What Is Heart Rate Variability?

Heart rhythm, the pattern of heart contraction and relaxation, is the response of the heart muscle fibers to electrical activation. The electrical signal comes from specialized cells and fibers within the upper and lower chambers of the heart, the atria and ventricles. Heart rate should be 60-99 beats per minute at rest.

Under normal conditions, a healthy heart displays slight beat-to-beat variability; that is, it is healthy to have variation in the time between your heartbeats. For example, in sinus arrhythmia, a healthy heart rhythm pattern, the interval between beats shortens during inspiration and lengthens during exhalation. A healthy heart rhythm is not strictly regular, but varies slightly, a result of numerous factors, especially vagus nerve activity. This is true for fetal heart monitoring in women in labor, and it is true throughout our lives, though HRV tends to decrease with age.¹

In an electrocardiogram (ECG), this is reflected in the R-R interval. R-R interval variability reflects a confluence of the complex interplay between many factors. Especially important is the balance between the sympathetic and parasympathetic arms of the autonomic nervous system, which is itself influenced by physical, emotional, pharmacologic, and pathophysiologic factors. Heart rate variability (HRV) may be taken as an indicator of baroreflex (blood pressure sensing) activity and psychophysiological resilience (the body’s response to the mind’s experience). High HRV signifies healthy systemic adaptability, and low HRV points to susceptibility to the negative consequences of stress and disease.²

Measuring HRV may provide useful clinical information about autonomic tone and heart function. In addition, reductions in HRV have been associated with a wide range of disorders.

There has been growing interest in the potential role of the heart as a sensory organ, specifically as relates to emotions and the interplay between brain and heart as collaborative interpreters of our environment. Some experts believe that people are most healthy when cardiac, respiratory, and central nervous system activities align and function in synchrony. This reflects as balanced autonomic nervous system tone and, in part, high HRV.

Clinical importance of Heart Rate Variability