Abstracts

Rationale: Nonconvulsive seizures are frequent after acute brain injury and independently associated with poor outcome. Some seizures on intracranial EEG can not be seen on surface EEG. Quantitative analysis of surface EEG is limited by electrode artifact, which is rare on depth EEG recordings. To report depth and surface EEG findings in poor-grade subarachnoid hemorrhage (SAH) patients. Methods: Between 6/06 and 4/10, 45 poor grade SAH patients (age 51 /-15 years, 71% women, 80% admission Hunt Hess grade 4-5) underwent multimodality monitoring with microdialysis, brain oxygen tension, cerebral blood flow, and ICP monitoring (duration 6 /- 4 days). Intracortical EEG monitoring with a miniature 8-contact depth electrode (2.5 mm between contact centers) was available in 30 of these patients. Each minute of surface and depth EEG (N=267,683) was categorized separately into non-ictal, on the ictal-interictal continuum including periodic discharges at 2 Hz or faster, or seizures. These categories were assigned based on consensus between two experienced study physicians (JC and LJH). Results: At any point of the recording surface seizures were seen in 7% of patients (3/45) and ictal-interictal patterns in an additional 16% (N=7). Depth seizures were seen in 37% of patients (11/30) with depth monitoring while an additional 17% of patients (N=5) had ictal-interictal patterns without clear evolution to seizures. Seizures were seen only on the depth in 7,629 minutes from 8 patients (in 85% of these minutes, the surface EEG did not show any ictal patterns, and in the remainder it was on the ictal interictal continuum). Depth-only ictal-interictal findings were seen in 15 patients, 2 of whom showed ictal-interictal and 3 showed seizures on the scalp at other times during their recording. Surface-only seizures were seen in only one patient (for a total of 47 minutes). However, 93% of this patient s surface seizures (633/678) were detected on the depth electrode and all minutes of surface-only seizures were part of evolving seizure activity that was detected on the depth electrode minutes after being seen on the surface. There was no difference in demographics, admission neurological or CT findings, delayed cerebral ischemia rates, or hospital complications between those with and those without ictal interictal findings or seizures on surface or depth. All 9 patients with depth only ictal-interictal patterns or seizures had poor outcome compared to 3 of 6 patients with ictal interictal or seizure on both depth and surface (OR 4.0; P=0.04). The analysis of multimodality findings is in progress. Conclusions: Half of patients had seizures or ictal-interictal patterns on intracortical EEG, and the majority of these patterns could not be appreciated on scalp EEG. Ictal patterns isolated to the depth may be associated with poor outcome. Depth EEG monitoring provides high quality, high signal:noise ratio recordings that enables real-time, continuous quantitative EEG monitoring with alarms. Intracortical EEG is a promising component of multimodality monitoring and neurotelemetry in acutely brain injured patients.