Abstracts

RATIONALE: Human epilepsy is associated with interictal abnormalities in HRV and approximate entropy (ApEn), but it is not known how these abnormailities are related to seizure experience. We demonstrated previously that maximal electroshock (MES) induced tonic seizures are associated with severe abnormalities in cardiac regulation, resulting in arrhythmia during the immediate postictal state. The severity of arrhythmia increased with increases in seizure severity and with daily seizure repetition. We now examine whether MES repetition induces interictal abnormalities in neurocardiac regulation.
METHODS: We obtained baseline EKG (3000 beats) from Sprague-Dawley rats (n=5) to calculate R-R interval, standard deviation (SD), ApEn, and normalized high and low frequency spectra (HFn, LFn respectively). The rats were submitted to daily MES for a total of 10 stimulations. From the EKG recordings (3000 beats), parameters were obtained from just prior to seizures for interictal data and during the late postictal phase (after the phase of obvious cardiac arrhythmia). The data were compared against baseline values using the Friedman and Wilcoxon test (post-hoc).
RESULTS: After a single seizure there was a mild, but significant loss of ApEn during the last postictal state (z=2.0, p[lt].05). No significant changes occurred in R-R interval, SD, LFn or Hfn. Prior to the 10th seizure, there was a significant reduction of variability shown by SD (z=1.8, p[lt].05), and a significant reduction of HFn (z=2.3), p[lt].05) in the interictal state. Following the 10th seizure there were significant reductions of SD (z=2.1, p[lt].05), HFn (z=1.7, p[lt].05) and ApEn (z=1.8, p[lt].05) during the late postictal state.
CONCLUSIONS: Seizure repetition with MES induces both interictal and postictal abnormalities in HRV in a kindling-like manner. The loss of HFn, which is believed to correlate with vagal function, suggests that at least some of the abnormalities induced by seizure repetition may be mediated by the vagal system. Since abnormalities in HRV have been related to sudden death in several disease states, the possibility the findings raise the question of whether seizure experience induces mechanisms that cause pathologic regulation of the cardiac autonomic system, and possibly underlie susceptibility to sudden unexpected death in epilepsy (SUDEP).
Participants should be able to understand the effect of experimentally-induced seizure repetition on neurocardiac regulation.
[Supported by: Southern Illinois University School of Medicine Central Research Committee]