Computer simulation of the human magnetocardiogram

A computer model of the magnetocardiogram has been developed. The magnetic field intensity,
H
, outside the body is determined from
4\piH = \int J^{i}x\nabla(1/r)dv + \int\sigmaV\nabla(1/r)xdS_{0}
where j
ⁱ
is the bioelectric source term,
V
is the electric potential (electro-cardiogram) on the body surface, S
0
, and σ is the torso conductivity. We have previously shown that the source term is proportional to the spatial gradient of intracellular potential of cardiac cells. To determine j
ⁱ
the ventricles are represented by a three dimensional array of approximately 4000 points, each corresponding to a small region of the heart muscle. Cellular action potentials are assigned to each point of the model. Ischemia is modelled by considering its effects on the action potentials of cells in the ischemic region. Magnetocardiograms were calculated at points on a grid over the chest for the normal heart as well as for several examples of ischemia and infarction. In addition, the magnetic dipole moment was calculated and a unipositional lead system for obtaining the dipole, described by Malmivuo and Wikswo, was simulated. The simulated normal magnetocardiogram showed much of the features observed experimentally by others. Good agreement was found between the simulation and experimental results reported for the Stanford unipositional lead system.