Magnetocardiography: three-dimensional localization of the origin of ventricular late fields in the signal averaged magnetocardiogram in patients with ventricular late potentials.

The purpose of this study was to detect ventricular late fields recorded by a biomagnetic multichannel system in patients with ventricular late potential and to determine the site of these ventricular late fields non-invasively in three dimensions. Biomagnetic signals of sinus beats during a 5-min acquisition period simultaneously recorded by a 37-channel system Krenikon were averaged in all channels. Ventricular late fields were determined in each channel according to the algorithm of Simson for ECG data. For the localization process, baseline correction from the averaged non-filtered signals was performed at the end of the QRS complex under visual control. The single current dipole model within the homogeneous half-space was applied. Eight patients post myocardial infarction with ventricular late potentials (four with recurrent sustained ventricular tachycardia) and four healthy individuals were examined. In the normal subjects, no ventricular late fields were detected. However, ventricular late fields were found in all patients, and were localized in six patients within the border zone of myocardial infarction. In the four patients with ventricular tachycardia, a spatial coincidence of the site of origin of ventricular late fields and the site of origin of ventricular tachycardia determined by catheter mapping was found in two. It is concluded that magnetocardiography is able to detect ventricular late fields and can be used to determine their site of origin.