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Walton RD, Benson AP, Hardy MEL, White E, Bernus O. Electrophysiological and structural determinants of electrotonic modulation of repolarization by the activation sequence. Front Physiol 2013; 4:281. [PMID: 24115934 PMCID: PMC3792354 DOI: 10.3389/fphys.2013.00281] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Accepted: 09/18/2013] [Indexed: 11/14/2022] Open
Abstract
Spatial dispersion of repolarization is known to play an important role in arrhythmogenesis. Electrotonic modulation of repolarization by the activation sequence has been observed in some species and tissue preparations, but to varying extents. Our study sought to determine the mechanisms underlying species- and tissue-dependent electrotonic modulation of repolarization in ventricles. Epi-fluorescence optical imaging of whole rat hearts and pig left ventricular wedges were used to assess epicardial spatial activation and repolarization characteristics. Experiments were supported by computer simulations using realistic geometries. Tight coupling between activation times (AT) and action potential duration (APD) were observed in rat experiments but not in pig. Linear correlation analysis found slopes of −1.03 ± 0.59 and −0.26 ± 0.13 for rat and pig, respectively (p < 0.0001). In rat, maximal dispersion of APD was 11.0 ± 3.1 ms but dispersion of repolarization time (RT) was relatively homogeneous (8.2 ± 2.7, p < 0.0001). However, in pig no such difference was observed between the dispersion of APD and RT (17.8 ± 6.1 vs. 17.7 ± 6.5, respectively). Localized elevations of APD (12.9 ± 8.3%) were identified at ventricular insertion sites of rat hearts both in experiments and simulations. Tissue geometry and action potential (AP) morphology contributed significantly to determining influence of electrotonic modulation. Simulations of a rat AP in a pig geometry decreased the slope of AT and APD relationships by 70.6% whereas slopes were increased by 75.0% when implementing a pig AP in a rat geometry. A modified pig AP, shortened to match the rat APD, showed little coupling between AT and APD with greatly reduced slope compared to the rat AP. Electrotonic modulation of repolarization by the activation sequence is especially pronounced in small hearts with murine-like APs. Tissue architecture and AP morphology play an important role in electrotonic modulation of repolarization.
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Affiliation(s)
- Richard D Walton
- Faculty of Biological Sciences, Multidisciplinary Cardiovascular Research Centre, School of Biomedical Sciences, Institute of Membrane and Systems Biology, University of Leeds Leeds, UK ; Unité Inserm 1045, Centre de Recherche Cardio-Thoracique, Université Bordeaux Segalen Bordeaux, France ; L'Institut de Rythmologie et Modélisation Cardiaque, Université de Bordeaux Bordeaux, France
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2
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Azarov JE, Kibler NA, Vaykshnorayte MA, Tsvetkova AS, Kharin SN, Vityazev VA, Shmakov DN. Effect of heart electric stimulation on repolarization of ventricular myocardium of fish and amphibians. J EVOL BIOCHEM PHYS+ 2013. [DOI: 10.1134/s0022093013020059] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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3
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Vaykshnorayte MA, Tsvetkova AS, Azarov JE. Epicardial activation-to-repolarization coupling differs in the local areas and on the entire ventricular surface. J Electrocardiol 2011; 44:131-7. [DOI: 10.1016/j.jelectrocard.2010.11.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2010] [Indexed: 10/18/2022]
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4
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Martin CA, Grace AA, Huang CLH. Spatial and temporal heterogeneities are localized to the right ventricular outflow tract in a heterozygotic Scn5a mouse model. Am J Physiol Heart Circ Physiol 2010; 300:H605-16. [PMID: 21097662 PMCID: PMC3044044 DOI: 10.1152/ajpheart.00824.2010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ventricular tachycardia (VT) in Brugada Syndrome patients often originates in the right ventricular outflow tract (RVOT). We explore the physiological basis for this observation using murine whole heart preparations. Ventricular bipolar electrograms and monophasic action potentials were recorded from seven epicardial positions in Langendorff-perfused wild-type and Scn5a+/− hearts. VT first appeared in the RVOT, implicating it as an arrhythmogenic focus in Scn5a+/− hearts. RVOTs showed the greatest heterogeneity in refractory periods, response latencies, and action potential durations, and the most fractionated electrograms. However, incidences of concordant alternans in dynamic pacing protocol recordings were unaffected by the Scn5a+/− mutation or pharmacological intervention. Conversely, particularly at the RVOT, Scn5a+/− hearts showed earlier and more frequent transitions into discordant alternans. This was accentuated by flecainide, but reduced by quinidine, in parallel with their respective pro- and anti-arrhythmic effects. Discordant alternans preceded all episodes of VT. The RVOT of Scn5a+/− hearts also showed steeper restitution curves, with the diastolic interval at which the gradient equaled one strongly correlating with the diastolic interval at which discordant alternans commenced. We attribute the arrhythmic tendency within the RVOT to the greater spatial heterogeneities in baseline electrophysiological properties. These, in turn, give rise to a tendency to drive concordant alternans phenomena into an arrhythmogenic discordant alternans. Our findings may contribute to future work investigating possible pharmacological treatments for a disease in which the current mainstay of treatment is implantable cardioverter defibrillator implantation.
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Affiliation(s)
- Claire A Martin
- Physiological Laboratory, Department of Biochemistry, University of Cambridge, Downing Site, Cambridge CB2 3EG, UK.
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5
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Chung CY, Bien H, Entcheva E. The role of cardiac tissue alignment in modulating electrical function. J Cardiovasc Electrophysiol 2007; 18:1323-9. [PMID: 17916158 DOI: 10.1111/j.1540-8167.2007.00959.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
INTRODUCTION Most cardiac arrhythmias are associated with pathology-triggered ion channel remodeling. However, multicellular effects, for example, exaggerated anisotropy and altered cell-to-cell coupling, can also indirectly affect action potential morphology and electrical stability via changed electrotonus. These changes are particularly relevant in structural heart disease, including hypertrophy and infarction. Recent computational studies showed that electrotonus factors into stability by altering dynamic properties (restitution). We experimentally address the question of how cell alignment and connectivity alter tissue function and whether these effects depend on the direction of wave propagation. METHODS AND RESULTS We show that cardiac cell arrangement can alter electrical stability in an in vitro cardiac tissue model by mechanisms both dependent and independent of the direction of wave propagation, and local structural remodeling can be felt beyond a space constant. Notably, restitution of action potential duration (APD) and conduction velocity was significantly steepened in the direction of cell alignment. Furthermore, prolongation of APD and calcium transient duration was found in highly anisotropic cell networks, both for longitudinal and transverse propagation. This is in contrast to expected correlation between wave propagation direction and APD based on electrotonic effects only, but is consistent with our findings of increased cell size and secretion of atrial natriuretic factor, a hypertrophy marker, in the aligned structures. CONCLUSION Our results show that anisotropic structure is a potent modulator of electrical stability via electrotonus and molecular signaling. Tissue alignment must be taken into account in experimental and computational models of arrhythmia generation and in designing effective treatment therapies.
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Affiliation(s)
- Chiung-Yin Chung
- Department of Biomedical Engineering, Stony Brook University, Stony Brook, New York, USA
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6
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Colli Franzone P, Pavarino LF, Taccardi B. Effects of transmural electrical heterogeneities and electrotonic interactions on the dispersion of cardiac repolarization and action potential duration: A simulation study. Math Biosci 2006; 204:132-65. [PMID: 16904130 DOI: 10.1016/j.mbs.2006.06.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Revised: 04/12/2006] [Accepted: 06/06/2006] [Indexed: 11/25/2022]
Abstract
It has been shown in the literature that myocytes isolated from the ventricular walls at various intramural depths have different action potential durations (APDs). When these myocytes are embedded in the ventricular wall, their inhomogeneous properties affect the sequence of repolarization and the actual distribution of the APDs in the entire wall. In this article, we implement a mathematical model to simulate the combined effect of (a) the non-homogeneous intrinsic membrane properties (in particular the non-homogeneous APDs) and (b) the electrotonic currents that modulate the APDs when the myocytes are embedded in the ventricular myocardium. In particular, we study the effect of (a) and (b) on the excitation and repolarization sequences and on the distribution of APDs in the ventricles. We implement a Monodomain tissue representation that includes orthotropic anisotropy, transmural fiber rotation and homogeneous or heterogeneous transmural intrinsic membrane properties, modeled according to the phase I Luo-Rudy membrane ionic model. Three-dimensional simulations are performed in a cartesian slab with a parallel finite element solver employing structured isoparametric trilinear finite elements in space and a semi-implicit adaptive method in time. Simulations of excitation and repolarization sequences elicited by epicardial or endocardial pacing show that in a homogeneous slab the repolarization pathways approximately follow the activation sequence. Conversely, in the heterogeneous cases considered in this study, we observed two repolarization wavefronts that started from the epi and the endocardial faces respectively and collided in the thickness of the wall and in one case an additional repolarization wave starting from an intramural site. Introducing the heterogeneities along the transmural epi-endocardial direction affected both the repolarization sequence and the APD dispersion, but these effects were clearly discernible only in transmural planes. By contrast, in planes parallel to epi- and endocardium the APD distribution remained remarkably similar to that observed in the homogeneous model. Therefore, the patterns of the repolarization sequence and APD dispersion on the epicardial surface (or any other intramural surface parallel to it) do not reveal the uniform transmural heterogeneity.
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Affiliation(s)
- P Colli Franzone
- Dipartimento di Matematica, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy.
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7
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Colli Franzone P, Pavarino LF, Taccardi B. Simulating patterns of excitation, repolarization and action potential duration with cardiac Bidomain and Monodomain models. Math Biosci 2005; 197:35-66. [PMID: 16009380 DOI: 10.1016/j.mbs.2005.04.003] [Citation(s) in RCA: 119] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2004] [Revised: 03/18/2005] [Accepted: 04/05/2005] [Indexed: 11/15/2022]
Abstract
Parallel numerical simulations of excitation and recovery in three-dimensional myocardial domains are presented. The simulations are based on the anisotropic Bidomain and Monodomain models, including intramural fiber rotation and orthotropic or axisymmetric anisotropy of the intra- and extra-cellular conductivity tensors. The Bidomain model consist of a system of two reaction-diffusion equations, while the Monodomain model consists of one reaction-diffusion equation. Both models are coupled with the phase I Luo-Rudy membrane model describing the ionic currents. Simulations of excitation and repolarization sequences on myocardial slabs of different sizes show how the distribution of the action potential durations (APD) is influenced by both the anisotropic electrical conduction and the fiber rotation. This influence occurs in spite of the homogeneous intrinsic properties of the cell membrane. The APD dispersion patterns are closely correlated to the anisotropic curvature of the excitation wavefront.
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Affiliation(s)
- P Colli Franzone
- Dipartimento di Matematica, Università di Pavia, Via Ferrata 1, 27100 Pavia, Italy.
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8
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Yue AM, Betts TR, Roberts PR, Morgan JM. Global Dynamic Coupling of Activation and Repolarization in the Human Ventricle. Circulation 2005; 112:2592-601. [PMID: 16246959 DOI: 10.1161/circulationaha.104.510412] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background—
The ability to determine spatial and dynamic changes in ventricular repolarization may help to understand arrhythmogenic mechanisms in humans. We hypothesized that noncontact mapping could be used to investigate global activation-repolarization coupling in the human ventricle during steady state and premature extrastimulation.
Methods and Results—
Activation-recovery intervals (ARIs) determined from reconstructed unipolar electrograms by the Ensite system were analyzed during sinus rhythm, constant pacing, spontaneous ventricular ectopic beats, and premature stimulation at intermediate and short coupling intervals in the left or right ventricle of 13 patients (6 female; mean age, 48 years) without structural myocardial disease. ARIs were measured from 32 sites in each ventricle with the use of a method validated with monophasic action potential recordings and unipolar contact electrograms. Global T-wave distribution was displayed on a 3-dimensional geometry of the ventricle, with polarities opposite to the direction of activation during steady state and premature stimulation. There was a significant inverse correlation between activation times and ARIs during sinus rhythm, ventricular ectopy, and premature stimulation (
r
=0.72, slope=−0.76,
P
<0.001). Premature stimuli at short coupling intervals flattened the regression slope compared with sinus rhythm (−0.61 versus −0.81;
P
=0.05), but the global pattern of repolarization was preserved. In comparison to our method, the Wyatt method of ARI measurement failed to demonstrate significant coupling between activation and repolarization (
r
=0.34, slope=0.19).
Conclusions—
Global, dynamic repolarization mapping of the human ventricle is feasible. An inverse coupling of activation and repolarization during steady state and premature stimulation may preserve electric stability in the normal ventricle.
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Affiliation(s)
- Arthur M Yue
- Wessex Cardiac Center, Southampton General Hospital, Southampton SO16 6YD, UK
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Sampson KJ, Henriquez CS. Electrotonic influences on action potential duration dispersion in small hearts: a simulation study. Am J Physiol Heart Circ Physiol 2005; 289:H350-60. [PMID: 15734889 DOI: 10.1152/ajpheart.00507.2004] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intrinsic spatial variations in repolarization currents in the heart can produce spatial gradients in action potential duration (APD) that serve as possible sites for conduction block and the initiation of reentrant activity. In well-coupled myocardium, however, electrotonic influences at the stimulus site and wavefront collision sites act to modulate any intrinsic heterogeneity in APD. These effects alter APD gradients over an extent larger than that suggested by the length constant associated with propagation and, thus, are hypothesized to play a greater role in smaller hearts used as experimental models of human disease. This study uses computer simulation to investigate how heart size, tissue properties, and the spatial assignment of cell types affect functional APD dispersion. Simulations were carried out using the murine ventricular myocyte model of Pandit et al. or the Luo-Rudy mammalian model in three-dimensional models of mouse and rabbit ventricular geometries. Results show that the spatial extent of the APD dispersion is related to the dynamic changes in transmembrane resistance during recovery. Also, because of the small dimensions of the mouse heart, electrotonic effects on APD primarily determine the functional dispersion of refractoriness, even in the presence of large intrinsic cellular heterogeneity and reduced coupling. APD dispersion, however, is found to increase significantly when the heart size increases to the size of a rabbit heart, unmasking intrinsic cell types.
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Affiliation(s)
- Kevin J Sampson
- 136 Hudson Hall, Dept. of Biomedical Engineering, Duke Univ., PO Box 90281, Durham, NC 27708-0281, USA
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Kharin SN. Depolarisation and repolarisation sequences of ventricular epicardium in chickens (Gallus gallus domesticus). Comp Biochem Physiol A Mol Integr Physiol 2004; 137:237-44. [PMID: 14720609 DOI: 10.1016/j.cbpb.2003.10.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Activation and recovery sequences were mapped by means of 64-channel synchronous recording of extracellular potentials on ventricular epicardium in chickens. Ventricular epicardium was depolarized due to multiple breakthroughs. The recovery of ventricular epicardium occurs from the apex to the base of heart and does not repeat the activation sequence. Gradients of repolarisation exist over the ventricular epicardium in birds. Repolarisation pattern of ventricular epicardium depends primarily on intrinsic spatial heterogeneities of ARIs over epicardium.
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Affiliation(s)
- Sergei N Kharin
- Department of Visceral Physiology, Institute of Physiology of the Russian Academy of Sciences, 50 Pervomayskaya st., GSP-2, Komi Republic, Syktyvkar 167982, Russia.
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11
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Zaniboni M, Pollard AE, Yang L, Spitzer KW. Beat-to-beat repolarization variability in ventricular myocytes and its suppression by electrical coupling. Am J Physiol Heart Circ Physiol 2000; 278:H677-87. [PMID: 10710334 DOI: 10.1152/ajpheart.2000.278.3.h677] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Single ventricular myocytes paced at a constant rate and held at a constant temperature exhibit beat-to-beat variations in action potential duration (APD). In this study we sought to quantify this variability, assess its mechanism, and determine its responsiveness to electrotonic interactions with another myocyte. Interbeat APD(90) (90% repolarization) of single cells was normally distributed. We thus quantified APD(90) variability as the coefficient of variability, CV = (SD/mean APD(90)) x 100. The mean +/- SD of the CV in normal solution was 2.3 +/- 0.9 (132 cells). Extracellular TTX (13 microM) and intracellular EGTA (14 mM) both significantly reduced the CV by 44 and 26%, respectively. When applied in combination the CV fell by 54%. In contrast, inhibition of the rapid delayed rectifier current with L-691,121 (100 nM) increased the CV by 300%. The CV was also significantly reduced by 35% when two normal myocytes were electrically connected with a junctional resistance (R(j)) of 100 MOmega. Electrical coupling (R(j) = 100 MOmega) of a normal myocyte to one producing early afterdepolarization (EAD) completely blocked EAD formation. These results indicate that beat-to-beat APD variability is likely mediated by stochastic behavior of ion channels and that electrotonic interactions act to limit temporal dispersion of refractoriness, a major contributor to arrhythmogenesis.
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Affiliation(s)
- M Zaniboni
- Department of Evolutive and Functional Biology, University of Parma, Parma, Italy 43100
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12
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Huiskamp G. Simulation of depolarization in a membrane-equations-based model of the anisotropic ventricle. IEEE Trans Biomed Eng 1998; 45:847-55. [PMID: 9644893 DOI: 10.1109/10.686792] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The results of a simulation study of the propagation of depolarization in inhomogeneous anisotropic (monodomain) myocardial tissue are presented. Simulations are based on modified Beeler-Reuter membrane equations, and performed on a block of anisotropic myocardium with rotating fiber geometry, measuring 1 cm x 1 cm x 0.3 cm, at various levels of spatial discretization (0.15 mm, 0.30 mm, 0.60 mm). At a discretization level of 0.6 mm the algorithm allowed the simulation in a realistically shaped model of the ventricle, including rotational anisotropy, as well. For this simulation results are justified by comparing results for the block at various levels of discretization, for which the surface to volume ratio has been adjusted. By placing the model ventricle in a realistically shaped (human) volume conductor model, realistic body surface potentials (QRST waveforms) are simulated.
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Affiliation(s)
- G Huiskamp
- Department of Clinical Neurophysiology, University Hospital Utrecht, The Netherlands.
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13
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Abstract
BACKGROUND While abnormalities of activation and repolarization play an important role in arrhythmogenesis, little information is available on the interaction between their spatial dispersions in the heart. This study examined the effects of activation spread on the spatial distribution of the repolarization properties during different depolarization patterns. METHODS AND RESULTS Left ventricular (LV) endocardial activation and repolarization patterns were mapped in 13 healthy pigs. LV local activation, repolarization, and activation-recovery interval (ARI) times were determined from the intracardiac unipolar electrograms, color-coded, and superimposed on a three-dimensional anatomic map of the ventricle generated with a nonfluoroscopic mapping system. ARI values correlated with the duration of monophasic activation potential recorded from onset of activation to time of 90% repolarization (r=.97, P<.01). Activation time range of the left ventricle was 42+/-5 ms (mean+/-SEM) during sinus rhythm and 54+/-5 ms during right ventricular septal pacing. ARI inversely correlated with the corresponding activation times during both sinus (r2=.76+/-.03) and paced (r2=.77+/-.02) rhythms. The longest ARIs were located at the sites of earliest activation and shortest at the latest activation areas, with gradual shortening between them. CONCLUSIONS The spatial distribution of repolarization is dependent on the activation pattern. Repolarization dispersion in the healthy swine heart is relatively small as the result of tight coupling of the action potential duration to the activation process, assigning longer ARIs to sites activated earlier. This coupling reduces global and regional dispersion of repolarization and may serve as an important antiarrhythmic mechanism present in normal myocardium.
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Affiliation(s)
- L Gepstein
- Cardiovascular System Laboratory, the Bruce Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel
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14
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Abstract
In a retrospective and prospective analysis of electrocardiograms, we noted that the JT interval is not independent of the ventricular depolarization pattern, but is paradoxically shorter for wider QRS morphologies. Such an affect on the JT interval must be accounted for if it is to be used as an accurate means of following the duration of ventricular repolarization for clinical purposes, such as guidance of drug administration.
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Affiliation(s)
- J Banker
- Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York, USA
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15
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Tachibana H, Kubota I, Yamaki M, Kondo T, Tomoike H. Effects of activation sequence on monophasic action potential configuration in the dog. J Electrocardiol 1997; 30:65-70. [PMID: 9005888 DOI: 10.1016/s0022-0736(97)80036-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The effects of altered activation sequence on the monophasic action potential (MAP) in in situ beating hearts are not known, although its effects on refractory periods are well documented. In nine anesthetized, open-chest dogs, complete atrioventricular block was produced, and the heart was driven by either right ventricular or left ventricular stimulation. The MAPs of the right and left ventricles were recorded by contact electrodes at cycle lengths of 1,000, 800, 600, and 400 ms. The MAP configuration was evaluated with regard to the difference between phase 1 and phase 2 MAP amplitudes and MAP duration at 50 and 90% repolarization. An MAP recorded from the ventricle that was being electrically stimulated was designated an ipsilateral ventricular stimulation, whereas the MAP recorded from the nonstimulated ventricle was termed a contralateral ventricular stimulation. The difference in amplitude and the 50% and 90% MAP durations for ipsilateral ventricular stimulation were consistently larger than for contralateral ventricular stimulation at all cycle lengths tested. Transient outward current did not appear to play a major role in producing such differences in MAP because intravenous treatment with 4-aminopyridine, a blocker of transient outward current, did not affect the configuration of the MAP. These findings provide an insight on the influence of ventricular activation sequence on the shape of the transmembrane action potential.
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Affiliation(s)
- H Tachibana
- First Department of Internal Medicine, Yamagata University School of Medicine, Japan
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16
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Burgess MJ, Pollard AE, Spitzer KW, Yang L. Effects of premature beats on repolarization of postextrasystolic beats. Circulation 1995; 92:1969-80. [PMID: 7545557 DOI: 10.1161/01.cir.92.7.1969] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
BACKGROUND A short-long-short sequence of cycle lengths predisposes to reentrant tachyarrhythmias. There is limited information about the effects of premature ventricular contractions (PVCs) on repolarization of postextrasystolic depolarizations (PEDs). Such information would contribute to understanding the mechanism for facilitating reentry with short-long-short cycle lengths. METHODS AND RESULTS We introduced PVCs, over a range of coupling intervals and during a range of basic drive cycle lengths (BCLs), and determined PED repolarization. Our results from whole-animal experiments, isolated cell studies, and computer simulations are reported. In the whole-animal experiments, PED refractory periods (RPs) were longer than RPBCL. The greatest difference between RPPED and RPBCL (delta RPmax) occurred after short coupling interval PVCs and was 4.3 +/- 0.8, 4.2 +/- 0.8, and 2.1 +/- 0.5 ms (mean +/- SEM) during drives with short, intermediate, and long BCLs, respectively. The diastolic interval preceding the PED (DIPED) was inversely related to the coupling interval between the basic drive beat and the PVC and directly related to RPPED. PED action potential durations (APDs) of isolated canine myocytes were 9.8 +/- 4.9 ms (mean +/- SEM) longer than APD BCL (n = 19). The DiFrancesco-Noble membrane equations were used in simulations of action potential propagation in a one-dimensional cable, with stimulation protocols duplicating those in the animal experiments. PVCs prolonged APDPED, and APDPED was prolonged more during short than during long BCL drives. There was a direct relation between DIPED and APDPED. Analysis of the membrane currents over the time course of the PVCs and PEDs suggested that the ionic basis for PED repolarization prolongation was the interaction of Ito and Ik. Hyperpolarizing constant-current injections introduced immediately after the spike of isolated myocyte action potentials caused APD prolongation. This observation is consistent with the Ito and Ik interaction causing PED repolarization prolongation. CONCLUSIONS PED repolarization prolongation could provide sites for unidirectional block to propagation of PVCs after PEDs and could facilitate initiation of reentrant tachyarrhythmias after short-long-short sequences of cycle lengths.
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Affiliation(s)
- M J Burgess
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City 84112, USA
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