Signal-averaged electrocardiography in the time and frequency domains.

The noninvasive signal-averaged electrocardiographic detection of late potentials correlates with the spontaneous occurrence of sustained ventricular tachycardia (VT). Frequency analysis of the electrocardiographic signal from the terminal QRS and ST segment also correlates with sustained VT. This study was designed to compare these 2 methods by analysis of signals recorded from the same hardware system. Signals were recorded from 234 patients with prior myocardial infarctions with a commercially available signal-averaging system. Patients were classified into 2 groups: group 1 consisted of 84 patients with VT and group 2 consisted of 150 patients without VT. In the frequency domain, magnitude and energy area ratios and peak ratios of the spectral plot from 20 to 50 Hz over 0 to 20 Hz were calculated for a 140-ms interval starting 60 ms after the beginning of the QRS. In the time domain, the duration of the filtered QRS was 121 +/- 29 ms for group 1 and 110 +/- 25 ms for group 2 (p less than 0.002). The duration of the terminal QRS less than 40 microV was 45 +/- 21 ms in group 1 and 36 +/- 18 ms in group 2 (p less than 0.001). The root-mean-square amplitude of the terminal 40 ms of the QRS was 25 +/- 24 microV in group 1 and 36 +/- 33 microV in group 2 (p less than 0.004).(ABSTRACT TRUNCATED AT 250 WORDS)