Noise properties in the isoelectric intervals of the ECG: a comparison

The authors have compared the variance and the histogram for the three isoelectric intervals of the ECG of 8 subjects. They have used a spectral filter in order to eliminate the power line frequency. They have found that when the noise variance is low, the histogram is bell shaped and similar for the three intervals. But when the noise variance is high, the histogram does not have any definite shape. When the relative difference between variances for the isoelectric intervals is low, these intervals can be considered as similar. But in some instances, noise histograms for different intervals have rather different variances. The authors have tested their analysis method by adding noise with different amplitude distributions to a clean ECG. They conclude that although the time record gives a clue about when to reject a noisy ECG, the measurement of the noise variance in the three isoelectric intervals would be better. Also, when searching for micropotentials in the PR or ST intervals, the noise behavior in the TP interval is not necessarily representative of the noise in the other intervals