MCG to ECG source differences: measurements and a two-dimensional computer model study.

In this work we combine body surface potential map (BSPM) and magnetocardiogram (MCG) measurements with computer simulations in order to elucidate a recent thesis that claims the orthogonality of the main sources of MCG and ECG. Body surface currents and MCG pseudo currents are calculated from measured BSPM and MCG data, respectively. In contrast to the MCG-ECG source orthogonality thesis, we observe the main orientation of the BSPM currents and MCG pseudo currents to have similar axis during most of the depolarization R wave. In an attempt to explain such measurements we simulate a 2D transmural slice of the left ventricle in contact to a volume conductor. The main magnetic source currents along the wave front are indeed orthogonal to the extracellular electric current. However, fiber orientation inhomogeneity through the ventricular wall, volume conductor interface, wave front shape and extra- and intracellular potential distributions, all distort the symmetry of the current loops that contain the wave front currents. The resulting asymmetry rotates the main axis of the pseudo MCG currents away from the orthogonal axis of the body surface currents. Thus, the simulation results could solve the apparent contradiction between the orthogonal source theory and the observed similar ECG and MCG main current axis.