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Multiple Components in the Unipolar Electrogram: A Simulation Study in a Three-Dimensional Model of Ventricular Myocardium (1998)

TACCARDI, BRUNO ; VERONESE, SILVIA ; FRANZONE, PIERO COLLI ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of cardiovascular electrophysiology 9 (1998), S. 0

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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

URL: http://dx.doi.org/10.1111/j.1540-8167.1998.tb00884.x

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Anisotropic Mechanisms for Multiphasic Unipolar Electrograms: Simulation Studies and Experimental Recordings (2000)

Franzone, Piero Colli ; Guerri, Luciano ; Pennacchio, Micol ; [et al.]

Springer

Annals of biomedical engineering 28 (2000), S. 1326-1342

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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