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  • 1
    Electronic Resource
    Electronic Resource
    Anisotropic Mechanisms for Multiphasic Unipolar Electrograms: Simulation Studies and Experimental Recordings (2000)
    Springer
    Annals of biomedical engineering 28 (2000), S. 1326-1342 
    Details
    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
    URL: http://dx.doi.org/10.1114/1.1327595
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  • 2
    Electronic Resource
    Electronic Resource
    A Novel Interpolation Method for Electric Potential Fields in the Heart during Excitation (1998)
    Springer
    Annals of biomedical engineering 26 (1998), S. 597-607 
    Details
    ISSN: 1573-9686
    Keywords: Electrocardiography ; Cardiac mapping ; Activation ; Electric potential fields ; Excitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In mapping the electrical activity of the heart, interpolation of electric potentials plays two important roles. First, it permits the estimation of potentials in regions that could not be sampled or where signal quality was poor, and second, it supports the construction of isopotential lines and surfaces for visualization. The difficulty in developing robust interpolation techniques for cardiac applications lies in the abrupt change in potential in the vicinity of the activation wave front. Despite the resulting nonlinearities in spatial potential distributions, simple linear interpolation methods are the current standard and the resulting errors due to aliasing can be large if electrode spacing does not lie on the order of 0.5–2 mm—the thickness of the activation wave front. We have developed a novel interpolation method that is based on two observations specific to the spread of excitation in the heart: (1) that propagation velocity changes smoothly within a region large enough to contain several measurement electrodes and (2) that electrogram morphology varies very little in the neighborhood of each sample point except for a time shift in the potential wave forms. The resulting interpolation scheme breaks the interpolation of one highly nonlinear variable—extracellular potential—into two separate interpolations of variables with much less drastic spatial variation—activation time and electrogram morphology. We have applied this method to potentials originally recorded at 1.5 mm spacing and then subsampled at a range of densities for testing of the interpolation. The results based both on reconstruction of isopotential contour maps and statistical comparison showed significant improvement of this novel approach over standard linear techniques. The applications of the new method include improved determination of electrophysiological parameters such as spatial gradients of potential and the path of cardiac activation and recovery, estimation of electrograms at desired locations, and visualization of electric potential distributions. © 1998 Biomedical Engineering Society. PAC98: 8790+y, 0260Ed, 8710+e
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1114/1.41
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