Non-dipolarity of heart potentials estimated by magnetocardiography in normal subjects

We studied non-dipolarity characteristics during ventricular excitation in normal adults and children by magnetocardiography (MCG) by recording magnet ic held on the thorax. The source and currents of the electrical dipole fro m the onset up to 60 ms of ventricular excitation were analyzed in 16 adult s and 5 children. A single equivalent current dipole (ECD) was estimated by Sarvas' formula for the sphere model at 1 ms intervals. The non-dipole val ue (NDV) was calculated from the magnetic field strength at each recording point and theoretically estimated by ECD, representing an index for the non dipolarity. At 32-34 ms from the beginning of QRS, the mean NDV was a minim um in all subjects suggesting at least a non-dipole component during this p eriod. High NDV (over 5%) were present in most subjects in both the early a nd late phase compared to this period. Thirteen of 16 adults had a high NDV in the early phase (9.3 +/- 3.0%, mean +/- SD) and all 16 subjects had a h igh nDV in the late phase (21.5 +/- 10.5%). All 5 children had high NDV in both the early (10.5 +/- 5.4%) and late phases (16.8 +/- 7.9%). A single EC D estimation by MCG showed a relatively low non dipolar component and MCG c ould be applied to the clinical evaluation of cardiac excitation in both no rmal and pathological conditions.