (INa). The 1795insD mutation in SCN5A causes sinus bradycardia, with a mean heart rate of 70 beats/min in mutation carriers vs. 77 beats/min in non-carriers from the same family (lowest heart rate 41 vs. 47 beats/min). To unravel the underlying mechanism, we incorporated the mutation-induced changes in INa into a recently developed comprehensive computational model of a single human sinoatrial node cell (Fabbri–Severi model). The 1795insD mutation reduced the beating rate of the model cell from 74 to 69 beats/min (from 49 to 43 beats/min in the simulated presence of 20 nmol/L acetylcholine). The mutation-induced persistent INa per se resulted in a substantial increase in beating rate. This gain-of-function effect was almost completely counteracted by the loss-of-function effect of the reduction in INa conductance. The further loss-of-function effect of the shifts in steady-state activation and inactivation resulted in an overall loss-of-function effect of the 1795insD mutation. We conclude that the experimentally identified mutation-induced changes in INa can explain the clinically observed sinus bradycardia. Furthermore, we conclude that the Fabbri–Severi model may prove a useful tool in understanding cardiac pacemaker activity in humans. [ABSTRACT FROM AUTHOR]

Objective(s): Jervell and Lange--Nielsen syndrome is an autosomal recessive disorder caused by mutations in KCNQ1 or KCNE1 genes. The disease is characterized by sensorineural hearing loss and long QT syndrome. Materials and Methods Here we present a 3.5-year-old female patient, an offspring of consanguineous marriage, who had a history of recurrent syncope and congenital sensorineural deafness. The patient and the family members were screened for mutations in KCNQ1 gene by linkage analysis and DNA sequencing. Results: DNA sequencing showed a c.1532_1534delG (p. A512Pfs*81) mutation in the KCNQ1 gene in homozygous form. The results of short tandem repeat (STR) markers showed that the disease in the family is linked to the KCNQ1 gene. The mutation was confirmed in the parents in heterozygous form. Conclusion: This is the first report of this variant in KCNQ1 gene in an Iranian family. The data of this study could be used for early diagnosis of the condition in the family and genetic counseling. [ABSTRACT FROM AUTHOR]

A 76-year-old man who had been diagnosed with long-QT syndrome type 2 had frequent syncopal attacks. The electrocardiogram was monitored, and frequent torsades de pointes (TdP) was detected despite administration of conventional medications: oral propranolol, verapamil, intravenous magnesium sulfate, verapamil, and lidocaine. In contrast, 2 μg/kg/min landiolol could completely suppress TdP. Subsequently, an implantable cardioverter defibrillator was placed, and he was diagnosed with silent myocardial ischemia using myocardial perfusion scintigraphy and coronary angiography. This is the first case report wherein landiolol effectively suppressed TdP due to long-QT syndrome with silent myocardial ischemia. [ABSTRACT FROM AUTHOR]

Congenital long QT syndrome (LQTS) is associated with high genetic and allelic heterogeneity. In some cases, more than one genetic variant is identified in the same (compound heterozygosity) or different (digenic heterozygosity) genes, and subjects with multiple pathogenic mutations may have a more severe disease. Standard-of-care clinical genetic testing for this and other arrhythmia susceptibility syndromes improves the identification of complex genotypes. Therefore, it is important to distinguish between pathogenic mutations and benign rare variants. We identified four genetic variants (KCNQ1-p.R583H, KCNH2-p.C108Y, KCNH2-p.K897T, and KCNE1-p.G38S) in an LQTS family. On the basis of in silico analysis, clinical data from our family, and the evidence from previous studies, we analyzed two mutated channels, KCNQ1-p.R583H and KCNH2-p.C108Y, using the whole-cell patch clamp technique. We found that KCNQ1-p.R583H was not associated with a severe functional impairment, whereas KCNH2-p.C108Y, a novel variant, encoded a non-functional channel that exerts dominant-negative effects on the wild-type. Notably, the common variants KCNH2-p.K897T and KCNE1-p.G38S were previously reported to produce more severe phenotypes when combined with disease-causing alleles. Our results indicate that the novel KCNH2-C108Y variant can be a pathogenic LQTS mutation, whereas KCNQ1-p.R583H, KCNH2-p.K897T, and KCNE1-p.G38S could be LQTS modifiers. [ABSTRACT FROM AUTHOR]

Background: Left cardiac sympathetic denervation (LCSD) is a surgical procedure that has been shown to have an antiarrhythmic and antifibrillatory effect. Evidence indicating its antiarrhythmic effect has been available for over 100 years. It involves the removal of the lower half of the stellate ganglion and T2-T4 of the sympathetic ganglia and is carried out as either a unilateral or bilateral procedure. With advancements in thoracic surgery, it can be safely performed via a minimally invasive Video-Assisted Thoracoscopic Surgery (VATS) approach resulting in significantly less morbidity and a shortened inpatient stay. LCSD provides a valuable treatment option for patients with life-threatening channelopathies and cardiomyopathies. Aims and Methods: This case series reports the preliminary paediatric and adult experience in the Republic of Ireland with LCSD and describes five cases recently treated in addition to an outline of the operative procedure employed. Of the five cases included, two were paediatric cases and three were adult cases. Results: One of the paediatric patients had a diagnosis of the rare catecholaminergic polymorphic ventricular tachycardia (CPVT) and the other a diagnosis of long-QT syndrome. Both paediatric patients experienced excellent outcomes. Of the three adult patients, two benefitted greatly and remain well at follow-up (one inappropriate sinus tachycardia and one CPVT). One patient with idiopathic ventricular fibrillation unfortunately passed away from intractable VF despite all attempts at resuscitation. Conclusion: In this case series, we highlight that LCSD provides a critical adjunct to existing medical therapies and should be considered for all patients with life-threatening refractory arrhythmias especially those patients on maximal medical therapy. [ABSTRACT FROM AUTHOR]

Background: Loss-of-function mutations in hERG (encoding the Kv11.1 voltage-gated potassium channel) cause long-QT syndrome type 2 (LQT2) because of prolonged cardiac repolarization. However, Kv11.1 is also present in pancreatic α and β cells and intestinal L and K cells, secreting glucagon, insulin, and the incretins glucagon-like peptide-1 (GLP-1) and GIP (glucose-dependent insulinotropic polypeptide), respectively. These hormones are crucial for glucose regulation, and long-QT syndrome may cause disturbed glucose regulation. We measured secretion of these hormones and cardiac repolarization in response to glucose ingestion in LQT2 patients with functional mutations in hERG and matched healthy participants, testing the hypothesis that LQT2 patients have increased incretin and β-cell function and decreased α-cell function, and thus lower glucose levels.Methods: Eleven patients with LQT2 and 22 sex-, age-, and body mass index-matched control participants underwent a 6-hour 75-g oral glucose tolerance test with ECG recording and blood sampling for measurements of glucose, insulin, C-peptide, glucagon, GLP-1, and GIP.Results: In comparison with matched control participants, LQT2 patients had 56% to 78% increased serum insulin, serum C-peptide, plasma GLP-1, and plasma GIP responses (P=0.03-0.001) and decreased plasma glucose levels after glucose ingestion (P=0.02) with more symptoms of hypoglycemia (P=0.04). Sixty-three percent of LQT2 patients developed hypoglycemic plasma glucose levels (<70 mg/dL) versus 36% control participants (P=0.16), and 18% patients developed serious hypoglycemia (<50 mg/dL) versus none of the controls. LQT2 patients had defective glucagon responses to low glucose, P=0.008. β-Cell function (Insulin Secretion Sensitivity Index-2) was 2-fold higher in LQT2 patients than in controls (4398 [95% confidence interval, 2259-8562] versus 2156 [1961-3201], P=0.03). Pharmacological Kv11.1 blockade (dofetilide) in rats had similar effect, and small interfering RNA inhibition of hERG in β and L cells increased insulin and GLP-1 secretion up to 50%. Glucose ingestion caused cardiac repolarization disturbances with increased QTc intervals in both patients and controls, but with a 122% greater increase in QTcF interval in LQT2 patients (P=0.004).Conclusions: Besides a prolonged cardiac repolarization phase, LQT2 patients display increased GLP-1, GIP, and insulin secretion and defective glucagon secretion, causing decreased plasma glucose and thus increased risk of hypoglycemia. Furthermore, glucose ingestion increased QT interval and aggravated the cardiac repolarization disturbances in LQT2 patients.Clinical Trial Registration: URL: http://clinicaltrials.gov. Unique identifier: NCT02775513. [ABSTRACT FROM AUTHOR]

Long-QT syndrome is a congenital or acquired disorder of the heart's electrical activity, inducing delayed repolarization that can cause ventricular arrhythmias and sudden cardiac death. Acquired forms can occur as a result of various drugs and given the fact that most patients have multiple comorbidities, the risk of polymedication and iatrogenesis is increasingly high. We present the case of a 60-year-old female admitted to the Cardiology Department for an arrhythmic storm, associating QT interval prolongation. The patient had a known history of atrial fibrillation and was undergoing antiarrhythmic therapy with flecainide. The hypothesis of a drug-induced long-QT syndrome was raised. Multiple ventricular arrhythmias requiring defibrillation occurred and intubation with mechanical ventilation was needed, followed by temporary ventricular pacing. We decided the discontinuation of flecainide therapy but over the next days, the patient presented persistent QT interval prolongation, multiple recurrences of ventricular arrhythmias and recurrent paroxysmal atrial fibrillation. In this context, the initial hypothesis of a flecainide-induced long QT syndrome was invalidated and given the persistent QT interval prolongation (QTc > 480 ms); the hypothesis of a congenital long-QT syndrome was raised. An implantable cardioverter defibrillator implantation was performed. The ECG holter monitoring after implantation showed the disappearance of ventricular arrhythmias, with favorable clinical evolution. [ABSTRACT FROM AUTHOR]

Background: In congenital long-QT syndrome, age, sex, and genotype have been associated with cardiac events, but their effect on the trend in QTc interval has never been established. We, therefore, aimed to assess the effect of age and sex on the QTc interval in children and adolescents with type 1 (LQT1) and type 2 (LQT2) long-QT syndrome.Methods and Results: QTc intervals of 12-lead resting electrocardiograms were determined, and trends over time were analyzed using a linear mixed-effects model. The study included 278 patients with a median follow-up of 4 years (interquartile range, 1-9) and a median number of 6 (interquartile range, 2-10) electrocardiograms per patient. Both LQT1 and LQT2 male patients showed QTc interval shortening after the onset of puberty. In LQT2 male patients, this was preceded by a progressive QTc interval prolongation. In LQT1, after the age of 12 years, male patients had a significantly shorter QTc interval than female patients. In LQT2, during the first years of life and from 14 to 26 years, male patients had a significantly shorter QTc interval than female patients. On the contrary, between 5 and 14 years, LQT2 male patients had significantly longer QTc interval than LQT2 female patients.Conclusions: There is a significant effect of age and sex on the QTc interval in long-QT syndrome, with a unique pattern per genotype. The age of 12 to 14 years is an important transitional period. In the risk stratification and management of long-QT syndrome patients, clinicians should be aware of these age-, sex-, and genotype-related trends in QTc interval and especially the important role of the onset of puberty. [ABSTRACT FROM AUTHOR]

A 27-year-old Japanese woman with a history of depression and an eating disorder presented to our emergency department with a chief complaint of generalized weakness. Electrocardiography showed prominent QT prolongation with multiple ventricular contractions. Chest X-ray plain computed tomography revealed pulmonary edema. Echocardiography showed decreased left ventricular systolic function. Suspecting acute myocarditis, we performed a myocardial biopsy from the right ventricular septum. The biopsy histology revealed extensive myocardial fibrosis and a very mild inflammatory cell infiltrate. In an additional detailed medical interview, the patient admitted that she had consumed three bottles of a first-aid liquid containing naphazoline approximately ~12 h before her presentation, in a suicide attempt. Her QTc and left ventricular ejection fraction improved during hospitalization., Learning Objective: Acute drug intoxication can cause QT prolongation and ventricular arrhythmias, cardiomyopathy, and pulmonary edema. When acute QT prolongation, myocardial damage, and pulmonary edema are seen (suggesting acute myocarditis), naphazoline intoxication should be investigated in the differential diagnosis., Competing Interests: None of the authors have any potential conflicts of interest associated with this research., (© 2023 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.)

Background Congenital long-QT syndrome (LQTS) is a potentially lethal cardiac electrophysiologic disorder characterized by QT interval prolongation and T-wave abnormalities. At least 13 LQTS-associated genes have been reported, but the high cost and low throughput of conventional Sanger sequencing has hampered the multi-gene-based LQTS diagnosis in clinical laboratories. Methods We developed an NGS (next-generation sequencing)-based targeted gene panel for 13 LQTS genes using the Ion PGM platform, and a cohort of 36 LQTS patients were studied for characterization of analytical performance specifications. Results This panel efficiently explored 212 of all 221 coding exons in 13 LQTS-associated genes. And for those genomic regions covered by the design of the NGS panel, the analytical sensitivity and analytical specificity for all potentially pathogenic variants were both 100% and showed 100% concordance with clinically validated Sanger sequencing results in five major LQTS genes ( KCNQ1 , KCNH2 , SCN5A , KCNE1 , and KCNE2 ). Conclusion This is the first description of an NGS panel targeting a multi-gene panel of 13 LQTS-associated genes. We developed and validated this robust, high-throughput NGS test and informatics pipeline for LQTS diagnosis suitable for the clinical testing laboratory. [ABSTRACT FROM AUTHOR]

Background: Risk stratification in patients with type 3 long-QT syndrome (LQT3) by clinical and genetic characteristics and effectiveness of β-blocker therapy has not been studied previously in a large LQT3 population.Methods: The study population included 406 LQT3 patients with 51 sodium channel mutations; 391 patients were known to be event free during the first year of life and were the focus of our study. Clinical, electrocardiographic, and genetic parameters were acquired for patients from 7 participating LQT3 registries. Cox regression analysis was used to evaluate the independent contribution of clinical, genetic, and therapeutic factors to the first occurrence of time-dependent cardiac events (CEs) from age 1 to 41 years.Results: Of the 391 patients, 118 (41 males, 77 females) patients (30%) experienced at least 1 CE (syncope, aborted cardiac arrest, or long-QT syndrome-related sudden death), and 24 (20%) suffered from LQT3-related aborted cardiac arrest/sudden death. The risk of a first CE was directly related to the degree of QTc prolongation. Cox regression analysis revealed that time-dependent β-blocker therapy was associated with an 83% reduction in CEs in females (P=0.015) but not in males (who had many fewer events), with a significant sex × β-blocker interaction (P=0.04). Each 10-ms increase in QTc duration up to 500 ms was associated with a 19% increase in CEs. Prior syncope doubled the risk for life-threatening events (P<0.02).Conclusions: Prolonged QTc and syncope predispose patients with LQT3 to life-threatening CEs. However, β-blocker therapy reduces this risk in females; efficacy in males could not be determined conclusively because of the low number of events. [ABSTRACT FROM AUTHOR]

Long- QT syndrome ( LQTS) is an arrhythmogenic disorder characterised by prolongation of the QT interval in the electrocardiogram, which can lead to sudden cardiac death. Pharmacological treatments are far from optimal for congenital forms of LQTS, while the acquired form, often triggered by drugs that (sometimes inadvertently) target the cardiac hERG channel, is still a challenge in drug development because of cardiotoxicity. Current experimental models in vitro fall short in predicting proarrhythmic properties of new drugs in humans. Here, we leveraged a series of isogenically matched, diseased and genetically engineered, human induced pluripotent stem cell-derived cardiomyocytes (hi PSC- CMs) from patients to test a novel hERG allosteric modulator for treating congenital LQTS, drug-induced LQTS or a combination of the two. By slowing IKr deactivation and positively shifting IKr inactivation, the small molecule LUF7346 effectively rescued all of these conditions, demonstrating in a human system that allosteric modulation of hERG may be useful as an approach to treat inherited and drug-induced LQTS. Furthermore, our study provides experimental support of the value of isogenic pairs of patient hi PSC- CMs as platforms for testing drug sensitivities and performing safety pharmacology. [ABSTRACT FROM AUTHOR]

A 73-year-old woman first visited our emergency room with multiple syncopal attacks. Before admission, she had received an antibiotic (Garenoxacin) for 3 days from a local clinic. First electrocardiogram (ECG) showed no ST-segment deviation but mild QT interval prolongation with a positive U wave. Second ECG recording 3 h later showed slightly slower heart rate and revealed marked QTU interval prolongation suggesting the cause of her syncopal attacks. After cessation of Garenoxacin, the QTU interval prolongation shortened. However, both epinephrine infusion and treadmill exercise test reproduced similar QTU interval prolongation and T wave deformities. Later, genetic analysis demonstrated that this patient had a mutation in KCNH2 gene, and she was diagnosed as a type-2 long-QT syndrome which was accentuated by use of garenoxacin. At the emergency out-patient clinic, repetitive ECG recordings can be useful and should be considered in order to identify the cause of syncopal attacks in patients who were prescribed antibiotics and had mild QT interval abnormalities. [ABSTRACT FROM AUTHOR]

Mutations in the human ether-à-go-go-related gene (hERG) are responsible for long-QT syndrome (LQTS) type 2 (LQT2). In the present study, a heterozygous missense mutation (A561V) linked to LQT2, syncope and epilepsy was identified in the S5/pore region of the hERG protein. The mutation, A561V, was prepared and subcloned into hERG-pcDNA3.0. Mutant plasmids were co-transfected into HEK-293 cells, which stably express wild-type (WT) hERG, in order to mimic a heterozygous genotype, and the whole-cell current was recorded using a patch-clamp technique. Confocal microscopy was performed to evaluate the membrane distribution of the hERG channel protein using a green fluorescent protein tagged to the N-terminus of hERG. A561V-hERG decreased the amplitude of the WT-hERG currents in a concentration-dependent manner. In addition, A561V-hERG resulted in alterations to activation, inactivation and recovery from inactivation in the hERG protein channels. Further evaluation of hERG membrane localization indicated that the A561V-hERG mutant protein was unable to travel to the plasma membrane, which resulted in a trafficking-deficient WT-hERG protein. In conclusion, A561V-hERG exerts a potent dominant-negative effect on WT-hERG channels, resulting in decreased hERG currents and impairment of hERG membrane localization. This may partially elucidate the clinical manifestations of LQTS patients who carry the A561V mutation. [ABSTRACT FROM AUTHOR]

Background: Recently, we identified a novel mutation of SCN5A (1795insD) in a large family with LQTS3. The aim of this study was to assess whether the various proposed corrections of the QT interval to heart rate help to improve the identification of carriers of the mutant gene. Methods: The study group consisted of 101 adult family members: 57 carriers and 44 noncarriers (mean age 44.6 ± 14.6 and 40.3 ± 12.8 years, respectively). In all individuals a 12‐lead ECG, exercise ECG, and 24‐hour Holter ECG were obtained. Results: Correction for heart rate significantly improved the diagnostic performance of the QT interval. Diagnostic performance of the Bazett formula was similar to that of the newer formulas (Fridericia, Hodges, Framingham, and a logarithmic formula). At a cut‐off value of 440 ms, the Bazett corrected QT interval was associated with a sensitivity and specificity of 90% and 91%, respectively. Using the 24‐hour Holter ECG, a prolonged QTc at heart rates less than 60 beats/min was almost pathognomonic for genetic mutation (sensitivity and specificity both 99%), whereas the QTc calculated at the lowest heart rate using Bazett's formula provided full discrimination. Conclusion: In the present family, the resting ECG gave a good indication about the presence or absence of genetic mutation but a 24‐hour Holter recording was mandatory to ascertain the diagnosis. In the diagnosis of this form of LQTS3, Bazett's formula was at least as good as other proposed corrections of the QT interval to heart rate.