Heart Rate Variability (HRV)

Heart rate is mainly determined by pacemaker current generated in the SA node. It, in turn, is regulated by autonomic nervous system. Sympathetic stimulation enhances chronotropic, ionotropic and dromotropic activity via α and β receptor activation whereas, parasympathetic stimulation causes reverse effect on heart via the M2 receptors. Varied input from these two branches of the ANS produces change in heart rate. So, HRV, therefore, is the change in the time interval between two consecutive heartbeats. In other words, HRV is the time difference between a given heart beat to the mean duration of heartbeat. Like all other organs of the body, heart is also susceptible to aging and diseases. These conditions influence heart rate and also HRV. Today, HRV has invited much investigation and debate. Electronic databases Google Scholar, IMSEAR (Index Medicus for South-East Asia Region), Scopemed and MEDLINE/PubMed were extensively explored with key words “HRV” or “Heart Rate Variability” from earliest possible date (1973) to December, 2016 and the available information summarized. Different aspects of HRV have been covered including historical background, HRV Analysis Methods, Interpretation of HRV, software’s used for HRV recording, importance of HRV measurement, HRV in varying conditions, drugs etc. HRV offers a relatively simple, well-tolerated, and inexpensive method for studying physiological and pathophysiological processes in a noninvasive manner. However, there are several important challenges in this area of study. There are a number of confounding variables which contribute to HRV data collection and interpretation open to question. Again, one should not compare one’s HRV with others, since HRV is affected by numerous internal and external factors, namely, age, lifestyle, hormones, body functions etc.