Istituto di Matematica Applicata e Tecnologie Informatiche     
Colli Franzone P., Guerri L., Pennacchio M., Taccardi B. Anisotropic mechanisms for multiphasic unipolar electrograms. Simulation studies and experimental recordings. Preprint ercim.cnr.ian//1999-1151, 1999.
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 conduction system. The electrograms were compared with those directly recorded from the surface of isolated dog hearts immersed in a conducting medium. The model accurately reproduced the recorded EG morphologies for excitation wave fronts that reach the recording sites by spreading either along or across fibers.The origin of the multiple waves that constitute the QRS complex could be better understood after splitting the current sources, the potential distributions and the EGs into a field component (further subdivided into an axial and a conormal component) and a "reference" component. The split model provides an explanation of the interaction between the three-dimensional geometry and direction of propagation of a spreading wave front, the architecture of the fibers through which excitation is spreading, the potential distributions and the QRS wave forms. Because epicardial potentials, electrograms and isochrone contours can be computed noninvasively from body surface measurements, interpreting epicardial EGs in terms of intramural events may have clinical relevance.
Subject Electrograms, bidomain model, reference potential, cardiac potential maps, anisotropic propagation, source splitting

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