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Oknińska M, Mączewski M, Mackiewicz U. Ventricular arrhythmias in acute myocardial ischaemia-Focus on the ageing and sex. Ageing Res Rev 2022; 81:101722. [PMID: 36038114 DOI: 10.1016/j.arr.2022.101722] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 08/17/2022] [Accepted: 08/20/2022] [Indexed: 01/31/2023]
Abstract
Annually, approximately 17 million people die from cardiovascular diseases worldwide, half of them suddenly. The most common direct cause of sudden cardiac death is ventricular arrhythmia triggered by an acute coronary syndrome (ACS). The study summarizes the knowledge of the mechanisms of arrhythmia onset during ACS in humans and in animal models and factors that may influence the susceptibility to life-threatening arrhythmias during ACS with particular focus on the age and sex. The real impact of age and sex on the arrhythmic susceptibility within the setting of acute ischaemia is masked by the fact that ACSs result from coronary artery disease appearing with age much earlier among men than among women. However, results of researches show that in ageing process changes with potential pro-arrhythmic significance, such as increased fibrosis, cardiomyocyte hypertrophy, decrease number of gap junction channels, disturbances of the intracellular Ca2+ signalling or changes in electrophysiological parameters, occur independently of the development of cardiovascular diseases and are more severe in male individuals. A review of the literature also indicates a marked paucity of research in this area in female and elderly individuals. Greater awareness of sex differences in the aging process could help in the development of personalized prevention methods targeting potential pro-arrhythmic factors in patients of both sexes to reduce mortality during the acute phase of myocardial infarction. This is especially important in an era of aging populations in which women will predominate due to their longer lifespan.
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Affiliation(s)
- Marta Oknińska
- Department of Clinical Physiology, Centre of Postgraduate Medical Education, Marymoncka 99/103, 01-813 Warsaw, Poland
| | - Michał Mączewski
- Department of Clinical Physiology, Centre of Postgraduate Medical Education, Marymoncka 99/103, 01-813 Warsaw, Poland
| | - Urszula Mackiewicz
- Department of Clinical Physiology, Centre of Postgraduate Medical Education, Marymoncka 99/103, 01-813 Warsaw, Poland.
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Varró A, Tomek J, Nagy N, Virág L, Passini E, Rodriguez B, Baczkó I. Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior. Physiol Rev 2020; 101:1083-1176. [PMID: 33118864 DOI: 10.1152/physrev.00024.2019] [Citation(s) in RCA: 86] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.
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Affiliation(s)
- András Varró
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary.,MTA-SZTE Cardiovascular Pharmacology Research Group, Hungarian Academy of Sciences, Szeged, Hungary
| | - Jakub Tomek
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Norbert Nagy
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary.,MTA-SZTE Cardiovascular Pharmacology Research Group, Hungarian Academy of Sciences, Szeged, Hungary
| | - László Virág
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Elisa Passini
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Blanca Rodriguez
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - István Baczkó
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
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Puga Bravo M, Castro J, Gallardo Y. QT interval greater than 460 ms in multiple electrocardiograms during follow-up in patients with Brugada syndrome: What does it contribute? Rev Port Cardiol 2020; 39:183-186. [PMID: 32416997 DOI: 10.1016/j.repc.2019.07.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 06/18/2019] [Accepted: 07/21/2019] [Indexed: 10/24/2022] Open
Abstract
INTRODUCTION Corrected QT interval (QTc) >460 ms in the right precordial leads has been described as a predictor of malignant ventricular arrhythmias (MVA) in patients with Brugada syndrome (BrS). OBJECTIVE To assess the presence of QTc>460 ms in multiple electrocardiograms (ECGs) during follow-up as a predictor of recurrence of MVA in patients with BrS. METHODS The study group included 43 patients with BrS and an implantable cardioverter-defibrillator. ECGs were performed serially between June 2000 and January 2017. QT interval was measured and QTc was obtained by Bazett's formula. The sample was divided into three groups: Group 1 (patients with no ECGs with QTc>460 ms); Group 2 (patients with only one ECG with QTc>460 ms); and Group 3 (patients with two or more ECGs with QTc>460 ms). RESULTS The following variables were more frequently observed in Group 3: family history of sudden death (p=0.023), previous history of cardiorespiratory arrest (p=0.032), syncope (p=0.039), documented MVA (p=0.002), and proportion of ECGs with coved-type ST interval during follow-up (p=0.002). In Group 3, 67% of BrS patients had events during follow-up, as opposed to only 22% of Group 1 and 14% of Group 2 (Group 1 vs. Group 2, p=0.33015; Group 1 vs. Group 3, p=0.04295; and Group 2 vs. Group 3, p=0.04155). CONCLUSIONS QTc>460 ms in more than one ECG during follow-up increases the risk of MVA events in patients with BrS.
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Affiliation(s)
| | - Jesús Castro
- Department of Arrhythmias and Cardiac Pacing, Cardiovascular Institute of Havana, Cuba
| | - Yisel Gallardo
- Department of Cardiology, Cardiovascular Institute of Havana, Cuba
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Puga Bravo M, Castro J, Gallardo Y. QT interval greater than 460 ms in multiple electrocardiograms during follow-up in patients with Brugada syndrome: What does it contribute? REVISTA PORTUGUESA DE CARDIOLOGIA (ENGLISH EDITION) 2020. [DOI: 10.1016/j.repce.2019.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Trenor B, Cardona K, Saiz J, Noble D, Giles W. Cardiac action potential repolarization revisited: early repolarization shows all-or-none behaviour. J Physiol 2017; 595:6599-6612. [PMID: 28815597 PMCID: PMC5663823 DOI: 10.1113/jp273651] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/09/2017] [Indexed: 12/15/2022] Open
Abstract
In healthy mammalian hearts the action potential (AP) waveform initiates and modulates each contraction, or heartbeat. As a result, AP height and duration are key physiological variables. In addition, rate-dependent changes in ventricular AP duration (APD), and variations in APD at a fixed heart rate are both reliable biomarkers of electrophysiological stability. Present guidelines for the likelihood that candidate drugs will increase arrhythmias rely on small changes in APD and Q-T intervals as criteria for safety pharmacology decisions. However, both of these measurements correspond to the final repolarization of the AP. Emerging clinical evidence draws attention to the early repolarization phase of the action potential (and the J-wave of the ECG) as an additional important biomarker for arrhythmogenesis. Here we provide a mechanistic background to this early repolarization syndrome by summarizing the evidence that both the initial depolarization and repolarization phases of the cardiac action potential can exhibit distinct time- and voltage-dependent thresholds, and also demonstrating that both can show regenerative all-or-none behaviour. An important consequence of this is that not all of the dynamics of action potential repolarization in human ventricle can be captured by data from single myocytes when these results are expressed as 'repolarization reserve'. For example, the complex pattern of cell-to-cell current flow that is responsible for AP conduction (propagation) within the mammalian myocardium can change APD and the Q-T interval of the electrocardiogram alter APD stability, and modulate responsiveness to pharmacological agents (such as Class III anti-arrhythmic drugs).
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Affiliation(s)
- Beatriz Trenor
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Karen Cardona
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Javier Saiz
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Denis Noble
- University Laboratory of PhysiologyUniversity of OxfordOxfordOX1 3PTUK
| | - Wayne Giles
- Faculties of Kinesiology and MedicineUniversity of CalgaryCalgaryAlbertaCanadaT2N 1N4
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Colman MA, Perez Alday EA, Holden AV, Benson AP. Trigger vs. Substrate: Multi-Dimensional Modulation of QT-Prolongation Associated Arrhythmic Dynamics by a hERG Channel Activator. Front Physiol 2017; 8:757. [PMID: 29046643 PMCID: PMC5632683 DOI: 10.3389/fphys.2017.00757] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 09/19/2017] [Indexed: 11/13/2022] Open
Abstract
Background: Prolongation of the QT interval of the electrocardiogram (ECG), underlain by prolongation of the action potential duration (APD) at the cellular level, is linked to increased vulnerability to cardiac arrhythmia. Pharmacological management of arrhythmia associated with QT prolongation is typically achieved through attempting to restore APD to control ranges, reversing the enhanced vulnerability to Ca2+-dependent afterdepolarisations (arrhythmia triggers) and increased transmural dispersion of repolarisation (arrhythmia substrate) associated with APD prolongation. However, such pharmacological modulation has been demonstrated to have limited effectiveness. Understanding the integrative functional impact of pharmacological modulation requires simultaneous investigation of both the trigger and substrate. Methods: We implemented a multi-scale (cell and tissue) in silico approach using a model of the human ventricular action potential, integrated with a model of stochastic 3D spatiotemporal Ca2+ dynamics, and parameter modification to mimic prolonged QT conditions. We used these models to examine the efficacy of the hERG activator MC-II-157c in restoring APD to control ranges, examined its effects on arrhythmia triggers and substrates, and the interaction of these arrhythmia triggers and substrates. Results: QT prolongation conditions promoted the development of spontaneous release events underlying afterdepolarisations during rapid pacing. MC-II-157c applied to prolonged QT conditions shortened the APD, inhibited the development of afterdepolarisations and reduced the probability of afterdepolarisations manifesting as triggered activity in single cells. In tissue, QT prolongation resulted in an increased transmural dispersion of repolarisation, which manifested as an increased vulnerable window for uni-directional conduction block. In some cases, MC-II-157c further increased the vulnerable window through its effects on INa. The combination of stochastic release event modulation and transmural dispersion of repolarisation modulation by MC-II-157c resulted in an integrative behavior wherein the arrhythmia trigger is reduced but the arrhythmia substrate is increased, leading to variable and non-linear overall vulnerability to arrhythmia. Conclusion: The relative balance of reduced trigger and increased substrate underlies a multi-dimensional role of MC-II-157c in modulation of cardiac arrhythmia vulnerability associated with prolonged QT interval.
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Affiliation(s)
- Michael A Colman
- School of Biomedical Sciences and Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, United Kingdom
| | - Erick A Perez Alday
- Division of Cardiovascular Medicine, Oregon Health and Science University, Portland, OR, United States
| | - Arun V Holden
- School of Biomedical Sciences and Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, United Kingdom
| | - Alan P Benson
- School of Biomedical Sciences and Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, United Kingdom
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Heine T, Lenis G, Reichensperger P, Beran T, Doessel O, Deml B. Electrocardiographic features for the measurement of drivers' mental workload. APPLIED ERGONOMICS 2017; 61:31-43. [PMID: 28237018 DOI: 10.1016/j.apergo.2016.12.015] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2016] [Revised: 11/26/2016] [Accepted: 12/21/2016] [Indexed: 06/06/2023]
Abstract
This study examines the effect of mental workload on the electrocardiogram (ECG) of participants driving the Lane Change Task (LCT). Different levels of mental workload were induced by a secondary task (n-back task) with three levels of difficulty. Subjective data showed a significant increase of the experienced workload over all three levels. An exploratory approach was chosen to extract a large number of rhythmical and morphological features from the ECG signal thereby identifying those which differentiated best between the levels of mental workload. No single rhythmical or morphological feature was able to differentiate between all three levels. A group of parameters were extracted which were at least able to discriminate between two levels. For future research, a combination of features is recommended to achieve best diagnosticity for different levels of mental workload.
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Affiliation(s)
- Tobias Heine
- Institute of Human and Industrial Engineering (ifab), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany.
| | - Gustavo Lenis
- Institute of Biomedical Engineering (IBT), Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 1, 76131 Karlsruhe, Germany
| | - Patrick Reichensperger
- Institute of Biomedical Engineering (IBT), Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 1, 76131 Karlsruhe, Germany
| | - Tobias Beran
- Institute of Human and Industrial Engineering (ifab), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany
| | - Olaf Doessel
- Institute of Biomedical Engineering (IBT), Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 1, 76131 Karlsruhe, Germany
| | - Barbara Deml
- Institute of Human and Industrial Engineering (ifab), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany
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Myocardial edema as a substrate of electrocardiographic abnormalities and life-threatening arrhythmias in reversible ventricular dysfunction of takotsubo cardiomyopathy: Imaging evidence, presumed mechanisms, and implications for therapy. Heart Rhythm 2015; 12:1867-77. [PMID: 25937439 DOI: 10.1016/j.hrthm.2015.04.041] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Indexed: 02/07/2023]
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Benoist D, Stones R, Benson AP, Fowler ED, Drinkhill MJ, Hardy MEL, Saint DA, Cazorla O, Bernus O, White E. Systems approach to the study of stretch and arrhythmias in right ventricular failure induced in rats by monocrotaline. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2014; 115:162-72. [PMID: 25016242 PMCID: PMC4210667 DOI: 10.1016/j.pbiomolbio.2014.06.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/25/2014] [Accepted: 06/27/2014] [Indexed: 02/05/2023]
Abstract
We demonstrate the synergistic benefits of using multiple technologies to investigate complex multi-scale biological responses. The combination of reductionist and integrative methodologies can reveal novel insights into mechanisms of action by tracking changes of in vivo phenomena to alterations in protein activity (or vice versa). We have applied this approach to electrical and mechanical remodelling in right ventricular failure caused by monocrotaline-induced pulmonary artery hypertension in rats. We show arrhythmogenic T-wave alternans in the ECG of conscious heart failure animals. Optical mapping of isolated hearts revealed discordant action potential duration (APD) alternans. Potential causes of the arrhythmic substrate; structural remodelling and/or steep APD restitution and dispersion were observed, with specific remodelling of the Right Ventricular Outflow Tract. At the myocyte level, [Ca(2+)]i transient alternans were observed together with decreased activity, gene and protein expression of the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA). Computer simulations of the electrical and structural remodelling suggest both contribute to a less stable substrate. Echocardiography was used to estimate increased wall stress in failure, in vivo. Stretch of intact and skinned single myocytes revealed no effect on the Frank-Starling mechanism in failing myocytes. In isolated hearts acute stretch-induced arrhythmias occurred in all preparations. Significant shortening of the early APD was seen in control but not failing hearts. These observations may be linked to changes in the gene expression of candidate mechanosensitive ion channels (MSCs) TREK-1 and TRPC1/6. Computer simulations incorporating MSCs and changes in ion channels with failure, based on altered gene expression, largely reproduced experimental observations.
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Affiliation(s)
- David Benoist
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK; L'Institut de Rythmologie et Modelisation Cardiaque, INSERM U1045, Université de Bordeaux, France
| | - Rachel Stones
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK
| | - Alan P Benson
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK
| | - Ewan D Fowler
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK
| | - Mark J Drinkhill
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK
| | - Matthew E L Hardy
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK; Faculty of Life Sciences, University of Manchester, UK
| | - David A Saint
- School of Medical Sciences, University of Adelaide, Australia
| | - Olivier Cazorla
- INSERM U1046, Université Montpellier 1, Université Montpellier 2, France
| | - Olivier Bernus
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK; L'Institut de Rythmologie et Modelisation Cardiaque, INSERM U1045, Université de Bordeaux, France
| | - Ed White
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, UK.
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Avci A, Demir K, Altunkeser BB, Yilmaz S, Yilmaz A, Ersecgin A, Demir T. Assessment of inhomogeneities of repolarization in patients with systemic lupus erythematosus. Ann Noninvasive Electrocardiol 2014; 19:374-82. [PMID: 24597863 PMCID: PMC6932449 DOI: 10.1111/anec.12145] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
OBJECTIVES Systemic lupus erythematosus (SLE) is a chronic disease that affects many organ systems and manifests a broad spectrum of laboratory and clinical features. SLE patients have an increased risk of developing cardiovascular disease. The aim of this study was to evaluate inhomogeneities of repolarization by using Tpeak -Tend (Tp-e) interval and Tp-e/QT ratio were measured from the 12-lead surface electrocardiogram (ECG) in patients with SLE. MATERIAL AND METHOD This study included 69 SLE patients (69 females; mean age 35.8 ± 10.2) and 57 control subjects (57 females; mean age 34.5 ± 8.9). Transthoracic echocardiographic examination was done in all participants. QT parameters, Tp-e intervals and Tp-e/QT ratio were measured from the 12-lead ECG. These parameters were compared between groups. RESULTS No statistically significant difference was found between two groups in terms of basic characteristics. Diastolic function parameters were similar between the two groups (P > 0.05). In electrocardiographic parameters analysis, QT dispersion (QTd) and corrected QT dispersion (cQTd) were significantly increased in SLE patients compared the control group (49.5 ± 16.4 ms vs. 32.8±11.7 ms and 56.7 ± 19.5 ms vs. 36.4 ± 13.1 ms, all P value < 0.001). Tp-e interval and Tp-e/QT ratio were also significantly higher in SLE patients (82.8 ± 18.9 vs. 72.4 ± 17.6 and 0.22 ± 0.05 vs. 0.19 ± 0.05, P = 0.002 and P = 0.001, respectively). Tp-e interval and Tp-e/QT were positively correlated with disease duration (r = 0.29, P = 0.01 and r = 0.24, P = 0.04, respectively). CONCLUSION Our study revealed that QTd, cQTd, Tp-e interval and Tp-e/QT ratio increased in patients with SLE. Also, Tp-e interval and Tp-e/QT were positively correlated with disease duration.
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Affiliation(s)
- Ahmet Avci
- Faculty of MedicineCardiology DepartmentSelcuk UniversityKonyaTurkey
| | - Kenan Demir
- Faculty of MedicineCardiology DepartmentSelcuk UniversityKonyaTurkey
| | | | - Sema Yilmaz
- Faculty of MedicineRheumatology DepartmentSelcuk UniversityKonyaTurkey
| | - Ahmet Yilmaz
- Faculty of MedicineCardiology DepartmentSelcuk UniversityKonyaTurkey
| | - Ahmet Ersecgin
- Faculty of MedicineCardiology DepartmentSelcuk UniversityKonyaTurkey
| | - Tarik Demir
- Faculty of Medicine, Internal Medicine DepartmentSelcuk UniversityKonyaTurkey
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Walton RD, Benson AP, Hardy MEL, White E, Bernus O. Electrophysiological and structural determinants of electrotonic modulation of repolarization by the activation sequence. Front Physiol 2013; 4:281. [PMID: 24115934 PMCID: PMC3792354 DOI: 10.3389/fphys.2013.00281] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 09/18/2013] [Indexed: 11/14/2022] Open
Abstract
Spatial dispersion of repolarization is known to play an important role in arrhythmogenesis. Electrotonic modulation of repolarization by the activation sequence has been observed in some species and tissue preparations, but to varying extents. Our study sought to determine the mechanisms underlying species- and tissue-dependent electrotonic modulation of repolarization in ventricles. Epi-fluorescence optical imaging of whole rat hearts and pig left ventricular wedges were used to assess epicardial spatial activation and repolarization characteristics. Experiments were supported by computer simulations using realistic geometries. Tight coupling between activation times (AT) and action potential duration (APD) were observed in rat experiments but not in pig. Linear correlation analysis found slopes of −1.03 ± 0.59 and −0.26 ± 0.13 for rat and pig, respectively (p < 0.0001). In rat, maximal dispersion of APD was 11.0 ± 3.1 ms but dispersion of repolarization time (RT) was relatively homogeneous (8.2 ± 2.7, p < 0.0001). However, in pig no such difference was observed between the dispersion of APD and RT (17.8 ± 6.1 vs. 17.7 ± 6.5, respectively). Localized elevations of APD (12.9 ± 8.3%) were identified at ventricular insertion sites of rat hearts both in experiments and simulations. Tissue geometry and action potential (AP) morphology contributed significantly to determining influence of electrotonic modulation. Simulations of a rat AP in a pig geometry decreased the slope of AT and APD relationships by 70.6% whereas slopes were increased by 75.0% when implementing a pig AP in a rat geometry. A modified pig AP, shortened to match the rat APD, showed little coupling between AT and APD with greatly reduced slope compared to the rat AP. Electrotonic modulation of repolarization by the activation sequence is especially pronounced in small hearts with murine-like APs. Tissue architecture and AP morphology play an important role in electrotonic modulation of repolarization.
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Affiliation(s)
- Richard D Walton
- Faculty of Biological Sciences, Multidisciplinary Cardiovascular Research Centre, School of Biomedical Sciences, Institute of Membrane and Systems Biology, University of Leeds Leeds, UK ; Unité Inserm 1045, Centre de Recherche Cardio-Thoracique, Université Bordeaux Segalen Bordeaux, France ; L'Institut de Rythmologie et Modélisation Cardiaque, Université de Bordeaux Bordeaux, France
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Zhang HX, Silva JR, Lin YW, Verbsky JW, Lee US, Kanter EM, Yamada KA, Schuessler RB, Nichols CG. Heterogeneity and function of K(ATP) channels in canine hearts. Heart Rhythm 2013; 10:1576-83. [PMID: 23871704 DOI: 10.1016/j.hrthm.2013.07.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Indexed: 01/08/2023]
Abstract
BACKGROUND The concept that pore-forming Kir6.2 and regulatory SUR2A subunits form cardiac ATP-sensitive potassium (K(ATP)) channels is challenged by recent reports that SUR1 is predominant in mouse atrial K(ATP) channels. OBJECTIVE To assess SUR subunit composition of K(ATP) channels and consequence of K(ATP) activation for action potential duration (APD) in dog hearts. METHODS Patch-clamp techniques were used on isolated dog cardiomyocytes to investigate K(ATP) channel properties. Dynamic current clamp, by injection of a linear K(+) conductance to simulate activation of the native current, was used to study the consequences of K(ATP) activation on APD. RESULTS Metabolic inhibitor (MI)-activated current was not significantly different from pinacidil (SUR2A-specific)-activated current, and both currents were larger than diazoxide (SUR1-specific)-activated current in both the atrium and the ventricle. Mean K(ATP) conductance (activated by MI) did not differ significantly between chambers, although, within the ventricle, both MI-induced and pinacidil-induced currents tended to decrease from the epicardium to the endocardium. Dynamic current-clamp results indicate that myocytes with longer baseline APDs are more susceptible to injected K(ATP) current, a result reproduced in silico by using a canine action potential model (Hund-Rudy) to simulate epicardial and endocardial myocytes. CONCLUSIONS Even a small fraction of K(ATP) activation significantly shortens APD in a manner that depends on existing heterogeneity in K(ATP) current and APD.
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Affiliation(s)
- Hai Xia Zhang
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri; Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri
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Zhang A, Sun C, Zhang L, Lv Y, Xue X, Li G, Cui C, Yan GX. L539 fs/47, a truncated mutation of human ether-a-go-go-related gene (hERG), decreases hERG ion channel currents in HEK 293 cells. Clin Exp Pharmacol Physiol 2012; 40:28-36. [DOI: 10.1111/1440-1681.12028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 10/12/2012] [Accepted: 11/04/2012] [Indexed: 01/09/2023]
Affiliation(s)
| | - Chaofeng Sun
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Li Zhang
- Main Line Health Heart Center; Lankenau Institute for Medical Research; Wynnewood; Pennsylvania; USA
| | - Ying Lv
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Xiaolin Xue
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Guoliang Li
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Changcong Cui
- Department of Cardiovascular Medicine; MOE; Ion Channel Disease Laboratory; MOE Key Laboratory of Environment and Genes Related to Diseases, The First Affiliated Hospital of Xi'an Jiaotong University; Xi'an; Shaanxi; China
| | - Gan-Xin Yan
- Main Line Health Heart Center; Lankenau Institute for Medical Research; Wynnewood; Pennsylvania; USA
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Zaniboni M. Heterogeneity of Intrinsic Repolarization Properties Within the Human Heart: New Insights From Simulated Three-Dimensional Current Surfaces. IEEE Trans Biomed Eng 2012; 59:2372-80. [DOI: 10.1109/tbme.2012.2204880] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- M Zaniboni
- Department of Evolutionary and Functional Biology, University of Parma, Parma, Italy.
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15
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Extramiana F, Messali A, Labbé JP, Maison-Blanche P, Denjoy I, De Jode P, Kedra A, Leenhardt A. Les réentrées. ARCHIVES OF CARDIOVASCULAR DISEASES SUPPLEMENTS 2011. [DOI: 10.1016/s1878-6480(11)70391-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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16
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Henao ÓA, Ferrero de Loma-Osorio JM, Sáiz J, Reynolds J. Arritmias potenciadas por isquemia sub-epicárdica en pared transmural heterogénea cardiaca: un estudio teórico de simulación. REVISTA COLOMBIANA DE CARDIOLOGÍA 2011. [DOI: 10.1016/s0120-5633(11)70164-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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17
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Novel algorithm for identifying T-wave current density alternans using synthesized 187-channel vector-projected body surface mapping. Heart Vessels 2010; 26:160-7. [PMID: 21052691 DOI: 10.1007/s00380-010-0042-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/23/2009] [Accepted: 03/25/2010] [Indexed: 10/18/2022]
Abstract
The noninvasive evaluation of ventricular T-wave alternans (TWA) in patients with lethal ventricular arrhythmias is an important issue. In this study, we propose a novel algorithm to identify T-wave current density alternans (TWCA) using synthesized 187-channel vector-projected body surface mapping (187-ch SAVP-ECG). We recorded 10 min of 187-ch SAVP-ECG using a Mason-Likar lead system in the supine position. A recovery time (RT) dispersion map was obtained by averaging the 187-ch SAVP-ECG. The TWCA value was determined from the relative changes in the averaged current density in the T-wave zone (Tpeak ± 50 ms) for two T-wave types. We registered 20 ECG recordings from normal controls and 11 ECG recordings from nine subjects with long QT syndrome (LQT). We divided LQT syndrome subjects into two groups: group 1 provided 9 ECG recordings without visually apparent TWAs, and group 2 provided 2 ECG recordings with visually apparent TWAs. The QTc interval values in the LQT groups were higher than those in the control (515 ± 60 ms in LQT G-1, 600 ± 27 ms in LQT G-2 vs. 415 ± 19 ms in control, P < 0.001). The RTendc dispersion values among the LQT subjects were higher than those of the control subjects (48 ± 19 ms in LQT G-1, 65 ± 30 ms in LQT G-2 vs. 24 ± 10 ms in control, P < 0.01). The mean TWCA value was significantly higher in the LQT G-2 group with visually apparent TWCAs (0.5 ± 0.2% in control, 2.1 ± 1.2% in LQT G-1, and 32.3 ± 6.9% in LQT G-2). Interestingly, the two-dimensional distribution of TWCA in LQT was inhomogeneous and correlated with the distribution of increased RT dispersion. We conclude that a novel algorithm using 187-ch SAVP-ECG might provide new insights into body surface TWCA.
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Fink M, Noble D. Pharmacodynamic effects in the cardiovascular system: the modeller's view. Basic Clin Pharmacol Toxicol 2010; 106:243-9. [PMID: 20470255 DOI: 10.1111/j.1742-7843.2009.00534.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Cardiovascular disease, and the cardiovascular side effects of drugs, are essentially multifactorial problems involving interactions between many proteins, dependent on highly organized cell, tissue and organ structures. This is one reason why the side effects of drugs are often unanticipated. It is impossible to unravel such problems without using a systems approach, i.e. focussing on processes, not just molecular components. This inevitably involves modelling as the interactions require quantitative analysis. Modelling is a tool of analysis aimed at understanding, first, and predicting, eventually. We illustrate these principles using modelling of the heart. Models of the cardiac myocyte have benefited from several decades of interaction between experimentation and simulation. They are now sufficiently detailed to have been of use in the development of new drug compounds like ranolazine and ivabradine. With the help of cardiac modelling, we have also been able to unravel the mechanisms underlying the beneficial effect of sodium calcium exchange block for long QT syndrome (LQTS) 2 and LQTS3 patients. Detailed models of the interaction between ion channels and blocking agents provide the basis for modelling drug action from basic principles and predict changes in the inhomogeneous tissue of the heart. We demonstrate that mathematical models are beneficial for unravelling the complex interactions of pharmacodynamics in the heart. Embedding these detailed biophysical cellular scale models into anatomically correct models of the ventricle geometry will enable reconstructions of Torsades de Pointes arrhythmias and of fibrillation, providing a mechanism for linking detailed cellular scale experimental data to clinical applications.
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Affiliation(s)
- Martin Fink
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
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Walton RD, Bernus O. Electrotonic effects on action potential duration in perfused rat hearts. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2010; 2009:4190-3. [PMID: 19964627 DOI: 10.1109/iembs.2009.5334052] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Electrotonic interactions in cardiac tissue have been shown previously to modulate dynamical properties of the myocardium such as action potential duration (APD) and action potential duration restitution. A recent computational study indicated that these electrotonic effects may be strongest in small murine hearts. In the present study, we investigate experimentally how APD is modulated by activation sequence and pacing rate using optical mapping in Langendorff perfused rat hearts. Our results show that following an epicardial point stimulus, a strong correlation exists between epicardial APD and activation time, with decreasing APD for increasing activation time. This effect is preserved for all pacing frequencies (6-14 Hz) investigated in this study. Our experimental results are validated by detailed three-dimensional computer simulations. These simulations also demonstrate a strong transmural APD dependence on activation sequence, which, near the pacing site, is sufficient to mask the intrinsic transmural gradient.
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Affiliation(s)
- Richard D Walton
- Multidisciplinary Cardiovascular Research Centre, University of Leeds
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20
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Borggrefe M, Schimpf R. J-wave syndromes caused by repolarization or depolarization mechanisms a debated issue among experimental and clinical electrophysiologists. J Am Coll Cardiol 2010; 55:798-800. [PMID: 20170819 DOI: 10.1016/j.jacc.2009.12.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 12/01/2009] [Indexed: 10/19/2022]
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21
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Hopenfeld B, Ashikaga H. Origin of the electrocardiographic U wave: effects of M cells and dynamic gap junction coupling. Ann Biomed Eng 2010; 38:1060-70. [PMID: 20127511 DOI: 10.1007/s10439-010-9941-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Accepted: 01/19/2010] [Indexed: 11/28/2022]
Abstract
The electrophysiological basis underlying the genesis of the U wave remains uncertain. Previous U wave modeling studies have generally been restricted to 1-D or 2-D geometries, and it is not clear whether the U waves generated by these models would match clinically observed U wave body surface potential distributions (BSPDs). We investigated the role of M cells and transmural dispersion of repolarization (TDR) in a 2-D, fully ionic heart tissue slice model and a realistic 3-D heart/torso model. In the 2-D model, while a U wave was present in the ECG with dynamic gap junction conductivity, the ECG with static gap junctions did not exhibit a U wave. In the 3-D model, TDR was necessary to account for the clinically observed potential minimum in the right shoulder area during the U wave peak. Peak T wave simulations were also run. Consistent with at least some clinical findings, the U wave body surface maximum was shifted to the right compared to the T wave maximum. We conclude that TDR can account for the clinically observed U wave BSPD, and that dynamic gap junction conductivity can result in realistic U waves generated by M cells.
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Affiliation(s)
- Bruce Hopenfeld
- Angel Medical Systems, Inc., 1163 Shrewsbury Avenue, Shrewsbury, NJ 07702, USA.
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22
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23
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Sicouri S, Antzelevitch C. Sudden cardiac death secondary to antidepressant and antipsychotic drugs. Expert Opin Drug Saf 2008; 7:181-94. [PMID: 18324881 DOI: 10.1517/14740338.7.2.181] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A number of antipsychotic and antidepressant drugs are known to increase the risk of ventricular arrhythmias and sudden cardiac death. Based largely on a concern over QT prolongation and the development of life-threatening arrhythmias, a number of antipsychotic drugs have been temporarily or permanently withdrawn from the market or their use restricted. Some antidepressants and antipsychotics have been linked to QT prolongation and the development of Torsade de pointes arrhythmias, whereas others have been associated with a Brugada syndrome phenotype and the development of polymorphic ventricular arrhythmias. This review examines the mechanisms and predisposing factors underlying the development of cardiac arrhythmias, and sudden cardiac death, associated with antidepressant and antipsychotic drugs in clinical use.
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Affiliation(s)
- Serge Sicouri
- Masonic Medical Research Laboratory, 2150 Bleecker Street, Utica, New York, NY 13501-1787, USA
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24
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Del Rio CL, Dawson TA, Clymer BD, Paterson DJ, Billman GE. Effects of acute vagal nerve stimulation on the early passive electrical changes induced by myocardial ischaemia in dogs: heart rate-mediated attenuation. Exp Physiol 2008; 93:931-44. [PMID: 18376003 DOI: 10.1113/expphysiol.2007.041558] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Parasympathetic activity during acute coronary artery occlusion (CAO) can protect against ischaemia-induced malignant arrhythmias; nonetheless, the mechanism mediating this protection remains unclear. During CAO, myocardial electrotonic uncoupling is associated with autonomically mediated immediate (i.e. type 1A) arrhythmias and can modulate pro-arrhythmic dispersion of repolarization. Therefore, the effects of acutely enhanced or decreased cardiac parasympathetic activity on early electrotonic coupling during CAO, as measured by myocardial electrical impedance (MEI), were investigated. Anaesthetized dogs were instrumented for MEI measurements, and left circumflex coronary arterial occlusions were performed in intact (CTRL) and vagotomized (VAG) animals. The CAO was followed by either vagotomy (CTRL) or vagal nerve stimulation (VNS, 10 Hz, 10 V) in the VAG dogs. Vagal nerve stimulation was studied in two additional sets of animals. In one set heart rate (HR) was maintained by pacing (220 beats min(-1)), while in the other set bilateral stellectomy preceded CAO. The MEI increased after CAO in all animals. A larger MEI increase was observed in vagotomized animals (+85 +/- 9 Omega, from 611 +/- 24 Omega, n = 16) when compared with intact control dogs (+43 +/- 5 Omega, from 620 +/- 20 Omega, n = 7). Acute vagotomy during ischaemia abruptly increased HR (from 155 +/- 11 to 193 +/- 15 beats min(-1)) and MEI (+12 +/- 1.1 Omega, from 663 +/- 18 Omega). In contrast, VNS during ischaemia (n = 11) abruptly reduced HR (from 206 +/- 6 to 73 +/- 9 beats min(-1)) and MEI (-16 +/- 2 Omega, from 700 +/- 44 Omega). These effects of VNS were eliminated by pacing but not by bilateral stellectomy. Vagal nerve stimulation during CAO also attenuated ECG-derived indices of ischaemia (e.g. ST segment, 0.22 +/- 0.03 versus 0.15 +/- 0.03 mV) and of rate-corrected repolarization dispersion [terminal portion of T wave (TPEc), 84.5 +/- 4.2 versus 65.8 +/- 5.9 ms; QTc, 340 +/- 8 versus 254 +/- 16 ms]. Vagal nerve stimulation during myocardial ischaemia exerts negative chronotropic effects, limiting early ischaemic electrotonic uncoupling and dispersion of repolarization, possibly via a decreased myocardial metabolic demand.
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Affiliation(s)
- Carlos L Del Rio
- Department of Physiology and Cell Biology, The Ohio State University, 1645 Neil Avenue, 305 Hamilton Hall, Columbus, OH 43210, USA
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25
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Stones R, Gilbert SH, Benoist D, White E. Inhomogeneity in the response to mechanical stimulation: cardiac muscle function and gene expression. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 97:268-81. [PMID: 18485455 DOI: 10.1016/j.pbiomolbio.2008.02.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Mechanical stimulation has important consequences for myocardial function. However, this stimulation and the response to it, is not uniform. The right ventricle is thinner walled and operates at lower pressure than the left ventricle. Within the ventricles, differences in the orientation of myocardial fibres exist. These differences produce inhomogeneity in the stress and strain between and across the ventricles. Possibly as a result of these variations in mechanical stimulation, there are well characterised inhomogeneities in gene expression and protein function within the ventricular myocardium, for example in the transient outward K+ current and its associated Kv channels. Perhaps not surprisingly, it is becoming apparent that gradients of expression and function exist for proteins that are intimately involved in the response to mechanical stimulation in the heart, for example in the left ventricle of the rat there is a transmural gradient in mRNA and current density of the mechanosensitive two-pore domain K+ channel TREK-1 (ENDO>EPI). In healthy hearts it is assumed that these gradients are important for normal function and therefore that their disruption in diseased myocardium is involved in the dysfunction that occurs.
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Affiliation(s)
- Rachel Stones
- Institute of Membrane and Systems Biology, University of Leeds, Leeds, UK
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26
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Nakai K, Miyake F, Kasanuki H, Shoda M, Futagawa K, Takahashi A, Matsuyama Y, Nirei T, Tsuboi J, Okabayashi H, Itoh M, Kawata H. Newly Developed Signal-Averaged Vector-Projected 187-Channel Electrocardiogram Can Evaluate the Spatial Distribution of Repolarization Heterogeneity. Int Heart J 2008; 49:153-64. [DOI: 10.1536/ihj.49.153] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Kenji Nakai
- Department of Laboratory Medicine, Iwate Medical University
| | - Fumihiko Miyake
- Department of Cardiology, St. Marianna University School of Medicine
| | | | - Morio Shoda
- Department of Cardiology, Tokyo Women’s Medical College
| | | | | | | | - Takashi Nirei
- Department of Cardiology, Tokyo Metropolitan Health and Medical Treatment Corporation Ebara Hospital
| | - Junichi Tsuboi
- Department of Cardiovascular Surgery, Iwate Medical University
| | | | | | - Hiroshi Kawata
- Division of Medical Engineering and Clinical Investigation Institute of Development, Aging and Cancer, Tohoku University
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Fish JM, Antzelevitch C. Cellular mechanism and arrhythmogenic potential of T-wave alternans in the Brugada syndrome. J Cardiovasc Electrophysiol 2007; 19:301-8. [PMID: 18031511 DOI: 10.1111/j.1540-8167.2007.01025.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION T-wave alternans (TWA) is characterized by beat to beat alteration in the amplitude, polarity and/or morphology of the electrocardiographic T wave. TWA has been reported in patients with the Brugada syndrome (BS) and is thought to be associated with an increased risk for development of VT/VF. The cellular mechanisms involved are not well-defined and are the subject of this investigation. METHODS In an experimental model of BS composed of an arterially perfused canine right ventricular wedge preparation pretreated with verapamil (1-7 microM), an agent with sodium and calcium channel blocking activity, we simultaneously recorded transmembrane action potentials from two epicardial and one endocardial site, together with a pseudo-ECG. At select frequencies, verapamil induced alternans of both the T-wave amplitude and QT interval. The alternans resulted from either loss of the epicardial action potential dome on alternate beats or concealed phase 2 reentry within the epicardium on alternate beats. Loss of the epicardial action potential dome significantly increased transmural dispersion of repolarization (TDR) when compared with control (18.0 +/- 7.8 ms vs. 82.1 +/- 16.8 ms, P < 0.001, n = 8). During alternans, TDR was greater in beats displaying a more negative T wave (55.1 +/- 45.2 ms vs. 89.8 +/- 39.3 ms, P < 0.001, n = 22 data points from 8 preparations). CONCLUSIONS Our data indicate that TWA in an experimental model of the Brugada syndrome is due to alternating loss of the epicardial AP dome and/or concealed phase 2 reentry, both serving to increase TDR and create the substrate for the development VT/VF.
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Affiliation(s)
- Jeffrey M Fish
- Masonic Medical Research Laboratory, Utica, New York 13501-1787, USA.
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Schimpf R, Veltmann C, Giustetto C, Gaita F, Borggrefe M, Wolpert C. In vivo Effects of Mutant HERG K+Channel Inhibition by Disopyramide in Patients with a Short QT-1 Syndrome: A Pilot Study. J Cardiovasc Electrophysiol 2007; 18:1157-60. [PMID: 17711440 DOI: 10.1111/j.1540-8167.2007.00925.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION Quinidine has been evaluated in patients with a short QT-1 syndrome caused by an IKr gain-of-function mutation of HERG. Recently, in vitro data with disopyramide showed an even stronger effect on the N588K mutant current. The aim of the present study was to test the in vivo effects of disopyramide in patients with short QT-1 syndrome caused by a N588K mutation in HERG. METHODS AND RESULTS Repetitive ECGs were recorded in two female patients with short QT-1 syndrome with a N588K-HERG mutation off drugs, on oral quinidine, and on oral disopyramide. One patient underwent exercise testing on drugs to determine the QT interval to heart rate relation, whereas the QT interval was calculated to the peak of the T wave in lead V3. In the same patient, drug-induced changes in ventricular effective refractory periods were determined by programmed ventricular stimulation via the ICD lead. Disopyramide increased the QT interval from QTc 329 ms/QTc 315 ms, respectively, off drugs to QTc 358 ms/QTc 333 ms in both patients and restored the heart rate dependence of the QT interval toward normal subjects (-0.39 ms/bpm off drugs, -0.58 ms/bpm on disopyramide vs. 1.29 +/- 0.33 ms/bpm in normal subjects). The ventricular effective refractory period increased under disopyramide by 40 ms. CONCLUSION These preliminary observations suggest that oral disopyramide may be a suitable alternative to quinidine for prolonging the QT interval and ventricular effective refractory periods in patients with short QT-1 syndrome. Further studies of this pharmacologic approach are warranted.
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Affiliation(s)
- Rainer Schimpf
- First Department of Medicine-Cardiology, University Hospital Mannheim, Mannheim, Germany.
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Abstract
First introduced as a new clinical entity in 1992, the Brugada syndrome is associated with a relatively high risk of sudden death in young adults, and occasionally in children and infants. Recent years have witnessed a striking proliferation of papers dealing with the clinical and basic aspects of the disease. Characterized by a coved-type ST-segment elevation in the right precordial leads of the electrocardiogram (ECG), the Brugada syndrome has a genetic basis that thus far has been linked only to mutations in SCN5A, the gene that encodes the alpha-subunit of the sodium channel. The Brugada ECG is often concealed, but can be unmasked or modulated by a number of drugs and pathophysiological states including sodium channel blockers, a febrile state, vagotonic agents, tricyclic antidepressants, as well as cocaine and propranolol intoxication. Average age at the time of initial diagnosis or sudden death is 40 +/- 22, with the youngest patient diagnosed at 2 days of age and the oldest at 84 years. This review provides an overview of the clinical, genetic, molecular, and cellular aspects of the Brugada syndrome, incorporating the results of two recent consensus conferences. Controversies with regard to risk stratification and newly proposed pharmacologic strategies are discussed.
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Stones R, Calaghan SC, Billeter R, Harrison SM, White E. Transmural variations in gene expression of stretch-modulated proteins in the rat left ventricle. Pflugers Arch 2007; 454:545-9. [PMID: 17345093 PMCID: PMC1950587 DOI: 10.1007/s00424-007-0237-z] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2006] [Revised: 01/24/2007] [Accepted: 02/12/2007] [Indexed: 11/18/2022]
Abstract
The properties of left ventricular cardiac myocytes vary transmurally. This may be related to the gradients of stress and strain experienced in vivo across the ventricular wall. We tested the hypothesis that within the rat left ventricle there are transmural differences in the expression of genes for proteins that are involved in mechanosensitive pathways and in associated physiological responses. Real time reverse transcription polymerase chain reaction was used to measure messenger RNA (mRNA) levels of selected targets in sub-epicardial (EPI) and sub-endocardial (ENDO) myocardium. Carbon fibres were attached to single myocytes to stretch them and to record contractility. We observed that the slow positive inotropic response to stretch was not different between EPI and ENDO myocytes and consistent with this, that the mRNA expression of two proteins implicated in the slow response, non-specific cationic mechanosensitive channels (TRPC-1) and Na/H exchanger, were not different. However, mRNA levels of other targets, e.g. the mechanosensitive K+ channel TREK-1, Brain Natriuretic Peptide and Endothelin-1 receptor B, were significantly greater in ENDO than EPI. No targets had significantly greater mRNA levels in EPI than ENDO. On the basis of these findings, we suggest that the response of the ventricle to stretch will depend upon both the regional differences in stimuli and the relative expression of the mechanosensitive targets and that generally, stretch sensitivity is predicted to be greater in ENDO.
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MESH Headings
- Animals
- Gene Expression Regulation
- Heart Ventricles/cytology
- Heart Ventricles/metabolism
- Mechanotransduction, Cellular/physiology
- Myocytes, Cardiac/cytology
- Myocytes, Cardiac/metabolism
- Natriuretic Peptide, Brain/genetics
- Natriuretic Peptide, Brain/metabolism
- Potassium Channels, Tandem Pore Domain/genetics
- Potassium Channels, Tandem Pore Domain/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
- Receptor, Endothelin B/genetics
- Receptor, Endothelin B/metabolism
- Sodium-Hydrogen Exchangers/genetics
- Sodium-Hydrogen Exchangers/metabolism
- TRPC Cation Channels/genetics
- TRPC Cation Channels/metabolism
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Affiliation(s)
- R. Stones
- Institute of Membrane and Systems Biology, University of Leeds, Worsley Building, Leeds, LS29JT UK
| | - S. C. Calaghan
- Institute of Membrane and Systems Biology, University of Leeds, Worsley Building, Leeds, LS29JT UK
| | - R. Billeter
- Institute of Membrane and Systems Biology, University of Leeds, Worsley Building, Leeds, LS29JT UK
- Centre for Integrated Systems Biology and Medicine, School of Biomedical Sciences, University of Nottingham Medical School, Nottingham, NG7 2UH UK
| | - S. M. Harrison
- Institute of Membrane and Systems Biology, University of Leeds, Worsley Building, Leeds, LS29JT UK
| | - E. White
- Institute of Membrane and Systems Biology, University of Leeds, Worsley Building, Leeds, LS29JT UK
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Michailova A, Lorentz W, McCulloch A. Modeling transmural heterogeneity of K(ATP) current in rabbit ventricular myocytes. Am J Physiol Cell Physiol 2007; 293:C542-57. [PMID: 17329404 DOI: 10.1152/ajpcell.00148.2006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To investigate the mechanisms regulating excitation-metabolic coupling in rabbit epicardial, midmyocardial, and endocardial ventricular myocytes we extended the LabHEART model (Puglisi JL and Bers DM. Am J Physiol Cell Physiol 281: C2049-C2060, 2001). We incorporated equations for Ca(2+) and Mg(2+) buffering by ATP and ADP, equations for nucleotide regulation of ATP-sensitive K(+) channel and L-type Ca(2+) channel, Na(+)-K(+)-ATPase, and sarcolemmal and sarcoplasmic Ca(2+)-ATPases, and equations describing the basic pathways (creatine and adenylate kinase reactions) known to communicate the flux changes generated by intracellular ATPases. Under normal conditions and during 20 min of ischemia, the three regions were characterized by different I(Na), I(to), I(Kr), I(Ks), and I(Kp) channel properties. The results indicate that the ATP-sensitive K(+) channel is activated by the smallest reduction in ATP in epicardial cells and largest in endocardial cells when cytosolic ADP, AMP, PCr, Cr, P(i), total Mg(2+), Na(+), K(+), Ca(2+), and pH diastolic levels are normal. The model predicts that only K(ATP) ionophore (Kir6.2 subunit) and not the regulatory subunit (SUR2A) might differ from endocardium to epicardium. The analysis suggests that during ischemia, the inhomogeneous accumulation of the metabolites in the tissue sublayers may alter in a very irregular manner the K(ATP) channel opening through metabolic interactions with the endogenous PI cascade (PIP(2), PIP) that in turn may cause differential action potential shortening among the ventricular myocyte subtypes. The model predictions are in qualitative agreement with experimental data measured under normal and ischemic conditions in rabbit ventricular myocytes.
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Affiliation(s)
- Anushka Michailova
- Dept of Bioengineering, PFBH 241, University of California San Diego, La Jolla, CA 92093-0412, USA.
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Suter W. Improving Decision-Making in Drug Development Using In Vitro Toxicology Screening. ACTA ACUST UNITED AC 2007. [DOI: 10.2165/00124363-200721050-00005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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de Souza D, Riera ARP, Bombig MT, Francisco YA, Brollo L, Filho BL, Dubner S, Schapachnik E, Povoa R. Electrocardiographic changes by accidental hypothermia in an urban and a tropical region. J Electrocardiol 2006; 40:47-52. [PMID: 17027018 DOI: 10.1016/j.jelectrocard.2006.08.094] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2006] [Accepted: 08/28/2006] [Indexed: 10/24/2022]
Abstract
BACKGROUND Hypothermia is defined as a condition in which core temperature (rectal, esophageal, or tympanic) reaches values below 35 degrees C. This may be accidental, metabolic, or therapeutic. The accidental form is frequent in cold-climate countries and rare in those with tropical or subtropical climate. The aim of this study was to evaluate electrocardiographic changes of patients with accidental hypothermia. METHODS In 59 patients with hypothermia, the following electrocardiogram parameters were analyzed: rhythm and heart rate (HR), P-wave characteristics, PR-interval duration, QRS-complex duration, presence of J wave and its location characteristics, polarity, voltage, aspect and its correlation with the degree of hypothermia, changes in T wave regarding its polarity and characteristics, duration of the QT interval corrected for HR using both Bazett and Friderica formulas, and possible presence of both supraventricular and ventricular arrhythmias were independently and blindly analyzed in the tracings by experienced cardiologists. RESULTS In 6 patients, electrocardiogram was normal. Sinus bradycardia was observed in 52.5% of the patients. J wave was present in 51 patients, and its voltage correlated inversely and was statistically significantly with the core temperature. Changes in T wave were observed in 47.4% of the cases. QT interval, adjusted for HR, was prolonged in 72.8% of the cases. Idioventricular rhythm was found in 6 cases, total atrioventricular block in 3 cases, and junctional rhythm and atrial fibrillation in 2 patients. CONCLUSIONS Electrocardiogram changes in accidental hypothermia are frequent and characteristic for this entity improving diagnosis in usually unconscious patients, and in many cases, it may be the diagnostic clue in patients with conscience deficit in emergency units, even in patients from a tropical climate where the population at risk may be exposed to temperatures below 20 degrees C.
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Affiliation(s)
- Dilma de Souza
- Escola Paulista de Medicina, UNIFESP, São Paulo CEP, Brazil
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Suter W. Predictive value of in vitro safety studies. Curr Opin Chem Biol 2006; 10:362-6. [PMID: 16815733 DOI: 10.1016/j.cbpa.2006.06.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2006] [Accepted: 06/21/2006] [Indexed: 10/24/2022]
Abstract
The predictive value of in vitro safety studies is discussed for three important areas of pharmaceutical safety evaluations. In genetic toxicology, currently assays are sensitive for the prediction of cancer, but their overall predictive value is strongly diminished because of their low specificity. In the area of safety pharmacology blockage of hERG channel in vitro has recently been introduced to predict cardiac repolarization delay (QT interval prolongation) in patients. There is a plethora of in vitro methods to predict and characterize liver toxicity. However, little data is available that demonstrate a reliable prediction for hepatotoxicity in vivo over a wide range of chemical structures. In all three areas, further improvements are needed. 'Omics' technologies and new cell lines derived from stem cells are expected to strongly contribute to establish new and more predictive in vitro assays.
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Affiliation(s)
- Willi Suter
- Exploratory Development, Safety Profiling and Assessment, Novartis Pharma AG, CH 4002 Basel, Switzerland.
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Wang Y, Cheng J, Joyner RW, Wagner MB, Hill JA. Remodeling of early-phase repolarization: a mechanism of abnormal impulse conduction in heart failure. Circulation 2006; 113:1849-56. [PMID: 16618832 PMCID: PMC1474070 DOI: 10.1161/circulationaha.106.615682] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
BACKGROUND The early phase of action potential (AP) repolarization is critical to impulse conduction in the heart because it provides current for charging electrically coupled cells. In the present study we tested the impact of heart failure-associated electrical remodeling on AP propagation. METHODS AND RESULTS Subepicardial, midmyocardial, and subendocardial myocytes were enzymatically dissociated from control and pressure-overload failing left ventricle (LV), and APs were recorded. A unique coupling-clamp technique was used to electrically couple 2 isolated myocytes with a controlled value of coupling conductance (Gc). In sham-operated mice, AP duration manifested a clear transmural gradient, with faster repolarization in subepicardial myocytes than in subendocardial myocytes. AP propagation from subendocardial to subepicardial myocytes required less Gc compared with conduction in the opposite direction. In failing heart, AP morphology was dramatically altered, with a significantly elevated plateau potential and prolonged AP duration. Spatially nonuniform alteration of AP duration in failing heart blunted the transmural gradient of repolarization. Furthermore, increased pacing rate prolonged AP duration exclusively in myocytes from failing heart, and the critical conductance required for successful AP propagation decreased significantly at high frequencies. Finally, in failing heart, asymmetry of transmural electrical propagation was abolished. CONCLUSIONS In failing heart, preferential conduction from subendocardial to subepicardial myocytes is lost, and failing myocytes manifest facilitated AP propagation at fast rates. Together, these electrical remodeling responses may promote conduction of premature impulses and heighten the risk of malignant arrhythmia, a prominent feature of heart failure.
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Affiliation(s)
- Yanggan Wang
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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Castro Hevia J, Antzelevitch C, Tornés Bárzaga F, Dorantes Sánchez M, Dorticós Balea F, Zayas Molina R, Quiñones Pérez MA, Fayad Rodríguez Y. Tpeak-Tend and Tpeak-Tend dispersion as risk factors for ventricular tachycardia/ventricular fibrillation in patients with the Brugada syndrome. J Am Coll Cardiol 2006; 47:1828-34. [PMID: 16682308 PMCID: PMC1474075 DOI: 10.1016/j.jacc.2005.12.049] [Citation(s) in RCA: 355] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Revised: 11/14/2005] [Accepted: 12/13/2005] [Indexed: 01/05/2023]
Abstract
OBJECTIVES Our objective in this study was to evaluate Tpeak-Tend interval (Tp-e) and other electrocardiographic parameters as risk factors for recurrence of life-threatening cardiac events in patients with the Brugada syndrome (BS). BACKGROUND The Tp-e interval in the electrocardiogram (ECG) has been reported to predict life-threatening arrhythmias in the long QT syndrome. METHODS Twenty-nine patients with the ECG pattern of BS and 29 healthy age- and gender-matched controls were studied. The follow-up period was 42.65 +/- 24.42 months (range 11 to 108 months). RESULTS Upon presentation, five patients had suffered aborted sudden death, five syncope, and two presyncope. Eleven patients with the ECG pattern of BS had a prolonged (>460 ms) QTc in V2 but usually not in inferior or left leads. No patient had abnormally prolonged QT dispersion. Programmed electrical stimulation induced ventricular tachycardia/fibrillation in 5 out of 26 patients. Inducibility did not predict recurrence of events. Cardioverter-defibrillators were implanted in 14 patients (all symptomatic and two asymptomatic). During follow-up, nine symptomatic patients experienced recurrences. Previous cardiac events and a QTc >460 ms in V2 were significant risk factors (p = 0.00002 and p = 0.03, respectively). Tp-e and Tp-e dispersion were significantly prolonged in patients with recurrences versus patients without events (104.4 and 35.6 ms vs. 87.4 and 23.2 ms; p = 0.006 and p = 0.03, respectively) or controls (90.7 and 17.9 ms; p = 0.02 and p = 0.001, respectively). CONCLUSIONS Our study demonstrates significant correlation between previous events, QTc >460 ms in V2, Tp-e, and Tp-e dispersion and occurrence of life-threatening arrhythmic events, suggesting that these parameters may be useful in risk stratification of patients with the Brugada syndrome.
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Affiliation(s)
- Jesus Castro Hevia
- Arrhythmia Unit, Cardiovascular Surgery and Cardiology Institute, Havana, Cuba
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Zareba W. Should QT replace ST for detecting myocardial ischemia? Heart Rhythm 2006; 3:433-4. [PMID: 16567290 DOI: 10.1016/j.hrthm.2006.01.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2006] [Indexed: 11/24/2022]
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Schimpf R, Kuschyk J, Veltmann C, Borggrefe M, Wolpert C. [Primary electrical heart disease in adulthood--electrophysiological findings and therapy]. Herzschrittmacherther Elektrophysiol 2005; 16:250-9. [PMID: 16362731 DOI: 10.1007/s00399-005-0492-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2005] [Accepted: 11/10/2005] [Indexed: 05/05/2023]
Abstract
Sudden cardiac death accounts for 100,000 victims in Germany per year. Predominantly, patients with structural heart disease such as coronary artery disease or dilated cardiomyopathy are affected. However, approximately 5-10% of sudden deaths hit patients without structural disease of the heart. The proportion of young patients (< 40 years of age) in this group is even higher (10-20%). In younger patients significantly more diseases like hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia and primary electrical diseases of the heart could be observed such as long QT syndrome, short QT syndrome, Brugada syndrome and catecholaminergic polymorphic ventricular tachycardia. The primary electrical diseases are different concerning their electrocardiographical pattern, clinical triggers of arrhythmias, results of invasive diagnostics and therapy. Meanwhile, molecular genetic screening can reveal specific mutations of ion channels and can identify consecutive functional defects. The significance of programmed ventricular stimulation is at present unclear concerning risk stratification in patients with Brugada syndrome and short QT syndrome and of no significance in long QT syndrome and catecholaminergic polymorphic ventricular tachycardias. The implantable cardioverter defibrillator is the therapy of choice in most symptomatic patients. With increasing knowledge as a result of sophisticated molecular genetic screening, identification of underlying ion channel defects and new details of the mechanisms of arrhythmogenesis, a potential genotype-guided therapy will gain more importance in the future.
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Affiliation(s)
- R Schimpf
- I. Medizinische Klinik, Universitätsklinikum Mannheim, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim.
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