An Engineering Perspective of External Cardiac Loop Recorder: A Systematic Review

Table 8

Filters and their frequency range for various ECG parameters.

Ref. number	Parameters acquired	Filter used	Freq range
[64]	Heart rate	Bandpass filter	—
[30]	Heart rate	Passive RC high pass filter	1 Hz
[31]	Heart rate	LPF, after IA notch, HPF, LPF	= 150 Hz, = 60 Hz,; = 0.5 Hz, = 35 Hz
[65]	Heart rate	LPF	= 40–80 Hz
[45]	Heart rate	8-pole Bessel bandpass filter	0.1–100 Hz
[37]	QRS complexes, heart rate	BPF
[28]	R-peak, heart rate	HPF, 2nd-order Butterworth filter (two 1st-order LPF)	= 0.05 Hz,; = 35 Hz
[32]	R-peak, abnormal heart beat	LPF, moving average filter	= 35 Hz
[66]	ECG and heart rate	Notch filter formed by ordinary amplifier TL062	= 50 Hz
[38]	ECG wave, R-peak	LPF, BPF	= 5–20 Hz
[67]	R-peaks	LPF, HPF
[44]	R-peak	Adaptive filter
[68]	Pk-Pk	Analog active RC filter, a second-order Butterworth
[29]	HRV	LPF
[42]	ECG, PPG, BP	HPF, LPF	= 0.16 Hz, = 103 Hz
[69]	QRS complex	Antialiasing 1-pole LPF	= 35 Hz,
[70]	QRS, T wave	HPF, sixth-order Bessel LPF	= 150 Hz
[50]	QRS complexes and T waves	RC high pass filters	= 0.16 Hz
[71]	PQRST wave	Bandpass filter	0.159–159 Hz
[72]	Points (P, Q, R, S, T)	BPF, notch filter	= 0.05 Hz to 150 Hz, = 6 Hz
[51]	QRS duration, RR interval, HBR, R amplitude, RT-interval: PR-interval: QT-interval features	LPF, HPF, LPF	= 0.03 Hz,; = 80 Hz,; = 58 Hz and 19 Hz