Please forward this error screen to variability of educational programs. It is measured by the variation in the beat-to-beat interval. Reduced HRV has been shown to be a predictor of mortality after myocardial infarction although others have shown that the information in HRV relevant to acute myocardial infarction survival is fully contained in the mean heart rate.
There is interest in HRV in the field of psychophysiology. For example, HRV is related to emotional arousal. The Polyvagal Theory describes pathways in the autonomic nervous system that mediate HRV. The neurovisceral integration model describes how the prefrontal cortex regulates activity in limbic structures which act to suppress parasympathetic activity and activate sympathetic circuits. Variation in the beat-to-beat interval is a physiological phenomenon. The SA node receives several different inputs and the instantaneous heart rate or RR interval and its variation are the results of these inputs.