Pc. Franzone et al., Anisotropic mechanisms for multiphasic unipolar electrograms: Simulation studies and experimental recordings, ANN BIOMED, 28(11), 2000, pp. 1326-1342
The origin of the multiple, complex morphologies observed in unipolar epica
rdial electrograms, and their relationships with myocardial architecture, h
ave not been their elucidated. To clarify this problem we simulated electro
grams (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 simpl
ified 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 th
e same multiphasic character of the recorded EGs. The origin of the multipl
e waves, Especially those appearing in the EGs for sites reached by excitat
ion wave fronts spreading across fibers, can be better understood after spl
itting the current sources, the potential distributions and the EGs into an
axial and a conormal component and after taking also into account the effe
ct of the reference or drift component. The split model provides an explana
tion of humps and spikes that appear in the QRS (the initial part of the ve
ntricular 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. (C) 2000 Biomedical Engineeri
ng Society. [S0090-6964(00)00511-7].