Reminder: RMSSD and SD1 are identical heart rate variability metrics

Assessment of heart rate variability (HRV) is a common approach to examine cardiac autonomic nervous system modulation that has been employed in a variety of settings. Frequently, both the root mean square of successive differences (RMSSD) and SD1, which is a Poincaré plot component, have been used to quantify short‐term heart rate variability. It is not typically appreciated, however, that RMSSD and SD1 are identical metrics of HRV. As a...