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Wang X, Landaw J, Qu Z. Intracellular ion accumulation in the genesis of complex action potential dynamics under cardiac diseases. Phys Rev E 2024; 109:024410. [PMID: 38491656 DOI: 10.1103/physreve.109.024410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 01/19/2024] [Indexed: 03/18/2024]
Abstract
Intracellular ions, including sodium (Na^{+}), calcium (Ca^{2+}), and potassium (K^{+}), etc., accumulate slowly after a change of the state of the heart, such as a change of the heart rate. The goal of this study is to understand the roles of slow ion accumulation in the genesis of cardiac memory and complex action-potential duration (APD) dynamics that can lead to lethal cardiac arrhythmias. We carry out numerical simulations of a detailed action potential model of ventricular myocytes under normal and diseased conditions, which exhibit memory effects and complex APD dynamics. We develop a low-dimensional iterated map (IM) model to describe the dynamics of Na^{+}, Ca^{2+}, and APD and use it to uncover the underlying dynamical mechanisms. The development of the IM model is informed by simulation results under the normal condition. We then use the IM model to perform linear stability analyses and computer simulations to investigate the bifurcations and complex APD dynamics, which depend on the feedback loops between APD and intracellular Ca^{2+} and Na^{+} concentrations and the steepness of the APD response to the ion concentrations. When the feedback between APD and Ca^{2+} concentration is positive, a Hopf bifurcation leading to periodic oscillatory behavior occurs as the steepness of the APD response to the ion concentrations increases. The negative feedback loop between APD and Na^{+} concentration is required for the Hopf bifurcation. When the feedback between APD and Ca^{2+} concentration is negative, period-doubling bifurcations leading to high periodicity and chaos occurs. In this case, Na^{+} accumulation plays little role in the dynamics. Finally, we carry out simulations of the detailed action potential model under two diseased conditions, which exhibit steep APD responses to ion concentrations. Under both conditions, Hopf bifurcations leading to slow oscillations or period-doubling bifurcations leading to high periodicity and chaotic APD dynamics occur, depending on the strength of the ion pump-Na^{+}-Ca^{2+} exchanger. Using functions reconstructed from the simulation data, the IM model accurately captures the bifurcations and dynamics under the two diseased conditions. In conclusion, besides using computer simulations of a detailed high-dimensional action-potential model to investigate the effects of slow ion accumulation and short-term memory on bifurcations and genesis of complex APD dynamics in cardiac myocytes under diseased conditions, this study also provides a low-dimensional mathematical tool, i.e., the IM model, to allow stability analyses for uncovering the underlying mechanisms.
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Affiliation(s)
- Xinyu Wang
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
| | - Julian Landaw
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
| | - Zhilin Qu
- Department of Medicine (Cardiology), David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA
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2
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Li P, Kim JK. Circadian regulation of sinoatrial nodal cell pacemaking function: Dissecting the roles of autonomic control, body temperature, and local circadian rhythmicity. PLoS Comput Biol 2024; 20:e1011907. [PMID: 38408116 PMCID: PMC10927146 DOI: 10.1371/journal.pcbi.1011907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Revised: 03/11/2024] [Accepted: 02/12/2024] [Indexed: 02/28/2024] Open
Abstract
Strong circadian (~24h) rhythms in heart rate (HR) are critical for flexible regulation of cardiac pacemaking function throughout the day. While this circadian flexibility in HR is sustained in diverse conditions, it declines with age, accompanied by reduced maximal HR performance. The intricate regulation of circadian HR involves the orchestration of the autonomic nervous system (ANS), circadian rhythms of body temperature (CRBT), and local circadian rhythmicity (LCR), which has not been fully understood. Here, we developed a mathematical model describing ANS, CRBT, and LCR in sinoatrial nodal cells (SANC) that accurately captures distinct circadian patterns in adult and aged mice. Our model underscores how the alliance among ANS, CRBT, and LCR achieves circadian flexibility to cover a wide range of firing rates in SANC, performance to achieve maximal firing rates, while preserving robustness to generate rhythmic firing patterns irrespective of external conditions. Specifically, while ANS dominates in promoting SANC flexibility and performance, CRBT and LCR act as primary and secondary boosters, respectively, to further enhance SANC flexibility and performance. Disruption of this alliance with age results in impaired SANC flexibility and performance, but not robustness. This unexpected outcome is primarily attributed to the age-related reduction in parasympathetic activities, which maintains SANC robustness while compromising flexibility. Our work sheds light on the critical alliance of ANS, CRBT, and LCR in regulating time-of-day cardiac pacemaking function and dysfunction, offering insights into novel therapeutic targets for the prevention and treatment of cardiac arrhythmias.
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Affiliation(s)
- Pan Li
- Biomedical Mathematics Group, Pioneer Research Center for Mathematical and Computational Sciences, Institute for Basic Science, Daejeon, Republic of Korea
| | - Jae Kyoung Kim
- Biomedical Mathematics Group, Pioneer Research Center for Mathematical and Computational Sciences, Institute for Basic Science, Daejeon, Republic of Korea
- Department of Mathematical Sciences, KAIST, Daejeon, Republic of Korea
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3
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Iravanian S, Uzelac I, Shah AD, Toye MJ, Lloyd MS, Burke MA, Daneshmand MA, Attia TS, Vega JD, El-Chami MF, Merchant FM, Cherry EM, Bhatia NK, Fenton FH. Complex repolarization dynamics in ex vivo human ventricles are independent of the restitution properties. Europace 2023; 25:euad350. [PMID: 38006390 PMCID: PMC10751849 DOI: 10.1093/europace/euad350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2023] [Accepted: 11/13/2023] [Indexed: 11/27/2023] Open
Abstract
AIMS The mechanisms of transition from regular rhythms to ventricular fibrillation (VF) are poorly understood. The concordant to discordant repolarization alternans pathway is extensively studied; however, despite its theoretical centrality, cannot guide ablation. We hypothesize that complex repolarization dynamics, i.e. oscillations in the repolarization phase of action potentials with periods over two of classic alternans, is a marker of electrically unstable substrate, and ablation of these areas has a stabilizing effect and may reduce the risk of VF. To prove the existence of higher-order periodicities in human hearts. METHODS AND RESULTS We performed optical mapping of explanted human hearts obtained from recipients of heart transplantation at the time of surgery. Signals recorded from the right ventricle endocardial surface were processed to detect global and local repolarization dynamics during rapid pacing. A statistically significant global 1:4 peak was seen in three of six hearts. Local (pixel-wise) analysis revealed the spatially heterogeneous distribution of Periods 4, 6, and 8, with the regional presence of periods greater than two in all the hearts. There was no significant correlation between the underlying restitution properties and the period of each pixel. CONCLUSION We present evidence of complex higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex vivo human hearts. We infer that the oscillation of the calcium cycling machinery is the primary mechanism of higher-order dynamics. These higher-order regions may act as niduses of instability and may provide targets for substrate-based ablation of VF.
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Affiliation(s)
- Shahriar Iravanian
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Ilija Uzelac
- Georgia Institute of Technology, Department of Physics, 837 State St NW, Atlanta, GA 30332, USA
| | - Anand D Shah
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Mikael J Toye
- Georgia Institute of Technology, Department of Physics, 837 State St NW, Atlanta, GA 30332, USA
| | - Michael S Lloyd
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Michael A Burke
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Mani A Daneshmand
- Department of Surgery, Division of Cardiovascular Surgery, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Tamer S Attia
- Department of Surgery, Division of Cardiovascular Surgery, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - John David Vega
- Department of Surgery, Division of Cardiovascular Surgery, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Mikhael F El-Chami
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Faisal M Merchant
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Elizabeth M Cherry
- Georgia Institute of Technology, Department of Physics, 837 State St NW, Atlanta, GA 30332, USA
| | - Neal K Bhatia
- Department of Medicine, Division of Cardiology, Emory University School of Medicine, 1364 Clifton Road, Atlanta, GA 30322, USA
| | - Flavio H Fenton
- Georgia Institute of Technology, Department of Physics, 837 State St NW, Atlanta, GA 30332, USA
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Chakraborty P, Azam MA, Massé S, Lai PF, Rose RA, Ibarra Moreno CA, Riazi S, Nanthakumar K. Uncoupling cytosolic calcium from membrane voltage by transient receptor potential melastatin 4 channel (TRPM4) modulation: A novel strategy to treat ventricular arrhythmias. Heart Rhythm O2 2023; 4:725-732. [PMID: 38034891 PMCID: PMC10685170 DOI: 10.1016/j.hroo.2023.10.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2023] Open
Abstract
The current antiarrhythmic paradigm is mainly centered around modulating membrane voltage. However, abnormal cytosolic calcium (Ca2+) signaling, which plays an important role in driving membrane voltage, has not been targeted for therapeutic purposes in arrhythmogenesis. There is clear evidence for bidirectional coupling between membrane voltage and intracellular Ca2+. Cytosolic Ca2+ regulates membrane voltage through Ca2+-sensitive membrane currents. As a component of Ca2+-sensitive currents, Ca2+-activated nonspecific cationic current through the TRPM4 (transient receptor potential melastatin 4) channel plays a significant role in Ca2+-driven changes in membrane electrophysiology. In myopathic and ischemic ventricles, upregulation and/or enhanced activity of this current is associated with the generation of afterdepolarization (both early and delayed), reduction of repolarization reserve, and increased propensity to ventricular arrhythmias. In this review, we describe a novel concept for the management of ventricular arrhythmias in the remodeled ventricle based on mechanistic concepts from experimental studies, by uncoupling the Ca2+-induced changes in membrane voltage by inhibition of this TRPM4-mediated current.
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Affiliation(s)
- Praloy Chakraborty
- Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Mohammed Ali Azam
- Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Stéphane Massé
- Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Patrick F.H. Lai
- Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Robert A. Rose
- Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada
| | - Carlos A. Ibarra Moreno
- Malignant Hyperthermia Investigation Unit, Department of Anesthesiology and Pain Medicine, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Sheila Riazi
- Malignant Hyperthermia Investigation Unit, Department of Anesthesiology and Pain Medicine, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
| | - Kumaraswamy Nanthakumar
- Hull Family Cardiac Fibrillation Management Laboratory, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada
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Jones CA, Wallace MJ, Bandaru P, Woodbury ED, Mohler PJ, Wold LE. E-cigarettes and arrhythmogenesis: a comprehensive review of pre-clinical studies and their clinical implications. Cardiovasc Res 2023; 119:2157-2164. [PMID: 37517059 PMCID: PMC10578912 DOI: 10.1093/cvr/cvad113] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 06/21/2023] [Accepted: 06/29/2023] [Indexed: 08/01/2023] Open
Abstract
Electronic cigarette use has grown exponentially in recent years, and while their popularity has increased, the long-term effects on the heart are yet to be fully studied and understood. Originally designed as devices to assist with those trying to quit traditional combustible cigarette use, their popularity has attracted use by teens and adolescents who traditionally have not smoked combustible cigarettes. Acute effects on the heart have been shown to be similar to traditional combustible cigarettes, including increased heart rate and blood pressure. The main components of electronic cigarettes that contribute to these arrhythmic effects are found in the e-liquid that is aerosolized and inhaled, comprised of nicotine, flavourings, and a combination of vegetable glycerin (VG) and propylene glycol (PG). Nicotine can potentially induce both ventricular and atrial arrhythmogenesis, with both the atrial and ventricular effects resulting from the interactions of nicotine and the catecholamines they release via potassium channels. Atrial arrhythmogenesis, more specifically atrial fibrillation, can also occur due to structural alterations, which happens because of nicotine downregulating microRNAs 133 and 590, both post-transcriptional growth factor repressors. Liquid flavourings and the combination of PG and VG can possibly lead to arrhythmic events by exposing users to acrolein, an aldehyde that stimulates TRPA1 that in turn causes a change towards sympathetic activation and autonomic imbalance. The design of these electronic delivery devices is constantly changing; therefore, it has proven extremely difficult to study the long-term effects on the heart caused by electronic cigarettes but will be important to understand given their rising popularity. The arrhythmic effects of electronic cigarettes appear similar to traditional cigarettes as well; however, a comprehensive review has not been compiled and is the focus of this article.
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Affiliation(s)
- Carson A Jones
- Dorothy M. Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Columbus, OH 43210, USA
| | - Michael J Wallace
- Dorothy M. Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Columbus, OH 43210, USA
| | - Priya Bandaru
- Dorothy M. Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Columbus, OH 43210, USA
| | - Emerson D Woodbury
- Dorothy M. Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Columbus, OH 43210, USA
| | - Peter J Mohler
- Dorothy M. Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Columbus, OH 43210, USA
- Department of Internal Medicine, Wexner Medical Center, The Ohio State University, Columbus, OH, USA
| | - Loren E Wold
- Dorothy M. Davis Heart and Lung Research Institute, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Columbus, OH 43210, USA
- Division of Cardiac Surgery, Department of Surgery, Wexner Medical Center, The Ohio State University, 473 W 12th Avenue, Room 603, Columbus, OH 43210, USA
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Feng HW, Zhao YT, Lin J, Weng CL. T-wave alternans: an ominous pattern for malignant arrhythmias. QJM 2023; 116:781-783. [PMID: 37202351 DOI: 10.1093/qjmed/hcad097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Indexed: 05/20/2023] Open
Affiliation(s)
- Hang-Wei Feng
- Department of Intensive Care Unit, The Shengli Clinical Medical College of Fujian Medical University, Fujian Provincial Hospital South Branch, No. 516, Jinrong South, Fuzhou, Fujian Province, China
| | - Yun-Tao Zhao
- Department of Cardiology, Aerospace Center Hospital, Beijing, China
| | - Jian Lin
- Department of Intensive Care Unit, The Shengli Clinical Medical College of Fujian Medical University, Fujian Provincial Hospital South Branch, No. 516, Jinrong South, Fuzhou, Fujian Province, China
| | - Cui-Lian Weng
- Department of Intensive Care Unit, The Shengli Clinical Medical College of Fujian Medical University, Fujian Provincial Hospital South Branch, No. 516, Jinrong South, Fuzhou, Fujian Province, China
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Eisner D, Neher E, Taschenberger H, Smith G. Physiology of intracellular calcium buffering. Physiol Rev 2023; 103:2767-2845. [PMID: 37326298 DOI: 10.1152/physrev.00042.2022] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 05/08/2023] [Accepted: 06/11/2023] [Indexed: 06/17/2023] Open
Abstract
Calcium signaling underlies much of physiology. Almost all the Ca2+ in the cytoplasm is bound to buffers, with typically only ∼1% being freely ionized at resting levels in most cells. Physiological Ca2+ buffers include small molecules and proteins, and experimentally Ca2+ indicators will also buffer calcium. The chemistry of interactions between Ca2+ and buffers determines the extent and speed of Ca2+ binding. The physiological effects of Ca2+ buffers are determined by the kinetics with which they bind Ca2+ and their mobility within the cell. The degree of buffering depends on factors such as the affinity for Ca2+, the Ca2+ concentration, and whether Ca2+ ions bind cooperatively. Buffering affects both the amplitude and time course of cytoplasmic Ca2+ signals as well as changes of Ca2+ concentration in organelles. It can also facilitate Ca2+ diffusion inside the cell. Ca2+ buffering affects synaptic transmission, muscle contraction, Ca2+ transport across epithelia, and the killing of bacteria. Saturation of buffers leads to synaptic facilitation and tetanic contraction in skeletal muscle and may play a role in inotropy in the heart. This review focuses on the link between buffer chemistry and function and how Ca2+ buffering affects normal physiology and the consequences of changes in disease. As well as summarizing what is known, we point out the many areas where further work is required.
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Affiliation(s)
- David Eisner
- Division of Cardiovascular Sciences, University of Manchester, Manchester, United Kingdom
| | - Erwin Neher
- Membrane Biophysics Laboratory, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
- Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen, Göttingen, Germany
| | - Holger Taschenberger
- Department of Molecular Neurobiology, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Godfrey Smith
- School of Cardiovascular and Metabolic Health, College of Medical, Veterinary, and Life Sciences, University of Glasgow, Glasgow, United Kingdom
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Iravanian S, Uzelac I, Shah AD, Toye MJ, Lloyd MS, Burke MA, Daneshmand MA, Attia TS, Vega JD, El-Chami M, Merchant FM, Cherry EM, Bhatia NK, Fenton FH. Higher-Order Dynamics Beyond Repolarization Alternans in Ex-Vivo Human Ventricles are Independent of the Restitution Properties. medRxiv 2023:2023.08.16.23293853. [PMID: 37662394 PMCID: PMC10473769 DOI: 10.1101/2023.08.16.23293853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
Background Repolarization alternans, defined as period-2 oscillation in the repolarization phase of the action potentials, provides a mechanistic link between cellular dynamics and ventricular fibrillation (VF). Theoretically, higher-order periodicities (e.g., periods 4, 6, 8,...) are expected but have minimal experimental evidence. Methods We studied explanted human hearts obtained from recipients of heart transplantation at the time of surgery. Optical mapping of the transmembrane potential was performed after staining the hearts with voltage-sensitive fluorescent dyes. Hearts were stimulated at an increasing rate until VF was induced. Signals recorded from the right ventricle endocardial surface prior to induction of VF and in the presence of 1:1 conduction were processed using the Principal Component Analysis and a combinatorial algorithm to detect and quantify higher-order dynamics. Results were correlated to the underlying electrophysiological characteristics as quantified by restitution curves and conduction velocity. Results A prominent and statistically significant global 1:4 peak (corresponding to period-4 dynamics) was seen in three of the six studied hearts. Local (pixel-wise) analysis revealed the spatially heterogeneous distribution of periods 4, 6, and 8, with the regional presence of periods greater than two in all the hearts. There was no significant correlation between the underlying restitution properties and the period of each pixel. Discussion We present evidence of higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex-vivo human hearts. We infer from the independence of the period to the underlying restitution properties that the oscillation of the excitation-contraction coupling and calcium cycling mechanisms is the primary mechanism of higher-order dynamics. These higher-order regions may act as niduses of instability that can degenerate into chaotic fibrillation and may provide targets for substrate-based ablation of VF.
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Affiliation(s)
- Shahriar Iravanian
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
| | - Ilija Uzelac
- Georgia Tech, Department of Physics, Atlanta, GA
| | - Anand D Shah
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
| | | | - Michael S. Lloyd
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
| | - Michael A. Burke
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
| | - Mani A Daneshmand
- Division of Cardiovascular Surgery, Department of Surgery, Emory University School of Medicine, Atlanta, GA
| | - Tamer S Attia
- Division of Cardiovascular Surgery, Department of Surgery, Emory University School of Medicine, Atlanta, GA
| | - J David Vega
- Division of Cardiovascular Surgery, Department of Surgery, Emory University School of Medicine, Atlanta, GA
| | - Michael El-Chami
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
| | - Faisal M. Merchant
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
| | | | - Neal K. Bhatia
- Department of Cardiovascular Medicine, Emory University School of Medicine, Atlanta, GA
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Phadumdeo VM, Mallare BL, Hund TJ, Weinberg SH. Long-term changes in heart rate and electrical remodeling contribute to alternans formation in heart failure: a patient-specific in silico study. Am J Physiol Heart Circ Physiol 2023; 325:H414-H431. [PMID: 37417871 DOI: 10.1152/ajpheart.00220.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Revised: 06/26/2023] [Accepted: 06/29/2023] [Indexed: 07/08/2023]
Abstract
Individuals with chronic heart failure (CHF) have an increased risk of ventricular arrhythmias, which has been linked to pathological cellular remodeling and may also be mediated by changes in heart rate. Heart rate typically fluctuates on a timescale ranging from seconds to hours, termed heart rate variability (HRV). This variability is reduced in CHF, and this HRV reduction is associated with a greater risk for arrhythmias. Furthermore, variations in heart rate influence the formation of proarrhythmic alternans, a beat-to-beat alternation in the action potential duration (APD), or intracellular calcium (Ca). In this study, we investigate how long-term changes in heart rate and electrical remodeling associated with CHF influence alternans formation. We measure key statistical properties of the RR-interval sequences from ECGs of individuals with normal sinus rhythm (NSR) and CHF. Patient-specific RR-interval sequences and synthetic sequences (randomly generated to mimicking these statistical properties) are used as the pacing protocol for a discrete time-coupled map model that governs APD and intracellular Ca handling of a single cardiac myocyte, modified to account for pathological electrical remodeling in CHF. Patient-specific simulations show that beat-to-beat differences in APD vary temporally in both populations, with alternans formation more prevalent in CHF. Parameter studies using synthetic sequences demonstrate that increasing the autocorrelation time or mean RR-interval reduces APD alternations, whereas increasing the RR-interval standard deviation leads to higher alternans magnitudes. Importantly, we find that although both the CHF-associated changes in heart rate and electrical remodeling influence alternans formation, variations in heart rate may be more influential.NEW & NOTEWORTHY Using patient-specific data, we show that both the changes in heart rate and electrical remodeling associated with chronic heart failure influence the formation of proarrhythmic alternans in the heart.
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Affiliation(s)
- Vrishti M Phadumdeo
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
| | - Brianna L Mallare
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
| | - Thomas J Hund
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio, United States
- Department of Internal Medicine, The Ohio State University, Columbus, Ohio, United States
| | - Seth H Weinberg
- Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio, United States
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10
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Ferreira G, Cardozo R, Sastre S, Costa C, Santander A, Chavarría L, Guizzo V, Puglisi J, Nicolson GL. Bacterial toxins and heart function: heat-labile Escherichia coli enterotoxin B promotes changes in cardiac function with possible relevance for sudden cardiac death. Biophys Rev 2023; 15:447-473. [PMID: 37681088 PMCID: PMC10480140 DOI: 10.1007/s12551-023-01100-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Accepted: 07/11/2023] [Indexed: 09/09/2023] Open
Abstract
Bacterial toxins can cause cardiomyopathy, though it is not its most common cause. Some bacterial toxins can form pores in the membrane of cardiomyocytes, while others can bind to membrane receptors. Enterotoxigenic E. coli can secrete enterotoxins, including heat-resistant (ST) or labile (LT) enterotoxins. LT is an AB5-type toxin that can bind to specific cell receptors and disrupt essential host functions, causing several common conditions, such as certain diarrhea. The pentameric B subunit of LT, without A subunit (LTB), binds specifically to certain plasma membrane ganglioside receptors, found in lipid rafts of cardiomyocytes. Isolated guinea pig hearts and cardiomyocytes were exposed to different concentrations of purified LTB. In isolated hearts, mechanical and electrical alternans and an increment of heart rate variability, with an IC50 of ~0.2 μg/ml LTB, were observed. In isolated cardiomyocytes, LTB promoted significant decreases in the amplitude and the duration of action potentials. Na+ currents were inhibited whereas L-type Ca2+ currents were augmented at their peak and their fast inactivation was promoted. Delayed rectifier K+ currents decreased. Measurements of basal Ca2+ or Ca2+ release events in cells exposed to LTB suggest that LTB impairs Ca2+ homeostasis. Impaired calcium homeostasis is linked to sudden cardiac death. The results are consistent with the recent view that the B subunit is not merely a carrier of the A subunit, having a role explaining sudden cardiac death in children (SIDS) infected with enterotoxigenic E. coli, explaining several epidemiological findings that establish a strong relationship between SIDS and ETEC E. coli. Supplementary Information The online version contains supplementary material available at 10.1007/s12551-023-01100-6.
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Affiliation(s)
- Gonzalo Ferreira
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics, Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - Romina Cardozo
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics, Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - Santiago Sastre
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics and Centro de Investigaciones Biomédicas (CeInBio), Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - Carlos Costa
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics, Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - Axel Santander
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics, Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - Luisina Chavarría
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics, Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - Valentina Guizzo
- Ion Channels, Biological Membranes and Cell Signaling Laboratory, Dept. Of Biophysics, Facultad de Medicina, Universidad de la Republica, Gral Flores 2125, 11800 Montevideo, CP Uruguay
| | - José Puglisi
- College of Medicine, California North State University, 9700 West Taron Drive, Elk Grove, CA 95757 USA
| | - G. L. Nicolson
- Institute for Molecular Medicine, Beach, Huntington, CA USA
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Iravanian S, Uzelac I, Shah AD, Toye MJ, Lloyd MS, Burke MA, Daneshmand MA, Attia TS, Vega JD, Merchant FM, Cherry EM, Bhatia NK, Fenton FH. Beyond Alternans: Detection of Higher-Order Periodicity in Ex-Vivo Human Ventricles Before Induction of Ventricular Fibrillation. bioRxiv 2023:2023.05.01.539003. [PMID: 37205562 PMCID: PMC10187180 DOI: 10.1101/2023.05.01.539003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Background Repolarization alternans, defined as period-2 oscillation in the repolarization phase of the action potentials, is one of the cornerstones of cardiac electrophysiology as it provides a mechanistic link between cellular dynamics and ventricular fibrillation (VF). Theoretically, higher-order periodicities (e.g., period-4, period-8,...) are expected but have very limited experimental evidence. Methods We studied explanted human hearts, obtained from the recipients of heart transplantation at the time of surgery, using optical mapping technique with transmembrane voltage-sensitive fluorescent dyes. The hearts were stimulated at an increasing rate until VF was induced. The signals recorded from the right ventricle endocardial surface just before the induction of VF and in the presence of 1:1 conduction were processed using the Principal Component Analysis and a combinatorial algorithm to detect and quantify higher-order dynamics. Results A prominent and statistically significant 1:4 peak (corresponding to period-4 dynamics) was seen in three of the six studied hearts. Local analysis revealed the spatiotemporal distribution of higher-order periods. Period-4 was localized to temporally stable islands. Higher-order oscillations (period-5, 6, and 8) were transient and primarily occurred in arcs parallel to the activation isochrones. Discussion We present evidence of higher-order periodicities and the co-existence of such regions with stable non-chaotic areas in ex-vivo human hearts before VF induction. This result is consistent with the period-doubling route to chaos as a possible mechanism of VF initiation, which complements the concordant to discordant alternans mechanism. The presence of higher-order regions may act as niduses of instability that can degenerate into chaotic fibrillation.
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Kanaporis G, Martinez‐Hernandez E, Blatter LA. Calcium- and voltage-driven atrial alternans: Insight from [Ca] i and V m asynchrony. Physiol Rep 2023; 11:e15703. [PMID: 37226365 PMCID: PMC10209431 DOI: 10.14814/phy2.15703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 04/21/2023] [Accepted: 04/23/2023] [Indexed: 05/26/2023] Open
Abstract
Cardiac alternans is defined as beat-to-beat alternations in contraction strength, action potential duration (APD), and Ca transient (CaT) amplitude. Cardiac excitation-contraction coupling relies on the activity of two bidirectionally coupled excitable systems, membrane voltage (Vm ) and Ca release. Alternans has been classified as Vm - or Ca-driven, depending whether a disturbance of Vm or [Ca]i regulation drives the alternans. We determined the primary driver of pacing induced alternans in rabbit atrial myocytes, using combined patch clamp and fluorescence [Ca]i and Vm measurements. APD and CaT alternans are typically synchronized; however, uncoupling between APD and CaT regulation can lead to CaT alternans in the absence of APD alternans, and APD alternans can fail to precipitate CaT alternans, suggesting a considerable degree of independence of CaT and APD alternans. Using alternans AP voltage clamp protocols with extra APs showed that most frequently the pre-existing CaT alternans pattern prevailed after the extra-beat, indicating that alternans is Ca-driven. In electrically coupled cell pairs, dyssynchrony of APD and CaT alternans points to autonomous regulation of CaT alternans. Thus, with three novel experimental protocols, we collected evidence for Ca-driven alternans; however, the intimately intertwined regulation of Vm and [Ca]i precludes entirely independent development of CaT and APD alternans.
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Affiliation(s)
- G. Kanaporis
- Department of Physiology & BiophysicsRush University Medical CenterChicagoIllinoisUSA
| | - E. Martinez‐Hernandez
- Department of Physiology & BiophysicsRush University Medical CenterChicagoIllinoisUSA
| | - L. A. Blatter
- Department of Physiology & BiophysicsRush University Medical CenterChicagoIllinoisUSA
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Netiazhenko VZ, Mostovyi SE, Safonova OM. The Impact of COVID-19 upon Intracardiac Hemodynamics and Heart Rate Variability in Stable Coronary Artery Disease Patients. ujcvs 2023. [DOI: 10.30702/ujcvs/23.31(01)/nm009-1928] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
Abstract
The aim. To study the impact of COVID-19 upon intracardiac hemodynamics and heart rate variability (HRV) in stable coronary artery disease (SCAD) patients.
Materials and methods. In this cross-sectional study we analyzed clinical and instrumental data obtained from a sample of 80 patients. The patients were divided into three groups: group 1 included patients with SCAD without COVID-19 (n=30), group 2 included patients with SCAD and COVID-19 (n=25), and group 3 included patients with COVID-19 without SCAD (n=25). The control group included 30 relatively healthy volunteers.
Results. The changes in intracardiac hemodynamics and HRV in group 2 were characterized by the impaired left ventricular systolic and diastolic function, dilation of both ventricles and elevated systolic pulmonary artery pressure. Left ventricular end-diastolic volume was higher in group 2 (205±21 ml) than that in group 1 (176±33 ml; р<0.001) and group 3 (130±21 ml; р<0.001). Patients in the groups 1–3, compared to controls, presented with the decrease in the overall HRV (by standard deviation [SD] of all NN intervals [SDNN]; SD of the averages of NN intervals in all 5 min segments of the entire recording; and mean of the SDs of all NN intervals for all 5 min segments of the entire recording) and parasympathetic activity (root-mean-square difference of successive NN intervals; the proportion derived by dividing the number of interval differences of successive NN intervals greater than 50 ms [NN50] by the total number of NN intervals [pNN50], and high frequency spectral component), along with QT interval prolongation and increase in its variability. Group 2 demonstrated the most advanced changes in HRV (by SDNN and pNN50) and both QT interval characteristics.
Conclusions. The patients with SCAD and concomitant COVID-19, along with both ventricles dilation and intracardiac hemodynamics impairment, presented with the sings of autonomic dysfunction, QT interval prolongation and increase in its variability. The heart rate variability and QT interval characteristics should be additionally considered in the management of such patients.
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