Postictal EEG changes following focal seizures: Interrater agreement and comparison to frequency analysis

Abstract

ObjectivesTo compare frequency analysis to human raters and determine the interrater agreement of postictal EEG changes after focal seizures. Methods24 focal seizures with and without impaired awareness recorded with scalp-EEG in the epilepsy monitoring unit were selected. Five board-certified neurophysiologists annotated seizure termination and end of postictal changes for all seizures. We assessed agreement using intraclass correlation, described the band-power changes by time-frequency analysis, and correlated these measures with the rater annotations. ResultsInterrater agreement on the duration of the postictal changes was moderate (0.64, 95% confidence interval: 0.36–0.82). The interrater agreement for seizure termination was excellent (1.00). Median duration of the postictal interval of seizures with impaired awareness was significantly shorter than for seizures with retained awareness (p = 0.0004). Mean postictal duration was 16.4 min. Seizure duration did not predict duration of the postictal changes. We found a strong correlation of 0.8 between the median human rater and the duration of the decrease in spectral edge frequency. ConclusionsThe agreement of neurophysiologists is moderate for duration of postictal changes and high for seizure termination. Rater determination of postictal duration is correlated with measures of EEG slowing. SignificanceDisagreement between neurophysiologists on postictal duration need to be considered.