A real-time system for high-resolution ECG signal averaging using the analog SFP alignment technique

We have developed a real-time, signal averaging system for high-resolution ECG, which implements an analog version of the single fiducial point (SFP) alignment technique. It consist essentially of a second order, highpass (3 Hz), Butterworth filtering operation applied to an ECG signal presenting predominantly monopolar QRS complexes. This operation is complemented by zero crossing detection after a signal amplitude threshold level crossing detection. The ECG signal is also lowpass filtered at 30 Hz to reduce the possibility of ambiguities at the zero crossing point (the SFP point), in the presence of 60 Hz mains interference, or other sources of high frequency noise. The output pulse from the analog SFP detector was used as the trigger signal channel in a digital averaging oscilloscope, with a moving average function. The performance of this ECG averaging system was evaluated in the spectral range between 100 and 300 Hz, which is the highest frequency bandwidth of interest in high-resolution electrocardiography. The system was capable of extracting cardiac electrical events, as short as 2 ms of duration, in the P-R interval. Hence, it can be appropriate for P-wave and His bundle potentials analysis