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Almarzuqi A, Kimber S, Quadros K, Senaratne J. Bidirectional Ventricular Tachycardia: Challenges and Solutions. Vasc Health Risk Manag 2022; 18:397-406. [PMID: 35698640 PMCID: PMC9188370 DOI: 10.2147/vhrm.s274857] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 05/14/2022] [Indexed: 11/23/2022] Open
Abstract
Bidirectional ventricular tachycardia (BiVT) is a rare form of ventricular tachycardia that manifests on surface electrocardiogram by dual QRS morphologies alternating on a beat-to-beat basis. It was first reported in the 1920s as a complication of digoxin, and since then, it has been reported in other conditions including fulminant myocarditis, sarcoidosis, catecholaminergic polymorphic ventricular tachycardia, and Andersen-Tawil syndrome. The mechanism for BiVT is not as well known as other forms of ventricular tachycardia but appears to include typical mechanisms including triggered activity from afterdepolarizations, abnormal automaticity, or reentry. This review will go beyond the definition, surface electrocardiogram, mechanisms, causes, and treatment of BiVT as per our current understanding.
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Affiliation(s)
- Ahmed Almarzuqi
- Division of Cardiology, Department of Medicine, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada
| | - Shane Kimber
- Division of Cardiology, Department of Medicine, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada
| | - Kenneth Quadros
- Division of Cardiology, Department of Medicine, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada
| | - Janek Senaratne
- Division of Cardiology, Department of Medicine, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Canada
- Department of Critical Care Medicine, University of Alberta, Edmonton, Canada
- Correspondence: Janek Senaratne, Tel +1 (780) 463-2184, Fax +1 (780) 450-8359, Email
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Cubeddu LX, de la Rosa D, Ameruoso M. Antiviral and anti-inflammatory drugs to combat COVID-19: Effects on cardiac ion channels and risk of ventricular arrhythmias. BIOIMPACTS : BI 2022; 12:9-20. [PMID: 35087712 PMCID: PMC8783084 DOI: 10.34172/bi.2021.23630] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Revised: 10/11/2021] [Accepted: 10/14/2021] [Indexed: 12/27/2022]
Abstract
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Introduction: Drugs with no indication for the treatment of cardiovascular diseases (e.g., drugs employed to treat COVID-19) can increase the risk of arrhythmias. Of interest, a six-fold increase in the number of arrhythmic events was reported in patients with severe COVID-19. In this study, we reviewed (i) the pro-arrhythmic action of drugs given to patients with COVID-19 infection, and (ii) the effects of inflammatory cytokines on cardiac ion channels and possible generation of arrhythmias.
Methods: We conducted a literature search on the drugs with purported or demonstrated efficacy against COVID-19 disease, emphasizing the mechanisms by which anti-COVID-19 drugs and inflammatory cytokines interfere with cardiac ion channels.
Results:Antibiotics (azithromycin), antimalarials (hydroxychloroquine, chloroquine), antivirals (ritonavir/lopinavir, atazanavir), and some of the tyrosine kinase inhibitors (vandetanib) could induce long QT and increase risk for ventricular arrhythmias. The pro-arrhythmic action results from drug-induced inhibition of Kv11.1 (hERG) channels interfering with the repolarizing potassium IKr currents, leading to long QT and increased risk of triggered arrhythmias. At higher concentrations, these drugs may interfere with IKs, IK1, and/or Ito potassium currents, and even inhibit sodium (INa) and calcium (ICa) currents, inducing additional cardiac toxicity. Ibrutinib, an inhibitor of Bruton’s TK, increased the incidence of atrial fibrillation and ventricular tachycardia associated with a short QT interval. Inflammatory cytokines IL-6 and TNF-α inhibit IKr and Ito repolarizing potassium currents. High levels of inflammatory cytokines could contribute to the arrhythmic events. For remdesivir, favipiravir, dexamethasone, tocilizumab, anakinra, baricitinib, and monoclonal antibodies (bamlanivimab, etesevimab, and casirivimab), no evidence supports significant effects on cardiac ion channels, changes in the QT interval, and increased risk for ventricular arrhythmias.
Conclusion: This study supports the concept of hERG channel promiscuity. Different drug classes given to COVID-19 patients might delay repolarization, and increase the risk of ventricular arrhythmias. The presence of comorbid pro-arrhythmic disease states, and elevated levels of pro-arrhythmic cytokines, could increase the risk of ventricular arrhythmias. Discontinuation of nonessential drugs and correction of electrolyte abnormalities could prevent severe ventricular arrhythmias. Altogether, the most effective therapies against COVID-19 (remdesivir, dexamethasone, monoclonal antibodies) lack pro-arrhythmic activity.
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Affiliation(s)
- Luigi X Cubeddu
- Nova SE University, Health Professions Division, 3200 S, University Drive, Davie, FL 33328, USA
| | - Daisy de la Rosa
- Nova SE University, Health Professions Division, 3200 S, University Drive, Davie, FL 33328, USA
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Reilly L, Eckhardt LL. Cardiac potassium inward rectifier Kir2: Review of structure, regulation, pharmacology, and arrhythmogenesis. Heart Rhythm 2021; 18:1423-1434. [PMID: 33857643 PMCID: PMC8328935 DOI: 10.1016/j.hrthm.2021.04.008] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Revised: 03/23/2021] [Accepted: 04/06/2021] [Indexed: 12/17/2022]
Abstract
Potassium inward rectifier channel Kir2 is an important component of terminal cardiac repolarization and resting membrane stability. This functionality is part of balanced cardiac excitability and is a defining feature of excitable cardiac membranes. “Gain-of-function” or “loss-of-function” mutations in KCNJ2, the gene encoding Kir2.1, cause genetic sudden cardiac death syndromes, and loss of the Kir2 current IK1 is a major contributing factor to arrhythmogenesis in failing human hearts. Here we provide a contemporary review of the functional structure, physiology, and pharmacology of Kir2 channels. Beyond the structure and functional relationships, we will focus on the elements of clinically used drugs that block the channel and the implications for treatment of atrial fibrillation with IK1-blocking agents. We will also review the clinical disease entities associated with KCNJ2 mutations and the growing area of research into associated arrhythmia mechanisms. Lastly, the presence of Kir2 channels has become a tipping point for electrical maturity in induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) and highlights the significance of understanding why Kir2 in iPS-CMs is important to consider for Comprehensive In Vitro Proarrhythmia Assay and drug safety testing.
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Affiliation(s)
- Louise Reilly
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin
| | - Lee L Eckhardt
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison, Madison, Wisconsin.
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Abstract
Andersen-Tawil syndrome (ATS) is a very rare orphan genetic multisystem channelopathy without structural heart disease (with rare exceptions). ATS type 1 is inherited in an autosomal dominant fashion and is caused by mutations in the KCNJ2 gene, which encodes the α subunit of the K+ channel protein Kir2.1 (in ≈ 50-60% of cases). ATS type 2 is in turn linked to a rare mutation in the KCNJ5-GIRK4 gene that encodes the G protein-sensitive-activated inwardly rectifying K+ channel Kir3.4 (15%), which carries the acetylcholine-induced potassium current. About 30% of cases are de novo/sporadic, suggesting that additional as-yet unidentified genes also cause the disorder. A triad of periodic muscle paralysis, repolarization changes in the electrocardiogram, and structural body changes characterize ATS. The typical muscular change is episodic flaccid muscle weakness. Prolongation of the QU/QUc intervals and normal or minimally prolonged QT/QTc intervals with a tendency to ventricular arrhythmias are typical repolarization changes. Bidirectional ventricular tachycardia is the hallmark ventricular arrhythmia, but also premature ventricular contractions, and rarely, polymorphic ventricular tachycardia of torsade de pointes type may be present. Patients with ATS have characteristic physical developmental dysmorphisms that affect the face, skull, limbs, thorax, and stature. Mild learning difficulties and a distinct neurocognitive phenotype (deficits in executive function and abstract reasoning) have been described. About 60% of affected individuals have all features of the major triad. The purpose of this review is to present historical aspects, nomenclature (observations/criticisms), epidemiology, genetics, electrocardiography, arrhythmias, electrophysiological mechanisms, diagnostic criteria/clues of periodic paralysis, prognosis, and management of ATS.
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Reilly L, Alvarado FJ, Lang D, Abozeid S, Van Ert H, Spellman C, Warden J, Makielski JC, Glukhov AV, Eckhardt LL. Genetic Loss of IK1 Causes Adrenergic-Induced Phase 3 Early Afterdepolariz ations and Polymorphic and Bidirectional Ventricular Tachycardia. Circ Arrhythm Electrophysiol 2020; 13:e008638. [PMID: 32931337 PMCID: PMC7574954 DOI: 10.1161/circep.120.008638] [Citation(s) in RCA: 8] [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: 04/01/2020] [Accepted: 06/23/2020] [Indexed: 11/16/2022]
Abstract
BACKGROUND Arrhythmia syndromes associated with KCNJ2 mutations have been described clinically; however, little is known of the underlying arrhythmia mechanism. We create the first patient inspired KCNJ2 transgenic mouse and study effects of this mutation on cardiac function, IK1, and Ca2+ handling, to determine the underlying cellular arrhythmic pathogenesis. METHODS A cardiac-specific KCNJ2-R67Q mouse was generated and bred for heterozygosity (R67Q+/-). Echocardiography was performed at rest, under anesthesia. In vivo ECG recording and whole heart optical mapping of intact hearts was performed before and after adrenergic stimulation in wild-type (WT) littermate controls and R67Q+/- mice. IK1 measurements, action potential characterization, and intracellular Ca2+ imaging from isolated ventricular myocytes at baseline and after adrenergic stimulation were performed in WT and R67Q+/- mice. RESULTS R67Q+/- mice (n=17) showed normal cardiac function, structure, and baseline electrical activity compared with WT (n=10). Following epinephrine and caffeine, only the R67Q+/- mice had bidirectional ventricular tachycardia, ventricular tachycardia, frequent ventricular ectopy, and/or bigeminy and optical mapping demonstrated high prevalence of spontaneous and sustained ventricular arrhythmia. Both R67Q+/- (n=8) and WT myocytes (n=9) demonstrated typical n-shaped IK1IV relationship; however, following isoproterenol, max outward IK1 increased by ≈20% in WT but decreased by ≈24% in R67Q+/- (P<0.01). R67Q+/- myocytes (n=5) demonstrated prolonged action potential duration at 90% repolarization and after 10 nmol/L isoproterenol compared with WT (n=7; P<0.05). Ca2+ transient amplitude, 50% decay rate, and sarcoplasmic reticulum Ca2+ content were not different between WT (n=18) and R67Q+/- (n=16) myocytes. R67Q+/- myocytes (n=10) under adrenergic stimulation showed frequent spontaneous development of early afterdepolarizations that occurred at phase 3 of action potential repolarization. CONCLUSIONS KCNJ2 mutation R67Q+/- causes adrenergic-dependent loss of IK1 during terminal repolarization and vulnerability to phase 3 early afterdepolarizations. This model clarifies a heretofore unknown arrhythmia mechanism and extends our understanding of treatment implications for patients with KCNJ2 mutation.
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Affiliation(s)
- Louise Reilly
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Francisco J Alvarado
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Di Lang
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Sara Abozeid
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Hannah Van Ert
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Cordell Spellman
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Jarrett Warden
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Jonathan C Makielski
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Alexey V Glukhov
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
| | - Lee L Eckhardt
- Cellular and Molecular Arrhythmia Research Program, Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin-Madison
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"Electrifying dysmorphology": Potassium channelopathies causing dysmorphic syndromes. ADVANCES IN GENETICS 2020; 105:137-174. [PMID: 32560786 DOI: 10.1016/bs.adgen.2020.03.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Potassium channels are a heterogeneous group of membrane-bound proteins, whose functions support a diverse range of biological processes. Genetic disorders arising from mutations in potassium channels are classically recognized by symptoms arising from acute channel dysfunction, such as periodic paralysis, ataxia, seizures, or cardiac conduction abnormalities, often in a patient with otherwise normal examination findings. In this chapter, we review a distinct subgroup of rare potassium channelopathies whose presentations are instead suggestive of a developmental disorder, with features including intellectual disability, craniofacial dysmorphism or other physical anomalies. Known conditions within this subgroup are: Andersen-Tawil syndrome, Birk-Barel syndrome, Cantú syndrome, Keppen-Lubinsky syndrome, Temple-Baraitser syndrome, Zimmerman-Laband syndrome and a very similar disorder called Bauer-Tartaglia or FHEIG syndrome. Ion channelopathies are unlikely to be routinely considered in the differential diagnosis of children presenting with developmental concerns, and so detailed description and photographs of the clinical phenotype are provided to aid recognition. For several of these disorders, functional characterization of the genetic mutations responsible has led to identification of candidate therapies, including drugs already commonly used for other indications, which adds further impetus to their prompt recognition. Together, these cases illustrate the potential for mechanistic insights gained from genetic diagnosis to drive translational work toward targeted, disease-modifying therapies for rare disorders.
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Mazzanti A, Guz D, Trancuccio A, Pagan E, Kukavica D, Chargeishvili T, Olivetti N, Biernacka EK, Sacilotto L, Sarquella-Brugada G, Campuzano O, Nof E, Anastasakis A, Sansone VA, Jimenez-Jaimez J, Cruz F, Sánchez-Quiñones J, Hernandez-Afonso J, Fuentes ME, Średniawa B, Garoufi A, Andršová I, Izquierdo M, Marinov R, Danon A, Expósito-García V, Garcia-Fernandez A, Muñoz-Esparza C, Ortíz M, Zienciuk-Krajka A, Tavazzani E, Monteforte N, Bloise R, Marino M, Memmi M, Napolitano C, Zorio E, Monserrat L, Bagnardi V, Priori SG. Natural History and Risk Stratification in Andersen-Tawil Syndrome Type 1. J Am Coll Cardiol 2020; 75:1772-1784. [PMID: 32299589 DOI: 10.1016/j.jacc.2020.02.033] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2019] [Revised: 01/25/2020] [Accepted: 02/11/2020] [Indexed: 11/25/2022]
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Horigome H, Ishikawa Y, Kokubun N, Yoshinaga M, Sumitomo N, Lin L, Kato Y, Tanabe-Kameda Y, Ohno S, Nagashima M, Horie M. Multivariate analysis of TU wave complex on electrocardiogram in Andersen-Tawil syndrome with KCNJ2 mutations. Ann Noninvasive Electrocardiol 2019; 25:e12721. [PMID: 31724784 PMCID: PMC7358888 DOI: 10.1111/anec.12721] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2019] [Accepted: 09/26/2019] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND The exact differences between the TU wave complex of ATS1 and that of healthy individuals remain to be investigated. We sought to characterize the TU wave complex of Andersen-Tawil syndrome type 1 (ATS1) using high frequency electrocardiogram (ECG) data. METHODS Electrocardiograms were recorded as time series data with a 2 kHz frequency ECG amplifier in 13 patients with ATS1 (positive for KCNJ2 mutation, ATS1 group) and age-matched healthy individuals (control group). Conventional ECG parameters were measured, and principal component analysis (PCA) and independent component analysis (ICA) were applied to the TU wave complex. RESULTS Time from T peak (Tp) to U peak (Up), time from bottom (B) to Up, and time from B to U end (BUe, U duration) (0.232 ± 0.018 vs. 0.165 ± 0.017, p < .0001), where B is the lowest point between T and U waves, were all longer in the ATS1 group than the control group. Multivariate logistic regression analysis revealed that BUe could completely differentiate the two groups. PCA ratios in the ATS1 group were significantly larger than the control group (26.5 ± 12.3 vs. 10.4 ± 6.2, p = .0005). ICA revealed 1 or 2 U-wave-specific independent components (ICs) that exclusively comprise the U wave in ATS1, whereas U waves in the control group were composed of some ICs that also comprised T waves. CONCLUSIONS U-wave-related temporal parameters, particularly BUe, and the existence of U-wave-specific ICs, extracted in the ICA, are useful for differentiation of U waves in ATS1 from those in healthy individuals.
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Affiliation(s)
- Hitoshi Horigome
- Department of Child Health, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
| | | | - Norito Kokubun
- Department of Neurology, Dokkyo Medical University, Tochigi, Japan
| | - Masao Yoshinaga
- Department of Pediatrics, National Hospital Organization Kagoshima Medical Center, Kagoshima, Japan
| | - Naokata Sumitomo
- Department of Pediatric Cardiology, Saitama Medical University International Medical Center, Hidaka, Japan
| | - Lisheng Lin
- Department of Child Health, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
| | - Yoshiaki Kato
- Department of Child Health, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
| | - Yuri Tanabe-Kameda
- Department of Child Health, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
| | - Seiko Ohno
- Department of Bioscience and Genetics, National Cerebral and Cardiovascular Center, Suita, Japan
| | | | - Minoru Horie
- Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science, Otsu, Japan
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Wilde AA, Garan H, Boyden PA. Role of the Purkinje system in heritable arrhythmias. Heart Rhythm 2019; 16:1121-1126. [DOI: 10.1016/j.hrthm.2019.01.034] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Indexed: 12/28/2022]
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Jebberi Z, Marazzato J, De Ponti R, Bagliani G, Leonelli FM, Boveda S. Polymorphic Wide QRS Complex Tachycardia: Differential Diagnosis. Card Electrophysiol Clin 2019; 11:333-344. [PMID: 31084854 DOI: 10.1016/j.ccep.2019.02.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Polymorphic wide QRS complex tachycardia is defined as a tachyarrhythmia showing variable and frequently alternating morphologies of the QRS complex with irregular R-R intervals. It may present with a specific and reproducible pattern including torsade de pointes and bidirectional ventricular tachycardia or with a nonspecific and very irregular pattern, different from ventricular fibrillation. Polymorphic ventricular tachycardia is a challenging diagnosis and is associated with a high risk for sudden cardiac death. Although rare, preexcited atrial fibrillation over multiple accessory pathways can also generate a polymorphic wide QRS complex tachycardia mimicking polymorphic ventricular tachycardia.
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Affiliation(s)
- Zeynab Jebberi
- Cardiac Arrhythmia Management Department, Clinique Pasteur, BP 27617, 45 Avenue de Lombez, Toulouse 31076, France
| | - Jacopo Marazzato
- Department of Heart and Vessels, Ospedale di Circolo and Macchi Foundation, University of Insubria, Viale Borri, 57, Varese 21100, Italy
| | - Roberto De Ponti
- Department of Heart and Vessels, Ospedale di Circolo and Macchi Foundation, University of Insubria, Viale Borri, 57, Varese 21100, Italy
| | - Giuseppe Bagliani
- Cardiology Department, Arrhythmology Unit, Foligno General Hospital, Foligno, Via Massimo Arcamone, Foligno, Perugia 06034, Italy; Cardiovascular Diseases Department, University of Perugia, Piazza Menghini 1, Perugia 06129, Italy
| | - Fabio M Leonelli
- Cardiology Department, James A. Haley Veterans' Hospital, University of South Florida, 13000 Bruce B Down Boulevard, Tampa, FL 33612, USA
| | - Serge Boveda
- Cardiac Arrhythmia Management Department, Clinique Pasteur, BP 27617, 45 Avenue de Lombez, Toulouse 31076, France.
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Meta-analysis of T peak-T end and T peak-T end/QT ratio for risk stratification in congenital long QT syndrome. J Electrocardiol 2018; 51:396-401. [PMID: 29550106 DOI: 10.1016/j.jelectrocard.2018.03.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2017] [Revised: 02/13/2018] [Accepted: 03/06/2018] [Indexed: 01/13/2023]
Abstract
BACKGROUND AND OBJECTIVES Congenital long QT syndrome (LQTS) predisposes affected individuals to ventricular tachycardia/fibrillation (VF/VF), potentially resulting in sudden cardiac death. The Tpeak-Tend interval and the Tpeak-Tend/QT ratio, electrocardiographic markers of dispersion of ventricular repolarization, were proposed for risk stratification but their predictive values in LQTS have been controversial. A systematic review and meta-analysis was conducted to examine the value of Tpeak-Tend intervals and Tpeak-Tend/QT ratios in predicting arrhythmic and mortality outcomes in congenital LQTS. METHOD PubMed and Embase databases were searched until 9th May 2017, identifying 199 studies. RESULTS Five studies on long QT syndrome were included in the final meta-analysis. Tpeak-Tend intervals were longer (mean difference [MD]: 13ms, standard error [SE]: 4ms, P=0.002; I2=34%) in congenital LQTS patients with adverse events [syncope, ventricular arrhythmias or sudden cardiac death] compared to LQTS patients without such events. By contrast, Tpeak-Tend/QT ratios were not significantly different between the two groups (MD: 0.02, SE: 0.02, P=0.26; I2=0%). CONCLUSION This meta-analysis showed that Tpeak-Tend interval is significant higher in individuals who are at elevated risk of adverse events in congenital LQTS, offering incremental value for risk stratification.
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Different responses to exercise between Andersen–Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia. Europace 2017; 20:1675-1682. [DOI: 10.1093/europace/eux351] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Accepted: 10/31/2017] [Indexed: 11/15/2022] Open
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Watanabe A, Morita H, Tsushima S, Nakagawa K, Nishii N, Ito H. Recording of isolated very delayed potentials on the right ventricular epicardium in a patient with Brugada syndrome. HeartRhythm Case Rep 2017; 3:344-347. [PMID: 28748141 PMCID: PMC5511986 DOI: 10.1016/j.hrcr.2017.05.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Affiliation(s)
- Atsuyuki Watanabe
- Cardiovascular Medicine, Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Hiroshi Morita
- Cardiovascular Medicine, Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Sho Tsushima
- Cardiovascular Medicine, Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Koji Nakagawa
- Cardiovascular Medicine, Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Nobuhiro Nishii
- Cardiovascular Medicine, Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
| | - Hiroshi Ito
- Cardiovascular Medicine, Graduate School of Medicine Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
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Klein MG, Shou M, Stohlman J, Solhjoo S, Haigney M, Tidwell RR, Goldstein RE, Flagg TP, Haigney MC. Role of suppression of the inward rectifier current in terminal action potential repolarization in the failing heart. Heart Rhythm 2017; 14:1217-1223. [PMID: 28396172 DOI: 10.1016/j.hrthm.2017.04.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Indexed: 11/19/2022]
Abstract
BACKGROUND The failing heart exhibits an increased arrhythmia susceptibility that is often attributed to action potential (AP) prolongation due to significant ion channel remodeling. The inwardly rectifying K+ current (IK1) has been reported to be reduced, but its contribution to shaping the AP waveform and cell excitability in the failing heart remains unclear. OBJECTIVE The purpose of this study was to define the effect of IK1 suppression on the cardiac AP and excitability in the normal and failing hearts. METHODS We used electrophysiological and pharmacological approaches to investigate IK1 function in a swine tachy-pacing model of heart failure (HF). RESULTS Terminal repolarization of the AP (TRAP; the time constant of the exponential fit to terminal repolarization) was markedly prolonged in both myocytes and arterially perfused wedges from animals with HF. TRAP was increased by 54.1% in HF myocytes (P < .001) and 26.2% in HF wedges (P = .014). The increase in TRAP was recapitulated by the potent and specific IK1 inhibitor, PA-6 (pentamidine analog 6), indicating that IK1 is the primary determinant of the final phase of repolarization. Moreover, we find that IK1 suppression reduced the ratio of effective refractory period to AP duration at 90% of repolarization, permitting re-excitation before full repolarization, reduction of AP upstroke velocity, and likely promotion of slow conduction. CONCLUSION Using an objective measure of terminal repolarization, we conclude that IK1 is the major determinant of the terminal repolarization time course. Moreover, suppression of IK1 prolongs repolarization and reduces postrepolarization refractoriness without marked effects on the overall AP duration. Collectively, these findings demonstrate how IK1 suppression may contribute to arrhythmogenesis in the failing heart.
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Affiliation(s)
- Michael G Klein
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.
| | - Matie Shou
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Jayna Stohlman
- Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, Maryland
| | - Soroosh Solhjoo
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland
| | - Myles Haigney
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Richard R Tidwell
- Department of Pathology and Laboratory Medicine, School of Medicine, The University of North Carolina, Chapel Hill, North Carolina
| | - Robert E Goldstein
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Thomas P Flagg
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Mark C Haigney
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
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Kuroda Y, Yuasa S, Watanabe Y, Ito S, Egashira T, Seki T, Hattori T, Ohno S, Kodaira M, Suzuki T, Hashimoto H, Okata S, Tanaka A, Aizawa Y, Murata M, Aiba T, Makita N, Furukawa T, Shimizu W, Kodama I, Ogawa S, Kokubun N, Horigome H, Horie M, Kamiya K, Fukuda K. Flecainide ameliorates arrhythmogenicity through NCX flux in Andersen-Tawil syndrome-iPS cell-derived cardiomyocytes. Biochem Biophys Rep 2017; 9:245-256. [PMID: 28956012 PMCID: PMC5614591 DOI: 10.1016/j.bbrep.2017.01.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 12/09/2016] [Accepted: 01/10/2017] [Indexed: 12/15/2022] Open
Abstract
Andersen-Tawil syndrome (ATS) is a rare inherited channelopathy. The cardiac phenotype in ATS is typified by a prominent U wave and ventricular arrhythmia. An effective treatment for this disease remains to be established. We reprogrammed somatic cells from three ATS patients to generate induced pluripotent stem cells (iPSCs). Multi-electrode arrays (MEAs) were used to record extracellular electrograms of iPSC-derived cardiomyocytes, revealing strong arrhythmic events in the ATS-iPSC-derived cardiomyocytes. Ca2+ imaging of cells loaded with the Ca2+ indicator Fluo-4 enabled us to examine intracellular Ca2+ handling properties, and we found a significantly higher incidence of irregular Ca2+ release in the ATS-iPSC-derived cardiomyocytes than in control-iPSC-derived cardiomyocytes. Drug testing using ATS-iPSC-derived cardiomyocytes further revealed that antiarrhythmic agent, flecainide, but not the sodium channel blocker, pilsicainide, significantly suppressed these irregular Ca2+ release and arrhythmic events, suggesting that flecainide's effect in these cardiac cells was not via sodium channels blocking. A reverse-mode Na+/Ca2+exchanger (NCX) inhibitor, KB-R7943, was also found to suppress the irregular Ca2+ release, and whole-cell voltage clamping of isolated guinea-pig cardiac ventricular myocytes confirmed that flecainide could directly affect the NCX current (INCX). ATS-iPSC-derived cardiomyocytes recapitulate abnormal electrophysiological phenotypes and flecainide suppresses the arrhythmic events through the modulation of INCX. iPS cells are generated from three patients with ATS. ATS-iPS cell-derived cardiomyocytes show abnormal electrophysiological phenotypes. Flecainide suppresses abnormal electrophysiological phenotypes in ATS-iPS cell-derived cardiomyocytes.
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Affiliation(s)
- Yusuke Kuroda
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan.,Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan.,Department of Cardiology, Nagoya University Graduate School of Medicine, Aichi, Japan
| | - Shinsuke Yuasa
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Yasuhide Watanabe
- Division of Pharmacological Science, Department of Health Science, Hamamatsu University School of Medicine, Shizuoka, Japan
| | - Shogo Ito
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Toru Egashira
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Tomohisa Seki
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Tetsuhisa Hattori
- Department of Cardiovascular Medicine, Shiga University of Medical Science, Shiga, Japan
| | - Seiko Ohno
- Department of Cardiovascular Medicine, Shiga University of Medical Science, Shiga, Japan.,Center for Epidemiologic Research in Asia, Shiga University of Medical Science, Shiga, Japan
| | - Masaki Kodaira
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Tomoyuki Suzuki
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan.,Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan.,Department of Cardiology, Nagoya University Graduate School of Medicine, Aichi, Japan
| | - Hisayuki Hashimoto
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Shinichiro Okata
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Atsushi Tanaka
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Yoshiyasu Aizawa
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Mitsushige Murata
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan.,Department of Laboratory Medicine, Keio University School of Medicine, Tokyo, Japan
| | - Takeshi Aiba
- Division of Arrhythmia and Electrophysiology, Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center, Osaka, Japan
| | - Naomasa Makita
- Department of Molecular Pathophysiology-1, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki, Japan
| | - Tetsushi Furukawa
- Department of Bio-informational Pharmacology, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan
| | - Wataru Shimizu
- Department of Cardiovascular Medicine, Nippon Medical School, Tokyo, Japan
| | - Itsuo Kodama
- Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan
| | - Satoshi Ogawa
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Norito Kokubun
- Department of Neurology, Dokkyo Medical University, Tochigi, Japan
| | - Hitoshi Horigome
- Department of Child Health, Faculty of Medicine, University of Tsukuba, Tsukuba, Japan
| | - Minoru Horie
- Department of Cardiovascular Medicine, Shiga University of Medical Science, Shiga, Japan
| | - Kaichiro Kamiya
- Department of Cardiovascular Research, Research Institute of Environmental Medicine, Nagoya University, Aichi, Japan
| | - Keiichi Fukuda
- Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
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16
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Hoeker GS, Skarsfeldt MA, Jespersen T, Poelzing S. Electrophysiologic effects of the IK1 inhibitor PA-6 are modulated by extracellular potassium in isolated guinea pig hearts. Physiol Rep 2017; 5:e13120. [PMID: 28087819 PMCID: PMC5256165 DOI: 10.14814/phy2.13120] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 12/14/2016] [Indexed: 12/02/2022] Open
Abstract
The pentamidine analog PA-6 was developed as a specific inward rectifier potassium current (IK1) antagonist, because established inhibitors either lack specificity or have side effects that prohibit their use in vivo. We previously demonstrated that BaCl2, an established IK1 inhibitor, could prolong action potential duration (APD) and increase cardiac conduction velocity (CV). However, few studies have addressed whether targeted IK1 inhibition similarly affects ventricular electrophysiology. The aim of this study was to determine the effects of PA-6 on cardiac repolarization and conduction in Langendorff-perfused guinea pig hearts. PA-6 (200 nm) or vehicle was perfused into ex-vivo guinea pig hearts for 60 min. Hearts were optically mapped with di-4-ANEPPS to quantify CV and APD at 90% repolarization (APD90). Ventricular APD90 was significantly prolonged in hearts treated with PA-6 (115 ± 2% of baseline; P < 0.05), but not vehicle (105 ± 2% of baseline). PA-6 slightly, but significantly, increased transverse CV by 7%. PA-6 significantly prolonged APD90 during hypokalemia (2 mmol/L [K+]o), although to a lesser degree than observed at 4.56 mmol/L [K+]o In contrast, the effect of PA-6 on CV was more pronounced during hypokalemia, where transverse CV with PA-6 (24 ± 2 cm/sec) was significantly faster than with vehicle (13 ± 3 cm/sec, P < 0.05). These results show that under normokalemic conditions, PA-6 significantly prolonged APD90, whereas its effect on CV was modest. During hypokalemia, PA-6 prolonged APD90 to a lesser degree, but profoundly increased CV Thus, in intact guinea pig hearts, the electrophysiologic effects of the IK1 inhibitor, PA-6, are [K+]o-dependent.
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Affiliation(s)
- Gregory S Hoeker
- Biomedical Engineering and Mechanics, Center for Heart and Regenerative Medicine, Virginia Tech Virginia Tech Carilion Research Institute, Roanoke, Virginia
| | - Mark A Skarsfeldt
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Thomas Jespersen
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Steven Poelzing
- Biomedical Engineering and Mechanics, Center for Heart and Regenerative Medicine, Virginia Tech Virginia Tech Carilion Research Institute, Roanoke, Virginia
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17
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Liu MB, Ko CY, Song Z, Garfinkel A, Weiss JN, Qu Z. A Dynamical Threshold for Cardiac Delayed Afterdepolarization-Mediated Triggered Activity. Biophys J 2016; 111:2523-2533. [PMID: 27926853 PMCID: PMC5153551 DOI: 10.1016/j.bpj.2016.10.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2016] [Revised: 09/22/2016] [Accepted: 10/11/2016] [Indexed: 11/18/2022] Open
Abstract
Ventricular myocytes are excitable cells whose voltage threshold for action potential (AP) excitation is ∼-60 mV at which INa is activated to give rise to a fast upstroke. Therefore, for a short stimulus pulse to elicit an AP, a stronger stimulus is needed if the resting potential lies further away from the INa threshold, such as in hypokalemia. However, for an AP elicited by a long duration stimulus or a diastolic spontaneous calcium release, we observed that the stimulus needed was lower in hypokalemia than in normokalemia in both computer simulations and experiments of rabbit ventricular myocytes. This observation provides insight into why hypokalemia promotes calcium-mediated triggered activity, despite the resting potential lying further away from the INa threshold. To understand the underlying mechanisms, we performed bifurcation analyses and demonstrated that there is a dynamical threshold, resulting from a saddle-node bifurcation mainly determined by IK1 and INCX. This threshold is close to the voltage at which IK1 is maximum, and lower than the INa threshold. After exceeding this dynamical threshold, the membrane voltage will automatically depolarize above the INa threshold due to the large negative slope of the IK1-V curve. This dynamical threshold becomes much lower in hypokalemia, especially with respect to calcium, as predicted by our theory. Because of the saddle-node bifurcation, the system can automatically depolarize even in the absence of INa to voltages higher than the ICa,L threshold, allowing for triggered APs in single myocytes with complete INa block. However, because INa is important for AP propagation in tissue, blocking INa can still suppress premature ventricular excitations in cardiac tissue caused by calcium-mediated triggered activity. This suppression is more effective in normokalemia than in hypokalemia due to the difference in dynamical thresholds.
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Affiliation(s)
- Michael B Liu
- Cardiovascular Research Laboratory, University of California, Los Angeles, Los Angeles, California; Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Christopher Y Ko
- Cardiovascular Research Laboratory, University of California, Los Angeles, Los Angeles, California; Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Zhen Song
- Cardiovascular Research Laboratory, University of California, Los Angeles, Los Angeles, California; Department of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Alan Garfinkel
- Cardiovascular Research Laboratory, University of California, Los Angeles, Los Angeles, California; Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Integrative Biology and Physiology, University of California, Los Angeles, Los Angeles, California
| | - James N Weiss
- Cardiovascular Research Laboratory, University of California, Los Angeles, Los Angeles, California; Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Physiology, University of California, Los Angeles, Los Angeles, California
| | - Zhilin Qu
- Cardiovascular Research Laboratory, University of California, Los Angeles, Los Angeles, California; Department of Medicine, University of California, Los Angeles, Los Angeles, California; Department of Biomathematics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California.
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18
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Durrani SA, Sung R, Scheinman M. Bidirectional Ventricular Tachycardia Due to a Mixture of Focal Fascicular Firing and Reentry. Card Electrophysiol Clin 2016; 8:753-764. [PMID: 27837895 DOI: 10.1016/j.ccep.2016.07.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Bidirectional ventricular tachycardia (BDVT) is a well-known phenomenon since it was first described in 1922. Various mechanisms have been proposed for BDVT, including digitalis toxicity, hypokalemia, Anderson-Tawil syndrome, acute myocarditis, and catecholaminergic polymorphic ventricular tachycardia. It is characterized by rapid, wide complex electrocardiogram pattern with alternating QRS morphology and axis. The alternation of the QRS is usually right bundle branch block with 180° swings in the frontal plane axis or, less commonly, alternation of right bundle branch and left bundle branch forms. Most of the proposed mechanisms involve triggered activity or enhanced automaticity. We describe a unique BDVT, with characteristics of both re-entry and triggered activity, which terminated with a focal Rf lesion.
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Affiliation(s)
- Sarfraz A Durrani
- MedStar Heart and Vascular Institute, #501 Hamaker court, Fairfax, VA 22031, USA.
| | - Raphael Sung
- Peninsula Primary Care, Cardiology, 30 Garden Court, Suite B, Monterey, CA 93940, USA
| | - Melvin Scheinman
- University of California San Francisco Medical Center, 500 Parnassus Avenue, MUE 436, San Francisco, CA 94143-1354, USA
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19
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Cubeddu LX. Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias. Curr Cardiol Rev 2016; 12:141-54. [PMID: 26926294 PMCID: PMC4861943 DOI: 10.2174/1573403x12666160301120217] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 02/29/2016] [Indexed: 01/11/2023] Open
Abstract
Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.
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Affiliation(s)
- Luigi X Cubeddu
- Division of Cardio-Metabolic Research, Department of Pharmaceutical Sciences, Health professions Division, Nova Southeastern University, 3200 S. University Dr., Davie, FL, 333218, USA.
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20
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Shenthar J. Unusual Incessant Ventricular Tachycardia: What Is the Underlying Cause and the Possible Mechanism? Circ Arrhythm Electrophysiol 2015; 8:1507-11. [PMID: 26671936 DOI: 10.1161/circep.115.002886] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Jayaprakash Shenthar
- From the Department of Cardiology, Sri Jayadeva Institute of Cardiovascular Sciences and Research, Bangalore, India.
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21
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Delayed afterdepolarizations generate both triggers and a vulnerable substrate promoting reentry in cardiac tissue. Heart Rhythm 2015; 12:2115-24. [PMID: 26072025 DOI: 10.1016/j.hrthm.2015.06.019] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Indexed: 11/23/2022]
Abstract
BACKGROUND Delayed afterdepolarizations (DADs) have been well characterized as arrhythmia triggers, but their role in generating a tissue substrate vulnerable to reentry is not well understood. OBJECTIVE The purpose of this study was to test the hypothesis that random DADs can self-organize to generate both an arrhythmia trigger and a vulnerable substrate simultaneously in cardiac tissue as a result of gap junction coupling. METHODS Computer simulations in 1-dimensional cable and 2-dimensional tissue models were performed. The cellular DAD amplitude was varied by changing the strength of sarcoplasmic reticulum calcium release. Random DAD latency and amplitude in different cells were simulated using gaussian distributions. RESULTS Depending on the strength of spontaneous sarcoplasmic reticulum calcium release and other conditions, random DADs in cardiac tissue resulted in the following behaviors: (1) triggered activity (TA); (2) a vulnerable tissue substrate causing unidirectional conduction block and reentry by inactivating sodium channels; (3) both triggers and a vulnerable substrate simultaneously by generating TA in regions next to regions with subthreshold DADs susceptible to unidirectional conduction block and reentry. The probability of the latter 2 behaviors was enhanced by reduced sodium channel availability, reduced gap junction coupling, increased tissue heterogeneity, and less synchronous DAD latency. CONCLUSION DADs can self-organize in tissue to generate arrhythmia triggers, a vulnerable tissue substrate, and both simultaneously. Reduced sodium channel availability and gap junction coupling potentiate this mechanism of arrhythmias, which are relevant to a variety of heart disease conditions.
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22
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Bhoelan BS, Stevering CH, van der Boog ATJ, van der Heyden MAG. Barium toxicity and the role of the potassium inward rectifier current. Clin Toxicol (Phila) 2014; 52:584-93. [DOI: 10.3109/15563650.2014.923903] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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23
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Combined inhibition of Na+ and Ca2+ channels: A novel paradigm for the treatment of incessant ventricular arrhythmias in Andersen-Tawil syndrome. Heart Rhythm 2014; 11:318-20. [DOI: 10.1016/j.hrthm.2013.11.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Indexed: 12/23/2022]
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25
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Wilde AAM. Andersen-Tawil syndrome, scarier for the doctor than for the patient? Who, when, and how to treat. Europace 2013; 15:1690-2. [PMID: 24128811 DOI: 10.1093/europace/eut326] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Arthur A M Wilde
- Department of Clinical and Experimental Cardiology, Academic Medical Center, Amsterdam 1100 DE, The Netherlands
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26
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Delannoy E, Sacher F, Maury P, Mabo P, Mansourati J, Magnin I, Camous JP, Tournant G, Rendu E, Kyndt F, Haïssaguerre M, Bézieau S, Guyomarch B, Le Marec H, Fressart V, Denjoy I, Probst V. Cardiac characteristics and long-term outcome in Andersen-Tawil syndrome patients related to KCNJ2 mutation. Europace 2013; 15:1805-11. [PMID: 23867365 DOI: 10.1093/europace/eut160] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS Andersen-Tawil syndrome (ATS) is an uncommon form of channelopathy linked to mutations in the KCNJ2 gene. Currently, little is known about the long-term arrhythmic prognosis of this disease. METHODS AND RESULTS We conducted a retrospective multicentre study in nine French hospitals. Patients were recruited only if they were KCNJ2 mutation carriers. Thirty-six patients (female n = 22, 61%) from 20 unrelated kindred were included with a mean follow-up of 9.5 ± 8.2 years. We found 12 distinct KCNJ2 mutations in the 20 probands. Three of them were novel. Thirteen patients (36%) experienced syncope and one patient was resuscitated from cardiac arrest before diagnosis. The mean QTc interval was 439 ± 57 ms and QUc was 642 ± 64 ms. All patients had normal ejection fraction. Holter recordings in 33 patients found 11 272 premature ventricular complexes (PVCs) per day on average, 25 patients had episodes of bigeminy, and 25 patients had polymorphic PVCs. Twenty-three patients (70%) had non-sustained polymorphic ventricular tachycardia (VT), and six sustained polymorphic VT. Only one patient presented with torsades de pointes. Patients were treated with beta-blocker (n = 20), beta-blocker and amiodarone (n = 2), beta-blocker and flecainide (n = 6), or acetazolamide (n = 6). Radiofrequency ablation was attempted in five patients without clinical success. An implantable cardiac defibrillator was implanted in three patients. During follow-up, none of the patients died, four patients experienced syncope under treatment, and one patient had non-fatal cardiac arrest. CONCLUSION Despite a severe clinical presentation with a very high rate of ventricular arrhythmias, the arrhythmic prognosis of the ATS patients is relatively good under treatment.
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Affiliation(s)
- Eric Delannoy
- L'Institut du Thorax, Department of Cardiology, Bd Monod, Nantes University Hospital, 44093, Nantes, France
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Abstract
The abrupt cessation of effective cardiac function due to an aberrant heart rhythm can cause sudden and unexpected death at any age, a syndrome called sudden cardiac death (SCD). Annually, more than 300,000 cases of SCD occur in the United States alone, making this a major public health concern. Our current understanding of the mechanisms responsible for SCD has emerged from decades of basic science investigation into the normal electrophysiology of the heart, the molecular physiology of cardiac ion channels, fundamental cellular and tissue events associated with cardiac arrhythmias, and the molecular genetics of monogenic disorders of heart rhythm. This knowledge has helped shape the current diagnosis and treatment of inherited arrhythmia susceptibility syndromes associated with SCD and has provided a pathophysiological framework for understanding more complex conditions predisposing to this tragic event. This Review presents an overview of the molecular basis of SCD, with a focus on monogenic arrhythmia syndromes.
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Affiliation(s)
- Alfred L George
- Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.
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Radwański PB, Greer-Short A, Poelzing S. Inhibition of Na+ channels ameliorates arrhythmias in a drug-induced model of Andersen-Tawil syndrome. Heart Rhythm 2012; 10:255-63. [PMID: 23041575 DOI: 10.1016/j.hrthm.2012.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Indexed: 10/27/2022]
Abstract
BACKGROUND Andersen-Tawil syndrome (ATS1)-associated ventricular tachycardias (VTs) are initiated by frequent, hypokalemia-exacerbated, premature ventricular activity (PVA). We previously demonstrated that a guinea pig model of drug-induced ATS1 (DI-ATS1) evidenced increased arrhythmias from regions with high Na(+)/Ca(2+)-exchange expression. OBJECTIVE Therefore, we hypothesize that reduced cytosolic Na(+) entry through either cardiac isoform of or tetrodotoxin (TTX)-sensitive Na(+) channels during DI-ATS1 can ameliorate arrhythmia burden. METHODS DI-ATS1 was induced with 10 μM BaCl(2) and 2 mM extracellular K(+). Ca(2+) transients and conduction velocity (CV) were optically mapped with indo-1 and di-4-ANEPPS, respectively, from Langendorff-perfused guinea pig ventricles. RESULTS Nonselective Na(+) channel blockade with 1 μM flecainide reduced amplitude (Ca(A)), slowed left ventricular CV, reduced tissue excitability, and abolished the incidence of VT while decreasing the incidence of PVA relative to DI-ATS1. Selective, TTX-sensitive Na(+) channel blockade with TTX (100 nM) during DI-ATS1 decreased Ca(A) and decreased the inducibility of VTs and PVA relative to DI-ATS1 without slowing CV. Ranolazine altered Ca(A), left ventricular CV, tissue excitability, and reduced inducibility of VT and PVA in a concentration-dependent manner. None of the aforementioned interventions altered diastolic Ca(2+) levels or Ca(2+) transient decay time constant. CONCLUSIONS These data suggest that cytosolic Na(+) entry and its modulation of Ca(2+) handling are necessary for arrhythmogenesis. During the loss of inward-rectifier K(+) current function, not only Na(+)/Ca(2+)-exchange dominance but Na(+) flux may determine arrhythmia burden. Therefore, selective inhibition of TTX-sensitive Na(+) channels may offer a potential therapeutic target to alleviate arrhythmias during states of Ca(2+) overload secondary to loss of inward-rectifier K(+) current function without compromising the excitability reserve.
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Affiliation(s)
- Przemysław B Radwański
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah 84112-5000, USA
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Shimizu W, Horie M. Phenotypic Manifestations of Mutations in Genes Encoding Subunits of Cardiac Potassium Channels. Circ Res 2011; 109:97-109. [DOI: 10.1161/circresaha.110.224600] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Since 1995, when a potassium channel gene,
hERG
(human ether-à-go-go-related gene), now referred to as
KCNH2
, encoding the rapid component of cardiac delayed rectifier potassium channels was identified as being responsible for type 2 congenital long-QT syndrome, a number of potassium channel genes have been shown to cause different types of inherited cardiac arrhythmia syndromes. These include congenital long-QT syndrome, short-QT syndrome, Brugada syndrome, early repolarization syndrome, and familial atrial fibrillation. Genotype-phenotype correlations have been investigated in some inherited arrhythmia syndromes, and as a result, gene-specific risk stratification and gene-specific therapy and management have become available, particularly for patients with congenital long-QT syndrome. In this review article, the molecular structure and function of potassium channels, the clinical phenotype due to potassium channel gene mutations, including genotype-phenotype correlations, and the diverse mechanisms underlying the potassium channel gene–related diseases will be discussed.
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Affiliation(s)
- Wataru Shimizu
- From the Division of Arrhythmia and Electrophysiology, Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center (W.S.), Suita, Japan, and the Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science (M.H.), Otsu, Japan
| | - Minoru Horie
- From the Division of Arrhythmia and Electrophysiology, Department of Cardiovascular Medicine, National Cerebral and Cardiovascular Center (W.S.), Suita, Japan, and the Department of Cardiovascular and Respiratory Medicine, Shiga University of Medical Science (M.H.), Otsu, Japan
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Radwański PB, Poelzing S. NCX is an important determinant for premature ventricular activity in a drug-induced model of Andersen-Tawil syndrome. Cardiovasc Res 2011; 92:57-66. [PMID: 21697145 DOI: 10.1093/cvr/cvr180] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS Andersen-Tawil syndrome (ATS1)-associated ventricular arrhythmias are initiated by premature ventricular activity (PVA) resulting from diastolic Ca(2+) (Ca(D)) accumulation. We hypothesized that relatively high Na(+)-Ca(2+) exchanger (NCX) expression coupled with slower Ca(2+) uptake may constitute an arrhythmogenic substrate during drug-induced ATS1 (DI-ATS1). METHODS AND RESULTS DI-ATS1 was induced with 10 µmol/L BaCl(2) and 2 mmol/L [K(+)](o). Ca(2+) transients and action potentials were optically mapped from Langendorff-perfused guinea pig ventricles. Intracellular Ca(2+) handling was modulated by either direct NCX inhibition with 5 µmol/L KB-R7943 or by sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) inhibition with cyclopiazonic acid (CPA). During DI-ATS1, PVA was more frequent in left ventricular (LV)-base (LVB) vs. LV-apex (LVA) (2.2 ± 0.8 vs. 0.6 ± 0.3 PVA/10 min), consistent with greater Ca(D) (1.65 ± 0.13 vs. 1.42 ± 0.09 normalized-Ca(D) units) and western blot-assessed NCX protein expression (81.2 ± 30.9%) in LVB relative to LVA. Further, regions of high NCX (LVB) evidenced a shorter PVA coupling interval relative to regions of low NCX expression (LVA, 67.7 ± 3.5 vs. 78.5 ± 3.6%). Inhibiting NCX during DI-ATS1 lowered the incidence of ventricular tachycardias (VTs, 0 vs. 25%) and PVA (1.5 ± 0.4 vs. 4.3 ± 1.4 PVA/10 min), but it did not affect PVA coupling intervals in LVB nor LVA (70.8 ± 4.3 vs. 73.8 ± 2.5%). Conversely, inhibition of SERCA2a with CPA, thereby increasing the role of NCX in Ca(2+) handling, significantly increased the incidence of VTs and PVA relative to DI-ATS1 alone, while decreasing the PVA coupling interval in all regions. CONCLUSION PVA preferentially occurs in regions of enhanced NCX expression with relatively slower Ca(2+) uptake and during perfusion of CPA which further reduces sarcoplasmic reticular Ca(2+) uptake.
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Affiliation(s)
- Przemysław B Radwański
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112-5000, USA
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Tricarico D, Camerino DC. Recent advances in the pathogenesis and drug action in periodic paralyses and related channelopathies. Front Pharmacol 2011; 2:8. [PMID: 21687503 PMCID: PMC3108473 DOI: 10.3389/fphar.2011.00008] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2011] [Accepted: 02/08/2011] [Indexed: 11/13/2022] Open
Abstract
The periodic paralysis (PP) are rare autosomal-dominant disorders associated to mutations in the skeletal muscle sodium, calcium, and potassium channel genes characterized by muscle fiber depolarization with un-excitability, episodes of weakness with variations in serum potassium concentrations. Recent advances in thyrotoxic PP and hypokalemic PP (hypoPP) confirm the involvement of the muscle potassium channels in the pathogenesis of the diseases and their role as target of action for drugs of therapeutic interest. The novelty in the gating pore currents theory help to explain the disease symptoms, and open the possibility to more specifically target the disease. It is now known that the fiber depolarization in the hypoPP is due to an unbalance between the novel identified depolarizing gating pore currents (Igp) carried by protons or Na+ ions flowing through aberrant alternative pathways of the mutant subunits and repolarizing inwardly rectifying potassium channel (Kir) currents which also includes the ATP-sensitive subtype. Abnormal activation of the Igp or deficiency in the Kir channels predispose to fiber depolarization. One pharmacological strategy is based on blocking the Igp without affecting normal channel gating. It remains safe and effective the proposal of targeting the KATP, Kir channels, or BK channels by drugs capable to specifically open at nanomolar concentrations the skeletal muscle subtypes with less side effects.
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Affiliation(s)
- Domenico Tricarico
- Department of Pharmacobiology, Faculty of Pharmacy, University of Bari Italy
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Maruyama M, Lin SF, Chen PS. Alternans of diastolic intracellular calcium elevation as the mechanism of bidirectional ventricular tachycardia in a rabbit model of Andersen-Tawil syndrome. Heart Rhythm 2010; 9:626-7. [PMID: 21167318 DOI: 10.1016/j.hrthm.2010.12.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2010] [Indexed: 11/17/2022]
Affiliation(s)
- Mitsunori Maruyama
- Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA
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Barajas-Martinez H, Hu D, Ontiveros G, Caceres G, Desai M, Burashnikov E, Scaglione J, Antzelevitch C. Biophysical and molecular characterization of a novel de novo KCNJ2 mutation associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry. ACTA ACUST UNITED AC 2010; 4:51-7. [PMID: 21148745 DOI: 10.1161/circgenetics.110.957696] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Mutations in KCNJ2, the gene encoding the human inward rectifier potassium channel Kir2.1 (IK1 or IKir2.1), have been identified in Andersen-Tawil syndrome. Andersen-Tawil syndrome is a multisystem inherited disease exhibiting periodic paralysis, cardiac arrhythmias, and dysmorphic features at times mimicking catecholaminergic polymorphic ventricular tachycardia. METHODS AND RESULTS Our proband displayed dysmorphic features including micrognathia, clinodactyly, and syndactyly and exhibited multiform extrasystoles and bidirectional ventricular tachycardia both at rest and during exercise testing. The patient's symptoms continued after administration of nadolol but subsided after treatment with flecainide. Molecular genetic screening revealed a novel heterozygous mutation (c.779G>C/p.R260P) in KCNJ2. Whole-cell patch-clamp studies conducted in TSA201 cells transfected with wild-type human KCNJ2 cDNA (WT-KCNJ2) yielded robust IKir2.1 but no measurable current in cells expressing the R260P mutant. Coexpression of WT and R260P-KCNJ2 (heterozygous expression) yielded a markedly reduced inward IKir2.1 compared with WT alone (-36.5±9.8 pA/pF versus -143.5±11.4 pA/pF, n=8 for both, P<0.001, respectively, at -90 mV), indicating a strong dominant negative effect of the mutant. The outward component of IKir2.1 measured at -50 mV was also markedly reduced with the heterozygous expression versus WT (0.52±5.5 pA/pF versus 23.4±6.7 pA/pF, n=8 for both, P<0.001, respectively). Immunocytochemical analysis indicates that impaired trafficking of R260P-KCNJ2 channels. CONCLUSIONS We report a novel de novo KCNJ2 mutation associated with classic phenotypic features of Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia mimicry. The R260P mutation produces a strong dominant negative effect leading to marked suppression of IK1 secondary to a trafficking defect.
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Haraoka K, Morita H, Saito Y, Toh N, Miyoshi T, Nishii N, Nagase S, Nakamura K, Kohno K, Kusano KF, Kawaguchi K, Ohe T, Ito H. Fragmented QRS is associated with torsades de pointes in patients with acquired long QT syndrome. Heart Rhythm 2010; 7:1808-14. [DOI: 10.1016/j.hrthm.2010.09.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 09/07/2010] [Indexed: 10/19/2022]
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Baher AA, Uy M, Xie F, Garfinkel A, Qu Z, Weiss JN. Bidirectional ventricular tachycardia: ping pong in the His-Purkinje system. Heart Rhythm 2010; 8:599-605. [PMID: 21118730 DOI: 10.1016/j.hrthm.2010.11.038] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/07/2010] [Accepted: 11/23/2010] [Indexed: 01/01/2023]
Abstract
BACKGROUND Bidirectional ventricular tachycardia (BVT), which is characterized by an alternating beat-to-beat ECG QRS axis, is a rare but intriguing arrhythmia associated with digitalis toxicity, familial catecholaminergic polymorphic ventricular tachycardia (CPVT), and several other conditions that predispose cardiac myocytes to delayed afterdepolarizations (DADs) and triggered activity. Evidence from human and animal studies attributes BVT to alternating ectopic foci originating from the distal His-Purkinje system in the left and/or right ventricle, respectively. OBJECTIVE The purpose of this study was to evaluate a simple "ping pong" model of reciprocating bigeminy to explain BVT. METHODS We constructed a two-dimensional anatomic model of the rabbit ventricles with a simplified His-Purkinje system, in which different sites in the His-Purkinje system had different heart rate thresholds for DAD-induced bigeminy. RESULTS When the heart rate exceeded the threshold for bigeminy at the first site in the His-Purkinje system, ventricular bigeminy developed, causing the heart rate to accelerate and exceed the threshold for bigeminy at the second site. Thus, the triggered beat from the first site induced a triggered beat from the second site. The triggered beat from the second site next reciprocated by inducing a triggered beat from the first site, and so forth. Bigeminy from two sites produced BVT, and that from three or more sites produced polymorphic VT. CONCLUSION This "ping pong" mechanism of reciprocating bigeminy readily produces the characteristic ECG pattern of BVT and its degeneration to polymorphic VT if additional sites develop bigeminy.
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Affiliation(s)
- Alex A Baher
- Cardiovascular Research Laboratory, Department of Medicine (Cardiology), David Geffen School of Medicine at UCLA, Los Angeles, California, USA
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Don't overlook overload of calcium. Heart Rhythm 2010; 7:1436-7. [PMID: 20430114 DOI: 10.1016/j.hrthm.2010.04.025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2010] [Indexed: 11/23/2022]
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Radwański PB, Veeraraghavan R, Poelzing S. Cytosolic calcium accumulation and delayed repolarization associated with ventricular arrhythmias in a guinea pig model of Andersen-Tawil syndrome. Heart Rhythm 2010; 7:1428-1435.e1. [PMID: 20380896 DOI: 10.1016/j.hrthm.2010.03.044] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Accepted: 03/31/2010] [Indexed: 11/25/2022]
Abstract
BACKGROUND Andersen-Tawil syndrome (ATS1)-associated ventricular arrhythmias are initiated by frequent, hypokalemia-exacerbated, triggered activity. Previous ex vivo studies in drug-induced Andersen-Tawil syndrome (DI-ATS1) models have proposed that arrhythmia propensity in DI-ATS1 derives from cytosolic Ca(2+) ([Ca(2+)](i)) accumulation leading to increased triggered activity. OBJECTIVE The purpose of this study was to test the hypothesis that elevated [Ca(2+)](i) with concomitant APD prolongation, rather than APD dispersion, underlies arrhythmia propensity during DI-ATS1. METHODS DI-ATS1 was induced in isolated guinea pig ventricles by perfusion of 2 mM KCl Tyrode solution containing 10 μM BaCl(2). APD and [Ca(2+)](i) from the anterior epicardium were quantified by ratiometric optical voltage (di-4-ANEPPS) or Ca(2+) (Indo-1) mapping during right ventricular pacing with or without the ATP-sensitive potassium channel opener pinacidil (15 μM). RESULTS APD gradients under all conditions were insufficient for arrhythmia induction by programmed stimulation. However, 38% of DI-ATS1 preparations experienced ventricular tachycardias (VTs), and all preparations experienced a high incidence of premature ventricular complexes (PVCs). Pinacidil decreased APD and APD dispersion and reduced VTs (to 6%), and PVC frequency (by 79.5%). However, PVC frequency remained significantly greater relative to control (0.5% ± 0.3% of DI-ATS1). Importantly, increased arrhythmia propensity during DI-ATS1 was associated with diastolic [Ca(2+)](i) accumulation and increased [Ca(2+)](i) transient amplitudes. Pinacidil partially attenuated the former but did not alter the latter. CONCLUSION The study data suggest that arrhythmias during DI-ATS1 may be a result of triggered activity secondary to prolonged APD and altered [Ca(2+)](i) cycling and less likely dependent on large epicardial APD gradients forming the substrate for reentry. Therefore, therapies aimed at reducing [Ca(2+)](i) rather than APD gradients may prove effective in treatment of ATS1.
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Affiliation(s)
- Przemysław B Radwański
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, Utah 84112-5000, USA
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Sung RJ, Wu YH, Lai NHJ, Teng CH, Luo CH, Tien HC, Lo CP, Wu SN. β-Adrenergic modulation of arrhythmogenesis and identification of targeted sites of antiarrhythmic therapy in Timothy (LQT8) syndrome: a theoretical study. Am J Physiol Heart Circ Physiol 2010; 298:H33-44. [DOI: 10.1152/ajpheart.00232.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Timothy syndrome (TS) is a malignant form of congenital long QT syndrome with a mode of arrhythmia onset often triggered by enhanced sympathetic tone. We sought to explore mechanisms by which β-adrenergic stimulation (BAS) modulates arrhythmogenesis and to identify potential targeted sites of antiarrhythmic therapy in TS. Using a dynamic Luo-Rudy ventricular myocyte model incorporated with detailed intracellular Ca2+ cycling, along with its one-dimensional multicellular strand, we simulated various clinical scenarios of TS, with stepwise increase in the percentage of G406R Cav1.2 channels from 0 to 11.5 and 23%, and to 38.5 and 77%, respectively, for heterozygous and homozygous states of TS1 and TS2. Progressive prolongation of action potential duration (APD) and QT interval, accompanied by amplification of transmural dispersion of repolarization, steepening of APD restitution, induction of delayed afterdepolariztions (DADs), and both DAD and phase 3 early afterdepolariztion-mediated triggered activities, correlated well with the extent of G406R Cav1.2 channel mutation. BAS amplified transmural dispersion of repolarization, steepened APD restitution, and facilitated inducibility of DAD-mediated triggered activity. Systematic analysis of intracellular Ca2+ cycling revealed that sarcoplasmic reticulum Ca2+ ATPase (uptake current) played an essential role in BAS-induced facilitation of DAD-mediated triggered activity and, in addition to L-type calcium current, it could be an effective site of antiarrhythmic therapy under the influence of BAS. Thus G406R Cav1.2 channel mutation confers not only a trigger, but also a substrate for lethal ventricular arrhythmias, which can be exaggerated by BAS. It is suggested that, besides β-adrenergic blockers and L-type calcium current channel blockers, an agent aimed at reduction of sarcoplasmic reticulum Ca2+ ATPase uptake current may provide additional antiarrhythmic effect in patients with TS.
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Affiliation(s)
- Ruey J. Sung
- Institute of Life Sciences, College of Sciences, National Central University, Taoyuan
- Division of Cardiovascular Medicine, Department of Medicine, Stanford University School of Medicine, Stanford, California
| | - Yung-Han Wu
- Institute of Basic Medical Research, College of Medicine,
| | | | | | - Ching-Hsing Luo
- Institute of Electrical Engineering, College of Engineering and Computer Science, National Cheng Kung University, Tainan; and
| | - Hui-Chun Tien
- Department of Applied Mathematics, Providence University, Taichung, Taiwan; and
| | - Chu-Pin Lo
- Department of Applied Mathematics, Providence University, Taichung, Taiwan; and
| | - Sheng-Nan Wu
- Institute of Basic Medical Research, College of Medicine,
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Skeletal muscle channelopathies: new insights into the periodic paralyses and nondystrophic myotonias. Curr Opin Neurol 2009; 22:524-31. [PMID: 19571750 DOI: 10.1097/wco.0b013e32832efa8f] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE OF REVIEW To summarize advances in our understanding of the clinical phenotypes, genetics, and molecular pathophysiology of the periodic paralyses, the nondystrophic myotonias, and other muscle channelopathies. RECENT FINDINGS The number of pathogenic mutations causing periodic paralysis, nondystrophic myotonias, and ryanodinopathies continues to grow with the advent of exon hierarchy analysis strategies for genetic screening and better understanding and recognition of disease phenotypes. Recent studies have expanded and clarified the role of gating pore current in channelopathy pathogenesis. It has been shown that the gating pore current can account for the molecular and phenotypic diseases observed in the muscle sodium channelopathies, and, given that homologous residues are affected in mutations of calcium channels, it is possible that pore leak represents a pathomechanism applicable to many channel diseases. Improvements in treatment of the muscle channelopathies are on the horizon. A randomized controlled trial has been initiated for the study of mexiletine in nondystrophic myotonias. The class IC antiarrhythmia drug flecainide has been shown to depress ventricular ectopy and improve exercise capacity in patients with Andersen-Tawil syndrome. SUMMARY Recent studies have expanded our understanding of gating pore current as a disease-causing mechanism in the muscle channelopathies and have allowed new correlations to be drawn between disease genotype and phenotype.
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Maruyama M, Joung B, Tang L, Shinohara T, On YK, Han S, Choi EK, Kim DH, Shen MJ, Weiss JN, Lin SF, Chen PS. Diastolic intracellular calcium-membrane voltage coupling gain and postshock arrhythmias: role of purkinje fibers and triggered activity. Circ Res 2009; 106:399-408. [PMID: 19926871 DOI: 10.1161/circresaha.109.211292] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
RATIONALE Recurrent ventricular arrhythmias after initial successful defibrillation are associated with poor clinical outcome. OBJECTIVE We tested the hypothesis that postshock arrhythmias occur because of spontaneous sarcoplasmic reticulum Ca release, delayed afterdepolarization (DAD), and triggered activity (TA) from tissues with high sensitivity of resting membrane voltage (V(m)) to elevated intracellular calcium (Ca(i)) (high diastolic Ca(i)-voltage coupling gains). METHODS AND RESULTS We simultaneously mapped Ca(i) and V(m) on epicardial (n=14) or endocardial (n=14) surfaces of Langendorff-perfused rabbit ventricles. Spontaneous Ca(i) elevation (SCaE) was noted after defibrillation in 32% of ventricular tachycardia/ventricular fibrillation at baseline and in 81% during isoproterenol infusion (0.01 to 1 micromol/L). SCaE was reproducibly induced by rapid ventricular pacing and inhibited by 3 mumol/L of ryanodine. The SCaE amplitude and slope increased with increasing pacing rate, duration, and dose of isoproterenol. We found TAs originating from 6 of 14 endocardial surfaces but none from epicardial surfaces, despite similar amplitudes and slopes of SCaEs between epicardial and endocardial surfaces. This was because DADs were larger on endocardial surfaces as a result of higher diastolic Ca(i)-voltage coupling gain, compared to those of epicardial surfaces. Purkinje-like potentials preceded TAs in all hearts studied (n=7). I(K1) suppression with CsCl (5 mmol/L, n=3), BaCl(2) (3 micromol/L, n=3), and low extracellular potassium (1 mmol/L, n=2) enhanced diastolic Ca(i)-voltage coupling gain and enabled epicardium to also generate TAs. CONCLUSIONS Higher diastolic Ca(i)-voltage coupling gain is essential for genesis of TAs and may underlie postshock arrhythmias arising from Purkinje fibers. I(K)(1) is a major factor that determines the diastolic Ca(i)-voltage coupling gain.
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Affiliation(s)
- Mitsunori Maruyama
- Krannert Institute of Cardiology and the Division of Cardiology, Department of Medicine, Indiana University School of Medicine, Indianapolis, USA
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Vega AL, Tester DJ, Ackerman MJ, Makielski JC. Protein kinase A-dependent biophysical phenotype for V227F-KCNJ2 mutation in catecholaminergic polymorphic ventricular tachycardia. Circ Arrhythm Electrophysiol 2009; 2:540-7. [PMID: 19843922 DOI: 10.1161/circep.109.872309] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND KCNJ2 encodes Kir2.1, a pore-forming subunit of the cardiac inward rectifier current, I(K1). KCNJ2 mutations are associated with Andersen-Tawil syndrome and catecholaminergic polymorphic ventricular tachycardia. The aim of this study was to characterize the biophysical and cellular phenotype of a KCNJ2 missense mutation, V227F, found in a patient with catecholaminergic polymorphic ventricular tachycardia. METHODS AND RESULTS Kir2.1-wild-type (WT) and V227F channels were expressed individually and together in Cos-1 cells to measure I(K1) by voltage clamp. Unlike typical Andersen-Tawil syndrome-associated KCNJ2 mutations, which show dominant negative loss of function, Kir2.1WT+V227F coexpression yielded I(K1) indistinguishable from Kir2.1-WT under basal conditions. To simulate catecholamine activity, a protein kinase A (PKA)-stimulating cocktail composed of forskolin and 3-isobutyl-1-methylxanthine was used to increase PKA activity. This PKA-simulated catecholaminergic stimulation caused marked reduction of outward I(K1) compared with Kir2.1-WT. PKA-induced reduction in I(K1) was eliminated by mutating the phosphorylation site at serine 425 (S425N). CONCLUSIONS Heteromeric Kir2.1-V227F and WT channels showed an unusual latent loss of function biophysical phenotype that depended on PKA-dependent Kir2.1 phosphorylation. This biophysical phenotype, distinct from typical Andersen-Tawil syndrome mutations, suggests a specific mechanism for PKA-dependent I(K1) dysfunction for this KCNJ2 mutation, which correlates with adrenergic conditions underlying the clinical arrhythmia.
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Affiliation(s)
- Amanda L Vega
- Department of Medicine, University of Wisconsin, Madison, Wisconsin 53792, USA
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Postema PG, Ritsema van Eck HJ, Opthof T, van Herpen G, van Dessel PFHM, Priori SG, Wolpert C, Borggrefe M, Kors JA, Wilde AAM. IK1 modulates the U-wave: insights in a 100-year-old enigma. Heart Rhythm 2008; 6:393-400. [PMID: 19251218 DOI: 10.1016/j.hrthm.2008.11.024] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Accepted: 11/22/2008] [Indexed: 11/16/2022]
Affiliation(s)
- Pieter G Postema
- Department of Cardiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
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Abstract
This Seminar presents the most recent information about the congenital long and short QT syndromes, emphasising the varied genotype-phenotype association in the ten different long QT syndromes and the five different short QT syndromes. Although uncommon, these syndromes serve as a Rosetta stone for the understanding of inherited ion-channel disorders leading to life-threatening cardiac arrhythmias. Ionic abnormal changes mainly affecting K(+), Na(+), or Ca(2+) currents, which either prolong or shorten ventricular repolarisation, can create a substrate of electrophysiological heterogeneity that predisposes to the development of ventricular tachyarrhythmias and sudden death. The understanding of the genetic basis of the syndromes is hoped to lead to genetic therapy that can restore repolarisation. Presently, symptomatic individuals are generally best treated with an implantable cardioverter defibrillator. Clinicians should be aware of these syndromes and realise that drugs, ischaemia, exercise, and emotions can precipitate sudden death in susceptible individuals.
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Affiliation(s)
- Hiroshi Morita
- Krannert Institute of Cardiology and the Division of Cardiology, Indiana University School of Medicine, Indianapolis, IN, USA
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Calcium channel blocker and adenosine triphosphate terminate bidirectional ventricular tachycardia in a patient with Andersen-Tawil syndrome. Heart Rhythm 2007; 5:498-9. [PMID: 18313615 DOI: 10.1016/j.hrthm.2007.12.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2007] [Indexed: 11/21/2022]
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