Part IV: visual determination of generators of the magnetocardiogram.

Previously it was shown that Bn, the component of the heart's magnetic field which is normal to the chest, is in large part produced directly by the generators in the heart; the volume-current (or boundary) contribution to Bn is relatively small. It was also shown that the distribution of Bn across the chest could be displayed as an arrow map which visually reveals the underlying dipole sources, in particular those dipole combinations which produce suppresed surface potentials but undiminished Bn. Arrow maps of two normal and one abnormal heart subject are here presented. The purpose is to demonstrate that the generators of the MCG can be coarsely estimated by visual inspection of these maps. The generators of the normal hearts are visually determined by comparing their arrow maps with those computed from the Cuffin-Selvester model. The generators of the abnormal heart are visually determined by trial-and-error, with the aid of a simple computing program. These examples are the first determinations, however approximate, of multi-dipole generators of the actual MCGs. Some possible new information is indicated.