Nonlinear high pass filter for R-wave detection in ECG signal.

A simple and easily implemented method for R-wave detection from ECG signals is presented. The method is based on the subtraction of a filtered version of the signal. The filter we used is a nonlinear median filter. The median filter is applied to the ECG signal. It results in a smoothed version of the signal, without any reminder of the R waves. This smoothed signal is then subtracted from the original and the resulting signal presents undistorted R-waves, without baseline drift. A simple threshold detection can then be performed on the filtered signal. Results are presented for simulated signals, with sinusoidal and step baseline drifts, as well as ECG complex shape change. The detection is accurate and the average error we obtained for 300 s length signals was of the order of 10(-8)s, for RR intervals of 1 s. Results are also presented for a real experimental signal with strong baseline drift, and the accuracy of the detection can be observed.