Rhythmical and periodic EEG patterns do not predict short-term outcome in critically ill patients with subarachnoid hemorrhage

INTRODUCTION:: Nonconvulsive seizures and nonconvulsive status epilepticus commonly occur in patients with aneurysmal subarachnoid hemorrhages. When continuous EEG is used in patients in the neuro-intensive care unit, rhythmical and periodic patterns of uncertain significance are frequently encountered. It is unknown how these findings impact patient outcome. METHODS:: Patients were enrolled from a single tertiary care center with subarachnoid hemorrhages secondary to ruptured intracranial aneurysm, and either a witnessed seizure or significantly impaired mental status. Prospective clinical, laboratory, imaging, and short-term outcome data were collected. Continuous EEG monitoring was performed and scored according to American Clinical Neurophysiology Society (ACNS) Subcommittee on Research Terminology for Continuous EEG Monitoring. RESULTS:: Sixty-eight patients were enrolled. Fifty-four had a poor-grade subarachnoid hemorrhage upon admission. Fifty-one patients had rhythmical or periodic patterns: 33 with periodic discharges and 38 with rhythmic delta activity. Four patients had unequivocal electrographic seizures. Patients did poorly in the short term: 14 died and 42 were severely disabled at discharge. In hospital, mortality was 19.6% in patients with rhythmical or periodic patterns and 23.5% in patients without. Age, female gender, and endovascular treatment had a positive correlation with the occurrence of periodic discharges. However, there was no correlation between rhythmical and periodic patterns and outcome. DISCUSSION:: Using the ACNS Research Terminology, it is shown that rhythmical and periodic patterns are very common in critically ill patients with subarachnoid hemorrhage. However, the presence and the abundance of these patterns did not predict short-term outcome in this prospective, single-center observational study. We were unable to show that rhythmical and periodic EEG patterns are an independent predictor for outcome relative to other clinical features. Large multicenter studies will be required to determine if these patterns independently predict outcome and to demonstrate the impact of treatment interventions that are directed at rhythmical and periodic continuous EEG patterns.