Abstracts

Rationale: EEG narrow band fast activity (NFA) on time-frequency map of ictal intracranial EEG (iEEG) is an important characteristics of “EEG fingerprint,” a novel bioelectrical marker of epileptogenic zone. However, the study on EEG fingerprint is still very limited. Here we hypothesized that NFA alone may provide localizing information of epileptogenic zone. We investigated the NFA with seizure onset pattern (SOP), seizure onset zone (SOZ), propagation zone (PZ) and epileptogenic zone.  Methods: We consecutively included 59 patients with drug-resistant focal epilepsy who underwent iEEG evaluation and resective epilepsy surgery. Morlet wavelet transform of iEEG data (bipolar montage) was applied, and EEG NFA was identified using following features: the narrow-band fast activity characterized by one or more high-intensity bands, and simultaneous suppression of low frequency activity. SOP, SOZ and PZ were defined by visual analysis. The parameters of NFA (maximum and minimum frequencies, start time, end time and total time) were defined by visual analyses and fast activity feature extraction in EZfringerprint software.  Results: Ictal NFA was observed in 52 (88%) patients. All EEG seizures were classified into 6 onset patterns (Fig 1.A): 31 with preictal spikes/sharps/polyspikes followed by fast activity (FA)(pattern 1), FA includes two categories, low-voltage fast activity (LVFA) (pattern 1.1) and high-voltage fast activity (HVFA) (pattern 1.2). 10 with slow wave/ DC shift followed by LVFA (pattern 2), 7 with spikes activity (pattern 3), 5 with LVFA (pattern 4), 5 with beta activity (pattern 5), and 1 with delta-brush (pattern 6).EEG NFA presented in all SOP except delta-brush (Fig 1.C).There were two type of NFA (Fig 1.B): type 1 associated with periodic spike (PS>10 Hz), and type 2 associated with fast activity (FA>25 Hz). PS-NFA appeared 24.3+-22.6s after seizure onset, FA-NFA appeared 14.0+-19.1s after seizure onset, the minimum frequency of PS-NFA was less than FA-NFA (P< 0.001), and there was no difference in resection rate of NFA between the two types (Fig 2.B).NFA occurred in either SOZ or PZ, but the distribution proportion; the maximum and minimum frequencies of NFA were higher within SOZ compared to PZ (P<0.001 respectively) (Fig 2.A).Patients with good outcome had a significantly larger proportion of NFA areas resection than patients with poor outcome (P<0.001). No such difference was seen for the SOZ (P=0.642) (Fig 2.C). The start time, end time and total time of NFA were no difference between good and poor outcome group.  Conclusions: EEG NFA presents in most SOP, and contain additional localizing information help to localize the epileptogenic zone in focal epilepsy. It is a feature of epileptogenic zone, even it present in late ictal period, which may reflect the hypersynchronous activity of neurons.  Funding: No funding