Changes in Late Potential Measurements as a Function of Decreasing Bandwidth

Bandwidth of Late Potentials Introduction: Limited bandwidth systems such as Holter recorders are being used to record cardiac late potentials. Standard late potential systems have a low‐pass frequency of 300 Hz. This suggests that Holter tape systems may significantly distort the late potential measurements, when compared to standard late potential systems. Methods and Results: Signal‐averaged recordings were obtained with an analog bandwidth of 0.05‐300 Hz. Digital filters were then used to do high‐pass filtering and low‐pass filtering. All XYZ signal‐averaged recordings were low‐pass filtered at frequencies of 250, 150, 100, 75, 50, and 25 Hz using a second order Butterworth filter. A fourth order 40 Hz bidirectional high‐pass filter was then applied to each set of recordings. The QRS duration (QRSd) was measured in the filtered vector magnitude. Thirty‐eight syncope patients who had negative electrophysiologic studies for ventricular tachycardia, no prior infarction, normal ejection fractions (> 50%), and a QRSd <120 msec served as the negative late potential group. Thirty‐seven patients with clinical ventricular tachycardia, a positive electrophysiologic study for ventricular tachycardia, and a QRSd>120 msec served as the positive late potential group. Conclusions: A statistically significant lengthening of the QRSd (P <0.05) was observed in the patients with late potentials between the 250 Hz and 25 Hz low‐pass filter. There was a statistically significant shortening of the QRSd in the negative late potential patients between 250 Hz and 25 Hz, as well as between 250 Hz and 50 Hz, with P<0.05 in both cases. Thus, significant changes in late potentials are seen in limited bandwidth recordings that may limit the clinical usefulness of such systems.