An Approach to Successful Power-line Interference Suppression in ECG Signals

The ECG signals acquisition is usually corrupted by presence of Power-Line Interference (PLI) induced by the electromagnetic field around us. Many methods for PLI suppression/elimination have been developed over the years. The easy to apply traditional notch filters suppress unacceptably the ECG spectrum around the rated PL frequencies of 50 or 60 Hz and their deviations, which are restricted by the standards within the range of ± 0.5 Hz. The changes are very slow but the current PL frequency has to be continuously checked to allow start and performance of adequate PLI suppression during any ECG recordings including the 24 hours Holter monitoring. According to the proposed approach, the corrupted ECG recording is bi-directional band-pass (BP) filtered. The resulting sinusoidal BP waves differ in amplitude from the PLI but their zero crossing points remain identical. The two out-sample distances located at both ends of each current sinusoidal curve are calculated and aided to the inter-sample distances. The obtained fractal wave period is converted into current PL frequency and used for bi-directional notch filtration with narrow stop-band. The results obtained demonstrate a very successful PLI suppression in ECG signals. The errors committed are within a few μV, except for the edges of the recordings due to the transition processes.