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Table 1 List of HRV parameters and their definitions

From: Prediction of adverse cardiac events in emergency department patients with chest pain using machine learning for variable selection

HRV parameter (unit) Definition
aRR (s) Average width of the RR interval
STD (s) Standard deviation of all RR intervals
avHR (beats/minute) Average of the instantaneous heart rate (HR)
sdHR (beats/minute) Standard deviation of the instantaneous HR
RMSSD (s) Root mean square of differences between adjacent RR intervals
NN50 (count) Number of consecutive RR intervals differing by more than 50 ms
pNN50 (%) Number and percentage of consecutive RR intervals differing by more than 50 ms
Triangular index Total number of all RR intervals divided by the height of the histogram of intervals
TINN Baseline width of a triangle fit into the RR interval histogram using a least squares
LF power (ms2) Power in low frequency range 0.04-0.15 Hz
HF power (ms2) Power in high frequency range 0.15-0.40 Hz
Total power (ms2) Total power estimated from RR intervals
LF norm (n.u.) LF power in normalized units: LF/(Total power-VLF) × 100
HF norm (n.u.) HF power in normalized units: HF/(Total power-VLF) × 100
LF/HF Ratio of LF power to HF power
  1. VLF: Very low frequency power in range ≤ 0.04 Hz.