The influence of open loop currents on bioelectric and biomagnetic measurements: a phantom study

Closed loop currents are discussed as possible sources of differential information in the magnetocardiogram and the electrocardiogram. It is, however, unclear if also open loops, such as spiral activation in the heart, can contribute to these differences. We model two types of open loops, based on the heart geometry, with the help of twelve artificial current dipoles in a physical torso phantom. Electric potentials and magnetic fields were measured simultaneously for an increasing number of active dipoles in the two source geometries. We found for the magnetic fields a continuous increase of the measured amplitudes up to a plateau value at ten active dipoles. For the electric potentials, we found increasing amplitudes up to six or eight active dipoles and thereafter decreasing amplitudes. We conclude that also open loop currents can contribute to the experimentally observed differences in magnetocardiograms and electrocardiograms. Combined bioelectric and biomagnetic measurements will provide greater insight into heart activity then do single modality measurements.