Coherent signal rejection in ECG

A method for monitoring an electrocardiogram (ECG) signal of a subject, comprising:

• digitally sampling an average signal from ECG electrodes attached to the subject, the average signal comprising a Wilson Central Terminal (WCT) signal;
• processing the WCT signal with a band-pass filter to establish a band-pass filter signal, the band-pass filter signal having a line interference component;
• processing the band-pass filter signal with a frequency meter and determining a frequency of the line interference component;
• determining an average interference frequency of the WCT signal based on the frequency of the line interference component;
• digitally sampling and buffering a raw ECG signal from another ECG electrode attached to the subject;
• calculating a moving average of the raw ECG signal;
• calculating a residual signal using the moving average of the raw ECG signal wherein the residual signal comprises frequency components at and above the average interference frequency;
• calculating, based on the residual signal, a first amplitude and a first phase shift of a primary interference signal at the average interference frequency and a second amplitude and a second phase shift of one or more harmonic interference signals at respective multiples of the average interference frequency;
• and
• digitally subtracting the primary interference signal and the one or more harmonic interference signals from the raw ECG signal so as to generate and output a clean ECG signal.