Power-line Interference Elimination from ECG Signals Using Modified Notch Filtration: A Real Time Version

The traditional notch filtration (NF) seems to be appropriate for successfully suppressing the power-line interference (PLI) commonly encountered in electrocardiographic (ECG) recordings. However, this can be achieved by a very narrow bandwidth that does not correspond to the PLI variations inducing unacceptably long transition periods. The present study is based on previous works cited below, where the contaminated ECG recording is band-pass (BP) filtered, the introduced phase shift is compensated by a back filtration, and the ongoing first harmonic frequency is off-line determined by measuring the time between two consecutive zero-line crossings. The proposed in this paper methodology subjects the contaminated ECG recording to two-fold one-way BP filtration, the second one contributing to a more accurate first harmonic extraction. Further one, a more precise sinusoidal interpolation for zero-line crossing detection enables high fidelity calculation of the ongoing PLI first harmonic. The frequency deviation of the PLI is compensated by calculating the first derivative of the phase response of the two-fold BP filtration, and the amplitude variation of the PLI - by calculating the gain from the frequency response. The NF coefficients determined in this way are applied to the subsequent specific band-stop filtration of the ECG signals. Two additional problems are also studied and taken in consideration - the elimination of high-order harmonics in power-line interference and the procedure adaptation to low sampling rates. The experiments are carried out in MATLAB environment.