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Background: Mutations in genes encoding the α (KCND3) and β (KCNE3) subunits of genes encoding the cardiac transient outward potassium (Ito) have been associated with inherited cardiac arrhythmia syndromes such as Brugada syndrome (BrS) and sudden infant death syndromes (SIDS). Here, we identify and characterize a novel genetic variant in DPP10 associated with severe pediatric J-wave syndrome (JWS) characterized by early repolarization syndrome (ERS). Methods and Results: The proband, a 14-year-old female, presented with atrial fibrillation. At age 16 she developed accentuated J waves in all ECG leads and multiple episodes of polymorphic ventricular tachycardia/ventricular fibrillation (VT/VF; type 3 ERS), resulting in appropriate ICD shocks. Cilostazol proved effective in quieting VT/VF. She died of an electrical storm at age 21. Genetic screening using Next Gen and Sanger methods uncovered a genetic variant in DPP10 but no variants in any other JWS susceptibility genes. Transversion of thymine for guanine at nucleotide 15 predicted substitution of aspartic acid (D) for glutamine acid (E) at position 5 in exon 1b in the N-terminal of DPP10. The variation was present in 5 of 448 ethnically matched healthy controls (1.1%). E5 is highly conserved among species. The E5D rare polymorphism was found in the proband’s aunt who was asymptomatic but displayed ER pattern in select ECG leads. Wild-type (WT) and mutant genes were expressed in TSA201 cells and studied using whole-cell patch-clamp techniques at 37°C. Coexpression of KCND3+KChIP2+DPP10/E5D generated Kv4.3 current density (Ito) 169.9% and 70.6% greater compared with KCND3+KChIP2+DPP10/WT when homozygously and heterozygously expressed, respectively (n = 9–12, P <.01). Inactivation of Ito and recovery from inactivation was slower in E5D channels. Quinidine (5 μM) and cilostazol (5 μM) inhibited Ito by approximately 50% at +20 mV in E5D channels but less so (20 %) in WT channels. Conclusions: Our results provide, for the first time, evidence supporting the hypothesis that DDP10 is a novel susceptibility gene for life-threatening arrhythmias associated with ERS. Our data suggest that DPP10-E5D contributes to generation of a pathogenic substrate by boosting Ito and that quinidine and cilostazol serve as therapeutic options in this setting by reducing Ito. [Copyright &y& Elsevier]

Sodium-glucose cotransporter type 2 inhibitors (SGLT2i) were initially recommended as oral anti-diabetic drugs to treat type 2 diabetes (T2D), by inhibiting SGLT2 in proximal tubule and reduce renal reabsorption of sodium and glucose. While many clinical trials demonstrated the tremendous potential of SGLT2i for cardiovascular diseases. 2022 AHA/ACC/HFSA guideline first emphasized that SGLT2i were the only drug class that can cover the entire management of heart failure (HF) from prevention to treatment. Subsequently, the antiarrhythmic properties of SGLT2i have also attracted attention. Although there are currently no prospective studies specifically on the anti-arrhythmic effects of SGLT2i. We provide clues from clinical and fundamental researches to identify its antiarrhythmic effects, reviewing the evidences and mechanism for the SGLT2i antiarrhythmic effects and establishing a novel paradigm involving intracellular sodium, metabolism and autophagy to investigate the potential mechanisms of SGLT2i in mitigating arrhythmias., (© 2024. The Author(s).)

Inherited cardiac arrhythmias are a group of genetic diseases predisposing to sudden cardiac arrest, mainly resulting from variants in genes encoding cardiac ion channels or proteins involved in their regulation. Currently available therapeutic options (pharmacotherapy, ablative therapy and device-based therapy) can not preclude the occurrence of arrhythmia events and/or provide complete protection. With growing understanding of the genetic background and molecular mechanisms of inherited cardiac arrhythmias, advancing insight of stem cell technology, and development of vectors and delivery strategies, gene therapy and stem cell therapy may be promising approaches for treatment of inherited cardiac arrhythmias. Recent years have witnessed impressive progress in the basic science aspects and there is a clear and urgent need to be translated into the clinical management of arrhythmic events. In this review, we present a succinct overview of gene and cell therapy strategies, and summarize the current status of gene and cell therapy. Finally, we discuss future directions for implementation of gene and cell therapy in the therapy of inherited cardiac arrhythmias., Competing Interests: Declaration of competing interest C.A. served as a consultant and received research grant support from Novartis and Trevena Inc. All other authors report no relationships to disclose., (Copyright © 2024. Published by Elsevier Inc.)

Atrial fibrillation (AF) is a very common cardiac arrhythmia with an estimated prevalence of 33.5 million patients globally. It is associated with an increased risk of death, stroke and peripheral embolism. Although genetic studies have identified a growing number of genes associated with AF, the definitive impact of these genetic findings is yet to be established. Several mechanisms, including electrical, structural and neural remodelling of atrial tissue, have been proposed to contribute to the development of AF. Despite over a century of exploration, the molecular and cellular mechanisms underlying AF have not been fully established. Current antiarrhythmic drugs are associated with a significant rate of adverse events and management of AF using ablation is not optimal, especially in cases of persistent AF. This review discusses recent advances in our understanding and management of AF, including new concepts of epidemiology, genetics and pathophysiological mechanisms. We review the current status of antiarrhythmic drug therapy for AF, new potential agents, as well as mechanism-based AF ablation. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

J wave syndrome (JWS) is an inherited cardiac channelopathy associated with malignant ventricular arrhythmias and sudden cardiac death (SCD), which comprises early repolarization syndrome and Brugada syndrome. Here, we explore the association between variants in the L -type calcium channel gene subunits, α 1C ( CACNA1C ) and β2b ( CACNB2b ), and the JWS phenotype. Using next-generation genetic sequencing of 402 JWS probands and their family members, we identified a CACNA1C -G37R (p.Gly37Arg) mutation in five individuals in four families, two of which had a family history of SCD as well as a CACNB2b -S143F (p.Ser143Phe) mutation in seven individuals in three families, two of which had a family history of SCD. The variants were located in exon 2 in CACNA1C and exon 5 in CACNB2b ; both were in highly conserved amino acid residues. Whole-cell patch-clamp results showed that compared with the wild-type group, calcium current density of CACNB2b- S143F and CACNA1C -G37R were significantly lower displaying a dominant-negative effect. Our findings provide further support for the hypothesis that variants in CACNA1C and CACNB2b are associated with JWS. The results suggest that mutations in these two genes lead to loss-of-function of the cardiac calcium channel current warranting their inclusion in genetic screening protocols. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Background: Brugada (BrS) and early repolarization syndromes (ERS), the so-called J wave syndromes (JWS), are associated with life-threatening ventricular arrhythmias. Pharmacologic approaches to therapy are currently limited. In this study, we examine the effects of ARumenamide-787 (AR-787) to suppress the electrocardiographic and arrhythmic manifestations of JWS and hypothermia., Methods: We studied the effects of AR-787 on INa and IKr in HEK-293 cells stably expressing the α- and β1-subunits of the cardiac (NaV1.5) sodium channel and hERG channel, respectively. In addition, we studied its effect on Ito, INa and ICa in dissociated canine ventricular myocytes along with action potentials and ECG from coronary-perfused right (RV) and left (LV) ventricular wedge preparations. The Ito agonist, NS5806 (5-10 μM), ICa blocker, verapamil (2.5 μM), and INa blocker, ajmaline (2.5 μM), were used to mimic the genetic defects associated with JWS and to induce the electrocardiographic and arrhythmic manifestations of JWS (prominent J waves/ST segment elevation, phase 2 reentry and polymorphic VT/VF) in canine ventricular wedge preparations., Results: AR-787 (1, 10 and 50 μM) exerted pleiotropic effects on cardiac ion channels. The predominant effect was inhibition of the transient outward current (Ito) and enhancement of the sodium channel current (INa), with lesser effects to inhibit IKr and augment calcium channel current (ICa). AR-787 diminished the electrocardiographic J wave and prevented and/or suppressed all arrhythmic activity in canine RV and LV experimental models of BrS, ERS and hypothermia., Conclusions: Our findings point to AR-787 as promising candidate for the pharmacologic treatment of JWS and hypothermia., Competing Interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: Dr. Antzelevitch has served as a consultant for Trevena Pharmaceutical Inc. and has received research funding from Trevena Pharmaceutical, In Carda Pharmaceutical and Kymera Pharmaceutical. The other co-authors have nothing to declare. This does not alter our adherence to PLOS ONE policies on sharing data and materials., (Copyright: © 2023 Di Diego et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Background: The transient outward current (Ito) that mediates early (phase 1) repolarization is conducted by the KCND3 -encoded Kv4.3 pore-forming α-subunit. KCND3 gain-of-function mutations have been reported previously as a pathogenic substrate for J wave syndromes (JWS), including the Brugada syndrome and early repolarization syndrome, as well as autopsy-negative sudden unexplained death (SUD). Acacetin, a natural flavone, is a potent Ito current blocker. Acacetin may be a novel therapeutic for KCND3 -mediated J wave syndrome., Methods: KCND3-V392I was identified in an 18-year-old male with J wave syndrome/early repolarization syndrome, and a history of cardiac arrest including ventricular tachycardia/ventricular fibrillation and atrial fibrillation/atrial flutter. Pathogenic KCND3 mutation was engineered by site-directed mutagenesis and co-expressed with wild-type KChIP2 in TSA201 cells. Gene-edited/variant-corrected isogenic control and patient-specific pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from the p. Val392Ile-KCND3-positive patient were generated. I to currents and action potentials were recorded before and after treatment with Acacetin using the whole cell patch-clamp and multielectrode array technique. Western blot and immunocytochemistry were performed to investigate KCND3 expression., Results: KCND3-V392I demonstrated a marked gain-of-function phenotype, increasing peak I to current density by 92.2% ( P <0.05 versus KCND3-WT). KCND3 expression was significantly increased in KCND3-V392I-derived iPSC-CMs ( P <0.05 versus isogenic control). While KCND3-WT revealed an IC50 of 7.2±1.0 µmol/L for acacetin effect, 30 µmol/L acacetin dramatically inhibited KCND3-V392I peak Ito current density by 96.2% ( P <0.05 versus before Acacetin). Ito was also increased by 60.9% in Kv4.3-V392I iPSC-CM ( P <0.05 versus isogenic control iPSC-CM). Ten micromoles per liter acacetin, a concentration approaching its IC50 value, inhibited Ito by ≈50% in patient-derived iPSC-CMs and reduced the accentuated action potential notch displayed in KCND3-V392I-derived iPSC-CMs., Conclusions: This preclinical study provides pharmacological and functional evidence to suggest that Acacetin may be a novel therapeutic for patients with KCND3 gain-of-function-associated J wave syndrome by inhibiting I to and abolishing the accentuated action potential notch in patient-derived iPSC-CMs.

Background and Purpose: QT prolongation and intracellular Ca 2+ loading with diastolic Ca 2+ release via ryanodine receptors (RyR2) are the predominant mechanisms underlying hypokalaemia-induced ventricular arrhythmia. We investigated the antiarrhythmic actions of two RyR2 inhibitors: dantrolene and VK-II-86, a carvedilol analogue lacking antagonist activity at β-adrenoceptors, in hypokalaemia., Experimental Approach: Surface ECG and ventricular action potentials (APs) were recorded from whole-heart murine Langendorff preparations. Ventricular arrhythmia incidence was compared in hearts perfused with low [K + ], and those pretreated with dantrolene or VK-II-86. Whole-cell patch clamping was used in murine and canine ventricular cardiomyocytes to study effects of dantrolene and VK-II-86 on AP parameters in low [K + ] and effects of VK-II-86 on the inward rectifier current (I K1 ), late sodium current (I Na&#95;L ) and the L-type Ca 2+ current (I Ca ). Effects of VK-II-86 on I Kr were investigated in transfected HEK-293 cells. A fluorogenic probe quantified the effects of VK-II-86 on oxidative stress in hypokalaemia., Key Results: Dantrolene reduced the incidence of ventricular arrhythmias induced by low [K + ] in explanted murine hearts by 94%, whereas VK-II-86 prevented all arrhythmias. VK-II-86 prevented hypokalaemia-induced AP prolongation and depolarization but did not alter AP parameters in normokalaemia. Hypokalaemia was associated with decreased I K1 and I Kr , and increased I Na-L , and I Ca . VK-II-86 prevented all hypokalaemia-induced changes in ion channel activity and oxidative stress., Conclusions and Implications: VK-II-86 prevents hypokalaemia-induced arrhythmogenesis by normalizing calcium homeostasis and repolarization reserve. VK-II-86 may provide an effective treatment in hypokalaemia and other arrhythmias caused by delayed repolarization or Ca 2+ overload., (© 2021 The Authors. British Journal of Pharmacology published by John Wiley & Sons Ltd on behalf of British Pharmacological Society.)

Myeloid-derived suppressor cells (MDSC) are a heterogeneous cell population with high immunosuppressive activity that proliferates in infections, inflammation, and tumor microenvironments. In tumors, MDSC exert immunosuppression mainly by producing reactive oxygen species (ROS), a process triggered by the NADPH oxidase 2 (NOX2) activity. NOX2 is functionally coupled with the Hv1 proton channel in certain immune cells to support sustained free-radical production. However, a functional expression of the Hv1 channel in MDSC has not yet been reported. Here, we demonstrate that mouse MDSC express functional Hv1 proton channel by immunofluorescence microscopy, flow cytometry, and Western blot, besides performing a biophysical characterization of its macroscopic currents via patch-clamp technique. Our results show that the immunosuppression by MDSC is conditional to their ability to decrease the proton concentration elevated by the NOX2 activity, rendering Hv1 a potential drug target for cancer treatment.

Genome-wide association studies indicate that SCN10A plays an important role in cardiac electrophysiology. Common and rare SCN10A variants are suggested to contribute to Brugada Syndrome (BrS), an inherited channelopathy resulting from genetic-determined loss-of-function in cardiac sodium channel. This study sought to characterize the role of SCN10A common variants in BrS. Clinical and genetic analyses were performed in 197 patients diagnosed with BrS. Baseline ECG parameters were evaluated in patients carrying each of four common variants associated with BrS. Cellular electrophysiological study was performed in SCN5A-SCN10A co-transfected TSA201 cells to investigate the possible electrophysiological characteristics of the allele of rs6795970, which displayed the most significant association with BrS. Four SCN10A common variants (rs7630989, rs57326399, rs6795970, rs12632942) displayed significant association with BrS susceptibility. There were no evident associations between baseline ECG parameters in BrS patients and the different genotypes of the four variants. Rs6795970 (V1073) was strongly associated with a risk for BrS, which suggests the different electrophysiological characters between these two alleles. Functional study showed a positive shift in steady-state activation (V1/2: -62.2 ± 2.6 vs. -53.5 ± 1.6 for A1073 and V1073 group, respectively; P < 0.05) and slower recovery from inactivation in mutant SCN5A-SCN10A co-transfected cells with, which contribute to the slow conduction in BrS patients with rs6795970. In conclusion, SCN10A common variants are associated with increased susceptibility to BrS. An allele rs6795970 (V1073) increases the risk for BrS. The electrophysiological changes in a positive shift in steady-state activation and slower recovery from inactivation by SCN10A-V1073 contribute to this variant associated BrS., (© The Author(s) 2021. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Oliceridine is a biased ligand at the μ-opioid receptor recently approved for the treatment of acute pain. In a thorough QT study, corrected QT (QTc) prolongation displayed peaks at 2.5 and 60 minutes after a supratherapeutic dose. The mean plasma concentration peaked at 5 minutes, declining rapidly thereafter., Objective: The purpose of this study was to examine the basis for the delayed effect of oliceridine to prolong the QTc interval., Methods: Repolarization parameters and tissue accumulation of oliceridine were evaluated in rabbit left ventricular wedge preparations over a period of 5 hours. The effects of oliceridine on ion channel currents were evaluated in human embryonic kidney and Chinese hamster ovary cells. Quinidine was used as a control., Results: Oliceridine and quinidine produced a progressive prolongation of the QTc interval and action potential duration over a period of 5 hours, paralleling slow progressive tissue uptake of the drugs. Oliceridine caused modest prolongation of these parameters, whereas quinidine produced a prominent prolongation of action potential duration and QTc interval as well as development of early afterdepolarization (after 2 hours), resulting in a high torsades de pointes score. The 50% inhibitory concentration values for the oliceridine inhibition of the rapidly activating delayed rectifier current (human ether a-go-go current) and late sodium channel current were 2.2 and 3.45 μM when assessed after traditional acute exposure but much lower after 3 hours of drug exposure., Conclusion: Our findings suggest that a gradual increase of intracellular access of drugs to the hERG channels as a result of their intracellular uptake and accumulation can significantly delay effects on repolarization, thus confounding the assessment of QT interval prolongation and arrhythmic risk when studied acutely. The multi-ion channel effects of oliceridine, late sodium channel current inhibition in particular, point to a low risk of devloping torsades de pointes., (Copyright © 2021 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Introduction: Myocardial infarction (MI) triggers structural and electrical remodeling. CC chemokine receptor 9 (CCR9) mediates chemotaxis of inflammatory cells in MI. In our previous study, CCR9 knockout has been found to improve structural remodeling after MI. Here, we further investigate the potential influence of CCR9 on electrical remodeling following MI in order to explore potential new measures to improve the prognosis of MI. Methods and Results: Mice was used and divided into four groups: CCR9 +/+ /Sham, CCR9 -/- /Sham, CCR9 +/+ /MI, CCR9 -/- /MI. Animals were used at 1 week after MI surgery. Cardiomyocytes in the infracted border zone were acutely dissociated and the whole-cell patch clamp was used to record action potential duration (APD), L-type calcium current ( I Ca,L ) and transient outward potassium current ( I to ). Calcium transient and sarcoplasmic reticulum (SR) calcium content under stimulation of Caffeine were measured in isolated cardiomyocytes by confocal microscopy. Multielectrode array (MEA) was used to measure the conduction of the left ventricle. The western-blot was performed for the expression level of connexin 43. We observed prolonged APD 90 , increased I Ca,L and decreased I to following MI, while CCR9 knockout attenuated these changes (APD 90 : 50.57 ± 6.51 ms in CCR9 -/- /MI vs. 76.53 ± 5.98 ms in CCR9 +/+ /MI, p < 0.05; I Ca,L : -13.15 ± 0.86 pA/pF in CCR9 -/- /MI group vs. -17.05 ± 1.11 pA/pF in CCR9 +/+ /MI, p < 0.05; I to : 4.01 ± 0.17 pA/pF in CCR9 -/- /MI group vs. 2.71 ± 0.16 pA/pF in CCR9 +/+ /MI, p < 0.05). The confocal microscopy results revealed CCR9 knockout reversed the calcium transient and calcium content reduction in sarcoplasmic reticulum following MI. MEA measurements showed improved conduction velocity in CCR9 -/- /MI mice (290.1 ± 34.47 cm/s in CCR9 -/- /MI group vs. 113.2 ± 14.4 cm/s in CCR9 +/+ /MI group, p < 0.05). Western-blot results suggested connexin 43 expression was lowered after MI while CCR9 knockout improved its expression. Conclusion: This study shows CCR9 knockout prevents the electrical remodeling by normalizing ion currents, the calcium homeostasis, and the gap junction to maintain APD and the conduction function. It suggests CCR9 is a promising therapeutic target for MI-induced arrhythmia, which warrants further investigation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Huang, Ding, Song, Chen, Wang, Tang, Barajas-Martinez, Huang and Hu.)

Irritable bowel syndrome (IBS) is one of the most widely recognized functional bowel disorders (FBDs) with a genetic component. SCN5A gene and SCN1B loci have been identified in population-based IBS cohorts and proposed to have a mechanistic role in the pathophysiology of IBS. These same genes have been associated with Brugada syndrome (BrS). The present study examines the hypothesis that these two inherited syndromes are linked. Prevalence of FBDs over a 12 months period were compared between probands with BrS/drug-induced type 1 Brugada pattern (DI-Type 1 BrP) (n = 148) and a control group (n = 124) matched for age, female sex, presence of arrhythmia and co-morbid conditions. SCN5A/SCN1B genes were screened in 88 patients. Prevalence of IBS was 25% in patients with BrS/DI-Type 1 BrP and 8.1% in the control group (p = 2.34 × 10 -4 ). On stepwise logistic regression analysis, presence of current and/or history of migraine (OR of 2.75; 95% CI: 1.08 to 6.98; p = 0.033) was a predictor of underlying BrS/DI-Type 1 BrP among patients with FBDs. We identified 8 putative SCN5A/SCN1B variants in 7 (12.3%) patients with BrS/DI-Type 1 BrP and 1 (3.2%) patient in control group. Five out of 8 (62.5%) patients with SCN5A/SCN1B variants had FBDs. In conclusion, IBS is a common co-morbidity in patients with BrS/DI-Type 1 BrP. Presence of current and/or history of migraine are a predictor of underlying BrS/DI-Type 1 BrP among patients with FBDs. Frequent co-existence of IBS and BrS/DI-Type 1 BrP necessitates cautious use of certain drugs among the therapeutic options for IBS that are known to exacerbate the Brugada phenotype., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are used for genetic models of cardiac diseases. We report an arrhythmia syndrome consisting of Early Repolarization Syndrome (ERS) and Short QT Syndrome (SQTS). The index patient (MMRL1215) developed arrhythmia-mediated syncope after electrocution and was found to carry six mutations. Functional alterations resulting from these mutations were examined in patient-derived hiPSC-CMs. Electrophysiological recordings were made in hiPSC-CMs from MMRL1215 and healthy controls. ECG analysis of the index patient showed slurring of the QRS complex and QTc = 326 ms. Action potential (AP) recordings from MMRL1215 myocytes showed slower spontaneous activity and AP duration was shorter. Field potential recordings from MMRL1215 hiPSC-CMs lack a "pseudo" QRS complex suggesting reduced inward current(s). Voltage clamp analysis of I Ca showed no difference in the magnitude of current. Measurements of I Na reveal a 60% reduction in I Na density in MMRL1215 hiPSC-CMs. Steady inactivation and recovery of I Na was unaffected. mRNA analysis revealed ANK2 and SCN5A are significantly reduced in hiPSC-CM derived from MMRL1215, consistent with electrophysiological recordings. The polygenic cause of ERS/SQTS phenotype is likely due to a loss of I Na due to a mutation in PKP2 coupled with and a gain of function in I K,ATP due to a mutation in ABCC9 .

Background: COVID-19 is a respiratory infectious disease caused by SARS-CoV-2, and cardiovascular damage is commonly observed in affected patients. We sought to investigate the effect of SARS-CoV-2 infection on cardiac injury and hypertension during the current coronavirus pandemic., Study Design and Methods: The clinical data of 366 hospitalized COVID-19-confirmed patients were analyzed. The clinical signs and laboratory findings were extracted from electronic medical records. Two independent, experienced clinicians reviewed and analyzed the data., Results: Cardiac injury was found in 11.19% (30/268) of enrolled patients. 93.33% (28/30) of cardiac injury cases were in the severe group. The laboratory findings indicated that white blood cells, neutrophils, procalcitonin, C-reactive protein, lactate, and lactic dehydrogenase were positively associated with cardiac injury marker. Compared with healthy controls, the 190 patients without prior hypertension have higher AngⅡ level, of which 16 (8.42%) patients had a rise in blood pressure to the diagnostic criteria of hypertension during hospitalization, with a significantly increased level of the cTnI, procalcitonin, angiotensin-II (AngⅡ) than those normal blood pressure ones. Multivariate analysis indicated that elevated age, cTnI, the history of hypertension, and diabetes were independent predictors for illness severity. The predictive model, based on the four parameters and gender, has a good ability to identify the clinical severity of COVID-19 in hospitalized patients (area under the curve: 0.932, sensitivity: 98.67%, specificity: 75.68%)., Conclusion: Hypertension, sometimes accompanied by elevated cTnI, may occur in COVID-19 patients and become a sequela. Enhancing Ang II signaling, driven by SARS-CoV-2 infection, might play an important role in the renin-angiotensin system, and consequently lead to the development of hypertension in COVID-19., Competing Interests: The authors report no relationships that could be construed as a conflict of interest.

Purpose: Stringent variant interpretation guidelines can lead to high rates of variants of uncertain significance (VUS) for genetically heterogeneous disease like long QT syndrome (LQTS) and Brugada syndrome (BrS). Quantitative and disease-specific customization of American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) guidelines can address this false negative rate., Methods: We compared rare variant frequencies from 1847 LQTS (KCNQ1/KCNH2/SCN5A) and 3335 BrS (SCN5A) cases from the International LQTS/BrS Genetics Consortia to population-specific gnomAD data and developed disease-specific criteria for ACMG/AMP evidence classes-rarity (PM2/BS1 rules) and case enrichment of individual (PS4) and domain-specific (PM1) variants., Results: Rare SCN5A variant prevalence differed between European (20.8%) and Japanese (8.9%) BrS patients (p = 5.7 × 10 -18 ) and diagnosis with spontaneous (28.7%) versus induced (15.8%) Brugada type 1 electrocardiogram (ECG) (p = 1.3 × 10 -13 ). Ion channel transmembrane regions and specific N-terminus (KCNH2) and C-terminus (KCNQ1/KCNH2) domains were characterized by high enrichment of case variants and >95% probability of pathogenicity. Applying the customized rules, 17.4% of European BrS and 74.8% of European LQTS cases had (likely) pathogenic variants, compared with estimated diagnostic yields (case excess over gnomAD) of 19.2%/82.1%, reducing VUS prevalence to close to background rare variant frequency., Conclusion: Large case-control data sets enable quantitative implementation of ACMG/AMP guidelines and increased sensitivity for inherited arrhythmia genetic testing.

Background: J wave syndromes (JWS), including Brugada (BrS) and early repolarization syndromes (ERS), are associated with increased risk for life-threatening ventricular arrhythmias. Pharmacologic approaches to therapy are currently very limited. Here, we evaluate the effects of the natural flavone acacetin., Methods: The effects of acacetin on action potential (AP) morphology and transient outward current (Ito) were first studied in isolated canine RV epicardial myocytes using whole-cell patch clamp techniques. Acacetin's effects on transmembrane APs, unipolar electrograms and transmural ECGs were then studied in isolated coronary-perfused canine RV and LV wedge preparations as well as in whole-heart, Langendorff-perfused preparations from which we recorded a 12 lead ECG and unipolar electrograms. Using floating glass microelectrodes we also recorded transmembrane APs from the RVOT of the whole-heart model. The Ito agonist NS5806, sodium channel blocker ajmaline, calcium channel blocker verapamil or hypothermia (32°C) were used to pharmacologically mimic the genetic defects and conditions associated with JWS, thus eliciting prominent J waves and provoking VT/VF., Results: Acacetin (5-10 μM) reduced Ito density, AP notch and J wave area and totally suppressed the electrocardiographic and arrhythmic manifestation of both BrS and ERS, regardless of the experimental model used. In wedge and whole-heart models of JWS, increasing Ito with NS5806, decreasing INa or ICa (with ajmaline or verapamil) or hypothermia all resulted in accentuation of epicardial AP notch and ECG J waves, resulting in characteristic BrS and ERS phenotypes. Phase 2-reentrant extrasystoles originating from the RVOT triggered VT/VF. The J waves in leads V1 and V2 were never associated with a delay of RVOT activation and always coincided with the appearance of the AP notch recorded from RVOT epicardium. All repolarization defects giving rise to VT/VF in the BrS and ERS models were reversed by acacetin, resulting in total suppression of VT/VF., Conclusions: We present experimental models of BrS and ERS capable of recapitulating all of the ECG and arrhythmic manifestations of the JWS. Our findings provide definitive support for the repolarization but not the depolarization hypothesis proposed to underlie BrS and point to acacetin as a promising new pharmacologic treatment for JWS., Competing Interests: The authors have declared that no competing interests exist.

Background: We report an inherited cardiac arrhythmia syndrome consisting of Brugada and Early Repolarization Syndrome associated with variants in SCN9A , PXDNL , and FKBP1B . The proband inherited the 3 mutations and exhibited palpitations and arrhythmia-mediated syncope, whereas the parents and sister, who carried one or two of the mutations, were asymptomatic., Methods and Results: We assessed the functional impact of these mutations in induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) derived from the proband and an unaffected family member. Current and voltage clamp recordings, as well as confocal microscopy analysis of Ca 2+ transients, were evaluated in hiPSC-CMs from the proband and compared these results with hiPSC-CMs from undiseased controls. Genetic analysis using next-generation DNA sequencing revealed heterozygous mutations in SCN9A , PXDNL , and FKBP1B in the proband. The proband displayed right bundle branch block and exhibited episodes of syncope. The father carried a mutation in FKBP1B , whereas the mother and sister carried the SCN9A mutation. None of the 3 family members screened developed cardiac events. Action potential recordings from control hiPSC-CM showed spontaneous activity and a low upstroke velocity. In contrast, the hiPSC-CM from the proband showed irregular spontaneous activity. Confocal microscopy of the hiPSC-CM of the proband revealed low fluorescence intensity Ca 2+ transients that were episodic in nature. Patch-clamp measurements in hiPSC-CM showed no difference in I Na but reduced I Ca in the proband compared with control. Coexpression of PXDNL -R391Q with SCN5A -WT displayed lower I Na density compared to PXDNL -WT. In addition, coexpression of PXDNL -R391Q with KCND3 -WT displayed significantly higher I to density compared to PXDNL -WT., Conclusion: SCN9A , PXDNL , and FKBP1B variants appeared to alter spontaneous activity in hiPSC-CM. Only the proband carrying all 3 mutations displayed the ERS/BrS phenotype, whereas one nor two mutations alone did not produce the clinical phenotype. Our results suggest a polygenic cause of the BrS/ERS arrhythmic phenotype due to mutations in these three gene variants caused a very significant loss of function of I Na and I Ca and gain of function of I to ., Competing Interests: The authors report no relationships that could be construed as a conflict of interest., (Copyright © 2020 Hector Barajas-Martinez et al.)

The mechanisms underlying atrial-selective prolongation of effective refractory period (ERP) and suppression of atrial fibrillation (AF) by NS8593 and UCL1684, small conductance calcium-activated potassium (SK) channel blockers, are poorly defined. The purpose of the study was to confirm the effectiveness of these agents to suppress AF and to probe the underlying mechanisms. Transmembrane action potentials and pseudoelectrocardiograms were recorded from canine isolated coronary-perfused canine atrial and ventricular wedge preparations. Patch clamp techniques were used to record sodium channel current (INa) in atrial and ventricular myocytes and human embryonic kidney cells. In both atria and ventricles, NS8593 (3-10 µM) and UCL1684 (0.5 µM) did not significantly alter action potential duration, suggesting little to no SK channel inhibition. Both agents caused atrial-selective: (1) prolongation of ERP secondary to development of postrepolarization refractoriness, (2) reduction of Vmax, and (3) increase of diastolic threshold of excitation (all are sodium-mediated parameters). NS8593 and UCL1684 significantly reduced INa density in human embryonic kidney cells as well as in atrial but not in ventricular myocytes at physiologically relevant holding potentials. NS8593 caused a shift of steady-state inactivation to negative potentials in atrial but not ventricular cells. NS8593 and UCL1684 prevented induction of acetylcholine-mediated AF in 6/6 and 8/8 preparations, respectively. This anti-AF effect was associated with strong rate-dependent depression of excitability. The SK channel blockers, NS8593 and UCL1684, are effective in preventing the development of AF due to potent atrial-selective inhibition of INa, causing atrial-selective prolongation of ERP secondary to induction of postrepolarization refractoriness.

Background: Although 21 causative mutations have been associated with PRKAG2 syndrome, our understanding of the syndrome remains incomplete. The aim of this project is to further investigate its unique genetic background, clinical manifestations, and underlying structural changes., Methods: We recruited 885 hypertrophic cardiomyopathy (HCM) probands and their families internationally. Targeted next-generation sequencing of sudden cardiac death (SCD) genes was performed. The role of the identified variants was assessed using histological techniques and computational modeling., Findings: Twelve PRKAG2 syndrome kindreds harboring 5 distinct variants were identified. The clinical penetrance of 25 carriers was 100.0%. Twenty-two family members died of SCD or heart failure (HF). All probands developed bradycardia (HRmin, 36.3 ± 9.8 bpm) and cardiac conduction defects, and 33% had evidence of atrial fibrillation/paroxysmal supraventricular tachycardia (PSVT) and 67% had ventricular preexcitation, respectively. Some carriers presented with apical hypertrophy, hypertension, hyperlipidemia, and renal insufficiency. Histological study revealed reduced AMPK activity and major cardiac channels in the heart tissue with K485E mutation. Computational modelling suggests that K485E disrupts the salt bridge connecting the β and γ subunits of AMPK, R302Q/P decreases the binding affinity for ATP, T400N and H401D alter the orientation of H383 and R531 residues, thus altering nucleotide binding, and N488I and L341S lead to structural instability in the Bateman domain, which disrupts the intramolecular regulation., Interpretation: Including 4 families with 3 new mutations, we describe a cohort of 12 kindreds with PRKAG2 syndrome with novel pathogenic mechanisms by computational modelling. Severe clinical cardiac phenotypes may be developed, including HF, requiring close follow-up., Competing Interests: Declaration of Competing Interest The authors report no relationships that could be construed as a conflict of interest., (Copyright © 2020 The Authors. Published by Elsevier B.V. All rights reserved.)

Although drug-induced short QT syndrome (SQTS) has been recognized, we currently report the first acquired SQTS case induced by bufotalinin (toad, an antineoplastic drug), which is a traditional Chinese folk prescription. It has cross reaction with digoxin and affects the Na + -K + -ATPase, the SR Ca 2+ release from ryanodine receptor-2 (RyR2), the reactive oxygen species (ROS) production from the mitochondria. The case presented with bradycardia, extreme QT shortening, and sinoatrial block that were resolved after gastric lavage, rehydration, electrolyte (hyperkalemia, hyponatremia, hypocalcemia) correction, and atropine injection. Clinicians should recognize a potential association between toad poisoning and SQTS from this case., (© 2019 Wiley Periodicals, Inc.)