Abstracts

Rationale: Heart rate variability (HRV) is an established parameter for the assessment of cardiac autonomic regulation, a balanced parasympathetic-sympathetic autonomic activity. Patients with epilepsy show abnormal HRV during interictal periods. Cardiac dysfunction is believed to correlate with sudden unexpected death in epilepsy, but HRV has not been compared between wakefulness and sleep in patients with epilepsy. Methods: Eight patients with epilepsy (3 men, aged 14-27 years) and 5 patients with psychogenic non-epileptic seizures (PNES; 1 man, aged 15-29 years) were included in this retrospective review of EKG and polysomnographic data during the first day and night of routine 4-day video EEG monitoring for epilepsy. Sleep stages were scored based on the American Academy of Sleep Medicine criteria. Spectra of HRV were analyzed using the maximum entropy method, to obtain high frequency (HF, 0.15-0.4 Hz), low frequency (LF, 0.04-0.15 Hz), and very low frequency (VLF, 0-0.04 Hz). The HF band represents the parasympathetic tone and the LF band reflects both sympathetic and parasympathetic tones. The HF/(HF+LF+VLF) ratio was used as the corrected index of parasympathetic modulation, and the LF/HF ratio was used as the index of sympathetic modulation. These analyses were performed for 3 hours of each wakefulness and non-rapid eye movement (NREM) sleep recording. Results: LF/HF ratio showed no difference between wakefulness and NREM sleep in the epilepsy group. LF/HF ratio was significantly higher in wakefulness than in NREM sleep in the PNES group, corresponding to the normal pattern reported previously. HF/(HF+LF+VLF) ratio showed no significant differences between the epilepsy and PNES groups. Conclusions: Decreased cardiac sympathetic nerve activity during wakefulness may provide a useful biomarker of epilepsy and exclude the diagnosis of PNES. Further study of HRV in the sleep-wake cycle is needed to elucidate the mechanisms of cardiac autonomic dysfunction in patients with epilepsy, especially the relationship with sudden unexpected death in epilepsy.