The corner frequencies of the ECG amplifier for heart rate variability analysis

Heart rate variability (HRV) analysis is considered a popular method both in clinical and research fields. However, several ignored technical artifacts may falsify its measurements. The current study investigates the effects of corner frequencies of the ECG amplifier on the precision of RR-interval detection. Clear or noise-corrupted ECG records with predefined parameters consisting of 21 cycles were generated, played back through analog filters and data-logged on a Pentium-based computer with a DaqBoard2000 data acquisition card. 0.1-10 Hz second-order high pass and 20-100 Hz fourth-order low pass Bessel and Butterworth filters were used. The RR-intervals were measured between seven reference points of the ventricular complexes before and after filtering. High and low pass at every frequency cutoff and with both filter types results in correct RR-intervals within 1 ms error. However, a lower cutoff below 1 Hz is needed to maintain ECG morphology. AC interference or Gaussian random noise can falsify the measured RR-intervals up to 16 or 34 ms, respectively. These errors may be reduced to 1-4 ms with appropriate low pass filters. A frequency range of 0.5-20 Hz for the ECG amplifier can be sufficient for HRV analysis reducing the errors from AC interference or random noise.