Objective: Survivors of prolonged (> 2 weeks) post-cardiac arrest (CA) coma are expected to remain permanently disabled. We aimed to investigate three outlier patients who ultimately achieved independent functional outcomes after prolonged post-CA coma to identify electroencephalographic (EEG) markers of their recovery potential. For validation purposes, we also aimed to evaluate these markers in an independent cohort of post-CA patients.
Methods: We identified three patients with late recovery from coma (17-37 days) following CA who recovered to functionally independent behavioral levels. We performed spectral power analyses of available EEGs during prominent burst suppression patterns (BSP) present in all three patients. Using identical methods, we also assessed the relationship of intra-burst spectral power and outcomes in a prospectively enrolled cohort of post-CA patients. We performed chart reviews of common clinical, imaging, EEG prognostic variables and clinical outcomes for all patients.
Results: All three patients with late recovery from coma lacked evidence of overwhelming cortical injury but demonstrated prominent BSP on EEG. Spectral analyses revealed a prominent theta (~4-7Hz) feature dominating the bursts during BSP in these patients. In the prospective cohort, similar intra-burst theta spectral features were evident in patients with favorable outcomes; patients with BSP and unfavorable outcomes showed either no features, transient burst features or decreasing intra-burst frequencies with time.
Interpretation: BSP with theta (~4-7Hz) peak intra-burst spectral power after CA may index a recovery potential. We discuss our results in the context of optimizing metabolic substrate availability and stimulating the cortico-thalamic system during recovery from prolonged post-CA coma.