Uncertainty Principle of Signal-Averaged Electrocardiography

Background—Signal-averaged ECG (SAECG) reproducibility is reported to have a component that is independent of residual noise. Methods and Results—In group 1, multiple paired SAECGs were obtained to noise levels of 0.3±0.1 and 0.5±0.2 μV. For the 0.5- and 0.3-μV noise recordings, QRS duration (QRSd) was 101.2±11.3 and 104.6±9.6 ms, respectively (P<0.0001), and the differences in paired QRSd (ΔQRSd) were normally distributed, with variances of 11.4 and 26.2 ms2 (P<0.0001). Paired SAECGs were obtained in group 2 patients without and with late potentials; ΔQRSd variance was 3.3 and 217.9 ms2 (P<0.0001). In group 3, ≥10 SAECGs were acquired at noise levels of 0.2 to 0.8 μV, in 0.1-μV increments. QRSd increased as noise level decreased. The variance was greater in low-noise (0.2 to 0.4 μV) versus higher-noise (0.5 to 0.8 μV) recordings. In group 4, SAECGs were analyzed with bidirectional and Bispec filters, with no difference in QRSd between the 2 filters and a normally distributed ΔQRSd. A computer simulation ...