Forward Problem of Electrocardiography

Abstract

Background-The relationship between epicardial and body surface potentials defines the forward problem of electrocardiography. A robust formulation of the forward problem is instrumental to solving the inverse problem, in which epicardial potentials are computed from known body surface potentials. Here, the accuracy of different forward models has been evaluated experimentally. Methods and Results-Body surface and epicardial potentials were recorded simultaneously in anesthetized closed-chest pigs (n=5) during sinus rhythm, and epicardial and endocardial ventricular pacing (65 records in total). Body surface potentials were simulated from epicardial recordings using experiment-specific volume conductor models constructed from magnetic resonance imaging. Results for homogeneous (isotropic electric properties) and inhomogeneous (incorporating lungs, anisotropic skeletal muscle, and subcutaneous fat) forward models were compared with measured body surface potentials. Correlation coefficients were 0.85±0.08 across all animals and activation sequences with no significant difference between homogeneous and inhomogeneous solutions (P=0.85). Despite this, there was considerable variance between simulated and measured body surface potential distributions. Differences between the body surface potential extrema predicted with homogeneous forward models were 55% to 78% greater than observed (P<0.05) and attenuation of potentials adjacent to extrema were 10% to 171% greater (P<0.03). The length and orientation of the vector between potential extrema were also significantly different. Inclusion of inhomogeneous electric properties in the forward model reduced, but did not eliminate these differences. Conclusions-These results demonstrate that homogeneous volume conductor models introduce substantial spatial inaccuracies in forward problem solutions. This probably affects the precision of inverse reconstructions of cardiac potentials, in which this assumption is made. (Circ Arrhythm Electrophysiol. 2015;8:677-684.

Optimization of Organ Conductivity for the Forward Problem of Electrocardiography

“…In-vivo, experimental data came from an anesthetized, closed-chest pig [1]. Epicardial and torso potentials were recorded simultaneously using an elastic "sock" (239 unipolar electrodes) and flexible strips attached to the body surface (184 electrodes).…”

“…In previous studies comparing directly recorded and forward computed body surface potentials in-vivo, it was shown that forward models incorporating inhomogeneous structures were more accurate than homogeneous models [1,2], improving both the magnitude and pattern of body surface potentials. Despite this, there still remained a difference between the forward and recorded body surface potentials.…”

“…Nonetheless, identification of an optimized transfer matrix would provide a better forward model than both a uniform isotropic model and a more complex physiologically based one. This study examines such a method for optimizing conductivities using previously obtained invivo experimental data [1].…”

A Comparison of Discretization Methods for the Inverse Problem of Electrocardiography

“…As the inverse problem is ill-posed, it is important to establish the limitations of each method and the extent to which lack of precision of the torso model impacts inverse mapping in-vivo. Studies have shown that body surface potentials reconstructed from epicardial potentials using homogeneous transfer matrices differ markedly from the potential distributions measured on the body surface [5,6]. These differences are reduced, but not eliminated by the inclusion of inhomogeneous torso electrical properties [6].…”

“…Studies have shown that body surface potentials reconstructed from epicardial potentials using homogeneous transfer matrices differ markedly from the potential distributions measured on the body surface [5,6]. These differences are reduced, but not eliminated by the inclusion of inhomogeneous torso electrical properties [6]. The primary objective of this study was first to evaluate the accuracy of the MFS and F-BEM approaches to inverse epicardial mapping.…”