Table 2.

Description of heart rate variability data to be analyzed from 24- hour Holter recording

Heart rate variability parameter (Acronym)	Description/Physiological representation
Low frequency (LF)	Represents contribution of baroreflex activity in overall cardiovascular control
High frequency (HF)	Represents contribution of cardiac parasympathetic/vagal nervous activity
Low to high frequency ratio (LF:HF)	Represents the interplay between sympathetic and parasympathetic limbs of the autonomic nervous system
Standard deviation of the normal
Wave (SDNN)	Variation (in units of standard deviation) between each successive R-wave in the ECG recording
Standard deviation of the average
Normal wave (SDANN)	Average of the variation (in units of standard deviation) between each successive R-wave when comparing multiple 5-minute sections of the ECG recording
Percentage of normal wave variation (pNN50%)	Percentage of normal R-waves that differ from the wave directly before it by ≥50 milliseconds