ANALYSIS AND INTERPRETATION OF HEART RATE VARIABILITY

Abstract

Heart Rate Variability is a normal physiological phenomenon of variations in instantaneous heart rate. A heartbeat is initiated by the sinoatrial (SA) node in the heart. During normal functioning, the SA node does not work as a periodic oscillator. Indeed, it oscillates in a complex pattern under the in uence of the autonomic nervous system. The analysis of complex patterns present in heart rate provides important insight into autonomic modulation of the heart, and overall cardiovascular health. However, the exact interpretation of heart rate variability is unknown and challenging to be explained precisely with the current understanding and knowledge in the eld. The clinical signi cance of heart rate variability was rst observed in 1965 by Hon and Lee. Spontaneous rhythms in the cardiovascular circulation and the heart rate were observed in 1968. In 1996, the Task Force set-up by the \European Society of Cardiology and the North American Society of Pacing and Electrophysiology" introduced standards for the analysis of heart rate variability. Since then, heart rate variability has gained popularity as a noninvasive marker for diagnosing several cardiac and non-cardiac abnormalities. It is strongly correlated with several physiological conditions such as cardiac and noncardiac diseases, stress, age, etc. The oscillations in heart rate that lead to heart rate variability are usually generated due to nonlinear physiological phenomena involved in modulation of the instantaneous heart rate. The autonomic nervous system's two branches, the sympathetic nervous system and the parasympathetic nervous system, in uence the heart rate in an opposite action. The sympathetic nervous system is known for speeding up the heart rate, while the parasympathetic nervous system is known for slowing it down. These two opposite actions do not represent a \zero-sum" process. The in uence of the sympathetic nervous system and parasympathetic nervous system on heart rate is neither identical nor at the same speed. Indeed, their interrelationship is very complex. Therefore, an imbalance is originated in the variability related to acceleration, and deceleration. This imbalance introduces an asymmetry in heart rate, popularly known as heart rate asymmetry. It provides additional physiological information as compared to traditional heart rate variability analysis.