The Inverse Problem in Electrocardiography: A Model Study of the Effects of Geometry and Conductivity Parameters on the Reconstruction of Epicardial Potentials

An idealized, analytic model using spherical harmonics was developed to analyze the effects of variations in torso geometry and volume conductivity parameters on the recovery of epicardial potentials from torso potentials. The model was also used to analyze the effects of these variations on individual terms in the orthogonal series expansion. The ability to reconstruct separate, local electrical events on the epicardium was examined under the following simulated situations: 1) all conductivity and geometry parameters were known accurately, 2) the conductivity of individual torso tissue layers was varied, 3) the torso-air boundary was eliminated (the "infinite medium" assumption), 4) the heart position was not accurately known, and 5) the heart size was not accurately known. Variation in conductivity and geometry parameters was found to exert a quantitative and qualitative effect on the amplitude, resolution, and position of the reconstructed epicardial maxima and minima. Significant differences were found in the ability of the inverse procedure to recover epicardial potentials resulting from posterior as opposed to anterior myocardial sources. Important conclusions regarding the narrow allowance for error in heart size and position, and the relative contributions of the torso tissue layer conductivities can provide guidelines for inverse reconstruction of epicardial potentials with a realistic model utilizing the true geometry.