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Ma JG, O’Neill MJ, Richardson E, Thomson KL, Ingles J, Muhammad A, Solus JF, Davogustto G, Anderson KC, Benjamin Shoemaker M, Stergachis AB, Floyd BJ, Dunn K, Parikh VN, Chubb H, Perrin MJ, Roden DM, Vandenberg JI, Ng CA, Glazer AM. Multi-site validation of a functional assay to adjudicate SCN5A Brugada Syndrome-associated variants. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2023:2023.12.19.23299592. [PMID: 38196587 PMCID: PMC10775332 DOI: 10.1101/2023.12.19.23299592] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2024]
Abstract
Brugada Syndrome (BrS) is an inheritable arrhythmia condition that is associated with rare, loss-of-function variants in the cardiac sodium channel gene, SCN5A. Interpreting the pathogenicity of SCN5A missense variants is challenging and ~79% of SCN5A missense variants in ClinVar are currently classified as Variants of Uncertain Significance (VUS). An in vitro SCN5A-BrS automated patch clamp assay was generated for high-throughput functional studies of NaV1.5. The assay was independently studied at two separate research sites - Vanderbilt University Medical Center and Victor Chang Cardiac Research Institute - revealing strong correlations, including peak INa density (R2=0.86). The assay was calibrated according to ClinGen Sequence Variant Interpretation recommendations using high-confidence variant controls (n=49). Normal and abnormal ranges of function were established based on the distribution of benign variant assay results. The assay accurately distinguished benign controls (24/25) from pathogenic controls (23/24). Odds of Pathogenicity values derived from the experimental results yielded 0.042 for normal function (BS3 criterion) and 24.0 for abnormal function (PS3 criterion), resulting in up to strong evidence for both ACMG criteria. The calibrated assay was then used to study SCN5A VUS observed in four families with BrS and other arrhythmia phenotypes associated with SCN5A loss-of-function. The assay revealed loss-of-function for three of four variants, enabling reclassification to likely pathogenic. This validated APC assay provides clinical-grade functional evidence for the reclassification of current VUS and will aid future SCN5A-BrS variant classification.
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Affiliation(s)
- Joanne G. Ma
- Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia
- School of Clinical Medicine, UNSW Sydney, Darlinghurst, NSW, Australia
| | | | - Ebony Richardson
- Clinical Genomics Laboratory, Centre for Population Genomics, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia and Murdoch Children Research Institute, Melbourne, Australia
| | - Kate L. Thomson
- Oxford Genetics Laboratories, Churchill Hospital, Oxford, UK
| | - Jodie Ingles
- Clinical Genomics Laboratory, Centre for Population Genomics, Garvan Institute of Medical Research, Darlinghurst, NSW, Australia and Murdoch Children Research Institute, Melbourne, Australia
| | - Ayesha Muhammad
- Vanderbilt University School of Medicine, Nashville, TN, USA
| | - Joseph F. Solus
- Vanderbilt Center for Arrhythmia Research and Therapeutics (VanCART), Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Giovanni Davogustto
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Katherine C. Anderson
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - M. Benjamin Shoemaker
- Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Andrew B. Stergachis
- University of Washington School of Medicine, Department of Medicine, Seattle, WA, USA
| | - Brendan J. Floyd
- Stanford Center for Inherited Cardiovascular Disease, Stanford University School of Medicine, Stanford, CA, USA
| | - Kyla Dunn
- Stanford Center for Inherited Cardiovascular Disease, Stanford University School of Medicine, Stanford, CA, USA
| | - Victoria N. Parikh
- Stanford Center for Inherited Cardiovascular Disease, Stanford University School of Medicine, Stanford, CA, USA
| | - Henry Chubb
- Stanford Center for Inherited Cardiovascular Disease, Stanford University School of Medicine, Stanford, CA, USA
| | - Mark J. Perrin
- Department of Genomic Medicine, Royal Melbourne Hospital, Victoria, Australia
| | - Dan M. Roden
- Vanderbilt Center for Arrhythmia Research and Therapeutics (VanCART), Departments of Medicine, Pharmacology, and Biomedical Informatics, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Jamie I. Vandenberg
- Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia
- School of Clinical Medicine, UNSW Sydney, Darlinghurst, NSW, Australia
| | - Chai-Ann Ng
- Mark Cowley Lidwill Research Program in Cardiac Electrophysiology, Victor Chang Cardiac Research Institute, Darlinghurst, NSW, Australia
- School of Clinical Medicine, UNSW Sydney, Darlinghurst, NSW, Australia
| | - Andrew M. Glazer
- Vanderbilt Center for Arrhythmia Research and Therapeutics (VanCART), Division of Clinical Pharmacology, Department of Medicine, Vanderbilt University Medical Center, Nashville, TN, USA
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Miller JA, Moise N, Weinberg SH. Modeling incomplete penetrance in long QT syndrome type 3 through ion channel heterogeneity: an in silico population study. Am J Physiol Heart Circ Physiol 2023; 324:H179-H197. [PMID: 36487185 PMCID: PMC10072004 DOI: 10.1152/ajpheart.00430.2022] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Revised: 11/16/2022] [Accepted: 11/29/2022] [Indexed: 12/14/2022]
Abstract
Many cardiac diseases are characterized by an increased late sodium current, including heart failure, hypertrophic cardiomyopathy, and inherited long QT syndrome type 3 (LQT3). The late sodium current in LQT3 is caused by a gain-of-function mutation in the voltage-gated sodium channel Nav1.5. Despite a well-defined genetic cause of LQT3, treatment remains inconsistent because of incomplete penetrance of the mutation and variability of antiarrhythmic efficacy. Here, we investigate the relationship between LQT3-associated mutation incomplete penetrance and variability in ion channel expression, simulating a population of 1,000 individuals with the O'Hara-Rudy model of the human ventricular myocyte. We first simulate healthy electrical activity (i.e., in the absence of a mutation) and then incorporate heterozygous expression for three LQT3-associated mutations (Y1795C, I1768V, and ΔKPQ), to directly compare the effects of each mutation on individuals across a diverse population. For all mutations, we find that susceptibility, defined by either the presence of an early afterdepolarization (EAD) or prolonged action potential duration (APD), primarily depends on the balance between the conductance of IKr and INa, for which individuals with a higher IKr-to-INa ratio are less susceptible. Furthermore, we find distinct differences across the population, observing individuals susceptible to zero, one, two, or all three mutations. Individuals tend to be less susceptible with an appropriate balance of repolarizing currents, typically via increased IKs or IK1. Interestingly, the more critical repolarizing current is mutation specific. We conclude that the balance between key currents plays a significant role in mutant-specific presentation of the disease phenotype in LQT3.NEW & NOTEWORTHY An in silico population approach investigates the relationship between variability in ion channel expression and gain-of-function mutations in the voltage-gated sodium channel associated with the congenital disorder long QT syndrome type 3 (LQT3). We find that ion channel variability can contribute to incomplete penetrance of the mutation, with mutant-specific differences in ion channel conductances leading to susceptibility to proarrhythmic action potential duration prolongation or early afterdepolarizations.
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Affiliation(s)
- Jacob A Miller
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio
| | - Nicolae Moise
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio
| | - Seth H Weinberg
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio
- Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, Ohio
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Precision medicine for long QT syndrome: patient-specific iPSCs take the lead. Expert Rev Mol Med 2023; 25:e5. [PMID: 36597672 DOI: 10.1017/erm.2022.43] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Long QT syndrome (LQTS) is a detrimental arrhythmia syndrome mainly caused by dysregulated expression or aberrant function of ion channels. The major clinical symptoms of ventricular arrhythmia, palpitations and syncope vary among LQTS subtypes. Susceptibility to malignant arrhythmia is a result of delayed repolarisation of the cardiomyocyte action potential (AP). There are 17 distinct subtypes of LQTS linked to 15 autosomal dominant genes with monogenic mutations. However, due to the presence of modifier genes, the identical mutation may result in completely different clinical manifestations in different carriers. In this review, we describe the roles of various ion channels in orchestrating APs and discuss molecular aetiologies of various types of LQTS. We highlight the usage of patient-specific induced pluripotent stem cell (iPSC) models in characterising fundamental mechanisms associated with LQTS. To mitigate the outcomes of LQTS, treatment strategies are initially focused on small molecules targeting ion channel activities. Next-generation treatments will reap the benefits from development of LQTS patient-specific iPSC platform, which is bolstered by the state-of-the-art technologies including whole-genome sequencing, CRISPR genome editing and machine learning. Deep phenotyping and high-throughput drug testing using LQTS patient-specific cardiomyocytes herald the upcoming precision medicine in LQTS.
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Kanaporis G, Blatter LA. Activation of small conductance Ca 2+ -activated K + channels suppresses Ca 2+ transient and action potential alternans in ventricular myocytes. J Physiol 2023; 601:51-67. [PMID: 36426548 PMCID: PMC9878619 DOI: 10.1113/jp283870] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 11/22/2022] [Indexed: 11/27/2022] Open
Abstract
At the cellular level, cardiac alternans is observed as beat-to-beat alternations in contraction strength, action potential (AP) morphology and Ca2+ transient (CaT) amplitude, and is a risk factor for cardiac arrhythmia. The (patho)physiological roles of small conductance Ca2+ -activated K+ (SK) channels in ventricles are poorly understood. We tested the hypothesis that in single rabbit ventricular myocytes pharmacological modulation of SK channels plays a causative role for the development of pacing-induced CaT and AP duration (APD) alternans. SK channel blockers (apamin, UCL1684) had only a minor effect on AP repolarization. However, SK channel activation by NS309 resulted in significant APD shortening, demonstrating that functional SK channels are well expressed in ventricular myocytes. The effects of NS309 were prevented or reversed by apamin and UCL1684, indicating that NS309 acted on SK channels. SK channel activation abolished or reduced the degree of pacing-induced CaT and APD alternans. Inhibition of KV 7.1 (with HMR1556) and KV 11.1 (with E4031) channels was used to mimic conditions of long QT syndromes type-1 and type-2, respectively. Both HMR1556 and E4031 enhanced CaT alternans that was prevented by SK channel activation. In AP voltage-clamped cells the SK channel activator had no effect on CaT alternans, confirming that suppression of CaT alternans was caused by APD shortening. APD shortening contributed to protection from alternans by lowering sarcoplasmic reticulum Ca2+ content and curtailing Ca2+ release. The data suggest that SK activation could be a potential intervention to avert development of alternans with important ramifications for arrhythmia prevention and therapy for patients with long QT syndrome. KEY POINTS: At the cellular level, cardiac alternans is observed as beat-to-beat alternations in contraction strength, action potential (AP) morphology and intracellular Ca2+ release amplitude, and is a risk factor for cardiac arrhythmia. The (patho)physiological roles of small conductance Ca2+ -activated K+ (SK) channels in ventricles are poorly understood. We investigated whether pharmacological modulation of SK channels affects the development of cardiac alternans in normal ventricular cells and in cells with drug-induced long QT syndrome (LQTS). While SK channel blockers have only a minor effect on AP morphology, their activation leads to AP shortening and abolishes or reduces the degree of pacing-induced Ca2+ and AP alternans. AP shortening contributed to protection against alternans by lowering sarcoplasmic reticulum Ca2+ content and curtailing Ca2+ release. The data suggest SK activation as a potential intervention to avert the development of alternans with important ramifications for arrhythmia prevention for patients with LQTS.
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Affiliation(s)
- Giedrius Kanaporis
- Department of Physiology & Biophysics, Rush University Medical Center, Chicago, Illinois, USA
| | - Lothar A Blatter
- Department of Physiology & Biophysics, Rush University Medical Center, Chicago, Illinois, USA
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vom Dahl C, Müller CE, Berisha X, Nagel G, Zimmer T. Coupling the Cardiac Voltage-Gated Sodium Channel to Channelrhodopsin-2 Generates Novel Optical Switches for Action Potential Studies. MEMBRANES 2022; 12:907. [PMID: 36295666 PMCID: PMC9607247 DOI: 10.3390/membranes12100907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Revised: 09/09/2022] [Accepted: 09/12/2022] [Indexed: 06/16/2023]
Abstract
Voltage-gated sodium (Na+) channels respond to short membrane depolarization with conformational changes leading to pore opening, Na+ influx, and action potential (AP) upstroke. In the present study, we coupled channelrhodopsin-2 (ChR2), the key ion channel in optogenetics, directly to the cardiac voltage-gated Na+ channel (Nav1.5). Fusion constructs were expressed in Xenopus laevis oocytes, and electrophysiological recordings were performed by the two-microelectrode technique. Heteromeric channels retained both typical Nav1.5 kinetics and light-sensitive ChR2 properties. Switching to the current-clamp mode and applying short blue-light pulses resulted either in subthreshold depolarization or in a rapid change of membrane polarity typically seen in APs of excitable cells. To study the effect of individual K+ channels on the AP shape, we co-expressed either Kv1.2 or hERG with one of the Nav1.5-ChR2 fusions. As expected, both delayed rectifier K+ channels shortened AP duration significantly. Kv1.2 currents remarkably accelerated initial repolarization, whereas hERG channel activity efficiently restored the resting membrane potential. Finally, we investigated the effect of the LQT3 deletion mutant ΔKPQ on the AP shape and noticed an extremely prolonged AP duration that was directly correlated to the size of the non-inactivating Na+ current fraction. In conclusion, coupling of ChR2 to a voltage-gated Na+ channel generates optical switches that are useful for studying the effect of individual ion channels on the AP shape. Moreover, our novel optogenetic approach provides the potential for an application in pharmacology and optogenetic tissue-engineering.
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Affiliation(s)
- Christian vom Dahl
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, 07740 Jena, Germany
| | - Christoph Emanuel Müller
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, 07740 Jena, Germany
| | - Xhevat Berisha
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, 07740 Jena, Germany
| | - Georg Nagel
- Institute of Physiology—Neurophysiology, Julius Maximilians University, 97070 Wuerzburg, Germany
| | - Thomas Zimmer
- Institute of Physiology II, University Hospital Jena, Friedrich Schiller University, 07740 Jena, Germany
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QTc Prolongation in Poison Center Exposures to CredibleMeds List of Substances with "Known Risk of Torsades de Pointes". Cardiovasc Toxicol 2022; 22:866-877. [PMID: 35930218 DOI: 10.1007/s12012-022-09764-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/03/2022] [Accepted: 07/11/2022] [Indexed: 11/03/2022]
Abstract
Many drugs carry some risk of QT interval prolongation, which can lead to life-threatening dysrhythmias including Torsades de Pointes (TdP). CredibleMeds.org identifies medications categorized as "Known Risk of TdP" but does not stratify risk in acute supratherapeutic ingestions. We sought to determine the proportion of cases exhibiting QTc prolongation and life-threatening dysrhythmias including ventricular tachycardia (VT)/ventricular fibrillation (VF), TdP, and asystole in patients exposed to these substances. Retrospective chart review of cases reported to our Regional Poison Center from 2014 to 2019 of exposures to one or more of the "Known Risk" substances was performed. Demographics, therapies, clinical effects, and medical outcome for each case were analyzed. There were 1125 exposures, of which 760 had a documented QTc interval. QTc ≥ 500 ms was reported in 138 (18.2%) of the 760 cases. The most common "Known Risk" substances were citalopram, escitalopram and cocaine. Although not in the "Known Risk" category, mirtazapine, amitriptyline, diphenhydramine, and trazodone had a statistically significant association with QTc > 500 ms. Life-threatening dysrhythmias occurred in 13 cases, with VT/VF in 6 of the 760 (0.8%) cases, and one case of TdP. Flecainide (OR 11.1, 95% CI 2.2-55.8) and methadone (OR 7.1, 95% CI 2.1-23.4) were associated with increased risk of all life-threatening dysrhythmias. Exposures to medications on the Credible Meds list of "Known Risk of TdP" QTc prolongation is common, but life-threatening dysrhythmias are rare. Mirtazapine, amitriptyline, diphenhydramine, and trazodone were associated with prolonged QTc. Flecainide and methadone had the highest associated risk of life-threatening dysrhythmias.
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Fouda MA, Ghovanloo MR, Ruben PC. Late sodium current: incomplete inactivation triggers seizures, myotonias, arrhythmias, and pain syndromes. J Physiol 2022; 600:2835-2851. [PMID: 35436004 DOI: 10.1113/jp282768] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2022] [Accepted: 04/12/2022] [Indexed: 11/08/2022] Open
Abstract
Acquired and inherited dysfunction in voltage-gated sodium channels underlies a wide range of diseases. "In addition to the defects in trafficking and expression, sodium channelopathies are also caused by dysfunction in one or several gating properties, for instance activation or inactivation. Disruption of the channel inactivation leads to the increased late sodium current, which is a common defect in seizure disorders, cardiac arrhythmias skeletal muscle myotonia and pain. An increase in late sodium current leads to repetitive action potential in neurons and skeletal muscles, and prolonged action potential duration in the heart. In this topical review, we compare the effects of late sodium current in brain, heart, skeletal muscle, and peripheral nerves. Abstract figure legend Shows cartoon illustration of general Nav channel transitions between (1) resting, (2) open, and (3) fast inactivated states. Disruption of the inactivation process exacerbates (4) late sodium currents. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Mohamed A Fouda
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada.,Department of Pharmacology and Toxicology, Alexandria University, Alexandria, Egypt
| | | | - Peter C Ruben
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, Canada
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Seed LM, Hearn TJ. A Systematic Review of Utilisation of Diurnal Timing Information in Clinical Trial Design for Long QT Syndrome. Front Pharmacol 2022; 13:867131. [PMID: 35370731 PMCID: PMC8965098 DOI: 10.3389/fphar.2022.867131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Accepted: 02/21/2022] [Indexed: 11/13/2022] Open
Abstract
Diurnal oscillations in human cardiac electrophysiology are thought to be under the control of the endogenous circadian clock. The incidence of arrhythmic events in patients with Long QT syndrome (LQTS) varies diurnally. The diurnal variation in QT interval has previously been identified as a potential for error in clinical trials which utilise ECG measurement. We performed a systematic review of clinical trials for LQTS to identify practice around specification of timing information for point electrocardiogram (ECG) measurements, analysis of continual ECG recordings ≥24 h, and drug delivery. Despite guidelines having been issued around the analysis of 24-h ECG recordings, we identify a lack of usage of detailed time of day information in trial design for LQTS studies, which has the potential to affect the interpretation of the results of drug trials. We identify that, in contrast, clinical trials for QT prolonging drugs demonstrate increased incorporation of time of day information of both QT analysis and drug dosing. We provide a visual portal to allow trial designers and clinicians to better understand timing of common cardiac-targeting drugs, and to bear this concept in mind in the design of future clinical trials.
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Affiliation(s)
- Lydia M Seed
- Department of Medical Genetics, University of Cambridge, Cambridge, United Kingdom
| | - Timothy J Hearn
- Department of Medical Genetics, University of Cambridge, Cambridge, United Kingdom
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Daimi H, Lozano-Velasco E, Aranega A, Franco D. Genomic and Non-Genomic Regulatory Mechanisms of the Cardiac Sodium Channel in Cardiac Arrhythmias. Int J Mol Sci 2022; 23:1381. [PMID: 35163304 PMCID: PMC8835759 DOI: 10.3390/ijms23031381] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 12/30/2021] [Accepted: 01/06/2022] [Indexed: 12/19/2022] Open
Abstract
Nav1.5 is the predominant cardiac sodium channel subtype, encoded by the SCN5A gene, which is involved in the initiation and conduction of action potentials throughout the heart. Along its biosynthesis process, Nav1.5 undergoes strict genomic and non-genomic regulatory and quality control steps that allow only newly synthesized channels to reach their final membrane destination and carry out their electrophysiological role. These regulatory pathways are ensured by distinct interacting proteins that accompany the nascent Nav1.5 protein along with different subcellular organelles. Defects on a large number of these pathways have a tremendous impact on Nav1.5 functionality and are thus intimately linked to cardiac arrhythmias. In the present review, we provide current state-of-the-art information on the molecular events that regulate SCN5A/Nav1.5 and the cardiac channelopathies associated with defects in these pathways.
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Affiliation(s)
- Houria Daimi
- Biochemistry and Molecular Biology Laboratory, Faculty of Pharmacy, University of Monastir, Monastir 5000, Tunisia
| | - Estefanía Lozano-Velasco
- Department of Experimental Biology, University of Jaen, 23071 Jaen, Spain; (E.L.-V.); (A.A.); (D.F.)
- Medina Foundation, Technology Park of Health Sciences, Av. del Conocimiento, 34, 18016 Granada, Spain
| | - Amelia Aranega
- Department of Experimental Biology, University of Jaen, 23071 Jaen, Spain; (E.L.-V.); (A.A.); (D.F.)
- Medina Foundation, Technology Park of Health Sciences, Av. del Conocimiento, 34, 18016 Granada, Spain
| | - Diego Franco
- Department of Experimental Biology, University of Jaen, 23071 Jaen, Spain; (E.L.-V.); (A.A.); (D.F.)
- Medina Foundation, Technology Park of Health Sciences, Av. del Conocimiento, 34, 18016 Granada, Spain
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Maddali M, Kandachar P, Al-Abri I, Al-Yamani M. Diagnostic lacunae and implications of an automated implantable cardioverter defibrillator implantation in a child with type 3 Long QT (LQT3) syndrome. Ann Card Anaesth 2022; 25:210-213. [PMID: 35417973 PMCID: PMC9244276 DOI: 10.4103/aca.aca_13_21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A diagnosis of congenital long QT interval syndrome based on history and electrocardiogram was made in a child in the absence of readily available genetic testing. A genotype 3 (LQT3) was suspected after exclusion of other variants as the child was non-responsive to beta-blocker and sodium channel blocker medication. As the child continues to show episodic bradycardia, polymorphic ventricular ectopy, and T-wave alternans, a single-chamber automated implantable cardioverter-defibrillator implantation was done successfully. This report highlights how the diagnosis of LQT3 was arrived at as well as the anesthetic challenges in the management of patients with LQTS.
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Lee MJ, Monteil DC, Spooner MT. Peripartum management of patient with long QT3 after successful implantable cardioverter defibrillator device discharge resulting in device failure: a case report. Eur Heart J Case Rep 2021; 5:ytab487. [PMID: 34926986 PMCID: PMC8672658 DOI: 10.1093/ehjcr/ytab487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 08/17/2021] [Accepted: 11/24/2021] [Indexed: 11/18/2022]
Abstract
Background Long QT3 syndrome type 3 (LQT3) is a gain of function mutation of the SCN5A gene that is inherited in an autosomal dominant fashion. Long QT3 syndrome type 3 results in an increase in arrhythmic events during rest, sleep, and bradycardia by extending the QT interval and inducing Torsades de pointes and sudden cardiac death. Attempting to block the sodium channel with Class I anti-arrhythmics or blocking adrenergic tone with beta-blockers especially in women has shown to be beneficial. There have been few large-scale studies on treating patients with LQT3 due to its lethality and underreported number of cases. Specifically, the safety and efficacy of pharmacologic treatment in pregnant LQT3 patients are unknown. Case summary This case demonstrates the safe use of Mexiletine and Propranolol in a 3rd-trimester pregnant LQT3 patient after a presumed ventricular arrhythmia and device-lead electrical short from therapy rendered her implantable cardioverter defibrillator inoperable in a VVI mode (venticular demand pacing). With appropriate medications, the patient was safely monitored through the remainder of her pregnancy and safely delivered at 36 weeks of pregnancy a healthy baby girl. The daughter, heterozygous for LQT3, showed no evidence of intrauterine growth restriction or other side effects from the medications. Discussion There are many variants of the SCN5A gene mutations that can lead to different phenotypes and not all mutations are responsive to the same medications. In this case, Mexiletine and Propranolol, both of which have only recently shown to benefit certain variants or LQT3 respectively, were safely started during the 3rd trimester of pregnancy without harming the foetus.
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Affiliation(s)
- Melissa J Lee
- Department of Internal Medicine, Naval Medical Center Portsmouth, 620 John Paul Jones Cir, Portsmouth, VA 23708, USA
| | - Danielle C Monteil
- Department of Neurodevelopmental Pediatrics, Naval Medical Center Portsmouth, 620 John Paul Jones Cir, Portsmouth, VA 23708, USA
| | - Michael T Spooner
- Department of Cardiology, Naval Medical Center Portsmouth, 620 John Paul Jones Cir, Portsmouth, VA 23708, USA
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Wu X, Hoeker GS, Blair GA, King DR, Gourdie RG, Weinberg SH, Poelzing S. Hypernatremia and intercalated disc edema synergistically exacerbate long-QT syndrome type 3 phenotype. Am J Physiol Heart Circ Physiol 2021; 321:H1042-H1055. [PMID: 34623182 DOI: 10.1152/ajpheart.00366.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Cardiac voltage-gated sodium channel gain-of-function prolongs repolarization in the long-QT syndrome type 3 (LQT3). Previous studies suggest that narrowing the perinexus within the intercalated disc, leading to rapid sodium depletion, attenuates LQT3-associated action potential duration (APD) prolongation. However, it remains unknown whether extracellular sodium concentration modulates APD prolongation during sodium channel gain-of-function. We hypothesized that elevated extracellular sodium concentration and widened perinexus synergistically prolong APD in LQT3. LQT3 was induced with sea anemone toxin (ATXII) in Langendorff-perfused guinea pig hearts (n = 34). Sodium concentration was increased from 145 to 160 mM. Perinexal expansion was induced with mannitol or the sodium channel β1-subunit adhesion domain antagonist (βadp1). Epicardial ventricular action potentials were optically mapped. Individual and combined effects of varying clefts and sodium concentrations were simulated in a computational model. With ATXII, both mannitol and βadp1 significantly widened the perinexus and prolonged APD, respectively. The elevated sodium concentration alone significantly prolonged APD as well. Importantly, the combination of elevated sodium concentration and perinexal widening synergistically prolonged APD. Computational modeling results were consistent with animal experiments. Concurrently elevating extracellular sodium and increasing intercalated disc edema prolongs repolarization more than the individual interventions alone in LQT3. This synergistic effect suggests an important clinical implication that hypernatremia in the presence of cardiac edema can markedly increase LQT3-associated APD prolongation. Therefore, to our knowledge, this is the first study to provide evidence of a tractable and effective strategy to mitigate LQT3 phenotype by means of managing sodium levels and preventing cardiac edema in patients.NEW & NOTEWORTHY This is the first study to demonstrate that the long-QT syndrome type 3 (LQT3) phenotype can be exacerbated or concealed by regulating extracellular sodium concentrations and/or the intercalated disc separation. The animal experiments and computational modeling in the current study reveal a critically important clinical implication: sodium dysregulation in the presence of edema within the intercalated disc can markedly increase the risk of arrhythmia in LQT3. These findings strongly suggest that maintaining extracellular sodium within normal physiological limits may be an effective and inexpensive therapeutic option for patients with congenital or acquired sodium channel gain-of-function diseases.
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Affiliation(s)
- Xiaobo Wu
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Gregory S Hoeker
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Grace A Blair
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - D Ryan King
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Robert G Gourdie
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Seth H Weinberg
- Department of Biomedical Engineering, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio
| | - Steven Poelzing
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
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13
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Kamga MVK, Reppel M, Hescheler J, Nguemo F. Modeling genetic cardiac channelopathies using induced pluripotent stem cells - Status quo from an electrophysiological perspective. Biochem Pharmacol 2021; 192:114746. [PMID: 34461117 DOI: 10.1016/j.bcp.2021.114746] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 08/24/2021] [Accepted: 08/24/2021] [Indexed: 12/15/2022]
Abstract
Long QT syndrome (LQTS), Brugada syndrome (BrS), and catecholaminergic polymorphic ventricular tachycardia (CPVT) are genetic diseases of the heart caused by mutations in specific cardiac ion channels and are characterized by paroxysmal arrhythmias, which can deteriorate into ventricular fibrillation. In LQTS3 and BrS different mutations in the SCN5A gene lead to a gain-or a loss-of-function of the voltage-gated sodium channel Nav1.5, respectively. Although sharing the same gene mutation, these syndromes are characterized by different clinical manifestations and functional perturbations and in some cases even present an overlapping clinical phenotype. Several studies have shown that Na+ current abnormalities in LQTS3 and BrS can also cause Ca2+-signaling aberrancies in cardiomyocytes (CMs). Abnormal Ca2+ homeostasis is also the main feature of CPVT which is mostly caused by heterozygous mutations in the RyR2 gene. Large numbers of disease-causing mutations were identified in RyR2 and SCN5A but it is not clear how different variants in the SCN5A gene produce different clinical syndromes and if in CPVT Ca2+ abnormalities and drug sensitivities vary depending on the mutation site in the RyR2. These questions can now be addressed by using patient-specific in vitro models of these diseases based on induced pluripotent stem cells (iPSCs). In this review, we summarize different insights gained from these models with a focus on electrophysiological perturbations caused by different ion channel mutations and discuss how will this knowledge help develop better stratification and more efficient personalized therapies for these patients.
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Affiliation(s)
- Michelle Vanessa Kapchoup Kamga
- Center for Physiology and Pathophysiology, Institute for Neurophysiology, Medical Faculty, University of Cologne, 50931 Cologne, Germany
| | - Michael Reppel
- Center for Physiology and Pathophysiology, Institute for Neurophysiology, Medical Faculty, University of Cologne, 50931 Cologne, Germany; Praxis für Kardiologie und Angiologie, Landsberg am Lech, Germany
| | - Jürgen Hescheler
- Center for Physiology and Pathophysiology, Institute for Neurophysiology, Medical Faculty, University of Cologne, 50931 Cologne, Germany
| | - Filomain Nguemo
- Center for Physiology and Pathophysiology, Institute for Neurophysiology, Medical Faculty, University of Cologne, 50931 Cologne, Germany.
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14
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Lankaputhra M, Voskoboinik A. Congenital Long QT Syndrome: A Clinician's Guide. Intern Med J 2021; 51:1999-2011. [PMID: 34151491 DOI: 10.1111/imj.15437] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 05/31/2021] [Accepted: 06/15/2021] [Indexed: 11/29/2022]
Abstract
Congenital long QT syndrome (LQTS) is a familial cardiac ion channelopathy first described over sixty years ago. It is characterised by prolonged ventricular repolarization (long QT on ECG), ventricular arrhythmias and associated syncope or sudden cardiac death. As the most closely studied cardiac channelopathy, over the decades we have gained a deep appreciation of the complex genetic model of LQTS. Variability in genetic expression and incomplete penetrance leads to a heterogenous phenotype that can be challenging to clinically classify. In recent times, progress has been made in diagnostic method, risk stratification and treatment options. This review has been written as a guide for the general cardiologist to understand the basic pathophysiology, diagnosis, and management priorities for the most encountered LQTS subtypes: LQT1, LQT2 and LQT3. This article is protected by copyright. All rights reserved.
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Affiliation(s)
| | - Aleksandr Voskoboinik
- Division of Cardiology, Alfred Health, Melbourne, Australia.,Division of Cardiology Western Health, Monash University & Baker Heart & Diabetes Institute, Melbourne, Australia
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15
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Brugada-Terradellas C, Hellemans A, Brugada P, Smets P. Sudden cardiac death: A comparative review of humans, dogs and cats. Vet J 2021; 274:105696. [PMID: 34148018 DOI: 10.1016/j.tvjl.2021.105696] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 05/22/2021] [Accepted: 05/24/2021] [Indexed: 01/14/2023]
Abstract
Sudden death is one of the most common causes of death in humans in Western countries. Approximately 85% of these cases are of cardiac origin. In dogs and cats, sudden cardiac death (SCD) also commonly occurs, but fewer pathophysiological and prevalence data are available. Both structural, primarily 'electrical' and ischemic heart diseases are known to cause SCD, many of which share similar underlying arrhythmogenic mechanisms between humans and companion animals. As for underlying genetics, numerous mutations on multiple loci have been related to SCD in humans, but only a few mutations associated with dilated cardiomyopathy and SCD have been identified in dogs, e.g. in the phospholamban and titin genes. Information published from human medicine can therefore inform future veterinary studies, but also dogs and cats could act as spontaneous models of SCD in humans. Further research in both fields is therefore warranted to better understand the pathophysiology, genetics, and prevention of SCD.
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Affiliation(s)
- Celine Brugada-Terradellas
- Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium.
| | - Arnaut Hellemans
- Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
| | - Pedro Brugada
- Pedro Brugada, Cardiovascular Division, UZ Brussel - VUB, Avenue du Laerbeek 101, 1090 Brussels, Belgium
| | - Pascale Smets
- Small Animal Department, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
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16
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Melgar Quicaño LA, Chipa Ccasani F. [Congenital long QT syndrome]. ARCHIVOS PERUANOS DE CARDIOLOGIA Y CIRUGIA CARDIOVASCULAR 2021; 2:49-57. [PMID: 37727265 PMCID: PMC10506569 DOI: 10.47487/apcyccv.v2i1.125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 03/17/2021] [Indexed: 09/21/2023]
Abstract
Congenital long QT syndrome (LQTS) represents a group of heart diseases of genetic origin characterized by prolongation of the QT interval and an abnormal T wave on the electrocardiogram (ECG). They can have a dominant or recessive expression, the latter associated with sensorineural deafness. In both cases, its clinical presentation is associated with recurrent syncope and sudden death as a consequence of ventricular tachycardia, specifically Torsades de Pointes. Currently they are classified according to the specific genetic defect, being able to compromise around 16 genes and almost 2000 mutations. It should be suspected in individuals with related symptoms, electrocardiographic findings, and family history. Management is based on the reduction or elimination of symptoms, and concomitantly the prevention of sudden death (SD), in those children with congenital deafness, the management requires the application of the otolaryngologist specialist's own measures. The cardiovascular management implies the modification of lifestyles, mainly the prohibition of competitive sports, including swimming, avoiding exposure to loud sounds or triggers. The medications used include beta-blockers, and more rarely flecainide, ranozaline, and verapamil; invasive management consists of the implantation of a cardioverter defibrillator or even left sympathetic denervation, each with its own risks and benefits. In any of the cases, we must avoid the circumstances that increase the QT interval, as well as carry out the appropriate analysis of the benefits and risks of each possible invasive measure.
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Affiliation(s)
| | - Fredy Chipa Ccasani
- Instituto Nacional de Salud del Niño, San Borja. Lima, PerúInstituto Nacional de Salud del NiñoLimaPerú
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17
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S Beserra S, Roman-Campos D. Impact of pacing frequency in amiodarone interaction with cardiomyocytes near physiological temperature in health and disease conditions. Basic Clin Pharmacol Toxicol 2020; 128:615-620. [PMID: 33124101 DOI: 10.1111/bcpt.13527] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 10/21/2020] [Accepted: 10/26/2020] [Indexed: 11/29/2022]
Abstract
Long QT syndrome type 3 (LQT-3) is a disease related to abnormal cardiac sodium channel function (Nav 1.5), usually due to augmented late sodium current (INaL ), and may lead to ventricular fibrillation. Amiodarone is approved for ventricular fibrillation. Thus, we investigated whether pacing frequency impacts the ability of amiodarone to reverse the arrhythmic phenotype observed in LQT-3. Anemone neurotoxin 2 (ATX-II, here named only ATX) was used to enhance INaL in mice left ventricular myocytes (LVM). A video detector system monitored sarcomere shortening. At 1 Hz, amiodarone attenuated sarcomere shortening only at 10 µmol/L; at 3 and 5 Hz, 0.1 and 1 µmol/L amiodarone also reduced sarcomere shortening. However, no effect of amiodarone was observed on time to 50% of sarcomere contraction and relaxation. In LVM exposed to ATX (10 nmol/L), an arrhythmic phenotype was observed, and it was more severe when cells were paced at 1 Hz. Amiodarone failed to reverse the ATX induced phenotype at different pacing frequencies. Thus, our results suggest that amiodarone's ability to reverse arrhythmias induced by augmentation of INaL is limited. These findings suggest further experimentation will be required to clarify whether a clinical effect can be ascribed to an effect of amiodarone on other ion channels in LQT-3.
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Affiliation(s)
- Samuel S Beserra
- Laboratory of CardioBiology, Department of Biophysics, Paulista School of Medicina, Federal University of Sao Paulo, Sao Paulo, Brazil
| | - Danilo Roman-Campos
- Laboratory of CardioBiology, Department of Biophysics, Paulista School of Medicina, Federal University of Sao Paulo, Sao Paulo, Brazil
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18
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Popa-Fotea NM, Cojocaru C, Scafa-Udriste A, Micheu MM, Dorobantu M. The Multifaced Perspectives of Genetic Testing in Pediatric Cardiomyopathies and Channelopathies. J Clin Med 2020; 9:E2111. [PMID: 32635562 PMCID: PMC7408669 DOI: 10.3390/jcm9072111] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 06/28/2020] [Accepted: 07/02/2020] [Indexed: 12/22/2022] Open
Abstract
Pediatric inherited cardiomyopathies (CMPs) and channelopathies (CNPs) remain important causes of death in this population, therefore, there is a need for prompt diagnosis and tailored treatment. Conventional evaluation fails to establish the diagnosis of pediatric CMPs and CNPs in a significant proportion, prompting further, more complex testing to make a diagnosis that could influence the implementation of lifesaving strategies. Genetic testing in CMPs and CNPs may help unveil the underlying cause, but needs to be carried out with caution given the lack of uniform recommendations in guidelines about the precise time to start the genetic evaluation or the type of targeted testing or whole-genome sequencing. A very diverse etiology and the scarce number of randomized studies of pediatric CMPs and CNPs make genetic testing of these maladies far more particular than their adult counterpart. The genetic diagnosis is even more puzzling if the psychological impact point of view is taken into account. This review aims to put together different perspectives, state-of-the art recommendations-synthetizing the major indications from European and American guidelines-and psychosocial outlooks to construct a comprehensive genetic assessment of pediatric CMPs and CNPs.
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Affiliation(s)
- Nicoleta-Monica Popa-Fotea
- Department of Cardiology, Clinical Emergency Hospital of Bucharest, Floreasca Street 8, 014461 Bucharest, Romania; (N.-M.P.-F.); (C.C.); (A.S.-U.); (M.D.)
- Department 4—Cardiothoracic Pathology, University of Medicine and Pharmacy Carol Davila, Eroii Sanitari Bvd. 8, 050474 Bucharest, Romania
| | - Cosmin Cojocaru
- Department of Cardiology, Clinical Emergency Hospital of Bucharest, Floreasca Street 8, 014461 Bucharest, Romania; (N.-M.P.-F.); (C.C.); (A.S.-U.); (M.D.)
| | - Alexandru Scafa-Udriste
- Department of Cardiology, Clinical Emergency Hospital of Bucharest, Floreasca Street 8, 014461 Bucharest, Romania; (N.-M.P.-F.); (C.C.); (A.S.-U.); (M.D.)
- Department 4—Cardiothoracic Pathology, University of Medicine and Pharmacy Carol Davila, Eroii Sanitari Bvd. 8, 050474 Bucharest, Romania
| | - Miruna Mihaela Micheu
- Department of Cardiology, Clinical Emergency Hospital of Bucharest, Floreasca Street 8, 014461 Bucharest, Romania; (N.-M.P.-F.); (C.C.); (A.S.-U.); (M.D.)
| | - Maria Dorobantu
- Department of Cardiology, Clinical Emergency Hospital of Bucharest, Floreasca Street 8, 014461 Bucharest, Romania; (N.-M.P.-F.); (C.C.); (A.S.-U.); (M.D.)
- Department 4—Cardiothoracic Pathology, University of Medicine and Pharmacy Carol Davila, Eroii Sanitari Bvd. 8, 050474 Bucharest, Romania
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19
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Alvarez-Collazo J, López-Requena A, Alvarez JL, Talavera K. The Citrus Flavonoid Hesperetin Has an Inadequate Anti-Arrhythmic Profile in the ΔKPQ Na V1.5 Mutant of the Long QT Type 3 Syndrome. Biomolecules 2020; 10:biom10060952. [PMID: 32599724 PMCID: PMC7355927 DOI: 10.3390/biom10060952] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Revised: 06/19/2020] [Accepted: 06/21/2020] [Indexed: 11/19/2022] Open
Abstract
Type 3 long QT syndromes (LQT3) are associated with arrhythmogenic gain-of-function mutations in the cardiac voltage-gated Na+ channel (hNaV1.5). The citrus flavanone hesperetin (HSP) was previously suggested as a template molecule to develop new anti-arrhythmic drugs, as it blocks slowly-inactivating currents carried by the LQT3-associated hNaV1.5 channel mutant R1623Q. Here we investigated whether HSP also has potentially beneficial effects on another LQT3 hNaV1.5 channel variant, the ΔKPQ, which is associated to lethal ventricular arrhythmias. We used whole-cell patch-clamp to record Na+ currents (INa) in HEK293T cells transiently expressing hNaV1.5 wild type or ΔKPQ mutant channels. HSP blocked peak INa and the late INa carried by ΔKPQ mutant channels with an effective concentration of ≈300 μM. This inhibition was largely voltage-independent and tonic. HSP decreased the rate of inactivation of ΔKPQ channels and, consequently, was relatively weak in reducing the intracellular Na+ load in this mutation. We conclude that, although HSP has potential value for the treatment of the R1623Q LQT3 variant, this compound is inadequate to treat the LQT3 associated to the ΔKPQ genetic variant. Our results underscore the precision medicine rationale of better understanding the basic pathophysiological and pharmacological mechanisms to provide phenotype- genotype-directed individualization of treatment.
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20
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Nowak MB, Greer-Short A, Wan X, Wu X, Deschênes I, Weinberg SH, Poelzing S. Intercellular Sodium Regulates Repolarization in Cardiac Tissue with Sodium Channel Gain of Function. Biophys J 2020; 118:2829-2843. [PMID: 32402243 DOI: 10.1016/j.bpj.2020.04.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Revised: 03/26/2020] [Accepted: 04/10/2020] [Indexed: 11/30/2022] Open
Abstract
In cardiac myocytes, action potentials are initiated by an influx of sodium (Na+) ions via voltage-gated Na+ channels. Na+ channel gain of function (GOF), arising in both inherited conditions associated with mutation in the gene encoding the Na+ channel and acquired conditions associated with heart failure, ischemia, and atrial fibrillation, enhance Na+ influx, generating a late Na+ current that prolongs action potential duration (APD) and triggering proarrhythmic early afterdepolarizations (EADs). Recent studies have shown that Na+ channels are highly clustered at the myocyte intercalated disk, facilitating formation of Na+ nanodomains in the intercellular cleft between cells. Simulations from our group have recently predicted that narrowing the width of the intercellular cleft can suppress APD prolongation and EADs in the presence of Na+ channel mutations because of increased intercellular cleft Na+ ion depletion. In this study, we investigate the effects of modulating multiple extracellular spaces, specifically the intercellular cleft and bulk interstitial space, in a novel computational model and experimentally via osmotic agents albumin, dextran 70, and mannitol. We perform optical mapping and transmission electron microscopy in a drug-induced (sea anemone toxin, ATXII) Na+ channel GOF isolated heart model and modulate extracellular spaces via osmotic agents. Single-cell patch-clamp experiments confirmed that the osmotic agents individually do not enhance late Na+ current. Both experiments and simulations are consistent with the conclusion that intercellular cleft narrowing or expansion regulates APD prolongation; in contrast, modulating the bulk interstitial space has negligible effects on repolarization. Thus, we predict that intercellular cleft Na+ nanodomain formation and collapse critically regulates cardiac repolarization in the setting of Na+ channel GOF.
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Affiliation(s)
- Madison B Nowak
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio; Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia
| | - Amara Greer-Short
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio; Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Xiaoping Wan
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio
| | - Xiaobo Wu
- Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Blacksburg, Virginia; Fralin Biomedical Research Institute at Virginia Tech Carilion, Virginia Polytechnic Institute and State University, Roanoke, Virginia
| | - Isabelle Deschênes
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, Ohio; Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio
| | - Seth H Weinberg
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio; Department of Biomedical Engineering, Virginia Commonwealth University, Richmond, Virginia.
| | - Steven Poelzing
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Virginia Polytechnic Institute and State University, Roanoke, Virginia; Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
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21
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Huang C, Song Z, Landaw J, Qu Z. Spatially Discordant Repolarization Alternans in the Absence of Conduction Velocity Restitution. Biophys J 2020; 118:2574-2587. [PMID: 32101718 DOI: 10.1016/j.bpj.2020.02.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 01/21/2020] [Accepted: 02/06/2020] [Indexed: 01/20/2023] Open
Abstract
Spatially discordant alternans (SDA) of action potential duration (APD) has been widely observed in cardiac tissue and is linked to cardiac arrhythmogenesis. Theoretical studies have shown that conduction velocity restitution (CVR) is required for the formation of SDA. However, this theory is not completely supported by experiments, indicating that other mechanisms may exist. In this study, we carried out computer simulations using mathematical models of action potentials to investigate the mechanisms of SDA in cardiac tissue. We show that when CVR is present and engaged, such as fast pacing from one side of the tissue, the spatial pattern of APD in the tissue undergoes either spatially concordant alternans or SDA, independent of initial conditions or tissue heterogeneities. When CVR is not engaged, such as simultaneous pacing of the whole tissue or under normal/slow heart rates, the spatial pattern of APD in the tissue can have multiple solutions, including spatially concordant alternans and different SDA patterns, depending on heterogeneous initial conditions or pre-existing repolarization heterogeneities. In homogeneous tissue, curved nodal lines are not stable, which either evolve into straight lines or disappear. However, in heterogeneous itssue, curved nodal lines can be stable, depending on their initial locations and shapes relative to the structure of the heterogeneity. Therefore, CVR-induced SDA and non-CVR-induced SDA exhibit different dynamical properties, which may be responsible for the different SDA properties observed in experimental studies and arrhythmogenesis in different clinical settings.
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Affiliation(s)
- Chunli Huang
- Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Systems Science, Beijing Normal University, Beijing, China
| | - Zhen Song
- Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Julian Landaw
- Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Zhilin Qu
- Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Computational Medicine, University of California, Los Angeles, Los Angeles, California.
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22
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Neira V, Enriquez A, Simpson C, Baranchuk A. Update on long QT syndrome. J Cardiovasc Electrophysiol 2019; 30:3068-3078. [PMID: 31596038 DOI: 10.1111/jce.14227] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Revised: 09/17/2019] [Accepted: 10/05/2019] [Indexed: 12/24/2022]
Abstract
Long QT syndrome (LQTS) is an inherited disorder characterized by a prolonged QT interval in the 12-lead electrocardiogram and increased risk of malignant arrhythmias in patients with a structurally normal heart. Since its first description in the 1950s, advances in molecular genetics have greatly improved our understanding of the cause and mechanisms of this disease. Sixteen genes linked to LQTS have been described and genetic testing had become an integral part of the diagnosis and risk stratification. This article provides an updated review of the genetic basis, diagnosis, and clinical management of LQTS.
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Affiliation(s)
- Víctor Neira
- Division of Cardiology, Queen's University, Kingston, Ontario, Canada
| | - Andrés Enriquez
- Division of Cardiology, Queen's University, Kingston, Ontario, Canada
| | - Chris Simpson
- Division of Cardiology, Queen's University, Kingston, Ontario, Canada
| | - Adrian Baranchuk
- Division of Cardiology, Queen's University, Kingston, Ontario, Canada
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23
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Flecainide: Electrophysiological properties, clinical indications, and practical aspects. Pharmacol Res 2019; 148:104443. [PMID: 31493514 DOI: 10.1016/j.phrs.2019.104443] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 08/03/2019] [Accepted: 09/03/2019] [Indexed: 12/19/2022]
Abstract
Over the last 35 years, flecainide proved itself one of the most commonly used arrhythmic drugs, expanding its original indication for ventricular arrhythmias and results nowadays as the cornerstone of the rhythm control strategy in atrial fibrillation management of patients without structural heart disease. While the increased mortality associated with flecainide in the Cardiac Arrhythmia Suppression Trial (CAST) still casts his shadow over flecainide clinical profile, this compound has subsequently demonstrated safe and is now used successfully for a plethora of indications, including pharmacological cardioversion of atrial fibrillation, cathecolaminergic polymorphic ventricular tachycardia, supraventricular tachyarrhythmias and ventricular pre-excitation. Moreover, the recent marketing of a controlled release formulation, along with the intravenous and immediate release formulations, increased the armamentarium to the clinician's disposal while improving patients' compliance. In the present paper, we offer a comprehensive review of the anti-arrhythmic effects of flecainide, detailing its electrophysiological properties, its effects on the conduction system, its clinical use and the major side effects and contraindications in clinical practice.
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24
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Ghorayeb N, Stein R, Daher DJ, Silveira ADD, Ritt LEF, Santos DFPD, Sierra APR, Herdy AH, Araújo CGSD, Colombo CSSDS, Kopiler DA, Lacerda FFRD, Lazzoli JK, Matos LDNJD, Leitão MB, Francisco RC, Alô ROB, Timerman S, Carvalho TD, Garcia TG. The Brazilian Society of Cardiology and Brazilian Society of Exercise and Sports Medicine Updated Guidelines for Sports and Exercise Cardiology - 2019. Arq Bras Cardiol 2019; 112:326-368. [PMID: 30916199 PMCID: PMC6424031 DOI: 10.5935/abc.20190048] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Affiliation(s)
- Nabil Ghorayeb
- Instituto Dante Pazzanese de Cardiologia, São Paulo, SP - Brazil
- Hospital do Coração (HCor), Associação do Sanatório Sírio, São Paulo, SP - Brazil
- Programa de Pós-Graduação em Medicina do Esporte da Universidade Federal de São Paulo (UNIFESP), São Paulo, SP - Brazil
- Instituto de Assistência Médica ao Servidor Público Estadual (IAMSPE), São Paulo, SP - Brazil
| | - Ricardo Stein
- Programa de Pós-Graduação em Cardiologia e Ciências Cardiovasculares da Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS - Brazil
- Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul (HCPA/UFRGS), Porto Alegre, RS - Brazil
- Vitta Centro de Bem Estar Físico, Porto Alegre, RS - Brazil
| | - Daniel Jogaib Daher
- Hospital do Coração (HCor), Associação do Sanatório Sírio, São Paulo, SP - Brazil
| | - Anderson Donelli da Silveira
- Programa de Pós-Graduação em Cardiologia e Ciências Cardiovasculares da Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS - Brazil
- Hospital de Clínicas de Porto Alegre, Universidade Federal do Rio Grande do Sul (HCPA/UFRGS), Porto Alegre, RS - Brazil
- Vitta Centro de Bem Estar Físico, Porto Alegre, RS - Brazil
| | - Luiz Eduardo Fonteles Ritt
- Hospital Cárdio Pulmonar, Salvador, BA - Brazil
- Escola Bahiana de Medicina e Saúde Pública, Salvador, BA - Brazil
| | | | | | - Artur Haddad Herdy
- Instituto de Cardiologia de Santa Catarina, Florianópolis, SC - Brazil
- Clínica Cardiosport de Prevenção e Reabilitação, Florianópolis, SC - Brazil
| | | | - Cléa Simone Sabino de Souza Colombo
- Hospital do Coração (HCor), Associação do Sanatório Sírio, São Paulo, SP - Brazil
- Sports Cardiology, Cardiology Clinical Academic Group - St George's University of London,14 London - UK
| | - Daniel Arkader Kopiler
- Sociedade Brasileira de Medicina do Esporte e do Exercício (SBMEE), São Paulo, SP - Brazil
- Instituto Nacional de Cardiologia (INC), Rio de Janeiro, RJ - Brazil
| | - Filipe Ferrari Ribeiro de Lacerda
- Programa de Pós-Graduação em Cardiologia e Ciências Cardiovasculares da Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS - Brazil
| | - José Kawazoe Lazzoli
- Sociedade Brasileira de Medicina do Esporte e do Exercício (SBMEE), São Paulo, SP - Brazil
- Federação Internacional de Medicina do Esporte (FIMS), Lausanne - Switzerland
| | | | - Marcelo Bichels Leitão
- Sociedade Brasileira de Medicina do Esporte e do Exercício (SBMEE), São Paulo, SP - Brazil
| | - Ricardo Contesini Francisco
- Instituto Dante Pazzanese de Cardiologia, São Paulo, SP - Brazil
- Hospital do Coração (HCor), Associação do Sanatório Sírio, São Paulo, SP - Brazil
| | - Rodrigo Otávio Bougleux Alô
- Instituto Dante Pazzanese de Cardiologia, São Paulo, SP - Brazil
- Hospital Geral de São Mateus, São Paulo, SP - Brazil
| | - Sérgio Timerman
- Instituto do Coração da Faculdade de Medicina da Universidade de São Paulo (InCor-FMUSP), São Paulo, SP - Brazil
- Universidade Anhembi Morumbi, Laureate International Universities, São Paulo, SP - Brazil
| | - Tales de Carvalho
- Clínica Cardiosport de Prevenção e Reabilitação, Florianópolis, SC - Brazil
- Departamento de Ergometria e Reabilitação Cardiovascular da Sociedade Brasileira de Cardiologia (DERC/SBC), Rio de Janeiro, RJ - Brazil
- Universidade do Estado de Santa Catarina (UDESC), Florianópolis, SC - Brazil
| | - Thiago Ghorayeb Garcia
- Instituto Dante Pazzanese de Cardiologia, São Paulo, SP - Brazil
- Hospital do Coração (HCor), Associação do Sanatório Sírio, São Paulo, SP - Brazil
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25
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Staudt GE, Watkins SC. Anesthetic Considerations for Pediatric Patients With Congenital Long QT Syndrome. J Cardiothorac Vasc Anesth 2018; 33:2030-2038. [PMID: 30553610 DOI: 10.1053/j.jvca.2018.11.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Indexed: 11/11/2022]
Affiliation(s)
- Genevieve E Staudt
- Department of Anesthesiology, Vanderbilt University School of Medicine, Monroe Carell Jr. Children's Hospital at Vanderbilt, Nashville, TN.
| | - Scott C Watkins
- Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Johns Hopkins All Children's Hospital, St. Petersburg, FL
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