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Ye C, Yang C, Zhang H, Gao R, Liao Y, Zhang Y, Jie L, Zhang Y, Cheng T, Wang Y, Ren J. Canonical Wnt signaling directs the generation of functional human PSC-derived atrioventricular canal cardiomyocytes in bioprinted cardiac tissues. Cell Stem Cell 2024; 31:398-409.e5. [PMID: 38366588 DOI: 10.1016/j.stem.2024.01.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2023] [Revised: 12/13/2023] [Accepted: 01/24/2024] [Indexed: 02/18/2024]
Abstract
The creation of a functional 3D bioprinted human heart remains challenging, largely due to the lack of some crucial cardiac cell types, including the atrioventricular canal (AVC) cardiomyocytes, which are essential to slow down the electrical impulse between the atrium and ventricle. By utilizing single-cell RNA sequencing analysis and a 3D bioprinting technology, we discover that stage-specific activation of canonical Wnt signaling creates functional AVC cardiomyocytes derived from human pluripotent stem cells. These cardiomyocytes display morphological characteristics and express molecular markers of AVC cardiomyocytes, including transcription factors TBX2 and MSX2. When bioprinted in prefabricated cardiac tissues, these cardiomyocytes successfully delay the electrical impulse, demonstrating their capability of functioning as the AVC cardiomyocytes in vitro. Thus, these findings not only identify canonical Wnt signaling as a key regulator of the AVC cardiomyocyte differentiation in vitro, but, more importantly, provide a critical cellular source for the biofabrication of a functional human heart.
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Affiliation(s)
- Chenxi Ye
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China
| | - Chuanlai Yang
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, National Institute of Diagnostics and Vaccine Development in Infectious Diseases, School of Life Sciences, School of Public Health, Xiamen University, Xiamen 361102, Fujian, China
| | - Heqiang Zhang
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China
| | - Rui Gao
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China
| | - Yingnan Liao
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China
| | - Yali Zhang
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, National Institute of Diagnostics and Vaccine Development in Infectious Diseases, School of Life Sciences, School of Public Health, Xiamen University, Xiamen 361102, Fujian, China
| | - Lingjun Jie
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China
| | - Yanhui Zhang
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China
| | - Tong Cheng
- State Key Laboratory of Molecular Vaccinology and Molecular Diagnostics, National Institute of Diagnostics and Vaccine Development in Infectious Diseases, School of Life Sciences, School of Public Health, Xiamen University, Xiamen 361102, Fujian, China
| | - Yan Wang
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China.
| | - Jie Ren
- Institute of Cardiovascular Diseases, Xiamen Cardiovascular Hospital, School of Medicine, Xiamen University, Xiamen 361006, Fujian, China.
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Da Silveira Cavalcante L, Higuita ML, González-Rosa JM, Marques B, To S, Pendexter CA, Cronin SE, Gopinathan K, de Vries RJ, Ellett F, Uygun K, Langenau DM, Toner M, Tessier SN. Zebrafish as a high throughput model for organ preservation and transplantation research. FASEB J 2023; 37:e23187. [PMID: 37718489 PMCID: PMC10754348 DOI: 10.1096/fj.202300076r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Revised: 08/15/2023] [Accepted: 08/24/2023] [Indexed: 09/19/2023]
Abstract
Despite decades of effort, the preservation of complex organs for transplantation remains a significant barrier that exacerbates the organ shortage crisis. Progress in organ preservation research is significantly hindered by suboptimal research tools that force investigators to sacrifice translatability over throughput. For instance, simple model systems, such as single cell monolayers or co-cultures, lack native tissue structure and functional assessment, while mammalian whole organs are complex systems with confounding variables not compatible with high-throughput experimentation. In response, diverse fields and industries have bridged this experimental gap through the development of rich and robust resources for the use of zebrafish as a model organism. Through this study, we aim to demonstrate the value zebrafish pose for the fields of solid organ preservation and transplantation, especially with respect to experimental transplantation efforts. A wide array of methods were customized and validated for preservation-specific experimentation utilizing zebrafish, including the development of assays at multiple developmental stages (larvae and adult), methods for loading and unloading preservation agents, and the development of viability scores to quantify functional outcomes. Using this platform, the largest and most comprehensive screen of cryoprotectant agents (CPAs) was performed to determine their toxicity and efficiency at preserving complex organ systems using a high subzero approach called partial freezing (i.e., storage in the frozen state at -10°C). As a result, adult zebrafish cardiac function was successfully preserved after 5 days of partial freezing storage. In combination, the methods and techniques developed have the potential to drive and accelerate research in the fields of solid organ preservation and transplantation.
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Affiliation(s)
- Luciana Da Silveira Cavalcante
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Manuela Lopera Higuita
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Juan Manuel González-Rosa
- Cardiovascular Research Center, Massachusetts General Hospital Research Institute, Harvard Medical School, Charlestown MA, USA
| | - Beatriz Marques
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
| | - Samantha To
- Cardiovascular Research Center, Massachusetts General Hospital Research Institute, Harvard Medical School, Charlestown MA, USA
| | - Casie A. Pendexter
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Stephanie E.J. Cronin
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Kaustav Gopinathan
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
| | - Reinier J. de Vries
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Felix Ellett
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Korkut Uygun
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - David M. Langenau
- Molecular Pathology Unit and Cancer Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA
| | - Mehmet Toner
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
| | - Shannon N. Tessier
- Center for Engineering in Medicine and Surgery, Harvard Medical School and Massachusetts General Hospital, Boston MA, USA
- Shriners Hospitals for Children - Boston, Boston MA, USA
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Lemke L, El Hamriti M, Braun M, Baridwan N, Sciacca V, Fink T, Khalaph M, Guckel D, Eitz T, Sohns C, Sommer P, Imnadze G. AV-node isolation as an alternative to AV-node ablation in patients undergoing pace & ablate strategy. J Cardiovasc Electrophysiol 2022; 33:2606-2613. [PMID: 36218022 DOI: 10.1111/jce.15699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/26/2022] [Accepted: 09/29/2022] [Indexed: 12/15/2022]
Abstract
INTRODUCTION Atrioventricular (AV)-node ablation (AVNA) is a common therapy option for rate control strategy of permanent atrial fibrillation (AF). We hypothesized that isolation of the AV nodal isolation (AVNI) is associated with a more frequent preservation of an adequate escape rhythm compared to AVNA. METHODS This retrospective study included 20 patients with therapy-refractory AF being treated with AVNI and 40 historical AVNA-controls. In AVNI the AV-node region was mapped using a 3D mapping system. Ablation was performed around the previously mapped HIS-cloud regions isolating the atrium from the AV-node. In the AVNI group, ablation was performed with irrigated tip ablation catheter in all cases. The two approaches were compared regarding rate of escape rhythm, delta QRS, and procedural data. RESULTS The number of patients with adequate escape rhythm in AVNI was significantly superior to AVNA immediately postoperative (90% vs. 40%, p < 0.01) and during follow-up (77% vs. 36%, p < 0.05). The median change in QRS width was 0 ms in AVNI versus +26 ms in AVNA (p < 0.01). Thirty percent new bundle branch blocks in AVNA were observed compared to 0% in AVNI (p < 0.01). In the AVNI group, fluoroscopy time and total dose area product were significantly lower (p < 0.01). CONCLUSION The present study suggests that AV-node isolation using 3D navigation mapping system is a feasible and effective alternative to conventional AVNA. The precise application of radiofrequency lesions preserves a stable AV-junctional rhythm.
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Affiliation(s)
- Lisa Lemke
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Mustapha El Hamriti
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Martin Braun
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Nafilah Baridwan
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Vanessa Sciacca
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Thomas Fink
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Moneeb Khalaph
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Denise Guckel
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Thomas Eitz
- Clinic for Thoracic and Cardiovascular Surgery, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Christian Sohns
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Philipp Sommer
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
| | - Guram Imnadze
- Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany
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Yuasa M, Kojima A, Mi X, Ding WG, Omatsu-Kanbe M, Kitagawa H, Matsuura H. Characterization and functional role of rapid- and slow-activating delayed rectifier K + currents in atrioventricular node cells of guinea pigs. Pflugers Arch 2021; 473:1885-1898. [PMID: 34704178 DOI: 10.1007/s00424-021-02617-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 08/05/2021] [Accepted: 08/19/2021] [Indexed: 01/28/2023]
Abstract
The atrioventricular (AV) node is the only conduction pathway where electrical impulse can pass from atria to ventricles and exhibits spontaneous automaticity. This study examined the function of the rapid- and slow-activating delayed rectifier K+ currents (IKr and IKs) in the regulation of AV node automaticity. Isolated AV node cells from guinea pigs were current- and voltage-clamped to record the action potentials and the IKr and IKs current. The expression of IKr or IKs was confirmed in the AV node cells by immunocytochemistry, and the positive signals of both channels were localized mainly on the cell membrane. The basal spontaneous automaticity was equally reduced by E4031 and HMR-1556, selective blockers of IKr and IKs, respectively. The nonselective β-adrenoceptor agonist isoproterenol markedly increased the firing rate of action potentials. In the presence of isoproterenol, the firing rate of action potentials was more effectively reduced by the IKs inhibitor HMR-1556 than by the IKr inhibitor E4031. Both E4031 and HMR-1556 prolonged the action potential duration and depolarized the maximum diastolic potential under basal and β-adrenoceptor-stimulated conditions. IKr was not significantly influenced by β-adrenoceptor stimulation, but IKs was concentration-dependently enhanced by isoproterenol (EC50: 15 nM), with a significant negative voltage shift in the channel activation. These findings suggest that both the IKr and IKs channels might exert similar effects on regulating the repolarization process of AV node action potentials under basal conditions; however, when the β-adrenoceptor is activated, IKs modulation may become more important.
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Affiliation(s)
- Mayumi Yuasa
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan
| | - Akiko Kojima
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan
| | - Xinya Mi
- Department of Physiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan
| | - Wei-Guang Ding
- Department of Physiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan.
| | - Mariko Omatsu-Kanbe
- Department of Physiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan
| | - Hirotoshi Kitagawa
- Department of Anesthesiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan
| | - Hiroshi Matsuura
- Department of Physiology, Shiga University of Medical Science, Otsu, Shiga, 520-2192, Japan
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Leonelli F, De Ponti R, Bagliani G. Atrio-ventricular junction: Can precision electrocardiology bridge cell and electrocardiogram? J Electrocardiol 2020; 60:82-91. [PMID: 32335413 DOI: 10.1016/j.jelectrocard.2020.02.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 01/24/2020] [Accepted: 02/20/2020] [Indexed: 11/18/2022]
Abstract
The Atrio Ventricular Junction (AVJ) is a well-defined anatomical region of the heart the physiology of which, despite extensive and numerous observations, it is not fully understood. The aim of this review is to present an up to date summary of old and more recent findings on histology, cellular electrophysiology and intracellular connectivity of this region. We have also attempted to relate our increasing understanding of nodal pathophysiology to the interpretation of the electrocardiographic (ECG) manifestations of AVN behavior. Bridging cellular observations with ECG analysis in a process we call "Precision Electrocardiology" renders this tool far more sensitive and clinically useful than the pattern analysis too often employed in the ECG interpretation.
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Affiliation(s)
- Fabio Leonelli
- James A Haley Veterans' Hospital, University of South Florida, Tampa, FL, United States of America.
| | - Roberto De Ponti
- Department of Heart and Vessels, Ospedale di Circolo-University of Insubria, Varese, Italy
| | - Giuseppe Bagliani
- Foligno General Hospital, Cardiology Department, Arrhythmology Unit, Foligno, Perugia, Italy
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6
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Lagerqvist E, Finnin B, Elliott D, Anderson D, Wu S, Pouton C, Haynes J. Comparing mouse and human pluripotent stem cell derived cardiac cells: Both systems have advantages for pharmacological and toxicological screening. J Pharmacol Toxicol Methods 2015; 74:17-25. [DOI: 10.1016/j.vascn.2015.04.009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Revised: 04/21/2015] [Accepted: 04/29/2015] [Indexed: 12/13/2022]
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7
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Pauza DH, Rysevaite K, Inokaitis H, Jokubauskas M, Pauza AG, Brack KE, Pauziene N. Innervation of sinoatrial nodal cardiomyocytes in mouse. A combined approach using immunofluorescent and electron microscopy. J Mol Cell Cardiol 2014; 75:188-97. [PMID: 25101952 DOI: 10.1016/j.yjmcc.2014.07.016] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Revised: 07/10/2014] [Accepted: 07/28/2014] [Indexed: 11/28/2022]
Abstract
Fluorescent immunohistochemistry on the cardiac conduction system in whole mount mouse heart preparations demonstrates a particularly dense and complex network of nerve fibres and cardiomyocytes which are positive to the hyperpolarization activated cyclic nucleotide-gated potassium channel 4 (HCN4-positive cardiomyocytes) in the sinoatrial node region and adjacent areas around the root of right cranial vein. The present study was designed to investigate the morphologic and histochemical pattern of nerve fibres and HCN4-positive cardiomyocytes using fluorescent techniques and/or electron microscopy. Adrenergic and cholinergic nerve fibres together with HCN4-positive cardiomyocytes were identified using primary antibodies for tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), and the HCN4 channel respectively. Amid HCN4-positive cardiomyocytes, fluorescence and electron microscopy data demonstrated a dense distribution of nerve fibres immunoreactive for ChAT and TH. In addition, novel electron microscopy data revealed that the mouse sinoatrial node contained exclusively unmyelinated nerve fibres, in which the majority of axons possess varicosities with clear mediatory vesicles that can be classified as cholinergic. Synapses occurred without any clear terminal connection with the effector cell, i.e. these synapes were of "en passant" type. In general, the morphologic pattern of innervation of mouse HCN4-positive cardiomyocytes identified using electron microscopy corresponds well to the dense network of nerve fibres demonstrated by fluorescent immunohistochemistry in mouse sinoatrial node and adjacent areas. The complex and extraordinarily dense innervation of HCN4-positive cardiomyocytes in mouse sinoatrial node underpins the importance of neural regulation for the cardiac conduction system. Based on the present observations, it is concluded that the occurrence of numerous nerve fibres nearby atrial cardiomyocytes serves as a novel reliable extracellular criterion for discrimination of SA nodal cardiomyocytes using electron microscopy.
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Affiliation(s)
- Dainius H Pauza
- Institute of Anatomy, Faculty of Medicine, Lithuanian University of Health Sciences, Kaunas, Lithuania.
| | - Kristina Rysevaite
- Institute of Anatomy, Faculty of Medicine, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Hermanas Inokaitis
- Institute of Anatomy, Faculty of Medicine, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Marius Jokubauskas
- Institute of Anatomy, Faculty of Medicine, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Audrys G Pauza
- Institute of Anatomy, Faculty of Medicine, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Kieran E Brack
- Department of Cardiovascular Sciences and NIHR Leicester Cardiovascular Biomedical Research Unit, University of Leicester, Leicester, UK
| | - Neringa Pauziene
- Institute of Anatomy, Faculty of Medicine, Lithuanian University of Health Sciences, Kaunas, Lithuania
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Aslanidi OV, Nikolaidou T, Zhao J, Smaill BH, Gilbert SH, Holden AV, Lowe T, Withers PJ, Stephenson RS, Jarvis JC, Hancox JC, Boyett MR, Zhang H. Application of micro-computed tomography with iodine staining to cardiac imaging, segmentation, and computational model development. IEEE TRANSACTIONS ON MEDICAL IMAGING 2013; 32:8-17. [PMID: 22829390 PMCID: PMC3493467 DOI: 10.1109/tmi.2012.2209183] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Micro-computed tomography (micro-CT) has been widely used to generate high-resolution 3-D tissue images from small animals nondestructively, especially for mineralized skeletal tissues. However, its application to the analysis of soft cardiovascular tissues has been limited by poor inter-tissue contrast. Recent ex vivo studies have shown that contrast between muscular and connective tissue in micro-CT images can be enhanced by staining with iodine. In the present study, we apply this novel technique for imaging of cardiovascular structures in canine hearts. We optimize the method to obtain high-resolution X-ray micro-CT images of the canine atria and its distinctive regions-including the Bachmann's bundle, atrioventricular node, pulmonary arteries and veins-with clear inter-tissue contrast. The imaging results are used to reconstruct and segment the detailed 3-D geometry of the atria. Structure tensor analysis shows that the arrangement of atrial fibers can also be characterized using the enhanced micro-CT images, as iodine preferentially accumulates within the muscular fibers rather than in connective tissues. This novel technique can be particularly useful in nondestructive imaging of 3-D cardiac architectures from large animals and humans, due to the combination of relatively high speed ( ~ 1 h/per scan of the large canine heart) and high voxel resolution (36 μm) provided. In summary, contrast micro-CT facilitates fast and nondestructive imaging and segmenting of detailed 3-D cardiovascular geometries, as well as measuring fiber orientation, which are crucial in constructing biophysically detailed computational cardiac models.
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Affiliation(s)
- Oleg V Aslanidi
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, London, UK.
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T N, OV A, H Z, IR E. Structure-function relationship in the sinus and atrioventricular nodes. Pediatr Cardiol 2012; 33:890-9. [PMID: 22391764 PMCID: PMC3703519 DOI: 10.1007/s00246-012-0249-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Accepted: 02/15/2012] [Indexed: 01/31/2023]
Abstract
Recently published optical mapping studies of larger mammals, including humans, have identified functionally discrete sinoatrial exit pathways of activation. This is in line with earlier mapping studies of the dog and the human but in contrast with findings in the mouse and the rabbit, wherein a propagation wave front pattern of activation has been described. It underpins the complex three-dimensional (3D) organization of the cardiac pacemaking and conduction system in larger species, wherein sinoatrial and atrioventricular nodal physiologies both demonstrate identifiable activation pathways, which coincide with anatomic landmarks and histologic architecture, so that in addition to muscle fiber orientation and cell coupling, these intrinsic factors act to determine excitation pathways. This complex 3D organization increases the effect of source-to-sink mismatch both by greater variability in the space constant of tissue and by the 3D projection of this effect in all directions. Mathematical modeling provides a means to study these interactions, and newer models should incorporate these additional factors and their effect into the 3D structure of large mammal physiology.
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Affiliation(s)
- Nikolaidou T
- Department of Biomedical Engineering, Washington University, St Louis, USA,Faculty of Medical & Human Sciences, University of Manchester, Manchester, UK
| | - Aslanidi OV
- Department of Biomedical Engineering, King's College London, London, UK,School of Physics & Astronomy, University of Manchester, Manchester, UK
| | - Zhang H
- School of Physics & Astronomy, University of Manchester, Manchester, UK
| | - Efimov IR
- Department of Biomedical Engineering, Washington University, St Louis, USA
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JAMALEDDINE RABIHS, VINET ALAIN. ROLE OF GAP JUNCTION RESISTANCE IN RATE-INDUCED DELAY IN CONDUCTION IN A CABLE MODEL OF THE ATRIOVENTRICULAR NODE. J BIOL SYST 2011. [DOI: 10.1142/s0218339099000279] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A constant fast heart rate results in a time and rate dependent increase in AV nodal conduction time. The origin of this delay in conduction remains unknown due to limited access to corresponding cellular events. We have investigated the possible contribution of gap junction resistance in rate-induced delay in conduction using a one-dimensional model of the AV node. We use a cable that includes 100 cells: 30 AN cells, 40 N cells and 30 NH cells. The three cell types are modeled by varying the parameters of a modified Beeler Reuter ionic model. N cells have a low density of sodium current and are mainly activated by an ICa,L type current. Their resting potential is less negative and their upstroke slower than those of AN and NH cells. Cells are connected by gap junctions whose resistance is controlled by the intracellular calcium concentration. Stimuli are applied to the first AN cells. At a pacing rate of 400 ms, the gap junction resistance was AN 1.8 MΩ, N 32.0 MΩ and NH 3.6 MΩ and the total conduction time was 48 ms. Following a sudden decrease of cycle length from 400 ms to 250 ms, the conduction time progressively increased and reached a new steady-state of 77.7 ms after 800 beats. This increase of conduction time was mainly caused by a gradual increase of the gap junction resistance between N cells, which reached 46 MΩ at steady state. Rate and time dependent increase of conduction time was abolished when the gap junction resistances were kept constant. This model study suggests that the dynamic changes in gap junction resistance may play a key role in rate-induced AV nodal conduction delay.
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Affiliation(s)
- RABIH S. JAMALEDDINE
- Institut de Génie Biomédical, Université de Montréal, Centre de Recherche de l'Hôpital du Sacré-Coeur, Canada
| | - ALAIN VINET
- Institut de Génie Biomédical, Université de Montréal, Centre de Recherche de l'Hôpital du Sacré-Coeur, Canada
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REN FX, NIU XL, OU Y, HAN ZH, LING FD, ZHOU SS, LI YJ. Morphological and electrophysiological properties of single myocardial cells from Koch triangle of rabbit heart. Chin Med J (Engl) 2006. [DOI: 10.1097/00029330-200612020-00009] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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12
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Kose S, Amasyali B, Aytemir K, Kilic A, Can I, Kursaklioglu H, Celik T, Isik E. Atrioventricular nodal reentrant tachycardia with multiple discontinuities in the atrioventricular node conduction curve: immediate success rates of radiofrequency ablation and long-term clinical follow-up results as compared to patients with single or no AH-jumps. J Interv Card Electrophysiol 2004; 10:249-54. [PMID: 15133363 DOI: 10.1023/b:jice.0000026920.40169.9f] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
BACKGROUND Some patients with atrioventricular nodal reentrant tachycardia (AVNRT) demonstrate multiple discontinuities (AH jump) in their antegrade AV node conduction curves. We evaluated and compared the immediate success rates, procedure-related complications, long-term clinical follow-up results and recurrence rates after slow pathway ablation in patients with multiple versus single or no AH jumps. METHODS The study group consists of 278 consecutive patients (mean age 36.6 +/- 15.7) who underwent ablation for typical AVNRT, divided into three categories according to the number of AH jumps (>/=50 ms) before ablation: Group-1 consisted of 63 patients (23%) with continuous AV node function curves; Group-2 of 183 patients (66%) with a single jump and Group-3 of 32 (12%) patients showing more than one AH jumps. RESULTS Age was significantly higher in Group-3 as compared to Group-1 (43 +/- 18 years vs. 34 +/- 16 years, p = 0.020). The electrophysiological features of AVNRT did not differ among groups. Before ablation, the maximum AH interval was significantly longer in Group-3 as compared to Groups-1 and -2 ( p < 0.001 for both). AV node antegrade ERP was significantly shorter in Group-3 than in Group-2, both before and after ablation ( p < 0.050 for both). AV node Wenckebach cycle length (WCL) was shorter in Group-3 as compared to both Groups-1 and -2, before and after ablation ( p < 0.050 for all). AV node WCL was prolonged significantly in all groups after ablation ( p < 0.001 for all). Residual dual pathways were present in 37 of 278 patients (13%) after ablation and were significantly more frequent in Group-3 than Group-2 (31% vs. 15%, p = 0.023). CONCLUSIONS Patients with multiple AH jumps are older and more often have residual dual atrioventricular nodal pathway physiology after successful ablation but these features do not affect the immediate and long-term success rates of slow pathway ablation as compared to patients with single or no AH jumps.
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Affiliation(s)
- Sedat Kose
- Gulhane Military Medical Academy, Department of Cardiology, Ankara, Turkey
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Geller JC, Biblo LA, Carlson MD. Relation Between the AH Interval and the Ablation Site in Patients with Atrioventricular Nodal Reentrant Tachycardia. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2004; 27:1347-54. [PMID: 15511243 DOI: 10.1111/j.1540-8159.2004.00638.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The determinants of slow pathway conduction in patients with AV nodal reentrant tachycardia (AVNRT) are still unknown, and great differences in the AH interval during slow pathway conduction are observed between patients. In 35 patients with typical AVNRT who underwent successful slow pathway ablation (defined as complete elimination of dual pathway physiology), the A2H2 interval at the "jump" during programmed atrial stimulation and the AH interval during AVNRT (as a reflection of slow pathway conduction time) and the fluoroscopic distance between the successful ablation site and the His-bundle recording site and between the coronary sinus ostium (CSO) and the His-bundle recording site were determined. The mean (+/- SEM) AH interval during slow pathway conduction was 323 +/- 12 ms with programmed stimulation and 310 +/- 10 ms during AVNRT. The mean number of energy applications was 8 +/- 1 (range 1-21). The mean distances between (1) the successful ablation site and the His bundle recording site and (2) between the CSO and the His-bundle recording site were 24 +/- 1 and 28 +/- 1 mm in the RAO and 23 +/- 1 and 28 +/- 1 mm in the LAO projections, respectively. The AH interval during slow pathway conduction correlated significantly with the distance between the successful ablation site and the His-bundle (P < 0.001) but not with the distance between CSO and His-bundle recording site. There is a significant correlation between the AH interval during slow pathway conduction and the distance of the successful ablation site from the His bundle. This relationship (1) suggests that, in addition to functional factors, anatomic factors influence slow pathway conduction and (2) may be helpful in determining the initial energy application site during slow pathway ablation.
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Affiliation(s)
- J Christoph Geller
- Division of Cardiology, University Hospitals of Cleveland, Case Western Reserve University, Cleveland, Ohio 44106, USA
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James TN. Structure and function of the sinus node, AV node and his bundle of the human heart: part II--function. Prog Cardiovasc Dis 2003; 45:327-60. [PMID: 12638096 DOI: 10.1053/pcad.2003.1] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Thomas N James
- Department of Medicine, The University of Texas Medical Branch at Galveston, TX 77555-0175, USA
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James TN. Structure and function of the sinus node, AV node and His bundle of the human heart: part I-structure. Prog Cardiovasc Dis 2002; 45:235-67. [PMID: 12525999 DOI: 10.1053/pcad.2002.130388] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Thomas N James
- Department of Medicine, The University of Texas Medical Branch at Galveston, 77555-0175, USA
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Affiliation(s)
- T N James
- Department of Medicine and the Department of Pathology, University of Texas Medical Branch, Galveston, TX 77555-0175, USA
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Tsuchiya T, Okumura K, Honda T, Iwasa A, Ashikaga K. Effects of verapamil and lidocaine on two components of the re-entry circuit of verapamil-senstitive idiopathic left ventricular tachycardia. J Am Coll Cardiol 2001; 37:1415-21. [PMID: 11300455 DOI: 10.1016/s0735-1097(01)01117-2] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OBJECTIVES We characterized pharmacologically the slow conduction zone of verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) with regard to the late diastolic potential (LDP). BACKGROUND We showed that the slow conduction zone of ILVT could be divided into two components by LDP; that is, the distal component with a tachycardia-dependent conduction delay property and the proximal one without it. METHODS Electrophysiologic studies were performed in eight consecutive patients. The LDP was recorded during left ventricular (LV) mapping during ILVT. Entrainment was performed from the right ventricular outflow tract while recording LDP. The effects of lidocaine (1 mg/kg body weight) and verapamil (0.5 or 1.0 mg) were examined during entrainment. RESULTS The LDPs preceding the Purkinje potential (PP) were serially recorded from the upper third to the middle of the LV septum along the narrow longitudinal line. The ventricular tachycardia (VT) cycle length increased after lidocaine (p < 0.05), and further after verapamil (p < 0.05). The increments in the VT cycle length after administration of the drugs strongly correlated with those in LDP-PP (r > 0.9 for both drugs). The interval from the ventricular potential to LDP was unchanged after administration of the drugs. In one patient, verapamil terminated VT by local conduction block between LDP and PP. The LDP-PP measured during entrainment increased after lidocaine, and further after verapamil, whereas the interval from the stimulus to LDP remained unchanged. CONCLUSIONS The component distal to LDP is mainly calcium channel-dependent and partly depressed sodium channel-dependent. The proximal component is considered to be sodium channel-dependent (normal).
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Affiliation(s)
- T Tsuchiya
- Cardiovascular Center, Saiseikai Kumamoto Hospital, Kumamoto City, Japan.
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Coppess MA, Altemose GT, Jayachandran JV, Al-Sheikh T, Zipes DP, Miller JM. Unusual features of intermediate septal bypass tracts. J Cardiovasc Electrophysiol 2000; 11:730-5. [PMID: 10921788 DOI: 10.1111/j.1540-8167.2000.tb00042.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION Intermediate septal (IS) AV bypass tracts, located along the tricuspid annulus between the His bundle and coronary sinus os, lie in close proximity to the AV node. Surgical or catheter ablation of IS bypass tracts incurs increased risk for development of complete heart block. We report additional unusual features of some IS bypass tracts that distinguish them from typical bypass tracts in other anatomic regions. METHODS AND RESULTS We analyzed a consecutive series of 150 patients with a history of Wolff-Parkinson-White syndrome and supraventricular tachycardia who underwent ablation of bypass tracts. We studied the incidence and characteristics of AV conduction of IS bypass tracts compared with bypass tracts in other locations. Of the 150 patients in the study, 21 had an IS bypass tract (all had anterograde AV conduction). Ten (48%) of these 21 IS bypass tracts demonstrated anterograde decremental properties with atrial pacing versus 3 (2%) of 129 non-IS bypass tracts (P < 0.001). During ablation, a change in delta wave morphology before total loss of conduction in the IS bypass tract also occurred in 3 (14%) of 21 IS bypass tracts versus 0 of 129 non-IS bypass tracts (P = 0.0004). During ablation, a change in P wave to delta wave interval occurred in 4 (19%) of 21 IS bypass tracts versus 0 of 129 non-IS bypass tracts (P < 0.0001). One IS patient exhibited retrograde Wenckebach block in the bypass tract, and two IS patients showed loss of retrograde bypass tract conduction after ablation attempts that first changed the delta wave morphology. No non-IS patient had these features (P < 0.0001 for each comparison). CONCLUSION Some IS bypass tracts have unusual properties that distinguish them from bypass tracts in other locations, perhaps due to the presence of multiple ventricular insertions of the bypass tract. It is possible that some cases represent true "nodoventricular" pathways.
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Affiliation(s)
- M A Coppess
- Department of Internal Medicine, Indiana University School of Medicine, Indianapolis, USA
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Abstract
In cardiac tissue, functional or structural current-to-load mismatches can induce local slow conduction or conduction block, which are important determinants of reentrant arrhythmias. This study tested whether spatially repetitive mismatches result in a steady-state slowing of conduction. Patterned growth of neonatal rat heart cells in culture was used to design unbranched cell strands or strands releasing branches from either a single point or multiple points at periodic intervals. Electrical activation was followed optically using voltage-sensitive dyes under control conditions and in elevated [K+]o (5.8 and 14.8 mmol/L, respectively; in the latter case, propagation was carried by the L-type Ca2+ current). Preparations with multiple branch points exhibited discontinuous and slow conduction that became slower with increasing branch length and/or decreasing inter-branch distance. Compared with unbranched strands, conduction was maximally slowed by 63% under control conditions (from 44.9+/-3.4 to 16.7+/-1.0 cm/s) and by 93% in elevated [K+]o (from 15.7+/-2.3 to 1.1+/-0.2 cm/s). Local activation delays induced at a single branch point were significantly larger than the delays per branch point in multiple branching structures. Also, selective inactivation of inward currents in the branches induced conduction blocks. These 2 observations pointed to a dual role of the branches in propagation: whereas they acted as current sinks for the approaching activation thus slowing conduction ("pull" effect), they supplied, once excited, depolarizing current supporting downstream activation ("push" effect). This "pull and push" action resulted in a slowing of conduction in which the safety was largely preserved by the "push" effect. Thus, branching microarchitectures might contribute to slow conduction in tissue with discontinuous geometry, such as infarct scars and the atrioventricular node.
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Affiliation(s)
- J P Kucera
- Department of Physiology, University of Bern, Switzerland
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Chiamvimonvat V, Newman D, Tang A, Green M, Mitchell J, Wulffhart Z, Dorian P. A double-blind placebo-controlled evaluation of the human electrophysiologic effects of zatebradine, a sinus node inhibitor. J Cardiovasc Pharmacol 1998; 32:516-20. [PMID: 9781918 DOI: 10.1097/00005344-199810000-00002] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The purpose of this study was to evaluate the electrophysiologic effects of zatebradine, a sinus node inhibitor, in human subjects. Patients without structural heart disease were randomized to receive intravenous zatebradine (23 patients) or placebo (12 patients). Electrophysiologic measures were obtained at baseline and repeated at 40 and 70 min after drug administration. In the placebo group, there were no significant changes in any parameter over time. After zatebradine, sinus node function changed significantly at 40 min, with no further change at 70 min; sinus cycle length was prolonged by 16 and 17% (p < 0.001), and corrected sinus node recovery time was prolonged by 30 and 22% (p = 0.008). Similarly, atrioventricular node function changed significantly at 40 min, with no further change at 70 min; atrio-His interval was prolonged by 15 and 15% (p = 0.02), atrioventricular node effective refractory period was prolonged by 12 and 11% (p = 0.01), and Wenckebach cycle length was prolonged by 15 and 11% (p = 0.002). Atrial refractoriness, His-Purkinje conduction, ventricular refractoriness, and action-potential duration were not affected by zatebradine. Zatebradine, a sinus node inhibitor, alters the conduction and refractory properties of the human atrioventricular node, in addition to the expected effect on sinus node function.
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Affiliation(s)
- V Chiamvimonvat
- Department of Medicine, St. Michael's Hospital, University of Toronto, Ontario, Canada
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Thibault B, de Bakker JM, Hocini M, Loh P, Wittkampf FH, Janse MJ. Origin of heat-induced accelerated junctional rhythm. J Cardiovasc Electrophysiol 1998; 9:631-41. [PMID: 9654230 DOI: 10.1111/j.1540-8167.1998.tb00946.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
INTRODUCTION The application of high-frequency current to the AV junctional area results in a temperature rise in the myocardium and may cause accelerated junctional rhythm (AJR). The aim of the study was to characterize heat-induced AJR in an in vitro animal model. METHODS AND RESULTS Studies were performed in isolated perfused pig and rabbit hearts. Using a small heating probe, we could induce AJR from a discrete area located in the middle of the triangle of Koch, which was smaller than the area from which RF energy application could elicit AJR. Histology showed that the heat-sensitive area was located over, or close to, the compact AV node. It did not correspond with the areas where double potentials were found or with the site(s) of earliest atrial activation during VA conduction. Microelectrode recordings revealed that AJR arose in nodal-type cells. Heat increased the slope of the phase 4 depolarization and shortened the action potential duration. Two types of AJR were observed: the first one was regular and the second one showed irregularity in the intervals. Interaction of multiple foci and the presence of conduction block between the foci and the His bundle caused the irregularity of the His-His intervals during the second type of AJR. CONCLUSION AJR observed during heat and RF application in the AV nodal area results from the effect of heat on AV nodal cells with underlying pacemaker activity. The heat-sensitive area is located over, or very close to, the compact AV node.
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Affiliation(s)
- B Thibault
- Department of Clinical and Experimental Cardiology, Academic Medical Center, Amsterdam, The Netherlands
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Chen SA, Tai CT, Lee SH, Chang MS. AV nodal reentrant tachycardia with unusual characteristics: lessons from radiofrequency catheter ablation. J Cardiovasc Electrophysiol 1998; 9:321-33. [PMID: 9554737 DOI: 10.1111/j.1540-8167.1998.tb00917.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
There are still some AV nodal reentrant tachycardias with unusual AV nodal properties that need further study to understand these complexities. Accordingly, the two-dimensional model with alpha and beta pathways in the AV nodal reentrant tachycardia circuit certainly is an oversimplification and does not explain adequately the anatomic and physiologic complexity of the AV junctional area. The modern concept suggests that this arrhythmia takes place in a highly complex three-dimensional model with nonuniform anisotropy and discontinuous conduction property in the AV junctional area. Application of radiofrequency energy within the AV junctional area should always be performed carefully to achieve a successful ablation procedure and to minimize possible injury of AV nodal conduction.
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Affiliation(s)
- S A Chen
- Department of Medicine, National Yang-Ming University, School of Medicine, and Veterans General Hospital-Taipei, Taiwan, Republic of China.
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Lee KL, Chun HM, Liem LB, Lauer MR, Young C, Sung RJ. Multiple atrioventricular nodal pathways in humans: electrophysiologic demonstration and characterization. J Cardiovasc Electrophysiol 1998; 9:129-40. [PMID: 9511887 DOI: 10.1111/j.1540-8167.1998.tb00894.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
INTRODUCTION Multiple AV nodal pathway physiology can be demonstrated in certain patients with clinical AV reentrant tachycardia. METHODS AND RESULTS Evidence suggesting multiple AV nodal pathway conduction was present in seven (two males; age range 15 to 75 years) of 78 patients (9%) who underwent electrophysiologic studies for AV nodal tachycardia. The presence of two discrete discontinuities in the AV nodal conduction curves suggested triple AV nodal pathway conduction. Detailed mapping of their retrograde atrial activation sequence was performed along the tricuspid annulus from the coronary sinus ostium to the His-bundle electrogram recording site. Three zones (anterior, middle, and posterior) correspond to the upper, middle, and lower third of the triangle of Koch, respectively. The fast pathway exits were determined as anterior (4/7) or middle (3/7), the intermediate pathway exits as middle (4/7) or posterior (3/7), and the slow pathway exits as middle (1/7) or posterior (6/7). Other evidence suggesting multiple AV nodal pathway conduction includes: (1) triple ventricular depolarizations from a single atrial impulse; (2) sequential dual ventricular echoes; (3) spontaneous transformation between the slow-fast and fast-slow forms of AV nodal reentrant tachycardia; and (4) persistent cycle length alternans during AV nodal reentrant tachycardia. In four patients, all three pathways were shown to be involved in AV nodal echoes or reentrant tachycardia. CONCLUSION Multiple AV nodal pathways are not uncommon and can be identified by careful electrophysiologic elucidation and mapping technique.
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Affiliation(s)
- K L Lee
- Stanford University Medical Center, California.
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Tai CT, Chen SA, Chiang CE, Lee SH, Chiou CW, Ueng KC, Wen ZC, Chen YJ, Chang MS. Multiple anterograde atrioventricular node pathways in patients with atrioventricular node reentrant tachycardia. J Am Coll Cardiol 1996; 28:725-31. [PMID: 8772763 DOI: 10.1016/0735-1097(96)00217-3] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
OBJECTIVES This study sought to investigate electrophysiologic characteristics and possible anatomic sites of multiple anterograde slow atrioventricular (AV) node pathways and to compare these findings with those in dual anterograde AV node pathways. BACKGROUND Although multiple anterograde AV node pathways have been demonstrated by the presence of multiple discontinuities in the AV node conduction curve, the role of these pathways in the initiation and maintenance of AV node reentrant tachycardia (AVNRT) is still unclear, and possible anatomic sites of these pathways have not been reported. METHODS This study included 500 consecutive patients with AVNRT who underwent electrophysiologic study and radiofrequency ablation. Twenty-six patients (5.2%) with triple or more anterograde AV node pathways were designated as Group I (16 female, 10 male, mean age 48 +/- 14 years), and the other 474 patients (including 451 with and 23 without dual anterograde AV node pathways) were designated as Group II (257 female, 217 male; mean age 52 +/- 16 years). RESULTS Of the 21 patients with triple anterograde AV node pathways, AVNRT was initiated through the first slow pathway only in 3, through the second slow pathway only in 8 and through the two slow pathways in 9. Of the five patients with quadruple anterograde AV node pathways, AVNRT was initiated through all three anterograde slow pathways in three and through the two slower pathways (the second and third slow pathways) in two. After radiofrequency catheter ablation, no patient had inducible AVNRT. Eleven patients (42.3%) in Group I had multiple anterograde slow pathways eliminated simultaneously at a single ablation site. Eight patients (30.7%) had these slow pathways eliminated at different ablation sites; the slow pathways with a longer conduction time were ablated more posteriorly in the Koch's triangle than those with a shorter conduction time. The remaining seven patients (27%) had a residual slow pathway after delivery of radiofrequency energy at a single or different ablation sites. The patients in Group I had a longer tachycardia cycle length, poorer retrograde conduction properties and a higher incidence of multiple types of AVNRT than those in Group II. CONCLUSIONS Multiple anterograde AV node pathways are not rare in patients with AVNRT. However, not all of the anterograde slow pathways were involved in the initiation and maintenance of tachycardia. Radiofrequency catheter ablation was safe and effective in eliminating critical slow pathways to cure AVNRT.
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Affiliation(s)
- C T Tai
- Department of Medicine, National Yang-Ming University, School of Medicine, Taipei, Taiwan, Republic of China
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Munk AA, Adjemian RA, Zhao J, Ogbaghebriel A, Shrier A. Electrophysiological properties of morphologically distinct cells isolated from the rabbit atrioventricular node. J Physiol 1996; 493 ( Pt 3):801-18. [PMID: 8799901 PMCID: PMC1159027 DOI: 10.1113/jphysiol.1996.sp021424] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
1. Experiments were conducted using the whole-cell patch clamp technique to determine the electrophysiological properties and ionic currents of ovoid and rod-shaped single isolated calcium-tolerant rabbit atrioventricular (AV) nodal cells. 2. Action potential morphologies observed in these cells were similar to those obtained previously from intracellular recordings of intact atrioventricular nodal preparations: ovoid cells had N- or NH-like action potential configurations (see below), whereas rod-shaped cells had AN-like configurations. 3. Action potential restitution in AV nodal cells was characterized by a progressive increase in overshoot potential, maximal upstroke velocity (Vmax) and action potential duration, as well as a decrease in latency from stimulus to Vmax. In rod-shaped cells, premature stimuli could induce regenerative membrane responses before full action potential repolarization, whereas ovoid cells showed only post-repolarization refractoriness. In ovoid cells stimulated at the low stimulus intensities there was no shortening of the action potential duration and the most premature action potentials were often prolonged. 4. The quasi-steady-state current-voltage relationship of ovoid cells was significantly steeper, at both depolarized and hyperpolarized potentials, than that of either the rod-shaped AV nodal cells or atrial cells. The rod-shaped AV nodal cells and the atrial cells had similar current-voltage (I-V) relationships in the positive potential range, but the I-V curves crossed over at potentials of about-90 mV. 5. A hyperpolarization-activated inward current (I(f)) was apparent in the range between -60 and -90 mV in 95% of the ovoid cells (n = 75), whereas in 88% of rod-shaped cells (n = 16) I(f) was activated at more negative potentials. The magnitude of I(f) in ovoid cells, measured at -100 mV, was approximately 25 times that in rod-shaped cells. 6. A rapid inward current (INa) greater than 1 nA was found in all rod-shaped cells (n = 16) but in only 30% of ovoid cells (n = 75). A transient outward current (I(to)) was found in 93% of rod-shaped cells (n = 14) and in 42% of ovoid cells (n = 54). The combination of I(to) and INa was found in 93% of rod-shaped cells but in only 24% of ovoid cells. 7. These results suggest that there are at least two populations of isolated AV nodal cells with distinct action potentials and ionic current profiles that may contribute to the complex electrophysiological properties observed in the intact AV node.
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Affiliation(s)
- A A Munk
- Department of Physiology, McGill University, Montréal, Québec, Canada
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Ho SY, Anderson RH. Morphologic aspects of pediatric arrhythmias. PROGRESS IN PEDIATRIC CARDIOLOGY 1995. [DOI: 10.1016/1058-9813(95)00128-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Munk AA. Electrophysiological properties of two distinct populations of myocytes isolated from the rabbit atrioventricular node. J Electrocardiol 1995; 28:352-3. [PMID: 8551188 DOI: 10.1016/s0022-0736(05)80062-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Affiliation(s)
- A A Munk
- Department of Physiology, McGill University, Montréal, Québec, Canada
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Abstract
With the advent of RF catheter modification of AV node conduction for the treatment of AV node reentrant tachycardia, considerable advances have been made with better understanding of the AV junctional anatomy, electrophysiology, and mechanism responsible for AV node reentrant tachycardia. Future studies should be designed to uncover the basic cellular electrophysiological mechanisms responsible for fast and slow AV node conduction, to define the exact tissue components of the reentrant circuit in order to make ablative procedures safer, and to study the long-term effects of RF catheter ablation on AV conduction. Special caution should be directed toward pediatric patients with more stringent indications for catheter ablation of the AV junctional area in these patients.
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Affiliation(s)
- R J Sung
- Clinical Electrophysiology Laboratory, Stanford University Medical Center, California 94305
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James TN. Normal and abnormal consequences of apoptosis in the human heart. From postnatal morphogenesis to paroxysmal arrhythmias. Circulation 1994. [DOI: 10.1161/01.cir.90.1.556] [Citation(s) in RCA: 198] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Apoptosis and necrosis are two distinctly different forms of cell death, and both occur in the human heart. In contrast to necrosis, apoptosis is not associated with inflammation for two reasons. First, the apoptotic cell does not swell or rupture before it is engulfed by either a macrophage or even a neighboring like cell. Second, the phagocytosis occurs with unusual rapidity. Apoptosis, also thought of as cell suicide, is a tidy way of removing cells no longer useful, in essence a form of selective deletion. These features make apoptosis a valuable component of morphogenesis, mediation of hormonal and immunologic responses, and the homeostatic balance between hypertrophy and atrophy or involution. In the human heart apoptosis has been found in the sinus node of patients with the long QT syndrome. It most likely participates in the important postnatal morphogenesis of the sinus node, AV node, and His bundle. Apoptosis may also participate in the genesis and pathophysiology of cardiomyopathy, paroxysmal arrhythmias, or conduction disturbances (some of which may be responsible for sudden death), focal fibromuscular dysplasia of small coronary arteries, hereditary medial degeneration of the tunica media of coronary arteries, and arrhythmogenic right ventricular dysplasia. The possible role apoptosis in numerous other changes in the human heart, among them the pathogenesis of atherosclerosis and mechanisms of aging in the myocardium, merits future investigation.
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Affiliation(s)
- T N James
- Department of Medicine, University of Texas Medical Branch, Galveston 77555-0129
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Ho SY, McComb JM, Scott CD, Anderson RH. Morphology of the cardiac conduction system in patients with electrophysiologically proven dual atrioventricular nodal pathways. J Cardiovasc Electrophysiol 1993; 4:504-12. [PMID: 8269317 DOI: 10.1111/j.1540-8167.1993.tb01239.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
INTRODUCTION Although the electrophysiologic criteria for dual atrioventricular nodal pathways are well established, the anatomical substrate is still unclear. METHODS AND RESULTS We examined the hearts from 10 patients who had been studied electrophysiologically prior to cardiac transplantation. All 10 patients were male, aged 22 to 60 years. Nine of the 10 patients had dual atrioventricular nodal pathways according to accepted criteria. Histologic studies of the atrioventricular conduction system showed normal structure of the atrioventricular node in all 10 hearts, with minor variations within the node in 3 cases, within the penetrating bundle in 3 cases, and within the nonbranching bundle in 3 cases. The atrial approaches to the atrioventricular node were generally scanty in 6 hearts. The solitary case that was shown electrophysiologically to lack dual pathways had no obvious difference in the structure of the nodal area other than sparsity of transitional cells. We were unable to locate any extranodal atrial tracts as described by other investigators. CONCLUSION The anatomical substrate for conduction over dual pathways may be too subtle to be detected by gross morphologic studies. Since dual pathways were unmasked in all patients but one during electrophysiologic studies, it may be that the potential for these pathways is ubiquitous.
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Affiliation(s)
- S Y Ho
- Department of Paediatrics, National Heart & Lung Institute, London, United Kingdom
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31
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Ehlert FA, Goldberger JJ, Deal BJ, Benson DW, Kadish AH. Successful radiofrequency energy ablation of automatic junctional tachycardia preserving normal atrioventricular nodal conduction. Pacing Clin Electrophysiol 1993; 16:54-61. [PMID: 7681176 DOI: 10.1111/j.1540-8159.1993.tb01535.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Automatic junctional tachycardia is frequently refractory to medical management and difficult to treat with nonpharmacological methods. A 12-year-old female with symptomatic, refractory automatic junctional tachycardia is reported. Earliest atrial activation during supraventricular tachycardia was in the posterior portion of the intraatrial septum. The patient underwent electrophysiological study and successful radiofrequency current ablation of the ectopic automatic focus within the atrioventricular junction. Normal atrioventricular junctional conduction was maintained, and at 7-month follow-up the patient has been free of tachycardia.
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Affiliation(s)
- F A Ehlert
- Department of Pediatrics, Northwestern University Medical School, Children's Memorial Hospital, Chicago, Illinois
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PERLOFF JOSEPHK, MOISE NSYDNEY, STEVENSON WILLIAMG, GILMOUR ROBERTF. Cardiac Electrophysiology in Duchenne Muscular Dystrophy: From Basic Science to Clinical Expression. J Cardiovasc Electrophysiol 1992. [DOI: 10.1111/j.1540-8167.1992.tb00982.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Pollard AE, Barr RC. Computer simulations of activation in an anatomically based model of the human ventricular conduction system. IEEE Trans Biomed Eng 1991; 38:982-96. [PMID: 1761299 DOI: 10.1109/10.88444] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Simulations of the electrical activity during excitation were performed in an anatomically based model of the human ventricular conduction system. Each of the 33,000 elements of this model represented a unit bundle of Purkinje or atrioventricular nodal tissue. The Ebihara-Johnson model for sodium defined the active membrane characteristics. Using a combination of new and existing modeling techniques, simulations of excitation were completed in approximately 5 min CPU time on an IBM 3090 at the Cornell National Supercomputer Facility. Activation times at sites in the model were compared to experimental measurements for the excitation of the ventricular myocardium on the endocardial surface. These "literature-based" times were estimated from a number of reported human heart mapping studies. Initially, the times fit poorly. The major factor for the discrepancy was the conduction velocities of the elements, which were a result of the physical and electrical parameters derived from a review of histologic and electrical properties studies. In addition, there was a latency between activation of the system in the left ventricle of the model and that in the right ventricle when compared to the experimental work. When the times were scaled to adjust for the conduction velocity and ventricular latency effects, the match between the simulation and literature-based times was much improved. Quantitative comparison between normalized times resulted in correlation coefficients CCF = 0.76 for the right ventricle and CCF = 0.64 for the left ventricle.
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Affiliation(s)
- A E Pollard
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City 84112
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Mazgalev T, Dreifus LS, Michelson EL. A new mechanism for atrioventricular nodal gap-vagal modulation of conduction. Circulation 1989; 79:417-30. [PMID: 2914354 DOI: 10.1161/01.cir.79.2.417] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The well-known paradoxic behavior of atrioventricular conduction, the so-called gap phenomenon, that occurs when impulses within a certain range of coupling intervals are blocked while impulses with shorter coupling intervals are conducted is attributed to differences in properties of refractoriness in neighboring regions of the conduction system. In contrast, in the present study a model was developed showing a similar phenomenon, dependent on different electrophysiologic mechanisms and localized within the atrioventricular node in an isolated rabbit heart tissue preparation (n = 11). The hearts were paced at cycle length of 400-500 msec, and atrioventricular nodal conduction times (A2H2) were measured versus atrial extrastimulus (A1A2) coupling intervals by standard extrastimulus techniques. Postganglionic vagal stimulation was applied in the atrioventricular node as short bursts of subthreshold (for myocardium) stimuli with duration of 50-150 msec, amplitude of 20-800 microA, and absolute phase (delay after A1) of 0-500 msec. Vagal bursts with appropriate parameters consistently produced bimodal conduction curves. Initially, gradual shortening of the A1A2 coupling interval was associated with an increasing A2H2, with an accentuated increase (or even atrioventricular block) within an intermediate A1A2 range. However, further shortening of the A1A2 coupling interval produced a decrease in A2H2, which subsequently was followed by a block at the effective refractory period. Microelectrode recordings indicated that this characteristic bimodal pattern of conduction curves, demonstrating a gap, reflected transient vagally induced hyperpolarization in the N region of the node. In those instances where conduction block occurred and gap was manifest, the most marked hyperpolarization coincided with the time of arrival of midcycle premature extrastimuli, whereas the conduction of extrastimuli with either more or less prematurity was under less-marked vagal influence. Thus, this study demonstrates a new electrophysiologic mechanism producing anomalous conduction curves and the gap phenomenon within the atrioventricular node based on vagal-induced nonuniform recovery of diastolic excitability.
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Affiliation(s)
- T Mazgalev
- Cardiovascular Division Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania
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Fitzgerald D, Lazzara R. Functional anatomy of the conduction system. HOSPITAL PRACTICE (OFFICE ED.) 1988; 23:81-90, 92. [PMID: 2454241 DOI: 10.1080/21548331.1988.11703487] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- D Fitzgerald
- Cardiovascular Section, University of Oklahoma College of Medicine, Oklahoma City
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Kirchhof CJ, Bonke FI, Allessie MA. Evidence for the presence of electrotonic depression of pacemakers in the rabbit atrioventricular node. The effects of uncoupling from the surrounding myocardium. Basic Res Cardiol 1988; 83:190-201. [PMID: 3395316 DOI: 10.1007/bf01907273] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In the isolated AV junctional preparation of the rabbit heart, the presence of electrotonic influences on impulse formation was investigated. After disconnection of the sinus node, impulse formation started in the junctional area with a mean frequency of 72 beats/min (n = 17), which is about 40% of the sinus rate. Intracellular recordings were obtained to determine pacemaker location and activation sequence in the junctional area. The pacemaker was always located in the area of the lower nodal fibers of the AV node (thus distally from the site of maximal conduction delay) and these fibers had the highest rate of diastolic depolarization. Since it is known that pacemaker fibers are electronically influenced by their neighbouring cells, we investigated whether AV nodal automaticity was influenced by its surrounding tissue. Therefore the AV node was isolated from the atrial tissue and His bundle. This caused an enormous increase in diastolic depolarization rate, especially in the lower nodal fibers, accompanied by a rhythm acceleration to a mean of 137 beats/min. From the findings of the present study it was concluded that under normal conditions impulse formation in the lower nodal fibers of the rabbit AV node is electronically depressed by the connecting myocardium.
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Affiliation(s)
- C J Kirchhof
- Department of Physiology, University of Limburg, Maastricht, The Netherlands
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Bonke FI, Kirchhof CJ, Allessie MA, Wit AL. Impulse propagation from the SA-node to the ventricles. EXPERIENTIA 1987; 43:1044-9. [PMID: 3311792 DOI: 10.1007/bf01956037] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Normally the pacemaker of the mammalian heart is located in the sinus node. In the rabbit the sinus node can be subdivided into two regions, the center of the node where the impulse originates and the border zone through which the impulse is conducted towards the atrium. Conduction properties of both regions were investigated. It appeared that conduction velocity increases and refractoriness decreases when one goes from the nodal center towards the atrium. The tissue mass of the atrium is large in comparison to the sinus node and normally the resting membrane potential of atrial fibers is more negative than that of nodal fibers; consequently, a potential difference exists causing a current flow between both areas. Evidently this hyperpolarizing current flow depresses impulse formation in the border zone fibers which have better intrinsic pacemaker properties than fibers in the nodal center. If the impulse has reached the atrium it is conducted with a relatively high safety factor and will reach the AV node in principle without difficulty. The AV node, if deprived of sinus nodal dominance, develops spontaneous activity originating from the lower nodal fibers. Also in this structure, electrotonic depression by surrounding tissue causes deceleration of the pacemaker.
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Affiliation(s)
- F I Bonke
- Dept. of Physiology, University of Limburg, Maastricht, The Netherlands
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Mazgalev T, Dreifus LS, Michelson EL, Pelleg A. Effect of postganglionic vagal stimulation on the organization of atrioventricular nodal conduction in isolated rabbit heart tissue. Circulation 1986; 74:869-80. [PMID: 3757195 DOI: 10.1161/01.cir.74.4.869] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Postganglionic stimulation of vagal terminals (PGVS) in the isolated rabbit heart atrioventricular (AV) node was used to study the effects of cholinergic influence on AV nodal conduction. Standard microelectrode techniques were used to record action potentials, predominantly from cells located in the N region of the AV node. In addition, programmed stimulation was used in conjunction with PGVS to initiate or terminate AVN reentry. The introduction of a single short burst of PGVS (total duration 50 to 100 msec, impulse duration 1 msec, and interimpulse interval 6 msec) with subthreshold amplitude for AV node fibers caused reproducible disorganization of the prevailing excitation front. This was manifest as local nonuniform depression of conduction, hump formations in the action potentials, and alteration in the sequence of depolarization. The introduction of repetitive bursts of PGVS revealed a triphasic time course of changes in AV nodal conduction time, representing initial maximal prolongation, relative shortening, and secondary inhibition. It was found that these phases corresponded to vagally induced initial disorganization and a subsequent rebound process. Vagally induced disorganization of the sequence of action potential depolarization was also a triggering mechanism for concealed as well as manifest AV nodal reentry. In the latter case the reentry circuit usually involved the AN region and perinodal atrial tissue. PGVS-induced depression of the N region was also able to block the retrograde wavefront, thereby terminating reentry. The possible relationship of PGVS-induced disorganization of conduction and the inhomogeneous structure of AV node are discussed. The present results provide additional information for better understanding of the AV nodal conduction abnormalities observed clinically and particularly those related to AV node-vagus interaction.
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Wesley RC, Belardinelli L. Role of adenosine on ventricular overdrive suppression in isolated guinea pig hearts and Purkinje fibers. Circ Res 1985; 57:517-31. [PMID: 4042282 DOI: 10.1161/01.res.57.4.517] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The present study was undertaken to demonstrate and characterize potentiation of ventricular overdrive suppression by adenosine. To substantiate that adenosine has an enhanced effect on overdrive suppression, it would be necessary to demonstrate that adenosine increases pause duration independent of slowing spontaneous pre-drive rate. In isolated perfused guinea pig hearts with surgically induced complete atrioventricular block, the effect of adenosine (2-20 microM) on pause duration was compared to two alternative means of slowing the pre-drive rate, i.e., hypothermia (28.0 degrees C to 34.0 degrees C) and cesium chloride (0.3-1.0 mM). The slope value of the linear regression line describing the relationship between pre-drive cycle length and pause duration for adenosine (15.8) was significantly greater than control (1.7), hypothermia (1.7), and cesium chloride (5.4). The competitive adenosine antagonist, aminophylline (60 microM), when infused at the initiation of overdrive during adenosine administration, significantly reduced the effect of adenosine on pause duration by 72.9 +/- 4.2% (mean +/- SEM). The reduction in pause duration by aminophylline was specific for adenosine and did not occur under control conditions or during cesium chloride administration. During hypoxia, aminophylline and adenosine deaminase, when infused at the initiation of overdrive, caused 72.3 +/- 5.6 and 63.3 +/- 6.1% reductions in pause duration, respectively. Endogenous adenosine levels rose significantly with hypoxia (1,687 +/- 202 vs. 36 +/- 4 pmol/min per g during normoxia) and increased significantly further during hypoxic overdrive (3,004 +/- 323 pmol/min per g). In isolated guinea pig Purkinje fibers (n = 4), adenosine (20 microM) increased pause duration by 73.6 +/- 9.9% while only minimally affecting the pre-drive cycle length (7.6 +/- 3.8%). These fibers, when stimulated at 1.5 Hz, also displayed an adenosine-induced reduction in action potential duration at 90% repolarization (16 +/- 2 msec). In addition, we demonstrated that adenosine had an enhanced effect on pause duration in the presence of ouabain (1 microM)-induced attenuation of overdrive suppression. Thus, in isolated Purkinje fibers, it is unlikely that the potentiating effect of adenosine on pause duration, which is independent of its chronotropic effect, is mediated via an enhancement of sodium potassium adenosine triphosphatase pump activity. The effect of adenosine is likely to be secondary to a direct action on outward potassium conductance.(ABSTRACT TRUNCATED AT 400 WORDS)
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