Spatial Dispersion of the Magnetocardiographically Determined QT Interval and Its Components in the Identification of Patients at Risk for Arrhythmia after Myocardial Infarction

Background Aim was the examination of the spatial distribution of QT interval in patients after Ml with and without VT. Analysis of the QT interval components was undertaken to identify those repolarization patterns that contribute essentially to heterogeneity of recovery times. Methods Multichannel magnetocardiography was performed in 10 healthy subjects as well as in 18 patients after Ml of whom 8 had experienced clinical episodes of sustained VT in a period up to 4 years after Ml. For each subject, the temporal dispersion of the intervals QT, QRS, JT apex, T apex‐T offset, and QT apex was calculated as the difference between its minimal and maximal value. The spatial dispersion of each interval was examined visually by plotting the deviations of each channel from the minimal value with respect to its position. Local and global spatial variability was quantified using two smoothness indices, SI and Sin. Results Dispersion and smoothness values for all intervals were generally significantly lower in the control group. When comparing patients with and without VT, dispersion values could not separate between patient groups. In contrast, SI and Sin values were significantly different, the VT group demonstrating higher values for QT, JT apex, and QT apex (P < 0.05). Conclusion Spatial analysis of the dispersion of cardiac time intervals is a better marker for increased risk for malignant arrhythmia than the strictly temporal approach using standard dispersion measures. In particular the results suggest that the heterogeneity of repolarization is the greatest during the interval between QRS offset and T apex.