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Nyman M, Stølen TO, Johnsen AB, Garten K, Burton FL, Smith GL, Loennechen JP. A comprehensive protocol combining in vivo and ex vivo electrophysiological experiments in an arrhythmogenic animal model. Am J Physiol Heart Circ Physiol 2024; 326:H203-H215. [PMID: 37975708 PMCID: PMC11213483 DOI: 10.1152/ajpheart.00358.2023] [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: 06/20/2023] [Revised: 11/08/2023] [Accepted: 11/09/2023] [Indexed: 11/19/2023]
Abstract
Ventricular arrhythmias contribute significantly to cardiovascular mortality, with coronary artery disease as the predominant underlying cause. Understanding the mechanisms of arrhythmogenesis is essential to identify proarrhythmic factors and develop novel approaches for antiarrhythmic prophylaxis and treatment. Animal models are vital in basic research on cardiac arrhythmias, encompassing molecular, cellular, ex vivo whole heart, and in vivo models. Most studies use either in vivo protocols lacking important information on clinical relevance or exclusively ex vivo protocols, thereby missing the opportunity to explore underlying mechanisms. Consequently, interpretation may be difficult due to dissimilarities in animal models, interventions, and individual properties across animals. Moreover, proarrhythmic effects observed in vivo are often not replicated in corresponding ex vivo preparations during mechanistic studies. We have established a protocol to perform both an in vivo and ex vivo electrophysiological characterization in an arrhythmogenic rat model with heart failure following myocardial infarction. The same animal is followed throughout the experiment. In vivo methods involve intracardiac programmed electrical stimulation and external defibrillation to terminate sustained ventricular arrhythmia. Ex vivo methods conducted on the Langendorff-perfused heart include an electrophysiological study with optical mapping of regional action potentials, conduction velocities, and dispersion of electrophysiological properties. By exploring the retention of the in vivo proarrhythmic phenotype ex vivo, we aim to examine whether the subsequent ex vivo detailed measurements are relevant to in vivo pathological behavior. This protocol can enhance greater understanding of cardiac arrhythmias by providing a standardized, yet adaptable model for evaluating arrhythmogenicity or antiarrhythmic interventions in cardiac diseases.NEW & NOTEWORTHY Rodent models are widely used in arrhythmia research. However, most studies do not standardize clinically relevant in vivo and ex vivo techniques to support their conclusions. Here, we present a comprehensive electrophysiological protocol in an arrhythmogenic rat model, connecting in vivo and ex vivo programmed electrical stimulation with optical mapping. By establishing this protocol, we aim to facilitate the adoption of a standardized model for investigating arrhythmias, enhancing research rigor and comparability in this field.
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Affiliation(s)
- Mathias Nyman
- Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
- Clinic of Cardiology, St. Olavs University Hospital, Trondheim, Norway
| | - Tomas O Stølen
- Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
| | - Anne Berit Johnsen
- Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
| | - Karin Garten
- Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
| | - Francis L Burton
- School of Cardiovascular and Metabolic Health, University of Glasgow, Glasgow, United Kingdom
| | - Godfrey L Smith
- School of Cardiovascular and Metabolic Health, University of Glasgow, Glasgow, United Kingdom
| | - Jan Pål Loennechen
- Department of Circulation and Medical Imaging, NTNU, Norwegian University of Science and Technology, Trondheim, Norway
- Clinic of Cardiology, St. Olavs University Hospital, Trondheim, Norway
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2
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Badr A, Hassinen M, Vornanen M. Spatial uniformity of action potentials indicates base-to-apex depolarization and repolarization of rainbow trout (Oncorhynchus mykiss) ventricle. J Exp Biol 2022; 225:276292. [PMID: 35950359 DOI: 10.1242/jeb.244466] [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: 04/26/2022] [Accepted: 08/02/2022] [Indexed: 11/20/2022]
Abstract
The spatial pattern of electrical activation is crucial for a full understanding of fish heart function. However, it remains unclear whether there is regional variation in action potential (AP) morphologies and underlying ion currents. Because the direction of depolarization and spatial differences in the durations of ventricular APs set limits to potential patterns of ventricular repolarization, we determined AP morphologies, underlying ion currents, and ion channel expression in 4 different regions (spongy myocardium; and apex, base, and middle of the compact myocardium), and correlated them with in vivo electrocardiogram (ECG) in rainbow trout (Oncorhynchus mykiss). ECG recorded from 3 leads indicated that the depolarization and repolarization of AP propagate from base-to-apex, and the main depolarization axis of the ventricle is between +90° and +120°. AP shape was uniform across the whole ventricle, and little regional differences were found in density of repolarizing K+ currents or depolarizing Ca2+ and Na+ currents and the underlying transcripts of ion channels, providing compelling evidence for the suggested excitation pattern. The spatial uniformity of AP durations and base-to-apex propagation of activation with a relatively slow velocity of propagation indicates no special ventricular conduction pathway in the trout ventricle like the His-Purkinje system of mammalian hearts. The sequence of repolarization is solely determined by activation time without being affected by regional differences in AP duration.
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Affiliation(s)
- Ahmed Badr
- University of Eastern Finland, Department of Environmental and Biological Sciences, P.O. Box 111, 80101 Joensuu, Finland.,Sohag University, Faculty of Science, Department of Zoology, 82524 Sohag, Egypt
| | - Minna Hassinen
- University of Eastern Finland, Department of Environmental and Biological Sciences, P.O. Box 111, 80101 Joensuu, Finland
| | - Matti Vornanen
- University of Eastern Finland, Department of Environmental and Biological Sciences, P.O. Box 111, 80101 Joensuu, Finland
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3
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Uzelac I, Crowley CJ, Iravanian S, Kim TY, Cho HC, Fenton FH. Methodology for Cross-Talk Elimination in Simultaneous Voltage and Calcium Optical Mapping Measurements With Semasbestic Wavelengths. Front Physiol 2022; 13:812968. [PMID: 35222080 PMCID: PMC8874316 DOI: 10.3389/fphys.2022.812968] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Accepted: 01/03/2022] [Indexed: 02/04/2023] Open
Abstract
Most cardiac arrhythmias at the whole heart level result from alteration of cell membrane ionic channels and intracellular calcium concentration ([Ca2+] i ) cycling with emerging spatiotemporal behavior through tissue-level coupling. For example, dynamically induced spatial dispersion of action potential duration, QT prolongation, and alternans are clinical markers for arrhythmia susceptibility in regular and heart-failure patients that originate due to changes of the transmembrane voltage (V m) and [Ca2+] i . We present an optical-mapping methodology that permits simultaneous measurements of the V m - [Ca2+] i signals using a single-camera without cross-talk, allowing quantitative characterization of favorable/adverse cell and tissue dynamical effects occurring from remodeling and/or drugs in heart failure. We demonstrate theoretically and experimentally in six different species the existence of a family of excitation wavelengths, we termed semasbestic, that give no change in signal for one dye, and thus can be used to record signals from another dye, guaranteeing zero cross-talk.
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Affiliation(s)
- Ilija Uzelac
- School of Physics, Georgia Institute of Technology, Atlanta, GA, United States
| | | | - Shahriar Iravanian
- Division of Cardiology, Section of Electrophysiology, Emory University Hospital, Atlanta, GA, United States
| | - Tae Yun Kim
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, United States
| | - Hee Cheol Cho
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, United States
- Department of Biomedical Engineering, Emory University School of Medicine, Atlanta, GA, United States
- The Sibley Heart Center, Children's Healthcare of Atlanta, Atlanta, GA, United States
| | - Flavio H. Fenton
- School of Physics, Georgia Institute of Technology, Atlanta, GA, United States
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4
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Müllenbroich MC, Kelly A, Acker C, Bub G, Bruegmann T, Di Bona A, Entcheva E, Ferrantini C, Kohl P, Lehnart SE, Mongillo M, Parmeggiani C, Richter C, Sasse P, Zaglia T, Sacconi L, Smith GL. Novel Optics-Based Approaches for Cardiac Electrophysiology: A Review. Front Physiol 2021; 12:769586. [PMID: 34867476 PMCID: PMC8637189 DOI: 10.3389/fphys.2021.769586] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 10/18/2021] [Indexed: 12/31/2022] Open
Abstract
Optical techniques for recording and manipulating cellular electrophysiology have advanced rapidly in just a few decades. These developments allow for the analysis of cardiac cellular dynamics at multiple scales while largely overcoming the drawbacks associated with the use of electrodes. The recent advent of optogenetics opens up new possibilities for regional and tissue-level electrophysiological control and hold promise for future novel clinical applications. This article, which emerged from the international NOTICE workshop in 2018, reviews the state-of-the-art optical techniques used for cardiac electrophysiological research and the underlying biophysics. The design and performance of optical reporters and optogenetic actuators are reviewed along with limitations of current probes. The physics of light interaction with cardiac tissue is detailed and associated challenges with the use of optical sensors and actuators are presented. Case studies include the use of fluorescence recovery after photobleaching and super-resolution microscopy to explore the micro-structure of cardiac cells and a review of two photon and light sheet technologies applied to cardiac tissue. The emergence of cardiac optogenetics is reviewed and the current work exploring the potential clinical use of optogenetics is also described. Approaches which combine optogenetic manipulation and optical voltage measurement are discussed, in terms of platforms that allow real-time manipulation of whole heart electrophysiology in open and closed-loop systems to study optimal ways to terminate spiral arrhythmias. The design and operation of optics-based approaches that allow high-throughput cardiac electrophysiological assays is presented. Finally, emerging techniques of photo-acoustic imaging and stress sensors are described along with strategies for future development and establishment of these techniques in mainstream electrophysiological research.
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Affiliation(s)
| | - Allen Kelly
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Corey Acker
- Center for Cell Analysis and Modeling, UConn Health, Farmington, CT, United States
| | - Gil Bub
- Department of Physiology, McGill University, Montréal, QC, Canada
| | - Tobias Bruegmann
- Institute for Cardiovascular Physiology, University Medical Center Goettingen, Goettingen, Germany
| | - Anna Di Bona
- Department of Cardiac, Thoracic, Vascular Sciences and Public Health, University of Padova, Padova, Italy
| | - Emilia Entcheva
- Department of Biomedical Engineering, The George Washington University, Washington, DC, United States
| | | | - Peter Kohl
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany
| | - Stephan E. Lehnart
- Heart Research Center Göttingen, University Medical Center Göttingen, Göttingen, Germany
- Department of Cardiology and Pneumology, Georg-August University Göttingen, Göttingen, Germany
- Cluster of Excellence “Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells” (MBExC), University of Göttingen, Göttingen, Germany
| | - Marco Mongillo
- Department of Biomedical Sciences, University of Padova, Padova, Italy
- Veneto Institute of Molecular Medicine, Padova, Italy
| | | | - Claudia Richter
- German Primate Center - Leibniz Institute for Primate Research, Göttingen, Germany
| | - Philipp Sasse
- Institute of Physiology I, Medical Faculty, University of Bonn, Bonn, Germany
| | - Tania Zaglia
- Department of Biomedical Sciences, University of Padova, Padova, Italy
- Veneto Institute of Molecular Medicine, Padova, Italy
| | - Leonardo Sacconi
- European Laboratory for Nonlinear Spectroscopy, Sesto Fiorentino, Italy
- Institute for Experimental Cardiovascular Medicine, University Heart Center and Medical Faculty, University of Freiburg, Freiburg, Germany
- National Institute of Optics, National Research Council, Florence, Italy
| | - Godfrey L. Smith
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
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Jabbour RJ, Owen TJ, Pandey P, Reinsch M, Wang B, King O, Couch LS, Pantou D, Pitcher DS, Chowdhury RA, Pitoulis FG, Handa BS, Kit-Anan W, Perbellini F, Myles RC, Stuckey DJ, Dunne M, Shanmuganathan M, Peters NS, Ng FS, Weinberger F, Terracciano CM, Smith GL, Eschenhagen T, Harding SE. In vivo grafting of large engineered heart tissue patches for cardiac repair. JCI Insight 2021; 6:e144068. [PMID: 34369384 PMCID: PMC8410032 DOI: 10.1172/jci.insight.144068] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Accepted: 06/23/2021] [Indexed: 11/20/2022] Open
Abstract
Engineered heart tissue (EHT) strategies, by combining cells within a hydrogel matrix, may be a novel therapy for heart failure. EHTs restore cardiac function in rodent injury models, but more data are needed in clinically relevant settings. Accordingly, an upscaled EHT patch (2.5 cm × 1.5 cm × 1.5 mm) consisting of up to 20 million human induced pluripotent stem cell–derived cardiomyocytes (hPSC-CMs) embedded in a fibrin-based hydrogel was developed. A rabbit myocardial infarction model was then established to test for feasibility and efficacy. Our data showed that hPSC-CMs in EHTs became more aligned over 28 days and had improved contraction kinetics and faster calcium transients. Blinded echocardiographic analysis revealed a significant improvement in function in infarcted hearts that received EHTs, along with reduction in infarct scar size by 35%. Vascularization from the host to the patch was observed at week 1 and stable to week 4, but electrical coupling between patch and host heart was not observed. In vivo telemetry recordings and ex vivo arrhythmia provocation protocols showed that the patch was not pro-arrhythmic. In summary, EHTs improved function and reduced scar size without causing arrhythmia, which may be due to the lack of electrical coupling between patch and host heart.
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Affiliation(s)
- Richard J Jabbour
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Thomas J Owen
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Pragati Pandey
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Marina Reinsch
- Department of Cardiovascular Science, Hamburg University, Hamburg, Germany
| | - Brian Wang
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Oisín King
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Liam Steven Couch
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Dafni Pantou
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - David S Pitcher
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Rasheda A Chowdhury
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Fotios G Pitoulis
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Balvinder S Handa
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Worrapong Kit-Anan
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Filippo Perbellini
- Institute of Molecular and Translational Therapeutic Strategies, Hannover Medical School, Hannover, Germany
| | - Rachel C Myles
- Department of Cardiovascular Science, University of Glasgow, Glasgow, Scotland, United Kingdom
| | - Daniel J Stuckey
- Centre for Advanced Biomedical Imaging, University College London, London, United Kingdom
| | - Michael Dunne
- Department of Cardiovascular Science, University of Glasgow, Glasgow, Scotland, United Kingdom
| | | | - Nicholas S Peters
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Fu Siong Ng
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Florian Weinberger
- Department of Cardiovascular Science, Hamburg University, Hamburg, Germany
| | - Cesare M Terracciano
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
| | - Godfrey L Smith
- Department of Cardiovascular Science, University of Glasgow, Glasgow, Scotland, United Kingdom
| | - Thomas Eschenhagen
- Department of Cardiovascular Science, Hamburg University, Hamburg, Germany
| | - Sian E Harding
- National Heart & Lung Institute, Imperial College London, London, United Kingdom
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6
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Marcotte CD, Fenton FH, Hoffman MJ, Cherry EM. Robust data assimilation with noise: Applications to cardiac dynamics. CHAOS (WOODBURY, N.Y.) 2021; 31:013118. [PMID: 33754752 PMCID: PMC7796825 DOI: 10.1063/5.0033539] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 12/17/2020] [Indexed: 05/05/2023]
Abstract
Reconstructions of excitation patterns in cardiac tissue must contend with uncertainties due to model error, observation error, and hidden state variables. The accuracy of these state reconstructions may be improved by efforts to account for each of these sources of uncertainty, in particular, through the incorporation of uncertainty in model specification and model dynamics. To this end, we introduce stochastic modeling methods in the context of ensemble-based data assimilation and state reconstruction for cardiac dynamics in one- and three-dimensional cardiac systems. We propose two classes of methods, one following the canonical stochastic differential equation formalism, and another perturbing the ensemble evolution in the parameter space of the model, which are further characterized according to the details of the models used in the ensemble. The stochastic methods are applied to a simple model of cardiac dynamics with fast-slow time-scale separation, which permits tuning the form of effective stochastic assimilation schemes based on a similar separation of dynamical time scales. We find that the selection of slow or fast time scales in the formulation of stochastic forcing terms can be understood analogously to existing ensemble inflation techniques for accounting for finite-size effects in ensemble Kalman filter methods; however, like existing inflation methods, care must be taken in choosing relevant parameters to avoid over-driving the data assimilation process. In particular, we find that a combination of stochastic processes-analogously to the combination of additive and multiplicative inflation methods-yields improvements to the assimilation error and ensemble spread over these classical methods.
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Affiliation(s)
- Christopher D. Marcotte
- School of Computational Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - Flavio H. Fenton
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
| | - Matthew J. Hoffman
- School of Mathematical Sciences, Rochester Institute of Technology, Rochester, New York 14623, USA
| | - Elizabeth M. Cherry
- School of Computational Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
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Hazim A, Belhamadia Y, Dubljevic S. A Simulation Study of the Role of Mechanical Stretch in Arrhythmogenesis during Cardiac Alternans. Biophys J 2020; 120:109-121. [PMID: 33248131 PMCID: PMC7820729 DOI: 10.1016/j.bpj.2020.11.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 11/03/2020] [Accepted: 11/13/2020] [Indexed: 12/20/2022] Open
Abstract
The deformation of the heart tissue due to the contraction can modulate the excitation, a phenomenon referred to as mechanoelectrical feedback (MEF), via stretch-activated channels. The effects of MEF on the electrophysiology at high pacing rates are shown to be proarrhythmic in general. However, more studies need to be done to elucidate the underlying mechanism. In this work, we investigate the effects of MEF on cardiac alternans, which is an alternation in the width of the action potential that typically occurs when the heart is paced at high rates, using a biophysically detailed electromechanical model of cardiac tissue. We observe that the transition from spatially concordant alternans to spatially discordant alternans, which is more arrhythmogenic than concordant alternans, may occur in the presence of MEF and when its strength is sufficiently large. We show that this transition is due to the increase of the dispersion of conduction velocity. In addition, our results also show that the MEF effects, depending on the stretch-activated channels’ conductances and reversal potentials, can result in blocking action potential propagation.
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Affiliation(s)
- Azzam Hazim
- Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Youssef Belhamadia
- Department of Mathematics and Statistics, American University of Sharjah, Sharjah, United Arab Emirates
| | - Stevan Dubljevic
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada.
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Two-photon excitation of FluoVolt allows improved interrogation of transmural electrophysiological function in the intact mouse heart. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2019; 154:11-20. [PMID: 31492464 PMCID: PMC7322535 DOI: 10.1016/j.pbiomolbio.2019.08.007] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 07/17/2019] [Accepted: 08/15/2019] [Indexed: 11/21/2022]
Abstract
BACKGROUND & AIMS Two-photon excitation of voltage sensitive dyes (VSDs) can measure rapidly changing electrophysiological signals deep within intact cardiac tissue with improved three-dimensional resolution along with reduced photobleaching and photo-toxicity compared to conventional confocal microscopy. Recently, a category of VSDs has emerged which records membrane potentials by photo-induced electron transfer. FluoVolt is a novel VSD in this category which promises fast response and a 25% fractional change in fluorescence per 100 mV, making it an attractive optical probe for action potential (AP) recordings within intact cardiac tissue. The purpose of this study was to characterize the fluorescent properties of FluoVolt as well as its utility for deep tissue imaging. METHODS Discrete tissue layers throughout the left ventricular wall of isolated perfused murine hearts loaded with FluoVolt or di-4-ANEPPS were sequentially excited with two-photon microscopy. RESULTS FluoVolt loaded hearts suffered significantly fewer episodes of atrio-ventricular block compared to di-4-ANEPPS loaded hearts, indicating comparatively low toxicity of FluoVolt in the intact heart. APs recorded with FluoVolt were characterized by a lower signal-to-noise ratio and a higher dynamic range compared to APs recorded with di-4-ANEPPS. Although both depolarization and repolarization parameters were similar in APs recorded with either dye, FluoVolt allowed deeper tissue excitation with improved three-dimensional resolution due to reduced out-of-focus fluorescence generation under two-photon excitation. CONCLUSION Our results demonstrate several advantages of two-photon excitation of FluoVolt in functional studies in intact heart preparations, including reduced toxicity and improved fluorescent properties.
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Kelly A, Salerno S, Connolly A, Bishop M, Charpentier F, Stølen T, Smith GL. Normal interventricular differences in tissue architecture underlie right ventricular susceptibility to conduction abnormalities in a mouse model of Brugada syndrome. Cardiovasc Res 2019; 114:724-736. [PMID: 29267949 PMCID: PMC5915948 DOI: 10.1093/cvr/cvx244] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Accepted: 12/16/2017] [Indexed: 01/09/2023] Open
Abstract
Aims Loss-of-function of the cardiac sodium channel NaV1.5 is a common feature of Brugada syndrome. Arrhythmias arise preferentially from the right ventricle (RV) despite equivalent NaV1.5 downregulation in the left ventricle (LV). The reasons for increased RV sensitivity to NaV1.5 loss-of-function mutations remain unclear. Because ventricular electrical activation occurs predominantly in the transmural axis, we compare RV and LV transmural electrophysiology to determine the underlying cause of the asymmetrical conduction abnormalities in Scn5a haploinsufficient mice (Scn5a+/−). Methods and results Optical mapping and two-photon microscopy in isolated-perfused mouse hearts demonstrated equivalent depression of transmural conduction velocity (CV) in the LV and RV of Scn5a+/− vs. wild-type littermates. Only RV transmural conduction was further impaired when challenged with increased pacing frequencies. Epicardial dispersion of activation and beat-to-beat variation in activation time were increased only in the RV of Scn5a+/− hearts. Analysis of confocal and histological images revealed larger intramural clefts between cardiomyocyte layers in the RV vs. LV, independent of genotype. Acute sodium current inhibition in wild type hearts using tetrodotoxin reproduced beat-to-beat activation variability and frequency-dependent CV slowing in the RV only, with the LV unaffected. The influence of clefts on conduction was examined using a two-dimensional monodomain computational model. When peak sodium channel conductance was reduced to 50% of normal the presence of clefts between cardiomyocyte layers reproduced the activation variability and conduction phenotype observed experimentally. Conclusions Normal structural heterogeneities present in the RV are responsible for increased vulnerability to conduction slowing in the presence of reduced sodium channel function. Heterogeneous conduction slowing seen in the RV will predispose to functional block and the initiation of re-entrant ventricular arrhythmias.
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Affiliation(s)
- Allen Kelly
- Department of Circulation and Medical Imaging, St Olav's Hospital, Norwegian University of Science and Technology (NTNU), Postboks 8905, 7491 Trondheim, Norway.,Institute of Cardiovascular & Medical Sciences, University of Glasgow G12 8QQ, UK
| | - Simona Salerno
- Department of Circulation and Medical Imaging, St Olav's Hospital, Norwegian University of Science and Technology (NTNU), Postboks 8905, 7491 Trondheim, Norway
| | - Adam Connolly
- Division of Imaging Sciences and Biomedical Engineering, Department of Biomedical Engineering, Kings College London SE1 7EH, UK
| | - Martin Bishop
- Division of Imaging Sciences and Biomedical Engineering, Department of Biomedical Engineering, Kings College London SE1 7EH, UK
| | | | - Tomas Stølen
- Department of Circulation and Medical Imaging, St Olav's Hospital, Norwegian University of Science and Technology (NTNU), Postboks 8905, 7491 Trondheim, Norway
| | - Godfrey L Smith
- Department of Circulation and Medical Imaging, St Olav's Hospital, Norwegian University of Science and Technology (NTNU), Postboks 8905, 7491 Trondheim, Norway.,Institute of Cardiovascular & Medical Sciences, University of Glasgow G12 8QQ, UK
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10
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Connolly A, Kelly A, Campos FO, Myles R, Smith G, Bishop MJ. Ventricular Endocardial Tissue Geometry Affects Stimulus Threshold and Effective Refractory Period. Biophys J 2018; 115:2486-2498. [PMID: 30503533 PMCID: PMC6301915 DOI: 10.1016/j.bpj.2018.11.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 10/15/2018] [Accepted: 11/05/2018] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND Understanding the biophysical processes by which electrical stimuli applied to cardiac tissue may result in local activation is important in both the experimental and clinical electrophysiology laboratory environments, as well as for gaining a more in-depth knowledge of the mechanisms of focal-trigger-induced arrhythmias. Previous computational models have predicted that local myocardial tissue architecture alone may significantly modulate tissue excitability, affecting both the local stimulus current required to excite the tissue and the local effective refractory period (ERP). In this work, we present experimental validation of this structural modulation of local tissue excitability on the endocardial tissue surface, use computational models to provide mechanistic understanding of this phenomena in relation to localized changes in electrotonic loading, and demonstrate its implications for the capture of afterdepolarizations. METHODS AND RESULTS Experiments on rabbit ventricular wedge preparations showed that endocardial ridges (surfaces of negative mean curvature) had a stimulus capture threshold that was 0.21 ± 0.03 V less than endocardial grooves (surfaces of positive mean curvature) for pairwise comparison (24% reduction, corresponding to 56.2 ± 6.4% of the energy). When stimulated at the minimal stimulus strength for capture, ridge locations showed a shorter ERP than grooves (n = 6, mean pairwise difference 7.4 ± 4.2 ms). When each site was stimulated with identical-strength stimuli, the difference in ERP was further increased (mean pairwise difference 15.8 ± 5.3 ms). Computational bidomain models of highly idealized cylindrical endocardial structures qualitatively agreed with these findings, showing that such changes in excitability are driven by structural modulation in electrotonic loading, quantifying this relationship as a function of surface curvature. Simulations further showed that capture of delayed afterdepolarizations was more likely in trabecular ridges than grooves, driven by this difference in loading. CONCLUSIONS We have demonstrated experimentally and explained mechanistically in computer simulations that the ability to capture tissue on the endocardial surface depends upon the local tissue architecture. These findings have important implications for deepening our understanding of excitability differences related to anatomical structure during stimulus application that may have important applications in the translation of novel experimental optogenetics pacing strategies. The uncovered preferential vulnerability to capture of afterdepolarizations of endocardial ridges, compared to grooves, provides important insight for understanding the mechanisms of focal-trigger-induced arrhythmias.
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Affiliation(s)
- Adam Connolly
- Department of Bioengineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Allen Kelly
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Fernando O Campos
- Department of Bioengineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Rachel Myles
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Godfrey Smith
- Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Martin J Bishop
- Department of Bioengineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.
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11
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Wang W, Zhang S, Ni H, Garratt CJ, Boyett MR, Hancox JC, Zhang H. Mechanistic insight into spontaneous transition from cellular alternans to arrhythmia-A simulation study. PLoS Comput Biol 2018; 14:e1006594. [PMID: 30500818 PMCID: PMC6291170 DOI: 10.1371/journal.pcbi.1006594] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Revised: 12/12/2018] [Accepted: 10/23/2018] [Indexed: 02/01/2023] Open
Abstract
Cardiac electrical alternans (CEA), manifested as T-wave alternans in ECG, is a clinical biomarker for predicting cardiac arrhythmias and sudden death. However, the mechanism underlying the spontaneous transition from CEA to arrhythmias remains incompletely elucidated. In this study, multiscale rabbit ventricular models were used to study the transition and a potential role of INa in perpetuating such a transition. It was shown CEA evolved into either concordant or discordant action potential (AP) conduction alternans in a homogeneous one-dimensional tissue model, depending on tissue AP duration and conduction velocity (CV) restitution properties. Discordant alternans was able to cause conduction failure in the model, which was promoted by impaired sodium channel with either a reduced or increased channel current. In a two-dimensional homogeneous tissue model, a combined effect of rate- and curvature-dependent CV broke-up alternating wavefronts at localised points, facilitating a spontaneous transition from CEA to re-entry. Tissue inhomogeneity or anisotropy further promoted break-up of re-entry, leading to multiple wavelets. Similar observations have also been seen in human atrial cellular and tissue models. In conclusion, our results identify a mechanism by which CEA spontaneously evolves into re-entry without a requirement for premature ventricular complexes or pre-existing tissue heterogeneities, and demonstrated the important pro-arrhythmic role of impaired sodium channel activity. These findings are model-independent and have potential human relevance.
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Affiliation(s)
- Wei Wang
- Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Shanzhuo Zhang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Haibo Ni
- Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Clifford J. Garratt
- Manchester Heart Centre, Manchester Royal Infirmary, Manchester, United Kingdom
| | - Mark R. Boyett
- Manchester Heart Centre, Manchester Royal Infirmary, Manchester, United Kingdom
| | - Jules C. Hancox
- Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom
- School of Physiology, Pharmacology and Neuroscience, and Cardiovascular Research Laboratories, School of Medical Sciences, University of Bristol, Bristol, United Kingdom
| | - Henggui Zhang
- Biological Physics Group, School of Physics & Astronomy, The University of Manchester, Manchester, United Kingdom
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
- Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, Sichuan, China
- Space Institute of Southern China, Shenzhen, China
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12
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Ghouri IA, Kelly A, Salerno S, Garten K, Stølen T, Kemi1 OJ, Smith GL. Characterization of Electrical Activity in Post-myocardial Infarction Scar Tissue in Rat Hearts Using Multiphoton Microscopy. Front Physiol 2018; 9:1454. [PMID: 30386255 PMCID: PMC6199960 DOI: 10.3389/fphys.2018.01454] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Accepted: 09/25/2018] [Indexed: 11/13/2022] Open
Abstract
Background: The origin of electrical behavior in post-myocardial infarction scar tissue is still under debate. This study aims to examine the extent and nature of the residual electrical activity within a stabilized ventricular infarct scar. Methods and Results: An apical infarct was induced in the left ventricle of Wistar rats by coronary artery occlusion. Five weeks post-procedure, hearts were Langendorff-perfused, and optically mapped using di-4-ANEPPS. Widefield imaging of optical action potentials (APs) on the left ventricular epicardial surface revealed uniform areas of electrical activity in both normal zone (NZ) and infarct border zone (BZ), but only limited areas of low-amplitude signals in the infarct zone (IZ). 2-photon (2P) excitation of di-4-ANEPPS and Fura-2/AM at discrete layers in the NZ revealed APs and Ca2+ transients (CaTs) to 500-600 μm below the epicardial surface. 2P imaging in the BZ revealed superficial connective tissue structures lacking APs or CaTs. At depths greater than approximately 300 μm, myocardial structures were evident that supported normal APs and CaTs. In the IZ, although 2P imaging did not reveal clear myocardial structures, low-amplitude AP signals were recorded at discrete layers. No discernible Ca2+ signals could be detected in the IZ. AP rise times in BZ were slower than NZ (3.50 ± 0.50 ms vs. 2.23 ± 0.28 ms) and further slowed in IZ (9.13 ± 0.56 ms). Widefield measurements of activation delay between NZ and BZ showed negligible difference (3.37 ± 1.55 ms), while delay values in IZ showed large variation (11.88 ± 9.43 ms). Conclusion: These AP measurements indicate that BZ consists of an electrically inert scar above relatively normal myocardium. Discrete areas/layers of IZ displayed entrained APs with altered electrophysiology, but the structure of this tissue remains to be elucidated.
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Affiliation(s)
- Iffath A. Ghouri
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Allen Kelly
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Simona Salerno
- Department of Circulation and Medical Imaging, St. Olav’s Hospital, Norwegian University of Science and Technology, Trondheim, Norway
| | - Karin Garten
- Department of Circulation and Medical Imaging, St. Olav’s Hospital, Norwegian University of Science and Technology, Trondheim, Norway
| | - Tomas Stølen
- Department of Circulation and Medical Imaging, St. Olav’s Hospital, Norwegian University of Science and Technology, Trondheim, Norway
| | - Ole-Johan Kemi1
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, United Kingdom
| | - Godfrey L. Smith
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, United Kingdom,*Correspondence: Godfrey L. Smith,
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13
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Lipovsky CE, Brumback BD, Khandekar A, Rentschler SL. Multi-Scale Assessments of Cardiac Electrophysiology Reveal Regional Heterogeneity in Health and Disease. J Cardiovasc Dev Dis 2018; 5:E16. [PMID: 29517992 PMCID: PMC5872364 DOI: 10.3390/jcdd5010016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 02/27/2018] [Accepted: 03/05/2018] [Indexed: 12/19/2022] Open
Abstract
The left and right ventricles of the four-chambered heart have distinct developmental origins and functions. Chamber-specific developmental programming underlies the differential gene expression of ion channel subunits regulating cardiac electrophysiology that persists into adulthood. Here, we discuss regional specific electrical responses to genetic mutations and cardiac stressors, their clinical correlations, and describe many of the multi-scale techniques commonly used to analyze electrophysiological regional heterogeneity.
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Affiliation(s)
- Catherine E Lipovsky
- Department of Medicine, Cardiovascular Division, Washington University School of Medicine, Campus Box 8103, 660 S Euclid Ave, St. Louis, MO 63110, USA.
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA.
| | - Brittany D Brumback
- Department of Medicine, Cardiovascular Division, Washington University School of Medicine, Campus Box 8103, 660 S Euclid Ave, St. Louis, MO 63110, USA.
- Department of Biomedical Engineering, Washington University, St. Louis, MO 63130, USA.
| | - Aditi Khandekar
- Department of Medicine, Cardiovascular Division, Washington University School of Medicine, Campus Box 8103, 660 S Euclid Ave, St. Louis, MO 63110, USA.
| | - Stacey L Rentschler
- Department of Medicine, Cardiovascular Division, Washington University School of Medicine, Campus Box 8103, 660 S Euclid Ave, St. Louis, MO 63110, USA.
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA.
- Department of Biomedical Engineering, Washington University, St. Louis, MO 63130, USA.
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14
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Weinberger F, Breckwoldt K, Pecha S, Kelly A, Geertz B, Starbatty J, Yorgan T, Cheng KH, Lessmann K, Stolen T, Scherrer-Crosbie M, Smith G, Reichenspurner H, Hansen A, Eschenhagen T. Cardiac repair in guinea pigs with human engineered heart tissue from induced pluripotent stem cells. Sci Transl Med 2017; 8:363ra148. [PMID: 27807283 DOI: 10.1126/scitranslmed.aaf8781] [Citation(s) in RCA: 175] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 09/19/2016] [Indexed: 12/16/2022]
Abstract
Myocardial injury results in a loss of contractile tissue mass that, in the absence of efficient regeneration, is essentially irreversible. Transplantation of human pluripotent stem cell-derived cardiomyocytes has beneficial but variable effects. We created human engineered heart tissue (hEHT) strips from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and hiPSC-derived endothelial cells. The hEHTs were transplanted onto large defects (22% of the left ventricular wall, 35% decline in left ventricular function) of guinea pig hearts 7 days after cryoinjury, and the results were compared with those obtained with human endothelial cell patches (hEETs) or cell-free patches. Twenty-eight days after transplantation, the hearts repaired with hEHT strips exhibited, within the scar, human heart muscle grafts, which had remuscularized 12% of the infarct area. These grafts showed cardiomyocyte proliferation, vascularization, and evidence for electrical coupling to the intact heart tissue in a subset of engrafted hearts. hEHT strips improved left ventricular function by 31% compared to that before implantation, whereas the hEET or cell-free patches had no effect. Together, our study demonstrates that three-dimensional human heart muscle constructs can repair the injured heart.
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Affiliation(s)
- Florian Weinberger
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
| | - Kaja Breckwoldt
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
| | - Simon Pecha
- German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany.,Department of Cardiovascular Surgery, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Allen Kelly
- K.G. Jebsen Center of Exercise in Medicine, Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, 7030 Trondheim, Norway.,Norwegian Council on Cardiovascular Disease, Oslo, Norway
| | - Birgit Geertz
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
| | - Jutta Starbatty
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
| | - Timur Yorgan
- Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Kai-Hung Cheng
- Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Boston, MA 02114, USA
| | - Katrin Lessmann
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
| | - Tomas Stolen
- K.G. Jebsen Center of Exercise in Medicine, Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, 7030 Trondheim, Norway.,Norwegian Council on Cardiovascular Disease, Oslo, Norway
| | | | - Godfrey Smith
- K.G. Jebsen Center of Exercise in Medicine, Department of Circulation and Medical Imaging, Norwegian University of Science and Technology, 7030 Trondheim, Norway.,Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK
| | - Hermann Reichenspurner
- German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany.,Department of Cardiovascular Surgery, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany
| | - Arne Hansen
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
| | - Thomas Eschenhagen
- Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany. .,German Centre for Cardiovascular Research (DZHK), partner site Hamburg/Kiel/Lübeck, Germany
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15
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Cheng H, Cannell MB, Hancox JC. Differential responses of rabbit ventricular and atrial transient outward current (I to) to the I to modulator NS5806. Physiol Rep 2017; 5:5/5/e13172. [PMID: 28270595 PMCID: PMC5350179 DOI: 10.14814/phy2.13172] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 01/26/2017] [Accepted: 01/27/2017] [Indexed: 02/06/2023] Open
Abstract
Transient outward potassium current (Ito) in the heart underlies phase 1 repolarization of cardiac action potentials and thereby affects excitation–contraction coupling. Small molecule activators of Ito may therefore offer novel treatments for cardiac dysfunction, including heart failure and atrial fibrillation. NS5806 has been identified as a prototypic activator of canine Ito. This study investigated, for the first time, actions of NS5806 on rabbit atrial and ventricular Ito. Whole cell patch‐clamp recordings of Ito and action potentials were made at physiological temperature from rabbit ventricular and atrial myocytes. 10 μmol/L NS5806 increased ventricular Ito with a leftward shift in Ito activation and accelerated restitution. At higher concentrations, stimulation of Ito was followed by inhibition. The EC50 for stimulation was 1.6 μmol/L and inhibition had an IC50 of 40.7 μmol/L. NS5806 only inhibited atrial Ito (IC50 of 18 μmol/L) and produced a modest leftward shifts in Ito activation and inactivation, without an effect on restitution. 10 μmol/L NS5806 shortened ventricular action potential duration (APD) at APD20‐APD90 but prolonged atrial APD. NS5806 also reduced atrial AP upstroke and amplitude, consistent with an additional atrio‐selective effect on Na+ channels. In contrast to NS5806, flecainide, which discriminates between Kv1.4 and 4.x channels, produced similar levels of inhibition of ventricular and atrial Ito. NS5806 discriminates between rabbit ventricular and atrial Ito, with mixed activator and inhibitor actions on the former and inhibitor actions against the later. NS5806 may be of significant value for pharmacological interrogation of regional differences in native cardiac Ito.
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Affiliation(s)
- Hongwei Cheng
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, U.K
| | - Mark B Cannell
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, U.K
| | - Jules C Hancox
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, U.K
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16
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Trenor B, Cardona K, Saiz J, Noble D, Giles W. Cardiac action potential repolarization revisited: early repolarization shows all-or-none behaviour. J Physiol 2017; 595:6599-6612. [PMID: 28815597 PMCID: PMC5663823 DOI: 10.1113/jp273651] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 08/09/2017] [Indexed: 12/15/2022] Open
Abstract
In healthy mammalian hearts the action potential (AP) waveform initiates and modulates each contraction, or heartbeat. As a result, AP height and duration are key physiological variables. In addition, rate-dependent changes in ventricular AP duration (APD), and variations in APD at a fixed heart rate are both reliable biomarkers of electrophysiological stability. Present guidelines for the likelihood that candidate drugs will increase arrhythmias rely on small changes in APD and Q-T intervals as criteria for safety pharmacology decisions. However, both of these measurements correspond to the final repolarization of the AP. Emerging clinical evidence draws attention to the early repolarization phase of the action potential (and the J-wave of the ECG) as an additional important biomarker for arrhythmogenesis. Here we provide a mechanistic background to this early repolarization syndrome by summarizing the evidence that both the initial depolarization and repolarization phases of the cardiac action potential can exhibit distinct time- and voltage-dependent thresholds, and also demonstrating that both can show regenerative all-or-none behaviour. An important consequence of this is that not all of the dynamics of action potential repolarization in human ventricle can be captured by data from single myocytes when these results are expressed as 'repolarization reserve'. For example, the complex pattern of cell-to-cell current flow that is responsible for AP conduction (propagation) within the mammalian myocardium can change APD and the Q-T interval of the electrocardiogram alter APD stability, and modulate responsiveness to pharmacological agents (such as Class III anti-arrhythmic drugs).
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Affiliation(s)
- Beatriz Trenor
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Karen Cardona
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Javier Saiz
- Centro de Investigación e BioingenieríaUniversitat Politècnica de ValènciaValenciaSpain
| | - Denis Noble
- University Laboratory of PhysiologyUniversity of OxfordOxfordOX1 3PTUK
| | - Wayne Giles
- Faculties of Kinesiology and MedicineUniversity of CalgaryCalgaryAlbertaCanadaT2N 1N4
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17
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Connolly AJ, Vigmond E, Bishop MJ. Bidomain Predictions of Virtual Electrode-Induced Make and Break Excitations around Blood Vessels. Front Bioeng Biotechnol 2017; 5:18. [PMID: 28396856 PMCID: PMC5366349 DOI: 10.3389/fbioe.2017.00018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 03/02/2017] [Indexed: 11/16/2022] Open
Abstract
Introduction and background Virtual electrodes formed by field stimulation during defibrillation of cardiac tissue play an important role in eliciting activations. It has been suggested that the coronary vasculature is an important source of virtual electrodes, especially during low-energy defibrillation. This work aims to further the understanding of how virtual electrodes from the coronary vasculature influence defibrillation outcomes. Methods Using the bidomain model, we investigated how field stimulation elicited activations from virtual electrodes around idealized intramural blood vessels. Strength–interval curves, which quantify the stimulus strength required to elicit wavefront propagation from the vessels at different states of tissue refractoriness, were computed for each idealized geometry. Results Make excitations occurred at late diastolic intervals, originating from regions of depolarization around the vessel. Break excitations occurred at early diastolic intervals, whereby the vessels were able to excite surrounding refractory tissue due to the local restoration of excitability by virtual electrode-induced hyperpolarizations. Overall, strength–interval curves had similar morphologies and underlying excitation mechanisms compared with previous experimental and numerical unipolar stimulation studies of cardiac tissue. Including the presence of the vessel wall increased the field strength required for make excitations but decreased the field strength required for break excitations, and the field strength at which break excitations occurred was generally greater than 5 V/cm. Finally, in a more realistic ventricular slice geometry, the proximity of virtual electrodes around subepicardial vessels was seen to cause break excitations in the form of propagating unstable wavelets to the subepicardial layer. Conclusion Representing the blood vessel wall microstructure in computational bidomain models of defibrillation is recommended as it significantly alters the electrophysiological response of the vessel to field stimulation. Although vessels may facilitate excitation of relatively refractory tissue via break excitations, the field strength required for this is generally greater than those used in the literature on low-energy defibrillation. However, the high-intensity shocks used in standard defibrillation may elicit break excitation propagation from the coronary vasculature.
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Affiliation(s)
- Adam J Connolly
- Department of Biomedical Engineering and Imaging Sciences, King's College London , London , UK
| | - Edward Vigmond
- IHU Liryc, Electrophysiology and Heart Modeling Instituté, Fondation Bordeaux Université, Bordeaux, France; IMB, UMR 5251, Univ. Bordeaux, Talence, France
| | - Martin J Bishop
- Department of Biomedical Engineering and Imaging Sciences, King's College London , London , UK
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18
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Martišienė I, Mačianskienė R, Treinys R, Navalinskas A, Almanaitytė M, Karčiauskas D, Kučinskas A, Grigalevičiūtė R, Zigmantaitė V, Benetis R, Jurevičius J. Voltage-Sensitive Fluorescence of Indocyanine Green in the Heart. Biophys J 2017; 110:723-732. [PMID: 26840736 DOI: 10.1016/j.bpj.2015.12.021] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Revised: 12/15/2015] [Accepted: 12/16/2015] [Indexed: 10/22/2022] Open
Abstract
So far, the optical mapping of cardiac electrical signals using voltage-sensitive fluorescent dyes has only been performed in experimental studies because these dyes are not yet approved for clinical use. It was recently reported that the well-known and widely used fluorescent dye indocyanine green (ICG), which has FDA approval, exhibits voltage sensitivity in various tissues, thus raising hopes that electrical activity could be optically mapped in the clinic. The aim of this study was to explore the possibility of using ICG to monitor cardiac electrical activity. Optical mapping experiments were performed on Langendorff rabbit hearts stained with ICG and perfused with electromechanical uncouplers. The residual contraction force and electrical action potentials were recorded simultaneously. Our research confirms that ICG is a voltage-sensitive dye with a dual-component (fast and slow) response to membrane potential changes. The fast component of the optical signal (OS) can have opposite polarities in different parts of the fluorescence spectrum. In contrast, the polarity of the slow component remains the same throughout the entire spectrum. Separating the OS into these components revealed two different voltage-sensitivity mechanisms for ICG. The fast component of the OS appears to be electrochromic in nature, whereas the slow component may arise from the redistribution of the dye molecules within or around the membrane. Both components quite accurately track the time of electrical signal propagation, but only the fast component is suitable for estimating the shape and duration of action potentials. Because ICG has voltage-sensitive properties in the entire heart, we suggest that it can be used to monitor cardiac electrical behavior in the clinic.
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19
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Gemmell P, Burrage K, Rodríguez B, Quinn TA. Rabbit-specific computational modelling of ventricular cell electrophysiology: Using populations of models to explore variability in the response to ischemia. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 121:169-84. [PMID: 27320382 PMCID: PMC5405055 DOI: 10.1016/j.pbiomolbio.2016.06.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 06/13/2016] [Indexed: 11/04/2022]
Abstract
Computational modelling, combined with experimental investigations, is a powerful method for investigating complex cardiac electrophysiological behaviour. The use of rabbit-specific models, due to the similarities of cardiac electrophysiology in this species with human, is especially prevalent. In this paper, we first briefly review rabbit-specific computational modelling of ventricular cell electrophysiology, multi-cellular simulations including cellular heterogeneity, and acute ischemia. This mini-review is followed by an original computational investigation of variability in the electrophysiological response of two experimentally-calibrated populations of rabbit-specific ventricular myocyte action potential models to acute ischemia. We performed a systematic exploration of the response of the model populations to varying degrees of ischemia and individual ischemic parameters, to investigate their individual and combined effects on action potential duration and refractoriness. This revealed complex interactions between model population variability and ischemic factors, which combined to enhance variability during ischemia. This represents an important step towards an improved understanding of the role that physiological variability may play in electrophysiological alterations during acute ischemia.
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Affiliation(s)
- Philip Gemmell
- Department of Computer Science, University of Oxford, Oxford, UK
| | - Kevin Burrage
- Department of Computer Science, University of Oxford, Oxford, UK; School of Mathematical Sciences and ARC Centre of Excellence, ACEMS, Queensland University of Technology, Brisbane, Australia
| | - Blanca Rodríguez
- Department of Computer Science, University of Oxford, Oxford, UK
| | - T Alexander Quinn
- Department of Physiology and Biophysics, Dalhousie University, 5850 College St, Lab 3F, Halifax, NS B3H 4R2, Canada; School of Biomedical Engineering, Dalhousie University, 5850 College St, Lab 3F, Halifax, NS B3H 4R2, Canada.
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20
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Mačianskienė R, Martišienė I, Navalinskas A, Vosyliūtė R, Treinys R, Vaidelytė B, Benetis R, Jurevičius J. Evaluation of excitation propagation in the rabbit heart: optical mapping and transmural microelectrode recordings. PLoS One 2015; 10:e0123050. [PMID: 25881157 PMCID: PMC4400155 DOI: 10.1371/journal.pone.0123050] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2014] [Accepted: 02/18/2015] [Indexed: 11/18/2022] Open
Abstract
Background Because of the optical features of heart tissue, optical and electrical action potentials are only moderately associated, especially when near-infrared dyes are used in optical mapping (OM) studies. Objective By simultaneously recording transmural electrical action potentials (APs) and optical action potentials (OAPs), we aimed to evaluate the contributions of both electrical and optical influences to the shape of the OAP upstroke. Methods and Results A standard glass microelectrode and OM, using an near-infrared fluorescent dye (di-4-ANBDQBS), were used to simultaneously record transmural APs and OAPs in a Langendorff-perfused rabbit heart during atrial, endocardial, and epicardial pacing. The actual profile of the transmural AP upstroke across the LV wall, together with the OAP upstroke, allowed for calculations of the probing-depth constant (k ~2.1 mm, n = 24) of the fluorescence measurements. In addition, the transmural AP recordings aided the quantitative evaluation of the influences of depth-weighted and lateral-scattering components on the OAP upstroke. These components correspond to the components of the propagating electrical wave that are transmural and parallel to the epicardium. The calculated mean values for the depth-weighted and lateral-scattering components, whose sum comprises the OAP upstroke, were (in ms) 10.18 ± 0.62 and 0.0 ± 0.56 for atrial stimulation, 9.37 ± 1.12 and 3.01 ± 1.30 for endocardial stimulation, and 6.09 ± 0.79 and 8.16 ± 0.98 for epicardial stimulation; (n = 8 for each). For this dye, 90% of the collected fluorescence originated up to 4.83 ± 0.18 mm (n = 24) from the epicardium. Conclusions The co-registration of OM and transmural microelectrode APs enabled the probing depth of fluorescence measurements to be calculated and the OAP upstroke to be divided into two components (depth-weighted and lateral-scattering), and it also allowed the relative strengths of their effects on the shape of the OAP upstroke to be evaluated.
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Affiliation(s)
- Regina Mačianskienė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Irma Martišienė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Antanas Navalinskas
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Rūta Vosyliūtė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Rimantas Treinys
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Birutė Vaidelytė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Rimantas Benetis
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Jonas Jurevičius
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas, Lithuania
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21
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Lu XL, Rubart M. Micron-scale voltage and [Ca(2+)]i imaging in the intact heart. Front Physiol 2014; 5:451. [PMID: 25520663 PMCID: PMC4251286 DOI: 10.3389/fphys.2014.00451] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2014] [Accepted: 11/03/2014] [Indexed: 12/03/2022] Open
Abstract
Studies in isolated cardiomyocytes have provided tremendous information at the cellular and molecular level concerning regulation of transmembrane voltage (Vm) and intracellular calcium ([Ca2+]i). The ability to use the information gleaned to gain insight into the function of ion channels and Ca2+ handling proteins in a more complex system, e.g., the intact heart, has remained a challenge. We have developed laser scanning fluorescence microscopy-based approaches to monitor, at the sub-cellular to multi-cellular level in the immobilized, Langendorff-perfused mouse heart, dynamic changes in [Ca2+]i and Vm. This article will review the use of single- or dual-photon laser scanning microscopy [Ca2+]i imaging in conjunction with transgenic reporter technology to (a) interrogate the extent to which transplanted, donor-derived myocytes or cardiac stem cell-derived de novo myocytes are capable of forming a functional syncytium with the pre-existing myocardium, using entrainment of [Ca2+]i transients by the electrical activity of the recipient heart as a surrogate for electrical coupling, and (b) characterize the Ca2+ handling phenotypes of cellular implants. Further, we will review the ability of laser scanning fluorescence microscopy in conjunction with a fast-response voltage-sensitive to resolve, on a subcellular level in Langendorff-perfused mouse hearts, Vm dynamics that typically occur during the course of a cardiac action potential. Specifically, the utility of this technique to measure microscopic-scale voltage gradients in the normal and diseased heart is discussed.
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Affiliation(s)
- Xiao-Long Lu
- Riley Heart Research Center, Department of Pediatrics, Wells Center for Pediatric Research, Indiana University School of Medicine Indianapolis, IN, USA
| | - Michael Rubart
- Riley Heart Research Center, Department of Pediatrics, Wells Center for Pediatric Research, Indiana University School of Medicine Indianapolis, IN, USA
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Campbell AS, Johnstone SR, Baillie GS, Smith G. β-Adrenergic modulation of myocardial conduction velocity: Connexins vs. sodium current. J Mol Cell Cardiol 2014; 77:147-54. [DOI: 10.1016/j.yjmcc.2014.09.030] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 08/15/2014] [Accepted: 09/10/2014] [Indexed: 12/21/2022]
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Bishop MJ, Connolly A, Plank G. Structural heterogeneity modulates effective refractory period: a mechanism of focal arrhythmia initiation. PLoS One 2014; 9:e109754. [PMID: 25291380 PMCID: PMC4188572 DOI: 10.1371/journal.pone.0109754] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 09/03/2014] [Indexed: 11/18/2022] Open
Abstract
Reductions in electrotonic loading around regions of structural and electrophysiological heterogeneity may facilitate capture of focal triggered activity, initiating reentrant arrhythmias. How electrotonic loading, refractoriness and capture of focal ectopics depend upon the intricate nature of physiological structural anatomy, as well as pathological tissue remodelling, however, is not well understood. In this study, we performed computational bidomain simulations with anatomically-detailed models representing the rabbit left ventricle. We used these models to quantify the relationship between local structural anatomy and spatial heterogeneity in action potential (AP) characteristics, electrotonic currents and effective refractory periods (ERPs) under pacing and restitution protocols. Regions surrounding vessel cavities, in addition to tissue surfaces, had significantly lower peak downstream electrotonic currents than well coupled myocardium ( vs A/cm2), with faster maximum AP upstroke velocities ( vs mV/ms), although noticeably very similar APDs ( vs ms) and AP restitution properties. Despite similarities in APDs, ERPs in regions of low electrotonic load in the vicinity of surfaces, intramural vessel cavities and endocardial structures were up to ms shorter compared to neighbouring well-coupled tissue, leading to regions of sharp ERP gradients. Consequently, focal extra-stimuli timed within this window of ERP heterogeneity between neighbouring regions readily induced uni-directional block, inducing reentry. Most effective induction sites were within channels of low ERPs between large vessels and epicardium. Significant differences in ERP driven by reductions in electrotonic loading due to fine-scale physiological structural heterogeneity provides an important mechanism of capture of focal activity and reentry induction. Application to pathological ventricles, particularly myocardial infarction, will have important implications in anti-arrhythmia therapy.
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Affiliation(s)
- Martin J. Bishop
- Department of Biomedical Engineering, Division of Imaging Sciences & Biomedical Engineering, King's College London, London, United Kingdom
- * E-mail:
| | - Adam Connolly
- Department of Biomedical Engineering, Division of Imaging Sciences & Biomedical Engineering, King's College London, London, United Kingdom
| | - Gernot Plank
- Institute of Biophysics, Medical University of Graz, Graz, Austria
- Oxford eResearch Centre, University of Oxford, Oxford, United Kingdom
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Bishop MJ, Plank G. Simulating photon scattering effects in structurally detailed ventricular models using a Monte Carlo approach. Front Physiol 2014; 5:338. [PMID: 25309442 PMCID: PMC4164003 DOI: 10.3389/fphys.2014.00338] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Accepted: 08/19/2014] [Indexed: 11/17/2022] Open
Abstract
Light scattering during optical imaging of electrical activation within the heart is known to significantly distort the optically-recorded action potential (AP) upstroke, as well as affecting the magnitude of the measured response of ventricular tissue to strong electric shocks. Modeling approaches based on the photon diffusion equation have recently been instrumental in quantifying and helping to understand the origin of the resulting distortion. However, they are unable to faithfully represent regions of non-scattering media, such as small cavities within the myocardium which are filled with perfusate during experiments. Stochastic Monte Carlo (MC) approaches allow simulation and tracking of individual photon “packets” as they propagate through tissue with differing scattering properties. Here, we present a novel application of the MC method of photon scattering simulation, applied for the first time to the simulation of cardiac optical mapping signals within unstructured, tetrahedral, finite element computational ventricular models. The method faithfully allows simulation of optical signals over highly-detailed, anatomically-complex MR-based models, including representations of fine-scale anatomy and intramural cavities. We show that optical action potential upstroke is prolonged close to large subepicardial vessels than further away from vessels, at times having a distinct “humped” morphology. Furthermore, we uncover a novel mechanism by which photon scattering effects around vessels cavities interact with “virtual-electrode” regions of strong de-/hyper-polarized tissue surrounding cavities during shocks, significantly reducing the apparent optically-measured epicardial polarization. We therefore demonstrate the importance of this novel optical mapping simulation approach along with highly anatomically-detailed models to fully investigate electrophysiological phenomena driven by fine-scale structural heterogeneity.
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Affiliation(s)
- Martin J Bishop
- Division of Imaging Sciences & Biomedical Engineering, Department of Biomedical Engineering, King's College London London, UK
| | - Gernot Plank
- Institute of Biophysics, Medical University of Graz Graz, Austria ; Oxford eResearch Centre, University of Oxford Oxford, UK
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25
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Filippi S, Gizzi A, Cherubini C, Luther S, Fenton FH. Mechanistic insights into hypothermic ventricular fibrillation: the role of temperature and tissue size. Europace 2014; 16:424-34. [PMID: 24569897 PMCID: PMC3934849 DOI: 10.1093/europace/euu031] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 01/27/2014] [Indexed: 12/26/2022] Open
Abstract
AIMS Hypothermia is well known to be pro-arrhythmic, yet it has beneficial effects as a resuscitation therapy and valuable during intracardiac surgeries. Therefore, we aim to study the mechanisms that induce fibrillation during hypothermia. A better understanding of the complex spatiotemporal dynamics of heart tissue as a function of temperature will be useful in managing the benefits and risks of hypothermia. METHODS AND RESULTS We perform two-dimensional numerical simulations by using a minimal model of cardiac action potential propagation fine-tuned on experimental measurements. The model includes thermal factors acting on the ionic currents and the gating variables to correctly reproduce experimentally recorded restitution curves at different temperatures. Simulations are implemented using WebGL, which allows long simulations to be performed as they run close to real time. We describe (i) why fibrillation is easier to induce at low temperatures, (ii) that there is a minimum size required for fibrillation that depends on temperature, (iii) why the frequency of fibrillation decreases with decreasing temperature, and (iv) that regional cooling may be an anti-arrhythmic therapy for small tissue sizes however it may be pro-arrhythmic for large tissue sizes. CONCLUSION Using a mathematical cardiac cell model, we are able to reproduce experimental observations, quantitative experimental results, and discuss possible mechanisms and implications of electrophysiological changes during hypothermia.
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Affiliation(s)
- Simonetta Filippi
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, Via A. del Portillo 21, I-00128 Rome, Italy
- International Center for Relativistic Astrophysics—I.C.R.A, University Campus Bio-Medico of Rome, Via A. del Portillo 21, I-00128 Rome, Italy
| | - Alessio Gizzi
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, Via A. del Portillo 21, I-00128 Rome, Italy
- International Center for Relativistic Astrophysics—I.C.R.A, University Campus Bio-Medico of Rome, Via A. del Portillo 21, I-00128 Rome, Italy
| | - Christian Cherubini
- Nonlinear Physics and Mathematical Modeling Laboratory, University Campus Bio-Medico of Rome, Via A. del Portillo 21, I-00128 Rome, Italy
- International Center for Relativistic Astrophysics—I.C.R.A, University Campus Bio-Medico of Rome, Via A. del Portillo 21, I-00128 Rome, Italy
| | - Stefan Luther
- Max Planck Institute for Dynamics and Self-Organization, Am Fassberg 17, D-37077 Göttingen, Germany
| | - Flavio H. Fenton
- School of Physics, Georgia Institute of Technology, 837 State Street Atlanta, Atlanta, GA 30332, USA
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Walton RD, Benson AP, Hardy MEL, White E, Bernus O. Electrophysiological and structural determinants of electrotonic modulation of repolarization by the activation sequence. Front Physiol 2013; 4:281. [PMID: 24115934 PMCID: PMC3792354 DOI: 10.3389/fphys.2013.00281] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 09/18/2013] [Indexed: 11/14/2022] Open
Abstract
Spatial dispersion of repolarization is known to play an important role in arrhythmogenesis. Electrotonic modulation of repolarization by the activation sequence has been observed in some species and tissue preparations, but to varying extents. Our study sought to determine the mechanisms underlying species- and tissue-dependent electrotonic modulation of repolarization in ventricles. Epi-fluorescence optical imaging of whole rat hearts and pig left ventricular wedges were used to assess epicardial spatial activation and repolarization characteristics. Experiments were supported by computer simulations using realistic geometries. Tight coupling between activation times (AT) and action potential duration (APD) were observed in rat experiments but not in pig. Linear correlation analysis found slopes of −1.03 ± 0.59 and −0.26 ± 0.13 for rat and pig, respectively (p < 0.0001). In rat, maximal dispersion of APD was 11.0 ± 3.1 ms but dispersion of repolarization time (RT) was relatively homogeneous (8.2 ± 2.7, p < 0.0001). However, in pig no such difference was observed between the dispersion of APD and RT (17.8 ± 6.1 vs. 17.7 ± 6.5, respectively). Localized elevations of APD (12.9 ± 8.3%) were identified at ventricular insertion sites of rat hearts both in experiments and simulations. Tissue geometry and action potential (AP) morphology contributed significantly to determining influence of electrotonic modulation. Simulations of a rat AP in a pig geometry decreased the slope of AT and APD relationships by 70.6% whereas slopes were increased by 75.0% when implementing a pig AP in a rat geometry. A modified pig AP, shortened to match the rat APD, showed little coupling between AT and APD with greatly reduced slope compared to the rat AP. Electrotonic modulation of repolarization by the activation sequence is especially pronounced in small hearts with murine-like APs. Tissue architecture and AP morphology play an important role in electrotonic modulation of repolarization.
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Affiliation(s)
- Richard D Walton
- Faculty of Biological Sciences, Multidisciplinary Cardiovascular Research Centre, School of Biomedical Sciences, Institute of Membrane and Systems Biology, University of Leeds Leeds, UK ; Unité Inserm 1045, Centre de Recherche Cardio-Thoracique, Université Bordeaux Segalen Bordeaux, France ; L'Institut de Rythmologie et Modélisation Cardiaque, Université de Bordeaux Bordeaux, France
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