A novel approach for the averaging of magnetocardiographically recorded heart beats

Performing signal averaging in an efficient and correct way is indispensable since it is a prerequisite for a broad variety of magnetocardiographic (MCG) analysis methods. One of the most common procedures for performing the signal averaging to increase the signal-to-noise ratio (SNR) in magnetocardiography, as well as in electrocardiography (ECG), is done by means of spatial or temporal techniques. In this paper, an improvement of the temporal averaging method is presented. In order to obtain an accurate signal detection, temporal alignment methods and objective classification criteria are developed. The processing technique based on hierarchical clustering is introduced to take into account the non-stationarity of the noise and, to some extent, the biological variability of the signals reaching the optimum SNR. The method implemented is especially designed to run fast and does not require any interaction from the operator. The averaging procedure described in this work is applied to the averaging of MCG data as an example, but with its intrinsic properties it can also be applied to the averaging of ECG recording, averaging of body-surface-potential mapping (BSPM) and averaging of magnetoencephalographic (MEG) or electroencephalographic (EEG) signals.

[Magnetocardiographic diagnostic of late fields. Current state and future perspectives]

The occurence of ventricular late potentials in the signal averaged surface ECG is an indicator for slow electrical excitation in myocardial tissue prone to arrhythmias. Signal averaged surface ECG is performed for identification of patients with ventricular late potentials who have a high risk for life threatening arrhythmias. Since every electrical field is combined with a magnetic field, established methods of the signal averaged surface ECG were applied on recorded magnetocardiograms of patients. The incidences and details of late ventricular activity in the signal averaged electrocardiogram (ventricular late potentials) were compared with those in the magnetocardiogram (ventricular late fields). A close correlation of the two different methods was found. The magnetocardiogram has the option for the determination of the site of origin of magnetic signals three-dimensionally. In the future, this method may help to find areas of slow conduction for ablative procedures to cure patients with a high risk for malignant arrhythmias.