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Seibertz F, Voigt N. High-throughput methods for cardiac cellular electrophysiology studies: the road to personalized medicine. Am J Physiol Heart Circ Physiol 2024; 326:H938-H949. [PMID: 38276947 PMCID: PMC11279751 DOI: 10.1152/ajpheart.00599.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 01/22/2024] [Accepted: 01/22/2024] [Indexed: 01/27/2024]
Abstract
Personalized medicine refers to the tailored application of medical treatment at an individual level, considering the specific genotype or phenotype of each patient for targeted therapy. In the context of cardiovascular diseases, implementing personalized medicine is challenging due to the high costs involved and the slow pace of identifying the pathogenicity of genetic variants, deciphering molecular mechanisms of disease, and testing treatment approaches. Scalable cellular models such as human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) serve as useful in vitro tools that reflect individual patient genetics and retain clinical phenotypes. High-throughput functional assessment of these constructs is necessary to rapidly assess cardiac pathogenicity and test new therapeutics if personalized medicine is to become a reality. High-throughput photometry recordings of single cells coupled with potentiometric probes offer cost-effective alternatives to traditional patch-clamp assessments of cardiomyocyte action potential characteristics. Importantly, automated patch-clamp (APC) is rapidly emerging in the pharmaceutical industry and academia as a powerful method to assess individual membrane-bound ionic currents and ion channel biophysics over multiple cells in parallel. Now amenable to primary cell and hiPSC-CM measurement, APC represents an exciting leap forward in the characterization of a multitude of molecular mechanisms that underlie clinical cardiac phenotypes. This review provides a summary of state-of-the-art high-throughput electrophysiological techniques to assess cardiac electrophysiology and an overview of recent works that successfully integrate these methods into basic science research that could potentially facilitate future implementation of personalized medicine at a clinical level.
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Affiliation(s)
- Fitzwilliam Seibertz
- Institute of Pharmacology and Toxicology, University Medical Center Göttingen, Georg-August University Göttingen, Göttingen, Germany
- German Center for Cardiovascular Research (DZHK), partner site Göttingen, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells," Georg-August University Göttingen, Göttingen, Germany
- Nanion Technologies, GmbH, Munich, Germany
| | - Niels Voigt
- Institute of Pharmacology and Toxicology, University Medical Center Göttingen, Georg-August University Göttingen, Göttingen, Germany
- German Center for Cardiovascular Research (DZHK), partner site Göttingen, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells," Georg-August University Göttingen, Göttingen, Germany
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2
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Zaniboni M. The electrical restitution of the non-propagated cardiac ventricular action potential. Pflugers Arch 2024; 476:9-37. [PMID: 37783868 PMCID: PMC10758374 DOI: 10.1007/s00424-023-02866-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 08/19/2023] [Accepted: 09/21/2023] [Indexed: 10/04/2023]
Abstract
Sudden changes in pacing cycle length are frequently associated with repolarization abnormalities initiating cardiac arrhythmias, and physiologists have long been interested in measuring the likelihood of these events before their manifestation. A marker of repolarization stability has been found in the electrical restitution (ER), the response of the ventricular action potential duration to a pre- or post-mature stimulation, graphically represented by the so-called ER curve. According to the restitution hypothesis (ERH), the slope of this curve provides a quantitative discrimination between stable repolarization and proneness to arrhythmias. ER has been studied at the body surface, whole organ, and tissue level, and ERH has soon become a key reference point in theoretical, clinical, and pharmacological studies concerning arrhythmia development, and, despite criticisms, it is still widely adopted. The ionic mechanism of ER and cellular applications of ERH are covered in the present review. The main criticism on ERH concerns its dependence from the way ER is measured. Over the years, in fact, several different experimental protocols have been established to measure ER, which are also described in this article. In reviewing the state-of-the art on cardiac cellular ER, I have introduced a notation specifying protocols and graphical representations, with the aim of unifying a sometime confusing nomenclature, and providing a physiological tool, better defined in its scope and limitations, to meet the growing expectations of clinical and pharmacological research.
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Affiliation(s)
- Massimiliano Zaniboni
- Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma (Italy), Parco Area Delle Scienze, 11/A, 43124, Parma, Italy.
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3
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Münkler P, Klatt N, Scherschel K, Kuklik P, Jungen C, Cavus E, Eickholt C, Christoph J, Lemoine MD, Christ T, Willems S, Riedel R, Kirchhof P, Meyer C. Repolarization indicates electrical instability in ventricular arrhythmia originating from papillary muscle. Europace 2022; 25:688-697. [PMID: 35989424 PMCID: PMC9935011 DOI: 10.1093/europace/euac126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2021] [Accepted: 06/30/2022] [Indexed: 11/12/2022] Open
Abstract
AIMS Cardiac arrhythmia originating from the papillary muscle (PM) can trigger ventricular fibrillation (VF) and cause sudden cardiac death even in the absence of structural heart disease. Most premature ventricular contractions, however, are benign and hitherto difficult to distinguish from a potentially fatal arrhythmia. Altered repolarization characteristics are associated with electrical instability, but electrophysiological changes which precede degeneration into VF are still not fully understood. METHODS AND RESULTS Ventricular arrhythmia (VA) was induced by aconitine injection into PMs of healthy sheep. To investigate mechanisms of degeneration of stable VA into VF in structurally healthy hearts, endocardial high-density and epicardial mapping was performed during sinus rhythm (SR) and VA. The electrical restitution curve, modelling the relation of diastolic interval and activation recovery interval (a surrogate parameter for action potential duration), is steeper in VA than in non-arrhythmia (ventricular pacing and SR). Steeper restitution curves reflect electrical instability and propensity to degenerate into VF. Importantly, we find the parameter repolarization time in relation to cycle length (RT/CL) to differentiate self-limiting from degenerating arrhythmia with high specificity and sensitivity. CONCLUSION RT/CL may serve as a simple index to aid differentiation between self-limiting and electrically instable arrhythmia with the propensity to degenerate to VF. RT/CL is independent of cycle length and could easily be measured to identify electrical instability in patients.
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Affiliation(s)
- Paula Münkler
- Corresponding author. Tel: +49 040 7410 0; fax: +49 040 7410 55862. E-mail address:
| | - Niklas Klatt
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany
| | - Katharina Scherschel
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany,Division of Cardiology, Angiology and Intensive Care, Cardiac Neuro- and Electrophysiology Research Consortium (cNEP), EKV Düsseldorf, Düsseldorf, Germany,Cardiac Neuro- and Electrophysiology Research Consortium (cNEP), Medical Faculty, Heinrich Heine University Düsseldorf, Kirchfeldstraße 40, 40217, Düsseldorf, Germany
| | - Pawel Kuklik
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,Department of Cardiology, Asklepios Hospital St Georg, Lohmühlenstraße 5, 20099, Hamburg, Germany
| | - Christiane Jungen
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany,Department of Cardiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Ersin Cavus
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany
| | - Christian Eickholt
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,Department of Cardiology, Asklepios Hospital St Georg, Lohmühlenstraße 5, 20099, Hamburg, Germany
| | - Jan Christoph
- Cardiovascular Research Institute University of California, San Francisco, 555 Mission Bay Blvd South, 352S, San Francisco, CA, USA
| | - Marc D Lemoine
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany
| | - Torsten Christ
- DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany,Institute of Experimental Pharmacology and Toxicology, University Medical Centre, Martinistraße 52, 20246 Hamburg, Germany
| | - Stephan Willems
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany,Department of Cardiology, Asklepios Hospital St Georg, Lohmühlenstraße 5, 20099, Hamburg, Germany
| | - René Riedel
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,Max Planck Institute for Evolutionary Biology, Plön, Germany,German Rheumatism Research Centre Berlin—an Institute of the Leibniz Association, Berlin, Germany
| | - Paulus Kirchhof
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany,Institute of Cardiovascular Sciences, University of Birmingham, Birmingham, UK
| | - Christian Meyer
- Department of Cardiology, University Heart and Vascular Center Hamburg, University Hospital Hamburg-Eppendorf, Martinistraße 52, 20246 Hamburg, Germany,DZHK (German Centre for Cardiovascular Research), Partner Site Hamburg/Kiel/Lübeck, Berlin, Germany,Division of Cardiology, Angiology and Intensive Care, Cardiac Neuro- and Electrophysiology Research Consortium (cNEP), EKV Düsseldorf, Düsseldorf, Germany,Cardiac Neuro- and Electrophysiology Research Consortium (cNEP), Medical Faculty, Heinrich Heine University Düsseldorf, Kirchfeldstraße 40, 40217, Düsseldorf, Germany
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Oshiyama NF, Pereira AHM, Cardoso AC, Franchini KG, Bassani JWM, Bassani RA. Developmental differences in myocardial transmembrane Na + transport: Implications for excitability and Na + handling. J Physiol 2022; 600:2651-2667. [PMID: 35489088 DOI: 10.1113/jp282661] [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: 11/29/2021] [Accepted: 04/20/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Previous studies showed that myocardial preparations from immature rats are less sensitive to electrical field stimulation than adult preparations. Freshly-isolated ventricular myocytes from neonatal rats showed lower excitability than adult cells, e.g., less negative threshold membrane potential and greater membrane depolarization required for action potential triggering. In addition to differences in mRNA levels for Na+ channels isoforms and greater Na+ current (INa ) density, Na+ channel voltage-dependence was shifted to the right in immature myocytes, which seems to be sufficient to decrease excitability, according to computer simulations. Only in neonatal myocytes did cyclic activity promote marked cytosolic Na+ accumulation, which was prevented by abolition of systolic Ca2+ transients by blockade of Ca2+ currents. Developmental changes in INa may account for the difference in action potential initiation parameters, but not for cytosolic Na+ accumulation, which seems to be due mainly to Na+ /Ca2+ exchanger-mediated Na+ influx. ABSTRACT Little is currently known about possible developmental changes in myocardial Na+ handling, which may have impact on cell excitability and Ca2+ content. Resting intracellular Na+ concentration ([Na+ ]i ), measured in freshly-isolated rat ventricular myocytes with CoroNa-green, was not significantly different in neonates (3-5 days old) and adults, but electrical stimulation caused marked [Na+ ]i rise only in neonates. Inhibition of L-type Ca2+ current by CdCl2 abolished not only systolic Ca2+ transients, but also activity-dependent intracellular Na+ accumulation in immature cells. This indicates that the main Na+ influx pathway during activity is the Na+ /Ca2+ exchanger, rather than voltage-dependent Na+ current (INa ), which was not affected by CdCl2 . In immature myocytes, INa density was 2-fold greater, inactivation was faster, and the current peak occurred at less negative transmembrane potential (Em ) than in adults. Na+ channel steady-state activation and inactivation curves in neonates showed a rightward shift, which should increase channel availability at diastolic Em , but also require greater depolarization for excitation, which was observed experimentally and reproduced in computer simulations. Ventricular mRNA levels of Nav 1.1, Nav 1.4 and Nav 1.5 pore-forming isoforms were greater in neonate ventricles, while decrease was seen for the β1 subunit. Both molecular and biophysical changes in the channel profile may contribute to the differences in INa density and voltage-dependence, and also to the less negative threshold Em in neonates, compared to adults. The apparently lower excitability in immature ventricle may confer protection against the development of spontaneous activity in this tissue. Abstract figure legend Little is currently known about possible developmental changes in myocardial Na+ transport, which may have impact on cell excitability and other physiological aspects. At the mRNA level, neonatal rat ventricle expresses a greater variety of Na+ channel isoforms than in adults. In immature ventricular cardiomyocytes, Na+ current (INa ) density was greater, but voltage-dependence is shifted to less negative potentials than in adults. This should increase channel availability at diastolic membrane potential, but also require greater depolarization for excitation, which was observed experimentally and reproduced in computer simulation. We also observed that electrical stimulation caused marked intracellular Na+ accumulation only in neonates, which was abolished when Ca2+ transients and the Na+ /Ca2+ exchanger (NCX) were inhibited by Cd2+ + Ni2+ . Thus, it seems that the main Na+ influx pathway during activity in neonates is the NCX, rather than voltage-dependent INa , which was not affected by these blockers. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Natália F Oshiyama
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Ana H M Pereira
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil
| | - Alisson C Cardoso
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil
| | - Kleber G Franchini
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil.,Department of Internal Medicine, School of Medicine, University of Campinas, Campinas, SP, Brazil
| | - José W M Bassani
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Rosana A Bassani
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
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5
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Howlett LA, Kirton HM, Al‐Owais MM, Steele D, Lancaster MK. Action potential responses to changes in stimulation frequency and isoproterenol in rat ventricular myocytes. Physiol Rep 2022; 10:e15166. [PMID: 35076184 PMCID: PMC8787729 DOI: 10.14814/phy2.15166] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2021] [Revised: 12/16/2021] [Accepted: 12/23/2021] [Indexed: 06/14/2023] Open
Abstract
PURPOSE Current understanding of ventricular action potential adaptation to physiological stress is generally based on protocols using non-physiological rates and conditions isolating rate effects from escalating adrenergic stimulation. To permit refined understanding, ventricular action potentials were assessed across physiological pacing frequencies in the presence and absence of adrenergic stimuli. Isolated and combined effects were analyzed to assess their ability to replicate in-vivo responses. METHODS Steady-state action potentials from ventricular myocytes isolated from male Wistar rats (3 months; N = 8 animals) were recorded at 37°C with steady-state pacing at 1, 2, 4, 6, 8 and 10 Hz using whole-cell patch-clamp. Action potential repolarization to 25, 50, 75, 90 and 100% of full repolarization (APD25-100 ) was compared before and after 5 nM, 100 nM and 1 µM isoproterenol doses. RESULTS A Repeated measures ANOVA found APD50-90 shortened with 5 nM isoproterenol infusion by 6-25% (but comparable across doses) (p ≤ 0.03). Pacing frequencies emulating a normal rat heart rate (6 Hz) prolonged APD50 23% compared with 1 Hz pacing. Frequencies emulating exercise or stress (10 Hz) shortened APD90 (29%). CONCLUSION These results demonstrate modest action potential shortening in response to adrenergic stimulation and elevations in pacing beyond physiological resting rates. Our findings indicate changes in action potential plateau and late repolarization predominantly underlie simulated exercise responses in the rat heart. This work provides novel action potential reference data and will help model cardiac responses to physiological stimuli in the rat heart via computational techniques.
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Affiliation(s)
| | | | | | - Derek Steele
- Faculty of Biological SciencesUniversity of LeedsLeedsUK
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6
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Brindley PJ, Bachini M, Ilyas SI, Khan SA, Loukas A, Sirica AE, Teh BT, Wongkham S, Gores GJ. Cholangiocarcinoma. Nat Rev Dis Primers 2021; 7:65. [PMID: 34504109 PMCID: PMC9246479 DOI: 10.1038/s41572-021-00300-2] [Citation(s) in RCA: 298] [Impact Index Per Article: 99.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/03/2021] [Indexed: 02/08/2023]
Abstract
Cholangiocarcinoma (CCA) is a highly lethal adenocarcinoma of the hepatobiliary system, which can be classified as intrahepatic, perihilar and distal. Each anatomic subtype has distinct genetic aberrations, clinical presentations and therapeutic approaches. In endemic regions, liver fluke infection is associated with CCA, owing to the oncogenic effect of the associated chronic biliary tract inflammation. In other regions, CCA can be associated with chronic biliary tract inflammation owing to choledocholithiasis, cholelithiasis, or primary sclerosing cholangitis, but most CCAs have no identifiable cause. Administration of the anthelmintic drug praziquantel decreases the risk of CCA from liver flukes, but reinfection is common and future vaccination strategies may be more effective. Some patients with CCA are eligible for potentially curative surgical options, such as resection or liver transplantation. Genetic studies have provided new insights into the pathogenesis of CCA, and two aberrations that drive the pathogenesis of non-fluke-associated intrahepatic CCA, fibroblast growth factor receptor 2 fusions and isocitrate dehydrogenase gain-of-function mutations, can be therapeutically targeted. CCA is a highly desmoplastic cancer and targeting the tumour immune microenvironment might be a promising therapeutic approach. CCA remains a highly lethal disease and further scientific and clinical insights are needed to improve patient outcomes.
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Affiliation(s)
- Paul J. Brindley
- Department of Microbiology, Immunology & Tropical Medicine, and Research Center for Neglected Diseases of Poverty, School of Medicine and Health Sciences, George Washington University, Washington, DC, USA
| | | | - Sumera I. Ilyas
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN, USA
| | - Shahid A. Khan
- Liver Unit, Division of Digestive Diseases, Imperial College London, London, UK
| | - Alex Loukas
- Centre for Molecular Therapeutics, Australian Institute of Tropical Health and Medicine, James Cook University, Cairns, Queensland, Australia
| | - Alphonse E. Sirica
- Department of Pathology, Virginia Commonwealth University School of Medicine, Richmond, VA, USA
| | - Bin Tean Teh
- Laboratory of Cancer Epigenome, Division of Medical Sciences, National Cancer Centre, Singapore, Singapore
| | - Sopit Wongkham
- Department of Biochemistry, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Gregory J. Gores
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN, USA,
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7
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Mesirca P, Nakao S, Nissen SD, Forte G, Anderson C, Trussell T, Li J, Cox C, Zi M, Logantha S, Yaar S, Cartensen H, Bidaud I, Stuart L, Soattin L, Morris GM, da Costa Martins PA, Cartwright EJ, Oceandy D, Mangoni ME, Jespersen T, Buhl R, Dobrzynski H, Boyett MR, D'Souza A. Intrinsic Electrical Remodeling Underlies Atrioventricular Block in Athletes. Circ Res 2021; 129:e1-e20. [PMID: 33849278 DOI: 10.1161/circresaha.119.316386] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
[Figure: see text].
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Affiliation(s)
- Pietro Mesirca
- IGF, Université de Montpellier, CNRS, INSERM, France (P.M., I.B., M.E.M.)
| | - Shu Nakao
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
- Department of Biomedical Sciences, Ritsumeikan University, Japan (S.N.)
| | - Sarah Dalgas Nissen
- Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences (S.D.N., H.C., R.B.), University of Copenhagen, Denmark
| | - Gabriella Forte
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Cali Anderson
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Tariq Trussell
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Jue Li
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Charlotte Cox
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Min Zi
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Sunil Logantha
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
- Liverpool Centre for Cardiovascular Sciences, University of Liverpool, United Kingdom (S.L.)
| | - Sana Yaar
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Helena Cartensen
- Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences (S.D.N., H.C., R.B.), University of Copenhagen, Denmark
| | - Isabelle Bidaud
- IGF, Université de Montpellier, CNRS, INSERM, France (P.M., I.B., M.E.M.)
| | - Luke Stuart
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | | | - Gwilym M Morris
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | | | - Elizabeth J Cartwright
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Delvac Oceandy
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
| | - Matteo E Mangoni
- IGF, Université de Montpellier, CNRS, INSERM, France (P.M., I.B., M.E.M.)
| | - Thomas Jespersen
- Department of Biomedical Sciences (T.J., M.R.B.), University of Copenhagen, Denmark
| | - Rikke Buhl
- Department of Veterinary Clinical Sciences, Faculty of Health and Medical Sciences (S.D.N., H.C., R.B.), University of Copenhagen, Denmark
| | - Halina Dobrzynski
- Department of Anatomy, Jagiellonian University Medical College, Poland (H.D.)
| | - Mark R Boyett
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
- Department of Biomedical Sciences (T.J., M.R.B.), University of Copenhagen, Denmark
| | - Alicia D'Souza
- Division of Cardiovascular Sciences, University of Manchester, United Kingdom (S.N., G.F., C.A., T.T., J.L., C.C., M.Z., S.L., S.Y., L. Stuart, L. Soattin, G.M.M., E.J.C., D.O., H.D., M.R.B., A.D.)
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8
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Vornanen M. Feeling the heat: source–sink mismatch as a mechanism underlying the failure of thermal tolerance. J Exp Biol 2020; 223:223/16/jeb225680. [DOI: 10.1242/jeb.225680] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
ABSTRACT
A mechanistic explanation for the tolerance limits of animals at high temperatures is still missing, but one potential target for thermal failure is the electrical signaling off cells and tissues. With this in mind, here I review the effects of high temperature on the electrical excitability of heart, muscle and nerves, and refine a hypothesis regarding high temperature-induced failure of electrical excitation and signal transfer [the temperature-dependent deterioration of electrical excitability (TDEE) hypothesis]. A central tenet of the hypothesis is temperature-dependent mismatch between the depolarizing ion current (i.e. source) of the signaling cell and the repolarizing ion current (i.e. sink) of the receiving cell, which prevents the generation of action potentials (APs) in the latter. A source–sink mismatch can develop in heart, muscles and nerves at high temperatures owing to opposite effects of temperature on source and sink currents. AP propagation is more likely to fail at the sites of structural discontinuities, including electrically coupled cells, synapses and branching points of nerves and muscle, which impose an increased demand of inward current. At these sites, temperature-induced source–sink mismatch can reduce AP frequency, resulting in low-pass filtering or a complete block of signal transmission. In principle, this hypothesis can explain a number of heat-induced effects, including reduced heart rate, reduced synaptic transmission between neurons and reduced impulse transfer from neurons to muscles. The hypothesis is equally valid for ectothermic and endothermic animals, and for both aquatic and terrestrial species. Importantly, the hypothesis is strictly mechanistic and lends itself to experimental falsification.
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Affiliation(s)
- Matti Vornanen
- Department of Environmental and Biological Sciences , University of Eastern Finland, 80101 Joensuu, Finland
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9
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Hoeker GS, James CC, Tegge AN, Gourdie RG, Smyth JW, Poelzing S. Attenuating loss of cardiac conduction during no-flow ischemia through changes in perfusate sodium and calcium. Am J Physiol Heart Circ Physiol 2020; 319:H396-H409. [PMID: 32678707 DOI: 10.1152/ajpheart.00112.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Myocardial ischemia leads to conduction slowing, cell-to-cell uncoupling, and arrhythmias. We previously demonstrated that varying perfusate sodium (Na+) and calcium (Ca2+) attenuates conduction slowing and arrhythmias during simulated ischemia with continuous perfusion. Cardioprotection was selectively associated with widening of the perinexus, a gap junction adjacent nanodomain important to ephaptic coupling. It is unknown whether perfusate composition affects the perinexus or ischemic conduction during nonsimulated ischemia, when coronary flow is reduced or halted. We hypothesized that altering preischemic perfusate composition could facilitate perinexal expansion and attenuate conduction slowing during global ischemia. To test this hypothesis, ex vivo guinea pig hearts (n = 49) were Langendorff perfused with 145 or 153 mM Na+ and 1.25 or 2.0 mM Ca2+ and optically mapped during 30 min of no-flow ischemia. Altering Na+ and Ca2+ did not substantially affect baseline conduction. Increasing Na+ and decreasing Ca2+ both lowered pacing thresholds, whereas increasing Ca2+ narrowed perinexal width (Wp). A least squares mean estimate revealed that reduced perfusate Na+ and Ca2+ resulted in the most severe conduction slowing during ischemia. Increasing Na+ alone modestly attenuated conduction slowing, yet significantly delayed the median time to conduction block (10 to 16 min). Increasing both Na+ and Ca2+ selectively widened Wp during ischemia (22.7 vs. 15.7 nm) and attenuated conduction slowing to the greatest extent. Neither repolarization nor levels of total or phosphorylated connexin43 correlated with conduction slowing or block. Thus, perfusate-dependent widening of the perinexus preserved ischemic conduction and may be an adaptive response to ischemic stress.NEW & NOTEWORTHY Conduction slowing during acute ischemia creates an arrhythmogenic substrate. We have shown that extracellular ionic concentrations can alter conduction by modulating ephaptic coupling. Here, we demonstrate increased extracellular sodium and calcium significantly attenuate conduction slowing during no-flow ischemia. This effect was associated with selective widening of the perinexus, an intercalated disc nanodomain and putative cardiac ephapse. These findings suggest that acute changes in ephaptic coupling may serve as an adaptive response to ischemic stress.
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Affiliation(s)
- Gregory S Hoeker
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia
| | - Carissa C James
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia
| | - Allison N Tegge
- Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Statistics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Robert G Gourdie
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - James W Smyth
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
| | - Steven Poelzing
- Center for Heart and Reparative Medicine Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia.,Translational Biology, Medicine, and Health Graduate Program, Virginia Polytechnic Institute and State University, Roanoke, Virginia.,Virginia Tech Carilion School of Medicine, Roanoke, Virginia.,Department of Biomedical Engineering and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, Virginia
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10
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Osadchii OE. Antiarrhythmic drug effects on premature beats are partly determined by prior cardiac activation frequency in perfused guinea-pig heart. Exp Physiol 2020; 105:819-830. [PMID: 32175633 DOI: 10.1113/ep088165] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2019] [Accepted: 03/13/2020] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? Can antiarrhythmic drug effects on repolarization, conduction time and excitation wavelength in premature beats be determined by prior cardiac activation frequency? What is the main finding and its importance? In premature beats induced after a series of cardiac activations at a slow rate, antiarrhythmics prolong repolarization but evoke little or no conduction delay, thus increasing the excitation wavelength, which indicates an antiarrhythmic effect. Fast prior activation rate attenuates prolongation of repolarization, while amplifying the conduction delay induced by drugs, which translates into the reduced excitation wavelength, indicating proarrhythmia. These findings suggest that a sudden increase in heart rate can shape adverse pharmacological profiles in patients with ventricular ectopy. ABSTRACT Antiarrhythmic drugs used to treat atrial fibrillation can occasionally induce ventricular tachyarrhythmia, which is typically precipitated by a premature ectopic beat through a mechanism related, in part, to the shortening of the excitation wavelength (EW). The arrhythmia is likely to occur when a drug induces a reduction, rather than an increase, in the EW of ectopic beats. In this study, I examined whether the arrhythmic drug profile is shaped by the increased cardiac activation rate before ectopic excitation. Ventricular monophasic action potential durations, conduction times and EW values were assessed during programmed stimulations applied at long (S1 -S1 [basic drive cycle length] = 550 ms) and short (S1 -S1 = 200 ms) cycle lengths in perfused guinea-pig hearts. The premature activations were induced with extrastimulus application immediately upon termination of the refractory period. With dofetilide, a class III antiarrhythmic agent, a prolongation in action potential duration and the resulting increase in the EW obtained at S1 -S1 = 550 ms were significantly attenuated at S1 -S1 = 200 ms, in both the regular (S1 ) and the premature (S2 ) beats. With class I antiarrhythmic agents (quinidine, procainamide and flecainide), fast S1 -S1 pacing was found to attenuate the drug-induced increase in action potential duration, while amplifying drug-induced conduction slowing, in both S1 and S2 beats. As a result, although the EW was increased (quinidine and procainamide) or not changed (flecainide) at the long S1 -S1 intervals, it was invariably reduced by these agents at the short S1 -S1 intervals. These findings indicate that the increased heart rate before ectopic activation shapes the arrhythmic profiles by facilitating drug-induced EW reduction.
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Affiliation(s)
- Oleg E Osadchii
- Department of Biomedical Sciences, University of Copenhagen, Copenhagen N, Denmark.,Department of Health Science and Technology, University of Aalborg, Aalborg, Denmark
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11
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Restitution and Stability of Human Ventricular Action Potential at High and Variable Pacing Rate. Biophys J 2019; 117:2382-2395. [PMID: 31514969 DOI: 10.1016/j.bpj.2019.08.020] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 08/07/2019] [Accepted: 08/19/2019] [Indexed: 11/23/2022] Open
Abstract
Despite the key role of beat-to-beat action potential (AP) variability in the onset of ventricular arrhythmias at high pacing rate, the knowledge of the involved dynamics and of effective prognostic parameters is largely incomplete. Electrical restitution (ER), the way AP duration (APD) senses changes in preceding cycle length (CL), has been used to monitor transition to arrhythmias. The use of standard ER (sER), though, is controversial, not always suitable for in vivo and only rarely for clinical applications. By means of simulations on a human ventricular AP model, I investigate the dynamics of APD at high pacing rate under sinusoidally, saw-tooth, and randomly variable pacing CLs. AP sequences were compared in terms of beat-to-beat restitution (btb-ER) and of the collections of sER curves generated from each beat. A definition of APD stability is also proposed, based on successive APD changes introduced in an AP sequence by a premature beat. The explored CL range includes values leading to APD alternans under constant pacing. Three different types of response to CL variability were found, corresponding to progressively higher rate of beat-to-beat CL changes. Low rates (∼1 ms/beat) generate a btb-ER dominated by steady-state rate dependence of APD (type 1), intermediate rates (∼5 ms/beat) lead to a btb-ER similar to a single sER (type 2), and high rates (∼20 ms/beat) to hysteretic btb-ER under periodic pacing and to a vertically spread btb-ER in the case of random pacing (type 3). Stability of AP repolarization always increases with the rate of CL changes. Thus, rather than looking at sER slope, which requires additional interventions during the recording of cardiac electrical activity, this study provides rationale for the use of btb-ER representations as predictors of repolarization stability under extreme pacing conditions, known to be critical for the arrhythmia development.
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12
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Ni H, Zhang H, Grandi E, Narayan SM, Giles WR. Transient outward K + current can strongly modulate action potential duration and initiate alternans in the human atrium. Am J Physiol Heart Circ Physiol 2019; 316:H527-H542. [PMID: 30576220 PMCID: PMC6415821 DOI: 10.1152/ajpheart.00251.2018] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 07/27/2018] [Accepted: 08/15/2018] [Indexed: 01/14/2023]
Abstract
Efforts to identify the mechanisms for the initiation and maintenance of human atrial fibrillation (AF) often focus on changes in specific elements of the atrial "substrate," i.e., its electrophysiological properties and/or structural components. We used experimentally validated mathematical models of the human atrial myocyte action potential (AP), both at baseline in sinus rhythm (SR) and in the setting of chronic AF, to identify significant contributions of the Ca2+-independent transient outward K+ current ( Ito) to electrophysiological instability and arrhythmia initiation. First, we explored whether changes in the recovery or restitution of the AP duration (APD) and/or its dynamic stability (alternans) can be modulated by Ito. Recent reports have identified disease-dependent spatial differences in expression levels of the specific K+ channel α-subunits that underlie Ito in the left atrium. Therefore, we studied the functional consequences of this by deletion of 50% of native Ito (Kv4.3) and its replacement with Kv1.4. Interestingly, significant changes in the short-term stability of the human atrial AP waveform were revealed. Specifically, this K+ channel isoform switch produced discontinuities in the initial slope of the APD restitution curve and appearance of APD alternans. This pattern of in silico results resembles some of the changes observed in high-resolution clinical electrophysiological recordings. Important insights into mechanisms for these changes emerged from known biophysical properties (reactivation kinetics) of Kv1.4 versus those of Kv4.3. These results suggest new approaches for pharmacological management of AF, based on molecular properties of specific K+ isoforms and their changed expression during progressive disease. NEW & NOTEWORTHY Clinical studies identify oscillations (alternans) in action potential (AP) duration as a predictor for atrial fibrillation (AF). The abbreviated AP in AF also involves changes in K+ currents and early repolarization of the AP. Our simulations illustrate how substitution of Kv1.4 for the native current, Kv4.3, alters the AP waveform and enhances alternans. Knowledge of this "isoform switch" and related dynamics in the AF substrate may guide new approaches for detection and management of AF.
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Affiliation(s)
- Haibo Ni
- Biological Physics Group, School of Physics and Astronomy, University of Manchester , Manchester , United Kingdom
- Department of Pharmacology, University of California , Davis, California
| | - Henggui Zhang
- Biological Physics Group, School of Physics and Astronomy, University of Manchester , Manchester , United Kingdom
| | - Eleonora Grandi
- Department of Pharmacology, University of California , Davis, California
| | - Sanjiv M Narayan
- Division of Cardiology, Cardiovascular Institute, Stanford University , Stanford, California
| | - Wayne R Giles
- Faculties of Kinesiology and Medicine, University of Calgary , Calgary, Alberta , Canada
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13
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Osadchii OE. Effects of antiarrhythmics on the electrical restitution in perfused guinea-pig heart are critically determined by the applied cardiac pacing protocol. Exp Physiol 2019; 104:490-504. [PMID: 30758086 DOI: 10.1113/ep087531] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Accepted: 02/12/2019] [Indexed: 01/11/2023]
Abstract
NEW FINDINGS What is the central question of this study? Are modifications in the restitution of ventricular action potential duration induced by antiarrhythmic drugs the same when assessed with premature extrastimulus application at variable coupling intervals (the standard stimulation protocol) and with steady state pacing at variable rates (the dynamic stimulation protocol)? What is the main finding and its importance? With class I and class III antiarrhythmics, the effects on electrical restitution determined with the standard stimulation protocol dissociate from those obtained during dynamic pacing. These findings indicate a limited value of the electrical restitution assessments based on extrasystolic stimulations alone, as performed in the clinical studies, in estimating the outcomes of antiarrhythmic drug therapies. ABSTRACT A steep slope of the ventricular action potential duration (APD) to diastolic interval (DI) relationships (the electrical restitution) can precipitate tachyarrhythmia, whereas a flattened slope is antiarrhythmic. The derangements in APD restitution responsible for transition of tachycardia to ventricular fibrillation can be assessed with cardiac pacing at progressively increasing rates (the dynamic stimulation protocol). Nevertheless, this method is not used clinically owing to the risk of inducing myocardial ischaemia. Instead, the restitution kinetics is determined with a premature extrastimulus application at variable coupling intervals (the standard stimulation protocol). Whether the two protocols are equivalent in estimating antiarrhythmic drug effects is uncertain. In this study, dofetilide and quinidine, the agents blocking repolarizing K+ currents, increased epicardial APD in perfused guinea-pig hearts, with effects being greater at long vs. short DIs. These changes were more pronounced during dynamic pacing compared to premature extrastimulations. Accordingly, although both agents markedly steepened the dynamic restitution, there was only a marginal increase in the standard restitution slope with dofetilide, and no effect with quinidine. Lidocaine and mexiletine, selective Na+ channel blockers, prolonged the effective refractory period without changing APD, and increased the minimum DI that enabled ventricular capture during extrastimulations. No change in the minimum DI was noted during dynamic pacing. Consequently, although lidocaine and mexiletine reduced the standard restitution slope, they failed to flatten the dynamic restitution. Overall, these findings imply a limited value of the electrical restitution assessments with premature extrastimulations alone in discriminating arrhythmic vs. antiarrhythmic changes during drug therapies.
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Affiliation(s)
- Oleg E Osadchii
- Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, 2200, Copenhagen N, Denmark.,Department of Health Science and Technology, University of Aalborg, Fredrik Bajers Vej 7E, 9220, Aalborg, Denmark
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14
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Abramochkin DV, Haverinen J, Mitenkov YA, Vornanen M. Temperature- and external K+-dependence of electrical excitation in ventricular myocytes of cod-like fishes. J Exp Biol 2019; 222:jeb.193607. [DOI: 10.1242/jeb.193607] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Accepted: 01/16/2019] [Indexed: 01/08/2023]
Abstract
Electrical excitability (EE) is vital for cardiac function and strongly modulated by temperature and external K+ concentration ([K+]o) as formulated in the hypothesis of temperature-dependent deterioration of electrical excitability (TDEE). Since little is known about EE of arctic stenothermic fishes, we tested the TDEE hypothesis on ventricular myocytes of polar cod (Boreogadus saida) and navaga cod (Eleginus navaga) of the Arctic Ocean and those of temperate freshwater burbot (Lota lota). Ventricular action potentials (APs) were elicited in current-clamp experiments at 3, 9 and 15°C, and AP characteristics and the current needed to elicit AP were examined. At 3°C, ventricular APs of polar and navaga cod were similar but differed from that of burbot in having lower rate of AP upstroke and higher rate of repolarization. EE of ventricular myocytes - defined as the ease with which all-or-none APs are triggered - was little affected by acute temperature changes between 3 and 15°C in any species. However, AP duration (APD50) was drastically reduced at higher temperatures. Elevation of [K+]o from 3 to 5.4 and further to 8 mM at 3, 9 and 15°C strongly affected EE and AP characteristics in polar and navaga cod, but less in burbot. In all species, ventricular excitation was resistant to acute temperature elevations, while small increases in [K+]o severely compromised EE, in particular in the marine stenotherms. This suggests that EE of the heart in these Gadiformes species is well equipped against acute warming, but less so against the simultaneous temperature and exercise stresses.
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Affiliation(s)
- Denis V. Abramochkin
- Department of human and animal physiology, Lomonosov Moscow State University, Leninskiye Gory, 1, 12, Moscow, Russia
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russia
- Laboratory of Cardiac Physiology, Institute of Physiology, Komi Science Center, Ural Branch, Russian Academy of Sciences, Syktyvkar, Russia
| | - Jaakko Haverinen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
| | - Yuri A. Mitenkov
- VNIRO Russian Federal Research Institute of Fisheries and Oceanography, Moscow, Russia
| | - Matti Vornanen
- Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland
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15
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Li RA, Keung W, Cashman TJ, Backeris PC, Johnson BV, Bardot ES, Wong AOT, Chan PKW, Chan CWY, Costa KD. Bioengineering an electro-mechanically functional miniature ventricular heart chamber from human pluripotent stem cells. Biomaterials 2018; 163:116-127. [PMID: 29459321 DOI: 10.1016/j.biomaterials.2018.02.024] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 02/09/2018] [Indexed: 12/14/2022]
Abstract
Tissue engineers and stem cell biologists have made exciting progress toward creating simplified models of human heart muscles or aligned monolayers to help bridge a longstanding gap between experimental animals and clinical trials. However, no existing human in vitro systems provide the direct measures of cardiac performance as a pump. Here, we developed a next-generation in vitro biomimetic model of pumping human heart chamber, and demonstrated its capability for pharmaceutical testing. From human pluripotent stem cell (hPSC)-derived ventricular cardiomyocytes (hvCM) embedded in collagen-based extracellular matrix hydrogel, we engineered a three-dimensional (3D) electro-mechanically coupled, fluid-ejecting miniature human ventricle-like cardiac organoid chamber (hvCOC). Structural characterization showed organized sarcomeres with myofibrillar microstructures. Transcript and RNA-seq analyses revealed upregulation of key Ca2+-handling, ion channel, and cardiac-specific proteins in hvCOC compared to lower-order 2D and 3D cultures of the same constituent cells. Clinically-important, physiologically complex contractile parameters such as ejection fraction, developed pressure, and stroke work, as well as electrophysiological properties including action potential and conduction velocity were measured: hvCOC displayed key molecular and physiological characteristics of the native ventricle, and showed expected mechanical and electrophysiological responses to a range of pharmacological interventions (including positive and negative inotropes). We conclude that such "human-heart-in-a-jar" technology could facilitate the drug discovery process by providing human-specific preclinical data during early stage drug development.
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Affiliation(s)
- Ronald A Li
- Ming-Wai Lau Centre for Reparative Medicine, Karolinska Institutet, Sweden; Dr. Li Dak-Sum Research Centre, The University of Hong Kong-Karolinska Institutet Collaboration on Regenerative Medicine, The University of Hong Kong, Pokfulam, Hong Kong; Stem Cell & Regenerative Medicine Consortium, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong; Novoheart Limited, Shatin, Hong Kong.
| | - Wendy Keung
- Ming-Wai Lau Centre for Reparative Medicine, Karolinska Institutet, Sweden; Dr. Li Dak-Sum Research Centre, The University of Hong Kong-Karolinska Institutet Collaboration on Regenerative Medicine, The University of Hong Kong, Pokfulam, Hong Kong; Stem Cell & Regenerative Medicine Consortium, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong
| | - Timothy J Cashman
- Cardiovascular Research Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Peter C Backeris
- Cardiovascular Research Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Bryce V Johnson
- Cardiovascular Research Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Evan S Bardot
- Cardiovascular Research Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - Andy O T Wong
- Dr. Li Dak-Sum Research Centre, The University of Hong Kong-Karolinska Institutet Collaboration on Regenerative Medicine, The University of Hong Kong, Pokfulam, Hong Kong; Stem Cell & Regenerative Medicine Consortium, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong
| | - Patrick K W Chan
- Ming-Wai Lau Centre for Reparative Medicine, Karolinska Institutet, Sweden; Stem Cell & Regenerative Medicine Consortium, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong
| | - Camie W Y Chan
- Stem Cell & Regenerative Medicine Consortium, LKS Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong; Novoheart Limited, Shatin, Hong Kong
| | - Kevin D Costa
- Cardiovascular Research Center, Icahn School of Medicine at Mount Sinai, New York, NY, USA; Novoheart Limited, Shatin, Hong Kong.
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Zaza A, Ronchi C, Malfatto G. Arrhythmias and Heart Rate: Mechanisms and Significance of a Relationship. Arrhythm Electrophysiol Rev 2018; 7:232-237. [PMID: 30588310 DOI: 10.15420/aer.2018.12.3] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Accepted: 05/17/2018] [Indexed: 11/04/2022] Open
Abstract
The occurrence of arrhythmia is often related to basic heart rate. Prognostic significance is associated with such a relationship; furthermore, heart rate modulation may result as an ancillary effect of therapy, or be considered as a therapeutic tool. This review discusses the cellular mechanisms underlying arrhythmia occurrence during tachycardia or bradycardia, considering rate changes per se or as a mirror of autonomic modulation. Besides the influence of steady-state heart rate, dynamic aspects of changes in rate and autonomic balance are considered. The discussion leads to the conclusion that the prognostic significance of arrhythmia relationship with heart rate, and the consequence of heart rate on arrhythmogenesis, may vary according to the substrate present in the specific case and should be considered accordingly.
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Affiliation(s)
- Antonio Zaza
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi Milano-Bicocca Milan, Italy.,CARIM, Maastricht University Maastricht, the Netherlands
| | - Carlotta Ronchi
- Dipartimento di Biotecnologie e Bioscienze, Università degli Studi Milano-Bicocca Milan, Italy
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17
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Osadchii OE. Role of abnormal repolarization in the mechanism of cardiac arrhythmia. Acta Physiol (Oxf) 2017; 220 Suppl 712:1-71. [PMID: 28707396 DOI: 10.1111/apha.12902] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
In cardiac patients, life-threatening tachyarrhythmia is often precipitated by abnormal changes in ventricular repolarization and refractoriness. Repolarization abnormalities typically evolve as a consequence of impaired function of outward K+ currents in cardiac myocytes, which may be caused by genetic defects or result from various acquired pathophysiological conditions, including electrical remodelling in cardiac disease, ion channel modulation by clinically used pharmacological agents, and systemic electrolyte disorders seen in heart failure, such as hypokalaemia. Cardiac electrical instability attributed to abnormal repolarization relies on the complex interplay between a provocative arrhythmic trigger and vulnerable arrhythmic substrate, with a central role played by the excessive prolongation of ventricular action potential duration, impaired intracellular Ca2+ handling, and slowed impulse conduction. This review outlines the electrical activity of ventricular myocytes in normal conditions and cardiac disease, describes classical electrophysiological mechanisms of cardiac arrhythmia, and provides an update on repolarization-related surrogates currently used to assess arrhythmic propensity, including spatial dispersion of repolarization, activation-repolarization coupling, electrical restitution, TRIaD (triangulation, reverse use dependence, instability, and dispersion), and the electromechanical window. This is followed by a discussion of the mechanisms that account for the dependence of arrhythmic vulnerability on the location of the ventricular pacing site. Finally, the review clarifies the electrophysiological basis for cardiac arrhythmia produced by hypokalaemia, and gives insight into the clinical importance and pathophysiology of drug-induced arrhythmia, with particular focus on class Ia (quinidine, procainamide) and Ic (flecainide) Na+ channel blockers, and class III antiarrhythmic agents that block the delayed rectifier K+ channel (dofetilide).
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Affiliation(s)
- O. E. Osadchii
- Department of Health Science and Technology; University of Aalborg; Aalborg Denmark
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18
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Fossa AA. Beat-to-beat ECG restitution: A review and proposal for a new biomarker to assess cardiac stress and ventricular tachyarrhythmia vulnerability. Ann Noninvasive Electrocardiol 2017; 22. [PMID: 28497858 DOI: 10.1111/anec.12460] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 04/06/2017] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Cardiac restitution is the ability of the heart to recover from one beat to the next. Ventricular arrhythmia vulnerability can occur when the heart does not properly adjust to sudden changes in rate or in hemodynamics leading to excessive temporal and/or spatial heterogeneity in conduction or repolarization. Restitution has historically been used to study, by invasive means, the dynamics of the relationship between action potential duration (APD) and diastolic interval (DI) in sedated subjects using various pacing protocols. Even though the analogous measures of APD and DI can be obtained using the surface ECG to acquire the respective QT and TQ intervals for ECG restitution, this methodology has not been widely adopted for a number of reasons. METHODS Recent development of more advanced software algorithms enables ECG intervals to be measured accurately, on a continuous beat-to-beat basis, in an automated manner, and under highly dynamic conditions (i.e., ambulatory or exercise) providing information beyond that available in the typical resting state. RESULTS Current breakthroughs in ECG technology will allow ECG restitution measures to become a practical approach for providing quantitative measures of the risks for ventricular arrhythmias as well as cardiac stress in general. CONCLUSIONS In addition to a review of the underlying principles and caveats of ECG restitution, a new approach toward an advancement of more integrated restitution biomarkers is proposed.
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19
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Vornanen M. The temperature dependence of electrical excitability in fish hearts. J Exp Biol 2016; 219:1941-52. [DOI: 10.1242/jeb.128439] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2016] [Accepted: 05/17/2016] [Indexed: 01/08/2023]
Abstract
ABSTRACT
Environmental temperature has pervasive effects on the rate of life processes in ectothermic animals. Animal performance is affected by temperature, but there are finite thermal limits for vital body functions, including contraction of the heart. This Review discusses the electrical excitation that initiates and controls the rate and rhythm of fish cardiac contraction and is therefore a central factor in the temperature-dependent modulation of fish cardiac function. The control of cardiac electrical excitability should be sensitive enough to respond to temperature changes but simultaneously robust enough to protect against cardiac arrhythmia; therefore, the thermal resilience and plasticity of electrical excitation are physiological qualities that may affect the ability of fishes to adjust to climate change. Acute changes in temperature alter the frequency of the heartbeat and the duration of atrial and ventricular action potentials (APs). Prolonged exposure to new thermal conditions induces compensatory changes in ion channel expression and function, which usually partially alleviate the direct effects of temperature on cardiac APs and heart rate. The most heat-sensitive molecular components contributing to the electrical excitation of the fish heart seem to be Na+ channels, which may set the upper thermal limit for the cardiac excitability by compromising the initiation of the cardiac AP at high temperatures. In cardiac and other excitable cells, the different temperature dependencies of the outward K+ current and inward Na+ current may compromise electrical excitability at temperature extremes, a hypothesis termed the temperature-dependent depression of electrical excitation.
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Affiliation(s)
- Matti Vornanen
- University of Eastern Finland, Department of Environmental and Biological Sciences, PO Box 111, Joensuu 80101, Finland
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Tikkanen E, Haverinen J, Egginton S, Hassinen M, Vornanen M. Effects of prolonged anoxia on electrical activity of the heart in Crucian carp (Carassius carassius). J Exp Biol 2016; 220:445-454. [DOI: 10.1242/jeb.145177] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Accepted: 11/15/2016] [Indexed: 01/08/2023]
Abstract
The effects of sustained anoxia on cardiac electrical excitability were examined in the anoxia-tolerant Crucian carp (Carassius carassius). The electrocardiogram (ECG) and expression of excitation-contraction coupling genes were studied in fish acclimatised to normoxia in summer (+18°C) or winter (+2°C), and in winter fish after 1, 3 and 6 weeks of anoxia. Anoxia induced a sustained bradycardia from a heart rate of 10.3±0.77 to 4.1±0.29 bpm (P<0.05) after 5 weeks, and heart rate slowly recovered to control levels when oxygen was restored. Heart rate variability greatly increased under anoxia, and completely recovered under re-oxygenation. The RT interval increased from 2.8±0.34 s in normoxia to 5.8±0.44 s under anoxia (P<0.05), which reflects a doubling of the ventricular action potential (AP) duration. Acclimatisation to winter induced extensive changes in gene expression relative to summer-acclimatised fish, including depression in those coding for the sarcoplasmic reticulum calcium pump (Serca2-q2) and ATP-sensitive K+ channels (Kir6.2) (P<0.05). Genes of delayed rectifier K+ (kcnh6) and Ca2+ channels (cacna1c) were up-regulated in winter fish (P<0.05). In contrast, the additional challenge of anoxia caused only minor changes in gene expression, e.g. depressed expression of Kir2.2b K+ channel gene (kcnj12b), whereas expression of Ca2+ (cacna1a, -c and –g) and Na+ channel genes (scn4a and scn5a) were not affected. These data suggest that low temperature pre-conditions the Crucian carp heart for winter anoxia, whereas sustained anoxic bradycardia and prolongation of AP duration are directly induced by oxygen shortage without major changes in gene expression.
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Affiliation(s)
- Elisa Tikkanen
- University of Eastern Finland, Department of Environmental and Biological Sciences, Finland
| | - Jaakko Haverinen
- University of Eastern Finland, Department of Environmental and Biological Sciences, Finland
| | | | - Minna Hassinen
- University of Eastern Finland, Department of Environmental and Biological Sciences, Finland
| | - Matti Vornanen
- University of Eastern Finland, Department of Environmental and Biological Sciences, Finland
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Effects of Na+ Channel Blockers on Extrasystolic Stimulation-evoked Changes in Ventricular Conduction and Repolarization. J Cardiovasc Pharmacol 2014; 63:240-51. [DOI: 10.1097/fjc.0000000000000041] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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22
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Abstract
PURPOSE Dofetilide is class III antiarrhythmic agent which prolongs cardiac action potential duration because of selective inhibition of I (Kr), the rapid component of the delayed rectifier K(+) current. Although clinical studies reported on proarrhythmic risk associated with dofetilide treatment, the contributing electrophysiological mechanisms remain poorly understood. This study was designed to determine if dofetilide-induced proarrhythmia may be attributed to abnormalities in ventricular repolarization and refractoriness. METHODS The monophasic action potential duration and effective refractory periods (ERP) were assessed at distinct epicardial and endocardial sites along with volume-conducted ECG recordings in isolated, perfused guinea-pig heart preparations. RESULTS Dofetilide was found to produce the reverse rate-dependent prolongation of ventricular repolarization, increased the steepness of action potential duration rate adaptation, and amplified transepicardial variability in electrical restitution kinetics. Dofetilide also prolonged the T peak-to-end interval on ECG, and elicited a greater prolongation of endocardial than epicardial ERP, thereby increasing transmural dispersion of refractoriness. At epicardium, dofetilide prolonged action potential duration to a greater extent than ERP, thus extending the critical interval for ventricular re-excitation. This change was associated with triangulation of epicardial action potential because of greater dofetilide-induced prolonging effect at 90 % than 30 % repolarization. Premature ectopic beats and spontaneous short-lasting episodes of monomorphic ventricular tachycardia were observed in 44 % of dofetilide-treated heart preparations. CONCLUSIONS Proarrhythmic potential of dofetilide in guinea-pig heart is attributed to steepened electrical restitution, increased transepicardial variability in electrical restitution kinetics, amplified transmural dispersion of refractoriness, increased critical interval for ventricular re-excitation, and triangulation of epicardial action potential.
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Affiliation(s)
- Oleg E Osadchii
- Department of Biomedical Sciences, University of Copenhagen, Blegdamsvej 3, 2200, Copenhagen N, Denmark.
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Osadchii OE. Electrophysiological determinants of arrhythmic susceptibility upon endocardial and epicardial pacing in guinea-pig heart. Acta Physiol (Oxf) 2012; 205:494-506. [PMID: 22356273 DOI: 10.1111/j.1748-1716.2012.02428.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2011] [Revised: 11/23/2011] [Accepted: 02/14/2012] [Indexed: 12/01/2022]
Abstract
AIM Endocardial pacing instituted to treat symptomatic bradycardia may nevertheless promote tachyarrhythmia in some pacemaker-implanted patients. We sought to determine the contributing electrophysiological mechanisms. METHODS Left ventricular (LV) monophasic action potential duration (APD(90)) and effective refractory periods were determined in perfused guinea-pig hearts along with volume-conducted ECG recordings during epicardial and endocardial stimulations. RESULTS Consistent with electrotonic modulation of repolarization, APD(90) at a given (either epicardial or endocardial) recording site tended to be longer while pacing from the ipsilateral LV site as compared to stimulations applied at the opposite side of ventricular wall. As a result, the intrinsic transmural repolarization gradient was amplified during endocardial pacing while being significantly reduced upon epicardial stimulations. The maximum slope of APD(90) restitution was greater upon endocardial than epicardial pacing. The excitability was found to recur at earlier repolarization time point at endocardium than epicardium, thereby contributing to increased endocardial critical intervals for re-excitation. Premature extrasystolic beats could have been elicited at shorter coupling stimulation intervals and propagated with greater transmural conduction delay upon endocardial than epicardial stimulations. Endocardial site exhibited lower ventricular fibrillation thresholds and greater inducibility of tachyarrhythmia upon extrasystolic stimulations as compared to epicardium. CONCLUSION Arrhythmic susceptibility in guinea-pig heart is greater during endocardial than epicardial pacing because of greater transmural APD(90) dispersion, steeper electrical restitution slopes, greater critical intervals for LV re-excitation and slower transmural conduction of the earliest premature ectopic beats. Further studies are warranted to determine whether these effects may contribute to proarrhythmia in paced human patients.
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Affiliation(s)
- O E Osadchii
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, The Panum Institute, University of Copenhagen, Copenhagen N, Denmark.
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Cherry EM, Fenton FH, Gilmour RF. Mechanisms of ventricular arrhythmias: a dynamical systems-based perspective. Am J Physiol Heart Circ Physiol 2012; 302:H2451-63. [PMID: 22467299 PMCID: PMC3378269 DOI: 10.1152/ajpheart.00770.2011] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 03/26/2012] [Indexed: 01/23/2023]
Abstract
Defining the cellular electrophysiological mechanisms for ventricular tachyarrhythmias is difficult, given the wide array of potential mechanisms, ranging from abnormal automaticity to various types of reentry and kk activity. The degree of difficulty is increased further by the fact that any particular mechanism may be influenced by the evolving ionic and anatomic environments associated with many forms of heart disease. Consequently, static measures of a single electrophysiological characteristic are unlikely to be useful in establishing mechanisms. Rather, the dynamics of the electrophysiological triggers and substrates that predispose to arrhythmia development need to be considered. Moreover, the dynamics need to be considered in the context of a system, one that displays certain predictable behaviors, but also one that may contain seemingly stochastic elements. It also is essential to recognize that even the predictable behaviors of this complex nonlinear system are subject to small changes in the state of the system at any given time. Here we briefly review some of the short-, medium-, and long-term alterations of the electrophysiological substrate that accompany myocardial disease and their potential impact on the initiation and maintenance of ventricular arrhythmias. We also provide examples of cases in which small changes in the electrophysiological substrate can result in rather large differences in arrhythmia outcome. These results suggest that an interrogation of cardiac electrical dynamics is required to provide a meaningful assessment of the immediate risk for arrhythmia development and for evaluating the effects of putative antiarrhythmic interventions.
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Affiliation(s)
- Elizabeth M Cherry
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA
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25
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Osadchii OE. Effects of ventricular pacing protocol on electrical restitution assessments in guinea-pig heart. Exp Physiol 2012; 97:807-21. [DOI: 10.1113/expphysiol.2012.065219] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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26
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Zaniboni M. Late phase of repolarization is autoregenerative and scales linearly with action potential duration in mammals ventricular myocytes: a model study. IEEE Trans Biomed Eng 2011; 59:226-33. [PMID: 21990326 DOI: 10.1109/tbme.2011.2170987] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Scaling of action potential (AP) duration (APD) in mammals of different size is a rather complex phenomenon, dominated by a regulatory type mechanism of ion channels expression. By means of simulations performed on six published mathematical models of cardiac ventricular APs of different mammals, it is shown that AP repolarization is autoregenerative in its later phase (ARRP) and that the duration of such phase scales linearly with APD. For each AP, a 3-D instantaneous time-voltage-current surface is constructed, which has been recently described in a more simplified model. This representation allows us to measure ARRP and to study the contribution to it for different ion currents. It has been found that the existence of an ARRP is not intrinsic to cardiac models formulation; one out of the six models does not show this phase. A linear correlation between ARRP duration and APD in the remaining models is also found. It is shown that ARRP neither simply depend on AP shape nor on APD. Though I(K1) current seems to be the main responsible for determining and modulating this phase, the mechanism by which ARRP scales linearly with APD remains unclear and raises further questions on the scaling strategies of cardiac repolarization in mammals.
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Affiliation(s)
- Massimiliano Zaniboni
- Department of Evolutionary and Functional Biology, Physiology Section, University of Parma, 43124 Parma, Italy.
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27
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Romero L, Carbonell B, Trenor B, Rodríguez B, Saiz J, Ferrero JM. Systematic characterization of the ionic basis of rabbit cellular electrophysiology using two ventricular models. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:60-73. [PMID: 21749896 DOI: 10.1016/j.pbiomolbio.2011.06.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 06/27/2011] [Indexed: 01/08/2023]
Abstract
Several mathematical models of rabbit ventricular action potential (AP) have been proposed to investigate mechanisms of arrhythmias and excitation-contraction coupling. Our study aims at systematically characterizing how ionic current properties modulate the main cellular biomarkers of arrhythmic risk using two widely-used rabbit ventricular models, and comparing simulation results using the two models with experimental data available for rabbit. A sensitivity analysis of AP properties, Ca²⁺ and Na⁺ dynamics, and their rate dependence to variations (±15% and ±30%) in the main transmembrane current conductances and kinetics was performed using the Shannon et al. (2004) and the Mahajan et al. (2008a,b) AP rabbit models. The effects of severe transmembrane current blocks (up to 100%) on steady-state AP and calcium transients, and AP duration (APD) restitution curves were also simulated using both models. Our simulations show that, in both virtual rabbit cardiomyocytes, APD is significantly modified by most repolarization currents, AP triangulation is regulated mostly by the inward rectifier K⁺ current (I(K1)) whereas APD rate adaptation as well as [Na⁺](i) rate dependence is influenced by the Na⁺/K⁺ pump current (I(NaK)). In addition, steady-state [Ca²⁺](i) levels, APD restitution properties and [Ca²⁺](i) rate dependence are strongly dependent on I(NaK), the L-Type Ca²⁺ current (I(CaL)) and the Na⁺/Ca²⁺ exchanger current (I(NaCa)), although the relative role of these currents is markedly model dependent. Furthermore, our results show that simulations using both models agree with many experimentally-reported electrophysiological characteristics. However, our study shows that the Shannon et al. model mimics rabbit electrophysiology more accurately at normal pacing rates, whereas Mahajan et al. model behaves more appropriately at faster rates. Our results reinforce the usefulness of sensitivity analysis for further understanding of cellular electrophysiology and validation of cardiac AP models.
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Affiliation(s)
- Lucía Romero
- Instituto de Investigación Interuniversitario en Bioingeniería y Tecnología Orientada al Ser Humano (I3BH), Universitat Politècnica de València (UPV), Camino de Vera s/n, 46022 Valencia, Spain.
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28
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Soltysinska E, Olesen SP, Osadchii OE. Myocardial structural, contractile and electrophysiological changes in the guinea-pig heart failure model induced by chronic sympathetic activation. Exp Physiol 2011; 96:647-63. [DOI: 10.1113/expphysiol.2011.058503] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Osadchii OE, Soltysinska E, Olesen SP. Na+ channel distribution and electrophysiological heterogeneities in guinea pig ventricular wall. Am J Physiol Heart Circ Physiol 2011; 300:H989-1002. [DOI: 10.1152/ajpheart.00816.2010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We sought to explore the distribution pattern of Na+ channels across ventricular wall, and to determine its functional correlates, in the guinea pig heart. Voltage-dependent Na+ channel (Nav) protein expression levels were measured in transmural samples of ventricular tissue by Western blotting. Isolated, perfused heart preparations were used to record monophasic action potentials and volume-conducted ECG, and to measure effective refractory periods (ERPs) and pacing thresholds, in order to assess excitability, electrical restitution kinetics, and susceptibility to stimulation-evoked tachyarrhythmias at epicardial and endocardial stimulation sites. In both ventricular chambers, Nav protein expression was higher at endocardium than epicardium, with midmyocardial layers showing intermediate expression levels. Endocardial stimulation sites showed higher excitability, as evidenced by lower pacing thresholds during regular stimulation and downward displacement of the strength-interval curve reconstructed after extrasystolic stimulation compared with epicardium. ERP restitution assessed over a wide range of pacing rates showed greater maximal slope and faster kinetics at endocardial than epicardial stimulation sites. Flecainide, a Na+ channel blocker, reduced the maximal ERP restitution slope, slowed restitution kinetics, and eliminated epicardial-to-endocardial difference in dynamics of electrical restitution. Greater excitability and steeper electrical restitution have been associated with greater arrhythmic susceptibility of endocardium than epicardium, as assessed by measuring ventricular fibrillation threshold, inducibility of tachyarrhythmias by rapid cardiac pacing, and the magnitude of stimulation-evoked repolarization alternans. In conclusion, higher Na+ channel expression levels may contribute to greater excitability, steeper electrical restitution slopes and faster restitution kinetics, and greater susceptibility to stimulation-evoked tachyarrhythmias at endocardium than epicardium in the guinea pig heart.
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Affiliation(s)
- Oleg E. Osadchii
- Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, Panum Institute, University of Copenhagen, Copenhagen, Denmark
| | - Ewa Soltysinska
- Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, Panum Institute, University of Copenhagen, Copenhagen, Denmark
| | - Soren Peter Olesen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, Panum Institute, University of Copenhagen, Copenhagen, Denmark
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Zhang P, Lader AS, Etcheverry MA, Cantiello HF. Crotoxin potentiates L-type calcium currents and modulates the action potential of neonatal rat cardiomyocytes. Toxicon 2010; 55:1236-43. [DOI: 10.1016/j.toxicon.2010.01.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2008] [Revised: 09/02/2009] [Accepted: 01/09/2010] [Indexed: 11/25/2022]
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Osadchii OE, Larsen AP, Olesen SP. Predictive value of electrical restitution in hypokalemia-induced ventricular arrhythmogenicity. Am J Physiol Heart Circ Physiol 2010; 298:H210-20. [DOI: 10.1152/ajpheart.00695.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ventricular action potential (AP) shortens exponentially upon a progressive reduction of the preceding diastolic interval. Steep electrical restitution slopes have been shown to promote wavebreaks, thus contributing to electrical instability. The present study was designed to assess the predictive value of electrical restitution in hypokalemia-induced arrhythmogenicity. We recorded monophasic APs and measured effective refractory periods (ERP) at distinct ventricular epicardial and endocardial sites and monitored volume-conducted ECG at baseline and after hypokalemic perfusion (2.5 mM K+ for 30 min) in isolated guinea pig heart preparations. The restitution of AP duration measured at 90% repolarization (APD90) was assessed after premature extrastimulus application at variable coupling stimulation intervals, and ERP restitution was assessed by measuring refractoriness over a wide range of pacing rates. Hypokalemia increased the amplitude of stimulation-evoked repolarization alternans and the inducibility of tachyarrhythmias and reduced ventricular fibrillation threshold. Nevertheless, these changes were associated with flattened rather than steepened APD90 restitution slopes and slowed restitution kinetics. In contrast, ERP restitution slopes were significantly increased in hypokalemic hearts. Although epicardial APD90 measured during steady-state pacing (S1-S1 = 250 ms) was prolonged in hypokalemic hearts, the left ventricular ERP was shortened. Consistently, the epicardial ERP measured at the shortest diastolic interval achieved upon a progressive increase in pacing rate was reduced in the hypokalemic left ventricle. In conclusion, this study highlights the superiority of ERP restitution at predicting increased arrhythmogenicity in the hypokalemic myocardium. The lack of predictive value of APD90 restitution is presumably related to different mode of changes in ventricular repolarization and refractoriness in a hypokalemic setting, whereby APD90 prolongation may be associated with shortened ERP.
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Affiliation(s)
- Oleg E. Osadchii
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
| | - Anders Peter Larsen
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
| | - Soren Peter Olesen
- The Danish National Research Foundation Centre for Cardiac Arrhythmia, Department of Biomedical Sciences, The Panum Institute, University of Copenhagen, Copenhagen, Denmark
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Abstract
The use of stem cells for cardiac regeneration is a revolutionary, emerging research area. For proper function as replacement tissue, stem cell-derived cardiomyocytes (SC-CMs) must electrically couple with the host cardiac tissue. Electrophysiological mapping techniques, including microelectrode array (MEA) and optical mapping, have been developed to study cardiomyocytes and cardiac cell monolayers, and these can be applied to study stem cells and SC-CMs. MEA recordings take extracellular measurements at numerous points across a small area of cell cultures and are used to assess electrical propagation during cell culture. Optical mapping uses fluorescent dyes to monitor electrophysiological changes in cells, most commonly transmembrane potential and intracellular calcium, and can be easily scaled to areas of different sizes. The materials and methods for MEA and optical mapping are presented here, together with detailed notes on their use, design, and fabrication. We also provide examples of voltage and calcium maps of mouse embryonic stem cell-derived cardiomyocytes (mESC-CMs), obtained in our laboratory using optical mapping techniques.
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Affiliation(s)
- Seth Weinberg
- Department of Biomedical Engineering, The Johns Hopkins University, Baltimore, MD, USA
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Romero L, Pueyo E, Fink M, Rodríguez B. Impact of ionic current variability on human ventricular cellular electrophysiology. Am J Physiol Heart Circ Physiol 2009; 297:H1436-45. [PMID: 19648254 DOI: 10.1152/ajpheart.00263.2009] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Abnormalities in repolarization and its rate dependence are known to be related to increased proarrhythmic risk. A number of repolarization-related electrophysiological properties are commonly used as preclinical biomarkers of arrhythmic risk. However, the variability and complexity of repolarization mechanisms make the use of cellular biomarkers to predict arrhythmic risk preclinically challenging. Our goal is to investigate the role of ionic current properties and their variability in modulating cellular biomarkers of arrhythmic risk to improve risk stratification and identification in humans. A systematic investigation into the sensitivity of the main preclinical biomarkers of arrhythmic risk to changes in ionic current conductances and kinetics was performed using computer simulations. Four stimulation protocols were applied to the ten Tusscher and Panfilov human ventricular model to quantify the impact of +/-15 and +/-30% variations in key model parameters on action potential (AP) properties, Ca(2+) and Na(+) dynamics, and their rate dependence. Simulations show that, in humans, AP duration is moderately sensitive to changes in all repolarization current conductances and in L-type Ca(2+) current (I(CaL)) and slow component of the delayed rectifier current (I(Ks)) inactivation kinetics. AP triangulation, however, is strongly dependent only on inward rectifier K(+) current (I(K1)) and delayed rectifier current (I(Kr)) conductances. Furthermore, AP rate dependence (i.e., AP duration rate adaptation and restitution properties) and intracellular Ca(2+) and Na(+) levels are highly sensitive to both I(CaL) and Na(+)/K(+) pump current (I(NaK)) properties. This study provides quantitative insights into the sensitivity of preclinical biomarkers of arrhythmic risk to variations in ionic current properties in humans. The results show the importance of sensitivity analysis as a powerful method for the in-depth validation of mathematical models in cardiac electrophysiology.
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Affiliation(s)
- Lucía Romero
- Instituto de Investigación Interuniversitario en Bioingeniería y Tecnología Orientada al Ser Humano, Universidad Politécnica de Valencia, Valencia, Spain.
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Ng GA, Mantravadi R, Walker WH, Ortin WG, Choi BR, de Groat W, Salama G. Sympathetic nerve stimulation produces spatial heterogeneities of action potential restitution. Heart Rhythm 2009; 6:696-706. [DOI: 10.1016/j.hrthm.2009.01.035] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Accepted: 01/26/2009] [Indexed: 11/28/2022]
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Effect of autonomic blockade on ventricular repolarization shortening: Response to behavioral stimulus in paced dogs. Auton Neurosci 2008; 140:66-71. [PMID: 18499531 DOI: 10.1016/j.autneu.2008.04.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2008] [Revised: 04/07/2008] [Accepted: 04/10/2008] [Indexed: 11/23/2022]
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The impact of varying autonomic states on the dynamic beat-to-beat QT-RR and QT-TQ interval relationships. Br J Pharmacol 2008; 154:1508-15. [PMID: 18663381 DOI: 10.1038/bjp.2008.123] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The beat-to-beat dynamicity of the QT-RR interval relationship is difficult to assess with the use of traditional correction factors (QTc) and changes in QTc do not accurately reflect or quantify arrhythmogenic risk. Further, the interpretation of arrhythmogenic risk is influenced by autonomic state. To visualize the QT-RR interval dynamics under varying conditions of autonomic state from impaired repolarization, we have developed a system to sequentially plot the beat-to-beat confluence of ECG data or 'clouds' obtained from conscious dogs and humans. To represent the non-uniformity of the clouds, a bootstrap sampling method that computes the mathematical centre of the uncorrected beat-to-beat QT value (QTbtb) and defines the upper and lower 95% confidence bounds is used. The same method can also be used to examine heterogeneity, hysteresis (both acceleration and deceleration) and restitution (beat-to-beat QT-TQ interval relationship). Impaired repolarization with the combination of E-4031 and L-768,673 (inhibitor of IKs current) increased heterogeneity of restitution at rest 55-91%; increased hysteresis during heart rate acceleration after isoproterenol challenge by approximately 40-60%; and dramatically diminished the minimum TQ boundary by 72% to only 28 ms. Impaired repolarization alters restitution during normal sinus rhythm and increases hysteresis/heterogeneity during heart rate acceleration following sympathetic stimulation. These findings are supported by similar clinical observations in LQT1 and LQT2 syndromes. Therefore, the assessment of the dynamic QT-RR and QT-TQ interval relationships through quantification of heterogeneity, hysteresis and restitution may allow a more accurate non-invasive evaluation of the conditions leading to cardiac arrhythmia.
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Different Effects of Antiarrhythmic Drugs on the Rate-Dependency of QT Interval: A Study With Amiodarone and Flecainide. J Cardiovasc Pharmacol 2007; 50:535-40. [DOI: 10.1097/fjc.0b013e3181451473] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Scatter in repolarization timing predicts clinical events in post-myocardial infarction patients. Heart Rhythm 2007; 5:208-14. [PMID: 18242541 DOI: 10.1016/j.hrthm.2007.10.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Accepted: 10/01/2007] [Indexed: 11/23/2022]
Abstract
BACKGROUND Increased spatial and temporal dispersion of repolarization contributes to ventricular arrhythmogenesis. Beat-to-beat fluctuations in T-wave timing are thought to represent such dispersion and may predict clinical events. OBJECTIVE The purpose of this study was to assess whether a novel noninvasive measure of beat-to-beat instability in T-wave timing would provide additive prognostic information in post-myocardial infarction patients. METHODS We studied 678 patients from 12 hospitals with 32-lead 5-minute electrocardiogram recordings 6-8 weeks after myocardial infarction. Custom software identified R wave-to-T wave intervals (RTIs) and diastolic intervals (DIs). Repolarization scatter (RTI:DI(StdErr)) was then calculated as the standard error about the RTI:DI regression line. In addition, left ventricular ejection fraction (LVEF), short-term heart rate variability (HRV) parameters, and QT variability index were measured. Patients were followed for the composite endpoint of death or life-threatening ventricular arrhythmia. RESULTS After a mean follow-up of 63 months, 134 patients met the composite endpoint. An RTI:DI(StdErr) >5.50 ms was associated with a 210% increase in arrhythmias or deaths (P <.001). After adjusting for LVEF, RTI:DI(StdErr) remained an independent predictor (P <.001). RTI:DI(StdErr) was also independent of short-term HRV parameters and the QT variability index. CONCLUSIONS Increased repolarization scatter, a measure of high-frequency, cycle-length-dependent repolarization instability, predicts poor outcomes in patients after myocardial infarction.
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Clayton RH, Panfilov AV. A guide to modelling cardiac electrical activity in anatomically detailed ventricles. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2007; 96:19-43. [PMID: 17825362 DOI: 10.1016/j.pbiomolbio.2007.07.004] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
One of the most recent trends in cardiac electrophysiology is the development of integrative anatomically accurate models of the heart, which include description of cardiac activity from sub-cellular and cellular level to the level of the whole organ. In order to construct this type of model, a researcher needs to collect a wide range of information from books and journal articles on various aspects of biology, physiology, electrophysiology, numerical mathematics and computer programming. The aim of this methodological article is to survey recent developments in integrative modelling of electrical activity in the ventricles of the heart, and to provide a practical guide to the resources and tools that are available for work in this exciting and challenging area.
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Affiliation(s)
- R H Clayton
- Department of Computer Science, University of Sheffield, Regent Court, 211 Portobello Street, Sheffield, S1 4DP, UK.
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40
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Abstract
The past 25 years have seen the implantable cardioverter defibrillator emerge as the treatment of choice for ventricular arrhythmias with reduction in size but increased therapeutic options. Understanding the complex mechanisms of ventricular arrhythmias and defibrillation in normal and diseased hearts has been the focus of many research teams including that of John Uther at the Westmead Hospital Department of Cardiology. Marked improvements in capacitor and battery technologies, arrhythmia discrimination, pacing algorithms, shock waveforms and monitoring capabilities enable wider use and patient acceptance. Emergence of cardiac resynchronisation therapy and the implantable defibrillator for treatment of chronic heart failure is not only giving quality of life and extended survival for heart failure patients but has also cast new light on the evolution of heart failure.
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Affiliation(s)
- Loraine K Holley
- Department of Medical and Molecular Biosciences, University of Technology, Sydney, PO Box 123, Broadway, NSW 2007, Australia.
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Pitruzzello AM, Krassowska W, Idriss SF. Spatial heterogeneity of the restitution portrait in rabbit epicardium. Am J Physiol Heart Circ Physiol 2007; 292:H1568-78. [PMID: 17122194 PMCID: PMC2003335 DOI: 10.1152/ajpheart.00619.2006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Spatial heterogeneity of repolarization can provide a substrate for reentry to occur in myocardium. This heterogeneity may result from spatial differences in action potential duration (APD) restitution. The restitution portrait (RP) measures many aspects of rate-dependent restitution: the dynamic restitution curve (RC), S1-S2 RC, and short-term memory response. We used the RP to characterize epicardial patterns of spatial heterogeneity of restitution that were repeatable across animals. New Zealand White rabbit ventricles were paced from the epicardial apex, midventricle, or base, and optical action potentials were recorded from the same three regions. A perturbed downsweep pacing protocol was applied that measured the RP over a range of cycle lengths from 1,000 to 140 ms. The time constant of short-term memory measured close to the stimulus was dependent on location. In the midventricle the mean time constant was 19.1 +/- 1.1 s, but it was 39% longer at the apex (P < 0.01) and 23% longer at the base (P = 0.03). The S1-S2 RC slope was dependent on pacing site (P = 0.015), with steeper slope when pacing from the apex than from the base. There were no significant repeatable spatial patterns in steady-state APD at all cycle lengths or in dynamic RC slope. These results indicate that transient patterns of epicardial heterogeneity of APD may occur after a change in pacing rate. Thus it may affect cardiac electrical stability at the onset of a tachycardia or during a series of ectopic beats. Differences in restitution with respect to pacing site suggest that vulnerability may be affected by the location of reentry or ectopic foci.
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Affiliation(s)
- Ann M Pitruzzello
- Duke University, Dept of Biomedical Engineering, Durham, NC 27708, USA.
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Knollmann BC, Schober T, Petersen AO, Sirenko SG, Franz MR. Action potential characterization in intact mouse heart: steady-state cycle length dependence and electrical restitution. Am J Physiol Heart Circ Physiol 2007; 292:H614-21. [PMID: 16963611 DOI: 10.1152/ajpheart.01085.2005] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transgenic mice have been increasingly utilized to investigate the molecular mechanisms of cardiac arrhythmias, yet the rate dependence of the murine action potential duration and the electrical restitution curve (ERC) remain undefined. In the present study, 21 isolated, Langendorff-perfused, and atrioventricular node-ablated mouse hearts were studied. Left ventricular and left atrial action potentials were recorded using a validated miniaturized monophasic action potential probe. Murine action potentials (AP) were measured at 30, 50, 70, and 90% repolarization (APD30–APD90) during steady-state pacing and varied coupling intervals to determine ERCs. Murine APD showed rate adaptation as well as restitution properties. The ERC time course differed dramatically between early and late repolarization: APD30 shortened with increasing S1–S2 intervals, whereas APD90 was prolonged. When fitted with a monoexponential function, APD30 reached plateau values significantly faster than APD90 (τ = 29 ± 2 vs. 78 ± 6 ms, P < 0.01, n = 12). The slope of early APD90 restitution was significantly <1 (0.16 ± 0.02). Atrial myocardium had shorter final repolarization and significantly faster ERCs that were shifted leftward compared with ventricular myocardium. Recovery kinetics of intracellular Ca2+ transients recorded from isolated ventricular myocytes at 37°C (τ = 93 ± 4 ms, n = 18) resembled the APD90 ERC kinetics. We conclude that mouse myocardium shows AP cycle length dependence and electrical restitution properties that are surprisingly similar to those of larger mammals and humans.
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Affiliation(s)
- Björn C Knollmann
- Oates Institute for Experimental Therapeutics, Vanderbilt Univ. School of Medicine, Division of Clinical Pharmacology, 1265 Medical Research Bldg. IV, Nashville, TN 37232-0575, USA.
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Stambler BS. Tachycardia-induced ventricular electrical remodeling: A perspective on unresolved experimental mechanisms and clinical implications. Heart Rhythm 2006; 3:1378-81. [PMID: 17074649 DOI: 10.1016/j.hrthm.2006.06.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2006] [Indexed: 11/23/2022]
Affiliation(s)
- Bruce S Stambler
- Division of Cardiology, Department of Medicine, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106, USA.
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Abstract
In the first section of this short review the change of the cardiac action potential (APD) with the rate of stimulation under physiological conditions is described and mechanistically analyzed. A fast phase of adaptation is mainly caused by changes in gating characteristics of ionic currents, and rapid modulation of the Na(+)/Ca(2+) exchanger. The slower phase is largely conditioned by incomplete recovery from inactivation of the late Na(+) current (late I(Na)) and changes in ion concentrations of [K(+)](e), [Na(+)](i), and [Ca(2+)](i), which cause secondary changes in the permeation and the gating of ion channels and flux through transporters. In a second section, an analysis is presented of the rate dependence of APD in pathological conditions and its importance in the genesis of arrhythmias in hypertrophy, heart failure, congenital, and acquired LQT syndromes is summarized. The role of the late I(Na), Na(+), and Ca(2+) overload is emphasized. Special attention is given to the paradoxical transient lengthening of APD in LQT3 syndrome for the sudden increase in rate in this setting. The third section consists of a short commentary on Na(+) and Ca(2+) overload and drugs which block the late I(Na).
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SOBIE ERICA, SONG LONGSHENG, LEDERER W. Restitution of Ca(2+) release and vulnerability to arrhythmias. J Cardiovasc Electrophysiol 2006; 17 Suppl 1:S64-S70. [PMID: 16686684 PMCID: PMC1540408 DOI: 10.1111/j.1540-8167.2006.00385.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
New information has recently been obtained along two essentially parallel lines of research: investigations into the fundamental mechanisms of Ca(2+)-induced Ca(2+) release (CICR) in heart cells, and analyses of the factors that control the development of unstable rhythms such as repolarization alternans. These lines of research are starting to converge such that we can begin to understand unstable and potentially arrhythmogenic cardiac dynamics in terms of the underlying mechanisms governing not only membrane depolarization and repolarization but also the complex bidirectional interactions between electrical and Ca(2+) signaling in heart cells. In this brief review, we discuss the progress that has recently been made in understanding the factors that control the beat-to-beat regulation of cardiac Ca(2+) release and attempt to place these results within a larger context. In particular, we discuss factors that may contribute to unstable Ca(2+) release and speculate about how instability in CICR may contribute to the development of arrhythmias under pathological conditions.
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Affiliation(s)
- ERIC A. SOBIE
- From the Division of Pediatric Cardiology, New York University School of Medicine, New York, New York, and
| | - LONG-SHENG SONG
- Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland, USA
| | - W.J. LEDERER
- Medical Biotechnology Center, University of Maryland Biotechnology Institute, Baltimore, Maryland, USA
- Address for correspondence: W.J. Lederer, Ph.D., Medical Biotechnology Center, 725 W. Lombard Street, Baltimore, MD 21201, USA. Fax: (410) 510-1545; E-mail:
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Kimura H, Kawahara K, Yamauchi Y, Miyaki J. On the mechanisms for the conversion of ventricular fibrillation to tachycardia by perfusion with ruthenium red. J Electrocardiol 2005; 38:364-70. [PMID: 16216614 DOI: 10.1016/j.jelectrocard.2005.05.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2004] [Revised: 04/24/2005] [Accepted: 05/09/2005] [Indexed: 11/19/2022]
Abstract
We have recently demonstrated that during pacing-induced sustained ventricular fibrillation (VF), perfusion of the heart with either ruthenium red (RR) or Ru 360, blockers of the mitochondrial Ca2+ uniporter, resulted in the reversible conversion of VF to ventricular tachycardia (VT). Here, we aimed at elucidating the electrophysiological mechanisms for the RR-induced conversion of VF to VT. The experiments were performed using Langendorff-perfused isolated rat hearts in which left ventricular pressure and left ventricular intracellular action potential were recorded. Perfusion with either RR or Ru 360 resulted in decreases in the action potential duration (APD), refractory period, and slope of APD restitution curves. These changes were antagonized by cotreatment with S(-)-Bay K8644. In addition, perfusion with verapamil produced the decreases in APD at 90% repolarization, refractory period and slope of APD restitution curves similar to the RR or Ru 360 perfusion. Such electrophysiological changes may be responsible for the reversible conversion of sustained VF to VT caused by perfusion with RR or Ru 360.
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Affiliation(s)
- Hiroyuki Kimura
- Laboratory of Cellular Cybernetics, Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan
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Kalb SS, Tolkacheva EG, Schaeffer DG, Gauthier DJ, Krassowska W. Restitution in mapping models with an arbitrary amount of memory. CHAOS (WOODBURY, N.Y.) 2005; 15:23701. [PMID: 16035891 DOI: 10.1063/1.1876912] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Restitution, the characteristic shortening of action potential duration (APD) with increased heart rate, has been studied extensively because of its purported link to the onset of fibrillation. Restitution is often represented in the form of mapping models where APD is a function of previous diastolic intervals (DIs) and/or APDs, A(n+1)=F(D(n),A(n),D(n-1),A(n-1),...), where A(n+1) is the APD following a DI given by D(n). The number of variables previous to D(n) determines the degree of memory in the mapping model. Recent experiments have shown that mapping models should contain at least three variables (D(n),A(n),D(n-1)) to reproduce a restitution portrait (RP) that is qualitatively similar to that seen experimentally, where the RP shows three different types of restitution curves (RCs) [dynamic, S1-S2, and constant-basic cycle length (BCL)] simultaneously. However, an interpretation of the different RCs has only been presented in detail for mapping models of one and two variables. Here we present an analysis of the different RCs in the RP for mapping models with an arbitrary amount of memory. We determine the number of variables necessary to represent the different RCs in the RP. We also present a graphical visualization of these RCs. Our analysis reveals that the dynamic and S1-S2 RCs reside on two-dimensional surfaces, and therefore provide limited information for mapping models with more than two variables. However, constant-BCL restitution is a feature of the RP that depends on higher dimensions and can possibly be used to determine a lower bound on the dimensionality of cardiac dynamics.
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Affiliation(s)
- Soma S Kalb
- Department of Biomedical Engineering and Center for Nonlinear and Complex Systems, Duke University, Durham, NC 27708, USA.
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Jordan PN, Christini DJ. Adaptive Diastolic Interval Control of Cardiac Action Potential Duration Alternans. J Cardiovasc Electrophysiol 2004; 15:1177-85. [PMID: 15485444 DOI: 10.1046/j.1540-8167.2004.04098.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
INTRODUCTION Recent experimental and computational studies have shown that beat-to-beat alternation in action potential duration can trigger cardiac reentry, suggesting that such "alternans" is a mechanistic precursor to arrhythmias. Given such a link, termination of alternans may help prevent the onset of arrhythmias. To this end, recent efforts have shown that chaos control methods can modulate the timing of electrical stimulation to eliminate alternans. METHODS AND RESULTS We have developed an alternative control method founded entirely in cardiac electrophysiology (rather than borrowing techniques from the control of physical systems as with existing control techniques). Using computer simulations, we show that this method, which exploits the rate-dependent behavior of cardiac tissue, can be used to control alternans (and higher-order) rhythms, and is robust to drift and noise. When applied to individual model cells exhibiting alternans, the algorithm converges to the period-1 rhythm over as wide, and in some cases a wider, range of feedback proportionality constant values relative to existing methods. Control success comparable to existing methods is achieved when the algorithm is applied to a simulated one-dimensional Purkinje fiber exhibiting alternans. CONCLUSION We have developed a method that adaptively controls the timing of electrical stimulation to rapidly eliminate action potential duration alternans in cardiac tissue. This control method may prove valuable in future arrhythmia prevention therapies.
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Affiliation(s)
- Peter N Jordan
- Department of Physiology and Biophysics, Weill Graduate School of Medical Sciences of Cornell University, New York, New York 10021, USA
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