Multichannel magnetocardiography measures the magnetic field distribution of the human heart non invasively from many sites over the body surface. Multichannel magnetocardiogram (MCG) analysis enables regional temporal differences in the distribution of cardiac magnetic field strength during depolarization and repolarization to be identified, allowing estimation of the global and local inhomogeneity of the cardiac activation process.
The aim of this study was to compare the spatial distribution of cardiac magnetic field strength during ventricular depolarization and repolarization in both normal subjects and patients with cardiac abnormalities, obtaining amplitude measurements by magnetocardiography.
MCGs were recorded at 49 sites over the heart from three normal subjects and two patients with inverted T-wave conditions. The magnetic field intensity during depolarization and repolarization was measured automatically for each channel and displayed spatially as contour maps. A Pearson correlation was used to determine the spatial relationship between the variables.
For normal subjects, magnetic field strength maps during depolarization (R-wave) showed two asymmetric regions of magnetic field strength with a high positive value in the lower half of the chest and a high negative value above this. The regions of high R-wave amplitude corresponded spatially to concentrated asymmetric regions of high magnetic field strength during repolarization (T-wave). Pearson-r correlation coefficients of 0.7 (p <0.01), 0.8 (p <0.01) and 0.9 (p <0.01) were obtained from this analysis for the three normal subjects. A negative correlation coefficient of -0.7 (p <0.01) was obtained for one of the subjects with inverted T-wave abnormalities, suggesting similar but inverted magnetic field and current distributions to normal subjects. Even with the high correlation values in these four subjects, the MCG was able to identify differences in the distribution of magnetic field strength, with a shift in the T-wave relative to the R-wave.
The measurement of cardiac magnetic field distribution during depolarization and repolarization of normal subjects and patients with clinical abnormalities should enable the improvement of theoretical models for the explanation of the cardiac depolarization and repolarization processes.
Smith FE, Langley P, Trahms L, Steinhoff U, Bourke JP, Murray A. Comparison of cardiac magnetic field distributions during depolarisation and repolarisation. J Bifurcation Chaos 2003; 12; 3783-90.
Dr. Fiona E. Smith, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-6161.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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