Lower instantaneous entropy of heartbeat dynamics during seizures in untreated temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is associated with dysfunction of the autonomic nervous system. While it is known that heart rate variability (HRV) changes in epilepsy comprise both ictal (CRI) and interictal (INT) autonomic cardiac effects, the mechanisms leading to these alterations are not well understood. In this paper we investigate the alterations in instantaneous autonomic complexity during CRI in untreated TLE using bipolar ECG recordings from 10 patients with at least one seizure originating from temporal regions as recorded by video-EEG monitoring. We isolated artifact-free INT and CRI periods and computed mean values of instantaneous point-process Approximate and Sample Entropy (ipApEn and ipSampEn, respectively). ipApEn was significantly lower (p<0.02) and ipSampEn was lower (p<0.065) in CRI vs. INT. The variability (median absolute deviation) of ipApEn was also significantly lower (p<0.03) in CRI vs INT. Our results suggest that ictal events in untreated TLE are associated with a decrease in heartbeat complexity and its variability, possibly pointing toward subtle autonomic changes which may accompany or precede seizures, and can only be detected using an instantaneous, time resolved approach to quantifying autonomic complexity.