DISCRIMINATION BETWEEN MYOCARDIAL INFARCT AND VENTRICULAR-TACHYCARDIA PATIENTS USING MAGNETOCARDIOGRAPHIC TRAJECTORY PLOTS AND ISO-INTEGRAL MAPS

Magnetocardiograms were recorded from 30 normal (N) subjects, 15 myocardial infarct (MI) patients, and 15 ventricular tachycardia (VT) patients. Discrimination between the groups was affected by iso-integral magnetic field mapping (MFM) and trajectory plotting of MFM extrema. Iso-integral MFM for the QRST, QRS, and ST-T intervals was created for each test group member. A polarity score, based on the number of extrema features present, was assigned to each iso-integral MFM. Differences in group mean integral QRST map polarity scores were significant (p < 0.05) between MI and N, between VT and N (p < 0.005), and between MI and VT (p < 0.05) subjects. Integral ST-T map polarity scores were significantly (p < 0.0001) different between VT and N and between MI and VT (p < 0.001) subjects. Discrimination between MI and VT patients, based on polarity score difference, was 56% accurate using integral QRS maps and 73% accurate using integral ST-T maps. For each subject, time-normalized MFM was used to construct trajectory plots of the maxima and minima in the QRS and ST-T intervals. Discrimination between MI and VT patients was based upon intergroup differences in fragmented trajectory plots. When the number of discrete trajectories and/or the total number (F) of trajectory points at which discrete trajectories coexist were considered, QRSmin trajectory plots were significantly (p < 0.05) different for VT and N, but not for MI and N subjects. The significant (p < 0.05) difference between MI and VT trajectory plots enabled 76% accuracy for MI and VT identification. ST-Tmax trajectory plots show significantly (p < 0.0001) higher F values for VT patients facilitating accurate (87%) discrimination between MI and VT patients. These results suggest that the abnormalities of repolarization processes, displayed by MFM as multipolar integral ST-T maps and/or as fragmented trajectory plots of ST-T extrema, may be useful indicators of the arrhythmia substrate/processes that characterize VT and vulnerable MI patients.