Computer model studies of the magnetocardiogram

Abstract

Digital computer models of cardiac excitation and the torso were used to investigate several aspects of the magnetocardiogram (MCG). Cardiac excitation was simulated by 20 current dipoles whose locations and moments are based on experimental data reported by others. Both a homogeneous torso and an inhomogeneous torso containing lung regions with a conductivity of one-half that of the rest of the torso were used. MCG's produced by components of the magnetic field normal to the skin were calculated at 15 sites on a grid over the anterior surface of the thorax. Incorporation of the lung inhomogeneity produced only small changes in the MCG's. Significantly different MCG's were produced by cardiac models which contained free versus fixed orientation current dipoles. A magnetic quasi-multipole expansion (MQME) differing from the classical magnetic multipole expansion, but having certain computational advantages, was developed. It was found that the first three terms in the MQME could represent MCG's to within 20%. A single current dipole model of cardiac excitation was shown to be inadequate for representing the precordial MCG's.