Table 2.
Definitions of abbreviations for HRV and HRF metrics
| Abbreviations | Definitions |
|---|---|
| Traditional heart rate variability (HRV) | |
| HR | Heart rate (in beats/min) |
| pNN50 | Percentage of successive NN intervals that differ by >50 ms (%) |
| HF power | Absolute power of the high-frequency band (0.15–0.4 Hz) (ms2) |
| SD1 | Short axis of Poincaré plot (ms) |
| Sample Entropy (SampEn) | Measure of regularity and complexity of the NN interval time series |
| SDNN | Standard deviation of NN intervals (ms) |
| Heart rate fragmentation (HRF) | |
| PIP | Percentage of inflection points in the NN interval time series |
| PIPH and PIPS | Percentage of beats that represent “hard” (“−1” to “+1” or vice versa) and “soft” (to or from “0”) inflection points in the NN interval time series (%) |
| W0–3 | Percentage of words in the NN interval time series that contain 0, 1, 2, or 3 inflection points, respectively (%) |
| Novel metric | |
| SARD | In an NN interval time series, a drop in HR by ≥20% from the previous beat that is sustained for four beats |