Identification of patients with ventricular tachycardia after myocardial infarction by high-resolution magnetocardiography and electrocardiography.

The value of time domain analysis of late fields in the high-resolution magnetocardiogram in the identification of myocardial infarction patients with ventricular tachycardia was investigated in 30 subjects: 10 patients with documented sustained ventricular tachycardia and old myocardial infarction, 10 patients with old myocardial infarction without complex ventricular arrhythmias, and 10 normal volunteers. The duration of the QRS complex in the magnetocardiogram was significantly longer in ventricular tachycardia patients compared to myocardial infarction patients (144 (SD, 33) vs 109 (SD, 8) ms; p = 0.004). The root-mean-square field of the last 60 ms of the QRS complex was smaller in ventricular tachycardia patients than in myocardial infarction patients (830 (SD, 650) vs 1,480 (SD, 730) fT, respectively; p = 0.047). Also, the duration of the low-amplitude signal less than 700 fT was longer in ventricular tachycardia patients than in myocardial infarction patients (47 (SD, 28) vs 28 (SD, 8) ms, respectively; p = 0.048). The sensitivity and specificity in identifying ventricular tachycardia patients were both 80%, and the positive and negative predictive values were 78% and 86%, respectively. High-resolution electrocardiography recorded during the same session performed slightly better: sensitivity 90%, specificity 90%, and positive and negative predictive values 90%. The signal-to-noise ratio of electrocardiogram was higher (approximately 2 x) than that of magnetocardiogram. It is concluded that the new magnetocardiographic technique seems helpful in screening patients at risk of ventricular arrhythmias after myocardial infarction. The results encourage further refinement of the technique and application in prospective studies.