Late QRS activity in signal-averaged magnetocardiography, body surface potential mapping, and orthogonal ECG in postinfarction ventricular tachycardia patients.

Background: Delayed electrical activity necessary for re-entrant ventricular tachycardia (VT) is detectable noninvasively with high resolution techniques. We compared high resolution signal-averaged analysis of magnetocardiography (MCG), body surface potential mapping (BSPM), and orthogonal three-lead ECG (SA-ECG) in the identification of patients prone to VT after myocardial infarction (MI). Methods: Patients with remote myocardial infarction and cardiac dysfunction were studied, 22 with (VT group) and 22 without VT (control group). MCG with seven channels and BSPM with 63 and SA-ECG with three orthogonal leads were registered. After signal-averaging and highpass filtering, three time domain analysis (TDA) parameters describing late electrical activity were computed: QRS duration (QRSd), root mean square amplitude (RMS) of the last 40 ms of QRS, and the duration of the low-amplitude QRS end (LAS). Results: All parameters by each method were significantly different between the patients' groups. For example, LAS parameter in MCG was 59 (SD 22) ms in the VT group vs. 37 (SD 13) ms in controls (P < 0.001), 77 (SD 22) ms vs. 56 (SD 19) ms in BSPM (P = 0.002), and 60 (SD 24) ms vs. 39 (SD 22) ms in SA-ECG (P = 0.005). The combination of LAS parameter in MCG and SA-ECG resulted in improved performance in comparison to any single parameter with 95% sensitivity and 68% specificity. Conclusions: All three high resolution methods identified VT propensity among post-MI patients with cardiac dysfunction and between-Method differences were small. Information in MCG and SA-ECG may be complementary and their combination could be of value in postinfarction arrhythmia risk assessment.