Effect of the heart-lung boundary on the magnetocardiogram.

Ionic currents flowing during the activation of the heart generate both electric potentials which can be recorded at the body surface as the electrocardiogram or ECG and magnetic fields which can also be recorded at the body surface as what is termed the magnetocardiogram (MCG). In order to apply the MCG to basic research or clinical diagnosis, one must understand the geometric sensitivity of the recorded signals to the cardiac source currents and evaluate the contribution of secondary ohmic body currents relative to the cardiac currents. The present study aims to evaluate the magnitude of the ohmic current contribution by electrically insulating the heart from the body. It is found that volume currents contribute a large part of the MCG signal recorded at distances greater than 10 cm from the heart, but that close to the heart at least one component of the MCG reflects primary cardiac source currents free of interference from volume currents flowing in the body.