Subtraction procedure for removing powerline interference from ECG: Dynamic threshold linearity criterion for interference suppression

This paper presents the subtraction procedure for interference cancellation in ECG. In contrast to the well-known hardware and software filters, the method does not affect the signal frequency components around the rated powerline frequency. The method searches for linear segments in the ECG signal. Then a digital filter is used to remove the interference from these segments. The samples of the interference signal are computed in these segments and later on these samples are used to remove by subtraction the interference from the signal where non-linear segments are encountered. The detection of linear segments in ECG signals is the most important stage. It is performed by a criterion for linearity using second differences of the sampled signal. Applying automatic adaptation of the `linearity criterion´ value in accordance to the signal altitude, the best conditions for application of the procedure can be obtained.