Value of magnetocardiographic QRST integral maps in the identification of patients at risk of ventricular arrhythmias

It has been shown that regional ventricular repolarization properties can b e reflected in body surface distributions of electrocardiographic QRST defl ection areas (integrals). We hypothesize that these properties can be refle cted also in the magnetocardiographic QRST areas and that this may be usefu l for predicting vulnerability to ventricular tachyarrhythmias. Magnetic fi eld maps were obtained during sinus rhythm from 49 leads above the anterior chest in 22 healthy (asymptomatic) control subjects (group A) and in 29 pa tients with ventricular arrhythmias (group B). In each subject, the QRST de flection area was calculated for each lead and displayed as an integral map . The mean value of maximum was significantly larger in the control group A than in the patient group B (1,626 +/- 694 pTms vs 582 +/- 547 pTms, P < 0 .0002). To quantitatively assess intragroup variability in the control grou p A and intergroup variability of the control and patient groups, rye used the correlation coefficient r and covariance a. These indices showed signif icantly less intragroup than intergroup variation (e.g., in terms of a 28.0 . 10(-6) +/- 12.3 . 10(-6) vs 3.4 . 10(-6) +/- 12.5 . 10(-6), P < 0.0001). Each QRST integral map was also represented as a weighted sum of 24 basis functions (eigenvectors) by means of Karhunen-Loeve transformation to calcu late the ontribution of the nondipolar eigenvectors (all eigenvectors beyon d the third). This percentage nondipolar content of magnetocardiographic QR ST integral maps rs as significantly higher in the patient group B than in the control group A (13.0% +/- 9.1% vs 2.6% +/- 2.0%, P < 0.0001). Discrimi nations between control subjects and patients with ventricular arrhythmias based on magnitude of the maximum, covariance a, and nondipolar control ere 90.2%, 90.2%, and 86.3% accurate, with a sensitivity of 89.7%, 93.1%, and 75.9%, and a specificity of 90.9%, 86.4%, and 100%. We have shown that magn itude of the maximum and indices of variability and nondipolarity of the ma gnetocardiographic QRST integral maps may predict arrhythmia vulnerability. This finding is in agreement with earlier studies that used body surface p otential mapping and suggests that magnetic field mapping may also be a use ful diagnostic fool for risk analysis.