Abstracts

Rationale: Patients with subarachnoid hemorrhage (SAH) undergo continuous electroencephalography (cEEG) monitoring in the ICU for the diagnosis of nonconvulsive status epilepticus (NCSE) in patients with impaired consciousness and for the identification of prognostic information in patients with poor-grade SAH. During prolonged monitoring, EEG patterns of unclear significance are often encountered. We describe and characterize commonly encountered EEG patterns in SAH patients. Methods: Patients with SAH admitted to two academic institutions between July 2009 and May 2012 were identified. SAH secondary to trauma, surgery, intraparenchymal bleeds or resulting from arteriovenous malformation rupture were excluded. Of 154 such patients, 52 (34%) received a routine EEG or cEEG monitoring during their hospitalization. EEG reports were reviewed and classified as to the presence of diffuse slowing, epileptiform activity, and frontally-predominant rhythmic and periodic slow activity. The presence of triphasic morphology in the latter category was also noted. Results: Seventeen of 52 (33%) exhibited frontally-predominant rhythmic and periodic slow activity, 15 of which had triphasic wave (TW) morphology without metabolic derangement (29%). In addition 21 of 52, (40%) exhibited diffuse arrhythmic slowing and 15 (29%) demonstrated focal or multifocal epileptiform discharges. One patient had severe diffuse suppression and 2 (4%) had a normal EEG. The average length of stay was 39 days in those with TW morphology and 24 in those without. Outcome upon discharge, however, was similar with good outcome (discharge to home or acute rehab) seen in 50% of patients with TW morphology and 47% of patients in those without. Conclusions: Nonmetabolic TW are scantly reported in the literature and typically associated with diencephalic and brainstem lesion. We find that nonmetabolic TW and frontally-predominant, rhythmic slow wave activity is a common EEG finding in patients with SAH. It may serve as a prognostic indicator of longer length of stay; however, further analysis is needed.