Heart Rate Variability During Short-Term Electroencephalography

Heart rate variability (HRV) is a measure of the function of the brainstem nuclei that modulate heart rhythm through the parasympathetic and sympathetic nervous systems. HRV is reduced in many health conditions. It is a predictor of increased mortality in patients who have had myocardial infarction, and of sudden death in persons with epilepsy.   Methods: We measured HRV in the single-channel electrocardiogram (ECG) of 103 patients undergoing a short electroencephalogram (EEG) of 20 to 90 minutes' duration, whose EEG results were normal.

We found that despite the normal EEG results of the patients, their measures of HRV were reduced compared to normal values. The single most widely used measure of HRV is the square root of mean squared differences of successive heartbeats (RMSSD), which was 28.1 ± 21.8 in our subjects. The high frequency (HF) band was specifically affected. In these patients, HRV was only slightly affected by state of wakefulness, and was stable during wakefulness, N1 sleep, and N2 sleep. A significant reduction in HRV with age was also observed in our subjects. There was a non-significant trend toward lower HRV in our female subjects.

In patients selected by their clinicians to undergo EEG, HRV is reduced. Our results indicate that HRV during the first five minutes of EEG, regardless of sleep state, is a reliable measure of HRV in patients undergoing short-term EEG. We conclude that a normal EEG result does not predict normal HRV and that routine measurement of HRV during EEG could provide useful prognostic information for patients undergoing EEG.