Stop the beat to see the rhythm: excitation-contraction uncoupling in cardiac research

Optical mapping is an imaging technique that is extensively used in cardiovascular research, wherein parameter-sensitive fluorescent indicators are used to study the electrophysiology and excitation-contraction coupling of cardiac tissues. Despite the many benefits of optical mapping, eliminating motion artifacts within the optical signals is a major challenge, as myocardial contraction interferes with the faithful acquisition of action potentials and intracellular calcium transients. As such, excitation-contraction uncoupling agents are frequently used to reduce signal distortion by suppressing contraction. Compared to other uncoupling agents, blebbistatin is the most frequently used as it offers increased potency with minimal direct effects on cardiac electrophysiology. Nevertheless, blebbistatin may exert secondary effects on electrical activity, metabolism, and coronary flow, and the incorrect administration of blebbistatin to cardiac tissue can prove detrimental, resulting in erroneous interpretation of optical mapping results. In this "Getting It Right" perspective, we briefly review the literature regarding the use of blebbistatin in cardiac optical mapping experiments, highlight potential secondary effects of blebbistatin on cardiac electrical activity and metabolic demand, and conclude with the consensus of the authors on best practices for effectively using blebbistatin in optical mapping studies of cardiac tissue.

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Optical mapping of the electrical activity of isolated adult zebrafish hearts: acute effects of temperature

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00002.2014 ◽

2014 ◽

Vol 306 (11) ◽

pp. R823-R836 ◽

Cited By ~ 27

Author(s):

Eric Lin ◽

Amanda Ribeiro ◽

Weiguang Ding ◽

Leif Hove-Madsen ◽

Marinko V. Sarunic ◽

...

Keyword(s):

Action Potential ◽

Electrical Activity ◽

Cardiac Electrophysiology ◽

Optical Mapping ◽

Cooling System ◽

Effect Of Temperature ◽

Adult Zebrafish ◽

Depth Analysis ◽

Zebrafish Heart ◽

Av Delay

The zebrafish ( Danio rerio) has emerged as an important model for developmental cardiovascular (CV) biology; however, little is known about the cardiac function of the adult zebrafish enabling it to be used as a model of teleost CV biology. Here, we describe electrophysiological parameters, such as heart rate (HR), action potential duration (APD), and atrioventricular (AV) delay, in the zebrafish heart over a range of physiological temperatures (18–28°C). Hearts were isolated and incubated in a potentiometric dye, RH-237, enabling electrical activity assessment in several distinct regions of the heart simultaneously. Integration of a rapid thermoelectric cooling system facilitated the investigation of acute changes in temperature on critical electrophysiological parameters in the zebrafish heart. While intrinsic HR varied considerably between fish, the ex vivo preparation exhibited impressively stable HRs and sinus rhythm for more than 5 h, with a mean HR of 158 ± 9 bpm (means ± SE; n = 20) at 28°C. Atrial and ventricular APDs at 50% repolarization (APD50) were 33 ± 1 ms and 98 ± 2 ms, respectively. Excitation originated in the atrium, and there was an AV delay of 61 ± 3 ms prior to activation of the ventricle at 28°C. APD and AV delay varied between hearts beating at unique HRs; however, APD and AV delay did not appear to be statistically dependent on intrinsic basal HR, likely due to the innate beat-to-beat variability within each heart. As hearts were cooled to 18°C (by 1°C increments), HR decreased by ∼40%, and atrial and ventricular APD50 increased by a factor of ∼3 and 2, respectively. The increase in APD with cooling was disproportionate at different levels of repolarization, indicating unique temperature sensitivities for ion currents at different phases of the action potential. The effect of temperature was more apparent at lower levels of repolarization and, as a whole, the atrial APD was the cardiac parameter most affected by acute temperature change. In conclusion, this study describes a preparation enabling the in-depth analysis of transmembrane potential dynamics in whole zebrafish hearts. Because the zebrafish offers some critical advantages over the murine model for cardiac electrophysiology, optical mapping studies utilizing zebrafish offer insightful information into the understanding and treatment of human cardiac arrhythmias, as well as serving as a model for other teleosts.

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Simultaneous Triple-Parametric Optical Mapping of Transmembrane Potential, Intracellular Calcium and NADH for Cardiac Physiology Assessment

10.1101/2021.09.09.459667 ◽

2021 ◽

Author(s):

Sharon A George ◽

Zexu Lin ◽

Igor R Efimov

Keyword(s):

Cardiac Electrophysiology ◽

Drug Testing ◽

Optical Mapping ◽

Dynamic Assessment ◽

Cardiac Physiology ◽

Cardiovascular Research ◽

Multiple Parameters ◽

Cellular Processes ◽

Complex Relationships ◽

Target Effects

AbstractInvestigation of the complex relationships and dependencies of multiple cellular processes that govern cardiac physiology and pathophysiology requires simultaneous dynamic assessment of multiple parameters. In this study, we introduce triple-parametric optical mapping to simultaneously image metabolism, electrical excitation, and calcium signaling from the same field of view and demonstrate its application in the field of drug testing and cardiovascular research. We applied this metabolism-excitation-contraction coupling (MECC) methodology to test the effects of blebbistatin, 4-aminopyridine and verapamil on cardiac physiology. While blebbistatin and 4-aminopyridine alter multiple aspects of cardiac function suggesting off-target effects, the effects of verapamil were on-target and it altered only one of ten tested parameters. Triple-parametric optical mapping was also applied during ischemia and reperfusion; and we identified that metabolic changes precede the effects of ischemia on cardiac electrophysiology.

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Cardiac tissue slices: preparation, handling, and successful optical mapping

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00556.2014 ◽

2015 ◽

Vol 308 (9) ◽

pp. H1112-H1125 ◽

Cited By ~ 29

Author(s):

Ken Wang ◽

Peter Lee ◽

Gary R. Mirams ◽

Padmini Sarathchandra ◽

Thomas K. Borg ◽

...

Keyword(s):

Cardiac Electrophysiology ◽

Cardiac Tissue ◽

Optical Mapping ◽

Tissue Injury ◽

Recovery Period ◽

Exponential Fitting ◽

Free Calcium ◽

Tangential Plane ◽

Tissue Slices ◽

Significant Difference

Cardiac tissue slices are becoming increasingly popular as a model system for cardiac electrophysiology and pharmacology research and development. Here, we describe in detail the preparation, handling, and optical mapping of transmembrane potential and intracellular free calcium concentration transients (CaT) in ventricular tissue slices from guinea pigs and rabbits. Slices cut in the epicardium-tangential plane contained well-aligned in-slice myocardial cell strands (“fibers”) in subepicardial and midmyocardial sections. Cut with a high-precision slow-advancing microtome at a thickness of 350 to 400 μm, tissue slices preserved essential action potential (AP) properties of the precutting Langendorff-perfused heart. We identified the need for a postcutting recovery period of 36 min (guinea pig) and 63 min (rabbit) to reach 97.5% of final steady-state values for AP duration (APD) (identified by exponential fitting). There was no significant difference between the postcutting recovery dynamics in slices obtained using 2,3-butanedione 2-monoxime or blebistatin as electromechanical uncouplers during the cutting process. A rapid increase in APD, seen after cutting, was caused by exposure to ice-cold solution during the slicing procedure, not by tissue injury, differences in uncouplers, or pH-buffers (bicarbonate; HEPES). To characterize intrinsic patterns of CaT, AP, and conduction, a combination of multipoint and field stimulation should be used to avoid misinterpretation based on source-sink effects. In summary, we describe in detail the preparation, mapping, and data analysis approaches for reproducible cardiac tissue slice-based investigations into AP and CaT dynamics.

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Machine-readable Yin–Yang imbalance: traditional Chinese medicine syndrome computer modeling based on three-dimensional noninvasive cardiac electrophysiology imaging

Journal of International Medical Research ◽

10.1177/0300060518824247 ◽

2019 ◽

Vol 47 (4) ◽

pp. 1580-1591 ◽

Cited By ~ 1

Author(s):

Wei Cen ◽

Ralph Hoppe ◽

Aiwu Sun ◽

Hongyan Ding ◽

Ning Gu

Keyword(s):

Chinese Medicine ◽

Traditional Chinese Medicine ◽

Electrical Activity ◽

Computer Modeling ◽

Cardiac Electrophysiology ◽

Three Dimensional ◽

Mathematical Physics ◽

Syndrome Differentiation ◽

Physics Model ◽

Machine Readable

Objectives The principal diagnostic methods of traditional Chinese medicine (TCM) are inspection, auscultation and olfaction, inquiry, and pulse-taking. Treatment by syndrome differentiation is likely to be subjective. This study was designed to provide a basic theory for TCM diagnosis and establish an objective means of evaluating the correctness of syndrome differentiation. Methods We herein provide the basic theory of TCM syndrome computer modeling based on a noninvasive cardiac electrophysiology imaging technique. Noninvasive cardiac electrophysiology imaging records the heart’s electrical activity from hundreds of electrodes on the patient’s torso surface and therefore provides much more information than 12-lead electrocardiography. Through mathematical reconstruction algorithm calculations, the reconstructed heart model is a machine-readable description of the underlying mathematical physics model that reveals the detailed three-dimensional (3D) electrophysiological activity of the heart. Results From part of the simulation results, the imaged 3D cardiac electrical source provides dynamic information regarding the heart’s electrical activity at any given location within the 3D myocardium. Conclusions This noninvasive cardiac electrophysiology imaging method is suitable for translating TCM syndromes into a computable format of the underlying mathematical physics model to offer TCM diagnosis evidence-based standards for ensuring correct evaluation and rigorous, scientific data for demonstrating its efficacy.

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Accelerating mono-domain cardiac electrophysiology simulations using OpenCL

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2015-0100 ◽

2015 ◽

Vol 1 (1) ◽

pp. 413-417

Author(s):

Eike M. Wülfers ◽

Zhasur Zhamoliddinov ◽

Olaf Dössel ◽

Gunnar Seemann

Keyword(s):

Cardiac Electrophysiology ◽

Cardiac Tissue ◽

Ionic Currents ◽

Domain Model ◽

Electrical Excitation ◽

Simulation Domain ◽

Speed Up ◽

Cross Platform ◽

Atrial Myocyte ◽

Intel Xeon

AbstractUsing OpenCL, we developed a cross-platform software to compute electrical excitation conduction in cardiac tissue. OpenCL allowed the software to run parallelized and on different computing devices (e.g., CPUs and GPUs). We used the macroscopic mono-domain model for excitation conduction and an atrial myocyte model by Courtemanche et al. for ionic currents. On a CPU with 12 HyperThreading-enabled Intel Xeon 2.7 GHz cores, we achieved a speed-up of simulations by a factor of 1.6 against existing software that uses OpenMPI. On two high-end AMD FirePro D700 GPUs the OpenCL software ran 2.4 times faster than the OpenMPI implementation. The more nodes the discretized simulation domain contained, the higher speed-ups were achieved.

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Living myocardial slices: a novel multicellular model for cardiac translational research

European Heart Journal ◽

10.1093/eurheartj/ehz779 ◽

2019 ◽

Vol 41 (25) ◽

pp. 2405-2408 ◽

Cited By ~ 1

Author(s):

Filippo Perbellini ◽

Thomas Thum

Keyword(s):

Translational Research ◽

Cardiac Tissue ◽

Heart Function ◽

Cell Types ◽

Human Model ◽

Mechanical Stimuli ◽

Cardiovascular Research ◽

Functional Changes

Abstract Heart function relies on the interplay of several specialized cell types and a precisely regulated network of chemical and mechanical stimuli. Over the last few decades, this complexity has often been undervalued and progress in translational cardiovascular research has been significantly hindered by the lack of appropriate research models. The data collected are often oversimplified and these make the translation of results from the laboratory to clinical trials challenging and occasionally misleading. Living myocardial slices are ultrathin (100–400μm) sections of living cardiac tissue that maintain the native multicellularity, architecture, and structure of the heart and can provide information at a cellular/subcellular level. They overcome most of the limitations that affect other in vitro models and they can be prepared from human specimens, proving a clinically relevant multicellular human model for translational cardiovascular research. The publication of a reproducible protocol, and the rapid progress in methodological and technological discoveries which prevent significant structural and functional changes associated with chronic in vitro culture, has overcome the last barrier for the in vitro use of this human multicellular preparations. This technology can bridge the gap between in vitro and in vivo human studies and has the potential to revolutionize translational research approaches.

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Computational approaches to understand cardiac electrophysiology and arrhythmias

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01081.2011 ◽

2012 ◽

Vol 303 (7) ◽

pp. H766-H783 ◽

Cited By ~ 52

Author(s):

Byron N. Roberts ◽

Pei-Chi Yang ◽

Steven B. Behrens ◽

Jonathan D. Moreno ◽

Colleen E. Clancy

Keyword(s):

Ion Channels ◽

Electrical Activity ◽

Cardiac Electrophysiology ◽

Cardiac Activity ◽

Computational Approaches ◽

Cardiac Electrical Activity ◽

Whole Heart ◽

Arrhythmia Therapy ◽

Emergent Behaviors ◽

The Brain

Cardiac rhythms arise from electrical activity generated by precisely timed opening and closing of ion channels in individual cardiac myocytes. These impulses spread throughout the cardiac muscle to manifest as electrical waves in the whole heart. Regularity of electrical waves is critically important since they signal the heart muscle to contract, driving the primary function of the heart to act as a pump and deliver blood to the brain and vital organs. When electrical activity goes awry during a cardiac arrhythmia, the pump does not function, the brain does not receive oxygenated blood, and death ensues. For more than 50 years, mathematically based models of cardiac electrical activity have been used to improve understanding of basic mechanisms of normal and abnormal cardiac electrical function. Computer-based modeling approaches to understand cardiac activity are uniquely helpful because they allow for distillation of complex emergent behaviors into the key contributing components underlying them. Here we review the latest advances and novel concepts in the field as they relate to understanding the complex interplay between electrical, mechanical, structural, and genetic mechanisms during arrhythmia development at the level of ion channels, cells, and tissues. We also discuss the latest computational approaches to guiding arrhythmia therapy.

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The Magnetic Field Produced by the Heart and Its Influence on MRI

Mathematical Problems in Engineering ◽

10.1155/2017/3035479 ◽

2017 ◽

Vol 2017 ◽

pp. 1-9

Author(s):

Dan Xu ◽

Bradley J. Roth

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Field ◽

Phase Shift ◽

Cardiac Tissue ◽

Spherical Model ◽

Motion Artifacts ◽

Resonance Imaging ◽

Physiological Noise ◽

Cardiac Action ◽

The Magnetic Field

Background. Action currents in the heart produce a magnetic field, which could provide a way to detect the propagation of electrical activity through cardiac tissue using magnetic resonance imaging. However, the magnetic field produced by current in the heart is small. The key question addressed in this study is are cardiac biomagnetic fields large enough to be detectable by MRI? Results. A spherical model is used to calculate the magnetic field inside the heart, which has a magnitude of about 14 nT. This field implies a phase shift in the MRI signal of about 0.2°. Conclusion. Phase shifts associated with cardiac action currents will be difficult to detect using current MRI technology but may be possible if motion artifacts and other physiological noise can be suppressed.

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