Influence of the selection of the baseline correction interval on the localisation of the electrical heart activity

The electric heart activity can be localised from body surface mapping data with computer algorithms. At higher heart rates the T and P waves merge. T hus, the offset can not be subtracted in the TP segment. We investigated 28 healthy volunteers with signal averaged 31-lead magnetoc ardiography. The offset of the baseline was determined in the TP-segment an d in the PR-segment, respectively. The electrical heart activity was locali sed in the initial 30 ms of the QRS complex (Q), at the QRS maximum (R), an d at the T wave maximum (T). The volume currents were considered by using a boundary element model with the compartments lungs and torso. The 3D posit ions of the dipoles, the dipole orientations, and the dipole strengths were calculated using the data preprocessed with two different offset correctio n intervals. The offsets of the TP and PR segments significantly differed o ne from another. The average deviations of the dipole localisation were wit hin a few centimetres (Q: 20+/-31 mm, R: 6+/-13 mm, T:14+/-30 mm). However, in a small number of subjects (Q: n = 5, R: n = 2, T: n = 5) we observed a deviation of more than 30 mm. These deviations were not linearly correlate d to the differences in the baseline offsets. High resolution recordings continuously detect heart activity in the PR seg ment. The correction of the baseline in the PR segment instead of the TP se gment may introduce artefacts in the source localisation and therefore shou ld be avoided.