Optimal bandpass filters for time-domain analysis of the signal-averaged electrocardiogram

The optimal bandpass filter for signal averaging of the surface QRS complex to detect late potentials is undefined. A study was conducted in 87 patients; 25 (mean age 34 +/- 10 years) were normal (group I), 29 (60 +/- 20 years) had organic heart disease without ventricular tachycardia (group II) and 33 (62 +/- 15 years) had sustained ventricular tachycardia (group III). In all patients signal-averaged electrocardiography (200 beats) was performed using a sharp, bidirectional filter and data analyzed using the following 7 high-pass filter settings: 10, 15, 20, 25, 40, 80 and 100 Hz. For each filter the duration of the signal-averaged QRS complex, the low-amplitude signals of less than 40 microV and the root-mean-square voltage of the terminal 40 ms (RMS-40) were determined. Normal values for each filter were determined from group I patients. In all 3 groups, quantitative signal-averaged variables were filter dependent. There was a progressive and marked decrease in RMS-40 and a progressive and marked increase in low-amplitude signal duration as the high-pass filtering was increased from 10 to 100 Hz. In contrast, high-pass, filter-dependent changes in signal-averaged QRS duration were less marked. The sensitivity and specificity for each filter using RMS-40 as the index of late potentials in separating group III patients from group II patients were: 10 Hz-64% and 52%; 15 Hz-57% and 72%; 20 Hz-57% and 76%; 25 Hz-42% and 90%; 40 Hz-61% and 83%; 80 Hz-88% and 69%; and 100 Hz-79% and 62%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)