Relation between spatial properties of repolarisation interval and T-wave amplitude using magnetocardiography

Spatial distribution of repolarisation interval and T-wave amplitude were examined using multi-channel magnetocardiograms (MCGs), which non-invasively measure variations in magnetic field strength at the body surface. MCGs were obtained using the Physikalisch-Technische Bundesanstalt (PTB) multi-channel SQUID system at 49 sites over the heart from eight healthy volunteers. Each recording channel was displayed on a computer screen. Repolarisation intervals and T-wave amplitudes in each channel were measured manually and displayed graphically as contour maps. Pearson correlation was used to determine the spatial relationship between the two variables. Mean(standard deviation) values of repolarisation interval and T-wave amplitude were 381(7) ms and 4(2) pT respectively. The standard deviation of the difference between repeat measurements for repolarisation interval and T-wave amplitude was 5.2 ms and 0.4 pT respectively. Repolarisation measurements tended to increase by approximately 8 ms for a doubling of T-wave height. Contour maps showed two distinct regions of high repolarisation interval (>380 ms), corresponding spatially to concentrated areas of high absolute T-wave amplitude (>4 pT). A Pearson correlation coefficient of 0.7 (p<0.0005) was obtained from this analysis. Repolarisation intervals and T-wave heights in normal subjects recorded from magnetocardiography have distinctive but related spatial distributions.