Authors :
Presenting Author: Kameel Karkar, MD – UT Health San Antonio
Sreekanth Koneru, MD – University of Texas Health sciences Sanantonio/South Texas Comprehensive Epilepsy Center
Amy Werry-McFarlin, PhD – UT Health San Antonio
Meera Karkar, BS – University of the Incarnate Word School of Osteopathic Medicine
crystal Wiedner, PhD – UT Health San Antonio
Jayandra Himali, PhD – UT Health San Antonio
Alexander Papanastassiou, MD – UT Health San Antonio
Rationale: Recent studies have challenged the conventional wisdom that brain activity is absent or only slow postictally, with reports of higher frequency postictal activity including increased gamma frequency power
1,2. However, there are conflicting reports as to whether high-frequency activity is present in the postictal period
3. To resolve this uncertainty, we performed a high-gain direct review combined with spectrographic analysis of postictal sEEG suppression. A better understanding of postictal suppression could improve our understanding of and ability to prevent sudden unexpected death in epilepsy (SUDEP).
Methods: sEEG of six focal to bilateral tonic-clonic seizures (FBTCS) were analyzed. The postictal sEEG was reviewed both at standard gain (50-100 μV /mm) and at ultra-high gain (2-5 μV /mm). Time-power/frequency spectrographic analysis was performed of one channel in the seizure onset zone (SOZ) during the peri-ictal period. The frequency spectrogram was obtained from 2 minutes before seizure onset through 1 minute from the end of ictal discharges (EOID). Power of the gamma frequency band was quantified in the first 15 seconds of the postictal period and compared to a pre-ictal baseline.
Results: 1. Direct review of the sEEG at ultra-high gain identified an otherwise invisible mixed-frequency background, including residual ictal activity in one seizure and early sharp activity in most seizures (Figure 1). 2. Time-power/frequency spectrogram of the peri-ictal period revealed a steep drop of EEG power postictally, across the entire 1-200 HZ spectrum, yet power was not completely absent (Figure 2). 3. The persistence of postictal power was not due to insufficient suppression, as this activity was present despite significant intracranial background suppression (18.46 μV, which is less than two times the scalp PGES threshold of 10 μV). 4. Quantification of postictal gamma power in the first 15 seconds from the end of ictal discharges (EOID) showed a significant reduction compared to a pre-ictal period. However, while gamma power was lower postictally, mean gamma band frequency was significantly higher than the pre-ictal baseline.
Conclusions: 1. While the sEEG appeared suppressed postictally, review at ultra-high gain identified evolving higher frequency activity, including residual ictal discharges and early postictal sharp activity. 2. The persistence of a lower power, yet non-absent, EEG activity postictally was confirmed with a peri-ictal time-power/frequency spectrographic analysis. Spectrographic analysis of the early postictal state revealed low-power fast activity yet did not replicate the report of higher gamma power postictally
2. 3. Taken together, unmasking this otherwise invisible EEG activity with high-gain review could explain seizure-like postictal behaviors and would challenge how the onset of the postictal state is declared - with therapeutic implications.
References:
1. Altenmüller DM et al. Epilepsy Behav. 09 2016;62:218-24.
2. Bateman LM et al. Epilepsia. 01 2019;60(1):74-84.
3. Marchi A et al. Epilepsia. 01 2019;60(1):63-73.
Funding: UT Health San Antonio Department of Neurology