Heart Rate Variability (HRV)

The following information has been gathered from the MacArthur Research Network on Socioeconomic Status and Health (http://www.macses.ucsf.edu/Research/Allostatic/notebook/heart.rate.html).
Please refer to this website for more details.

Description
Heart rate variability (HRV) refers to the beat-to-beat alterations in heart rate. Under resting conditions, the Electro Cardiogram (ECG) of healthy individuals exhibits periodic variation in R-R intervals. This rhythmic phenomenon, known as respiratory sinus arrhythmia (RSA), fluctuates with the phase of respiration -- cardio-acceleration during inspiration, and cardio-deceleration during expiration. RSA is predominantly mediated by respiratory gating of parasymphathetic efferent activity to the heart: vagal efferent traffic to the sinus node occurs primarily in phase with expiration and is absent or attenuated during inspiration and is absent or attenuated during inspiration

Significance of Measurement
The major reason for the interest in measuring HRV stems from its ability to predict survival after heart attack. Over half a dozen prospective studies have shown that reduced HRV predicts sudden death in patients with MI, independent of other prognostic indicators such as ejection fraction.

Method of Measurement
Originally, HRV was assessed manually from calculation of the mean R-R interval and its standard deviation measured on short-term (e.g., 5 minute) electrocardiograms. The smaller the standard deviation in R-R intervals, the lower is the HRV. To date, over 26 different types of arithmetic manipulations of R-R intervals have been used in the literature to represent HRV. The measurement of HRV is becoming increasingly standardized.

References
· John, D., & Catherine, T. MacArthur Research Network on Socioeconomic Status and Health. (2000). heart rate variability. Retrieved March 25, 2005, from http://www.macses.ucsf.edu/Research/Allostatic/notebook/heart.rate.html