Abstracts

Rationale: Psychogenic non-epileptic seizures (PNES) superficially resemble epileptic seizures, but only epileptic seizures are associated with ictal epileptic discharges in the brain. Several previous studies show that abnormalities in resting autonomic nervous system (ANS) tone can be identified in both seizure disorders. However, little is known about ictal ANS activity changes in epilepsy and PNES. This study compares heart rate variability (HRV) parameters as a reflection of sympathetic and parasympathetic ictal and interictal tone in epileptic and nonepileptic seizures.Methods: HRV parameters were extracted from ictal EKG recordings of 26 subjects with temporal lobe epilepsy and 24 age- and sex-matched patients with PNES. Data from one seizure per patient were analysed. Interictal EKG data were available for comparison from seven of the patients with epilepsy and nine of those with PNES. HRV parameters in time and frequency domains were analysed (RR, VLF, LF, HF, SDNN, RMSSD). CVI (cardiovagal index), CSI (cardio sympathetic index), ApEn (approximate entropy) were calculated from Lorenz plots.Results: The HF (p<0.003) component of HRV and RMSSD (p<0.003) were significantly lower, RR (p<0.002) and CSI (p< 0.001) were significantly higher in epileptic seizures than in PNES. Comparison between resting and ictal states revealed no significant differences in the PNES group. In patients with epilepsy RR, RMSSD, HF were lower, and CSI was higher in the ictal state (all p <0.05).Conclusions: Our results clearly show a greater ANS activation in epileptic seizures than in PNES. The biggest ictal HRV changes associated with epileptic seizures were seen in CSI, HF, and RMSSD, reflecting high sympathetic system activation and reduced vagal tone. When compared to epileptic seizures, PNES were associated with a significantly higher RMSSD. Given that there were no significant differences between interictal and ictal HRV in the PNES group, it is likely that this difference is explained by a more marked lowering of vagal tone during epileptic seizures rather than a phenomenon specifically related to the process of experiencing PNES. However, larger intra-group comparisons between ictal and resting states are needed to come to a more definitive conclusion. The fact that there were significant differences between interictal and ictal HRV in epilepsy but not PNES suggests that the HRV profile associated with epileptic seizures could be used to detect seizures for the purpose of ictal vagus nerve or deep brain stimulation.