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  • 1
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Spatial Distribution of the QT Interval. Introduction: The role of QT dispersion as a predictor of arrhythmia vulnerability has not been consistently confirmed in the literature. Therefore, it is important to identify the electrophysiologic mechanisms that affect QT duration and distribution. We compared the spatial distributions of QT intervals (QTI) with potential distributions on cardiac and body surfaces and with recovery times on the cardiac surface. We hypothesized that the measure of QTI is affected by the presence of the zero potential line in the potential distribution, as well as the sequence of recovery. We also investigated use of the STT area as a possible indicator of recovery times on the cardiac surface. Methods and Results: High-resolution spatial distributions of QTI and potentials were determined on the body surface of human subjects and on the surface of a torso-shaped tank containing an isolated canine heart. Additionally, spatial distributions of QTI, recovery times, and STT areas were determined on the surface of exposed canine hearts. Unipolar electrograms were recorded during atrial and ventricular pacing for normal hearts and cases of myocardial infarction. Regions of shortest QTI always coincided with the location of the zero potential line on the cardiac and body surfaces. On the cardiac surface, in regions away from the zero line, similarities were observed between the patterns of QTI and the sequence of recovery. STT areas and recovery times were highly correlated on the cardiac surface. Conclusion: QTI is not a robust index of local recovery time on the cardiac surface. QTI distributions were affected by the position of the zero potential line, which is unrelated to local recovery times. However, similarities in the patterns of QTI and recovery times in some regions may help explain the frequently reported predictive value of QT dispersion. Preliminary results indicate STT area may be a better index of recovery time and recovery time dispersion on the epicardium than QTI.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 9 (1998), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Multiple Components in the Unipolar Electrogram. Introduction: For many decades, the interpretation of unipolar electrograms (EGs) and ECGs was based on simple models of the heart as a current generator, e.g., the uniform dipole layer, and, more recently, the “oblique dipole layer.” However, a number of recent and old experimental data are inconsistent with the predictions of these models. To address this problem, we implemented a numerical model simulating the spread of excitation through a parallelepipedal myocardial slab, with a view to identifying the factors that affect the shape, amplitude, and polarity of unipolar EGs generated by the spreading wavefront. Methods and Results: The numerical model represents a portion of the left ventricular wall as a parallelepipedal slab (6.5 × 6.5 × 1 cm); the myocardial tissue is represented as an anisotropic bidomain with epi-endocardial rotation of fiber direction and unequal anisotropy ratio. Following point stimulation, excitation times in the entire volume are computed by using an eikonal formulation. Potential distributions are computed by assigning a fixed shape to the action potential profile. EGs at multiple sites in the volume are computed from the time varying potential distributions. The simulations show that the unipolar QRS waveforms are the sum of a “field” component, representing the effect of an approaching or receding wavefront on the potential recorded by a unipolar electrode, and a previously unrecognized “reference” component, which reflects the drift, during the spread of excitation, of the reference potential, which moves from near the positive to near the negative extreme of the potential distribution during the spread of excitation. Conclusion: The drift of the reference potential explains the inconsistencies between the predictions of the models and the actual shapes of the EGs. The drift modifies the slopes of EG waveforms during excitation and recovery and can be expected to affect the assessment of excitation and recovery times and QRS and ST-T areas. Removing the drift reestablishes consistency between potential distributions and electrographic waveforms.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 4 (1993), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Spread of Excitation in a Myocardial Volume. Introduction: The purpose of this study was to present simulations of excitation wavefronts spreading through a parallelepipedal slab of ventricular tissue measuring 6.5 × 6.5 × 1.0cm. Methods and Results: The slab incorporates the anisotropic properties of the myocardium including the transmural counterclockwise fiber rotation from epicardium to endocardium. Simulations were based on an eikonal model that determines excitation times throughout the ventricular wall, which is represented as an anisotropic bidomain. Excitation was initiated by delivering ectopic stimuli at various intramural depths. We also investigated the effect of a simplified Purkinje network on excitation patterns. Excitation wavefronts in the plane of pacing, parallel to epicardial-endocardial surfaces, were oblong with the major axis approximately oriented along the local fiber direction, with bulges and deformations due to attraction from rotating fibers in adjacent planes. The oblong intersections of the wavefront with planes at increasing distance from pacing plane rotated clockwise or counterclockwise, depending on pacing depth, but wavefront rotation was always less than fiber rotation in the same plane. For all pacing depths, excitation returned toward the plane of pacing. Return occurred in multiple, varying sectors of the slab depending on pacing depth, and was observed as close as 6 mm to the pacing site. Conclusion: Curvature of wavefronts and collision with boundaries of slab markedly affected local velocities. Shape and separation of epicardial isochrones and spatial distribution of epicardial velocities varied as a function of site and depth of pacing. When the Purkinje network was added to the model, epicardial velocities revealed the subendocardial location of the Purkinje-myocardial junctions. Considerable insight into intramural events could be obtained from epicardial isochrones. If validated experimentally, results may be applicable to epicardial isochrones recorded at surgery.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 9 (1998), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Useful Lessons from Body Surface Mapping. Body surface potential maps (BSMs) depict the time varying distribution of cardiac potentials on the entire surface of the torso. Hundreds of studies have shown that BSMs contain more diagnostic and prognostic information than can he elicited from the 12-lead ECG. Despite these advantages, body surface mapping has not become a routinely used clinical method. One reason is that visual examination and sophisticated analysis of BSMs do not permit inferring the sequence of excitation and repolarization in the heart with a sufficient degree of certainty and detail. These limitations can be partially overcome by implementing inverse procedures that reconstruct epicardial potentials, isochrones, and ECGs from body surface measurements. Furthermore, ongoing experimental work and simulation studies show that a great deal of information about intramural events can he elicited from measured or reconstructed epicardial potential distributions. Interpreting epicardial data in terms of deep activity requires extensive knowledge of the architecture of myocardial fibers, their anisotropic properties, and the role of rotational anisotropy in affecting propagation and the associated potential fields.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 4 (1993), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Potential Patterns in a 3-D Cardiac Depolarization Model, introduction: We present simulations of extracellular potential patterns elicited by delivering ectopic stimuli to a parallelepipedal slab of ventricular tissue represented as an anisotropic bidomain incorporating epiendocardial fiber rotation. Methods and Results: Simulations were based on an eikonal model that determines wave-front shapes throughout the slab at every time instant during the depolarization phase, coupled with an approximate model of the action potential profile. The endocardial face of the slab was in contact with blood and the composite volume was surrounded by an insulating medium. The effect of a simplified Purkinje network was also studied. Results: (1) For all pacing depths, except endocardial pacing, a central negative area and two potential maxima were observed at QKS onset in all intramural planes parallel to the cpicardium. In all planes, the axis joining the two maxima was approximately aligned with the direction of fibers in the plane of pacing. Endocardial pacing generated a different pattern, but only when blood was present; (2) During later stages of excitation, outflowing currents (from the wavefront toward the resting tissue) were always emitted, at all intramural depths, only from those portions of the wavefront that spread along fibers. At any given instant, the position of the two potential maxima in a series of planes parallel to the epicardium and intersecting the wavefront rotated as a function of depth, following the rotating direction of intramural fibers. Purkinje involvement modified the above patterns. Conclusion: Epicardial and endocardial potential maps provided information on pacing site and depth and on subsequent intramural propagation by reflecting the clockwise or counterclockwise rotation of the deep positivity. Results may be applicable to epicardial and endocardial potential maps recorded at surgery or from endocavitary probes.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Noncontact Endocardial Mapping. Introduction: Mapping endocardial activation and repolarization processes is critical to the study of arrhythmias and selection of therapeutic procedures. Previously, we developed methodology for reconstructing endocardial potentials from potentials measured with a noncontact, intracavitary probe. This study further develops and evaluates the ability of the approach to provide detailed information on the spatiotemporal characteristics of the activation process. Specifically, we reconstructed endocardial electrograms and isochrones throughout the activation process over the entire endocardium during a single beat. Methods and Results: Cavity potentials were measured with a 65-electrode probe placed inside an isolated canine left ventricle. Endocardial potentials were measured simultaneously using 52 electrodes. Potentials were acquired during subendocardial pacing from different locations. Computed electrograms at various sites closely resemble the measured electrograms (correlation coefficient 〉 0.9 at 60% of the electrodes). Computed isochrones locate subendocardial pacing sites with 10-mm accuracy. Two pacing sites, 17 mm apart, were resolved. Critical regions, such as areas of isochrone crowding, were accurately reconstructed. Conclusions: Results indicate the applicability of the approach to mapping the cardiac excitation process on a beat-by-beat basis without occluding the ventricle. The ability of locating electrical events (e.g., single or multiple initiation sites) is demonstrated. Importantly, the method is shown to be capable of reconstructing electrograms over the entire endocardium and determining nonuniformities of activation spread (e.g., areas of slow conduction). These capabilities are important to clinical application in the electrophysiology laboratory and experimental studies of arrhythmias in the intact animal.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Noncontact Mapping of Arrhythmogenic Substrates. Introduction: In previous studies, we established methodology for reconstructing endocardial potential maps, electrograms, and isochrones from a noncontact intracavitary catheter during a single beat. Recently, we evaluated this approach using a 9-French (3-mm) spiral catheter in a normal heart preparation. Here we extend the approach to hearts with structural disease and examine its ability to detect and characterize abnormal electrophysiologic (EP) substrates and to map ventricular arrhythmias on a beat-by-beat basis. Methods and Results: Reconstruction of endocardial potentials from cavity potentials measured with 82 electrodes mounted on a 9-French spiral catheter was performed in an isolated canine left ventricle (LV). Endocardial potentials were recorded with 91 intramural needles, providing a gold standard for evaluating the noncontact reconstruction. Studies were performed in a normal LV (control) and the same LV 3 hours after left anterior descending coronary artery occlusion and ethanol injection to create an infarct. Abnormal EP characteristics over the infarct were faithfully reconstructed, including (1) low potentials and electrogram derivatives; (2) fractionated electrograms; (3) small deflections on electrograms reflecting local activation; and (4) slow discontinuous conduction transverse to fibers. During arrhythmia, beat-to-beat dynamic shifts of initiation site and activation pattern were captured by the reconstruction. Conclusion: Noncontact, nonexpendable catheter mapping can locate and characterize abnormal EP substrates and can capture the endocardial sequence of an arrhythmia during a single beat.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Inc
    Journal of cardiovascular electrophysiology 13 (2002), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of cardiovascular electrophysiology 11 (2000), S. 0 
    ISSN: 1540-8167
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Electrophysiologic Noncontact Endocardial Mapping. Introduction: The need for high-resulution simultaneous mapping of cardiac excitation and arrhythmias on a heat-hy-heat basis is widely recognized. Here we validate a noncontact mapping approach that combines a spiral catheter design with mathematical reconstruction to generate potential maps, electrograms, and activation maps (isochrones) on the entire left ventricular endocardial surface during a single beat. The approach is applicable to any heart chamher.Methods and Results: The catheter is 3 mm (9 French) in diameter and carries 96 electrodes. Reconstruction accuracy is evaluated through direct comparison with endocardial data measured with 95 needle electrodes. Results show that endocardial potentials, electrograms, and isochrones are reconstructed with good accuracy during pacing from single or multiple sites (simulating ectopic activity). Pacing sites can be located to within 5 mm of their actual position, and intersite distances of 17 mm can be resolved during dual pacing. The reconstructed potential pattern reflects the intramural depth of pacing. The reconstructions are robust in the presence of geometric errors, and the accuracy is minimally reduced when only 62 catheter electrodes are used (32 are sufficient for pacing site localization).Conclusion: The study demonstrates that simultaneous endocardial mapping can be accomplished during a single beat from a spiral-shaped noncontact catheter with good accuracy.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1573-9686
    Keywords: Electrograms ; Bidomain model ; Reference potential ; Cardiac potential maps ; Anisotropic propagation ; Source splitting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract The origin of the multiple, complex morphologies observed in unipolar epicardial electrograms, and their relationships with myocardial architecture, have not been fully elucidated. To clarify this problem we simulated electrograms (EGs) with a model representing the heart as an anisotropic bidomain with unequal anisotropy ratio, ellipsoidal ventricular geometry, transmural fiber rotation, epi-endocardial obliqueness of fiber direction and a simplified Purkinje network. The EGs were compared with those directly recorded from isolated dog hearts immersed in a conducting medium during ventricular excitation initiated by epicardial stimulation. The simulated EGs share the same multiphasic character of the recorded EGs. The origin of the multiple waves, especially those appearing in the EGs for sites reached by excitation wave fronts spreading across fibers, can be better understood after splitting the current sources, the potential distributions and the EGs into an axial and a conormal component and after taking also into account the effect of the reference or drift component. The split model provides an explanation of humps and spikes that appear in the QRS (the initial part of the ventricular EG) wave forms, in terms of the interaction between the geometry and direction of propagation of the wave front and the architecture of the fibers through which excitation is spreading. © 2000 Biomedical Engineering Society. PAC00: 8719Nn, 8710+e, 8719Hh
    Type of Medium: Electronic Resource
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