| Abstract: | Beat-by-Beat Recording of Terminal QRS. Introduction: Beat-by-beat recordings of quasiorthogonal leads were performed in 82 normal subjects (35 male and 47 female) with normal standard electrocardiograms (ECGs) in order to: (1) establish normal values for parameters that were similar to those used in signal-averaged ECG; (2) compare these data with the signal-averaged ECG; and (3) assess the noise level in beat-by-beat recording. Methods and Results: Low-noise recordings were achieved by special instrumentation, preparation of subjects, and screening recording sites for an optimal magnetic field at 60 Hz or its harmonics without using a shielded room. Using a 40-Hz bidirectional high-pass filter, 95% of normal subjects had a beat-by-beat duration of vector magnitude complex ≤ 107 msec, a duration of low-amplitude signal under 40 μV ≤ 37 msec, and a root mean square (RMS) voltage of last 40 msec ≥ 24.1 μV. Significant difference was found in duration of vector magnitude complex (P < 0.0001) between gender groups; this difference disappeared after normalization for height (P > 0.3). Although the beat-by-beat and signal-averaged data were highly correlated in all three parameters, the beat-by-beat recordings exhibited a shorter duration of low-amplitude signal (P < 0.0004) and a higher RMS voltage of last 40 msec (P < 0.002), and no significant variation in duration of vector magnitude complex (P > 0.2). The mean RMS noise in the vector magnitude lead from the normal group was 1.52 ± 0.65 μV (mean ± SD) while over 80% of the subjects had RMS noise under 1 μV in an individual lead. Conclusion: The normal values from beat-by-beat recordings are correlated to but different from those of signal-averaged ECGs. Every-beat high-resolution recordings of terminal QRS are stable and reproducible in normal subjects. Also, the use of individual lead (s) with lower noise is recommended for better detection of low-level terminal QRS. (J Cardiovasc Electrophysiol, Vol. 3, pp. 109–118, April 1992) |
