Suppression of power-line interference by analog notch filtering in the ECG signal for heart rate variability analysis: to do or not to do?
BACKGROUND
Heart rate variability analysis has developed recently to a promising field of cardiology. Measures of heart rate variability can be corrupted by environmental noise or technical artifacts arising from analog and digital signal processing.


METHODS
The present investigation addressed the analysis of the effects of AC interference and its filtering on the precision and accuracy of heart rate detection. Artificial ECG recordings with predefined parameters were simulated by a computer and a data acquisition card, consecutively filtered by an analog notch filter (Q=2, 5 and 10) and digitized at 1 kHz by the same card ahead of and subsequent to the filter circuit. These latter signals were analyzed: the relative time points corresponding to the uncorrupted series at 7 points of the ventricular complexes were obtained and their means, standard deviations and maxima were computed separately.


RESULTS
The filtering of uncorrupted ECG signals does not result in heart rate period deviations < or=1 ms. Power-line interference contamination proportionally alters the accuracy of representative point detection (maximal shift: 5% - 2 ms, 10% - 4 ms, 25% - 8 ms, 50% - 14 ms), which is consistently restored by notch filtering with a slight error (L1 ms on the ascending slope and at the peak). The descending slope is more distorted at filter Q=2 and at lower ventricular complex width; however this is constant, which also results in reliable RR-interval detection.


CONCLUSIONS
AC notch filtering of ECG signals for heart rate variability analysis is considered important, and further investigation of this area is encouraged.
Hejjel
Laszlo
L
Heart Institute, Medical Faculty, University of Pecs, Pecs, Hungary. lhejjel@freemail.hu
D000704:Analysis of Variance; D011211:Electric Power Supplies; D004562:Electrocardiography / Q000706:statistics & numerical data*; D006339:Heart Rate; D006801:Humans; D012815:Signal Processing, Computer-Assisted