Prognostic Significance of EEG Patterns in Post–Cardiac Arrest Coma

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Objective: The EEG (electroencephalogram) plays a crucial role in prognosticating outcomes for comatose patients after cardiac arrest (CA), but the precise probability of poor outcome (PPO) associated with specific EEG patterns and how it changes over time is not well understood. We aimed to quantify the PPO for individual EEG patterns, assess its precision, and evaluate time-dependent changes after CA. Methods: We retrospectively analyzed continuous EEGs from comatose adults treated at three Boston hospitals for CA (2010-2023). We evaluated the prognostic significance of 22 ACNS-standard patterns, and one additional pattern, "flat EEG (<2μV)", using PPO (i.e., positive predictive value for poor outcome) with 95 % Wilson confidence intervals as the primary metric; sensitivity, and false-positive rate (FPR) were secondary. Temporal variabilities were assessed in four epochs (0-24, 24-48, 48-72, >72 h) using linear regression. Poor and favorable outcomes were defined as death and survival to discharge, respectively. Results: Among 1,000 patients, the mean age was 58 years for survivors and 60 years for non-survivors; 59% of patients were male. Flat EEG demonstrated PPO of 1.00 across epochs, but CIs ranged from 0.89-1.00 at 24 hours and widened to 0.54-1.00 beyond 72 hours. Status epilepticus (SE) showed PPO of 0.80 (0.44-0.97) at 24 hours, 1.00 (0.74-1.00) at 48 hours, and 0.67 (0.09-0.99) after 72 hours. Suppression (< 10 μV), the most common historically termed highly "malignant" pattern (prevalence 50-65%), had a PPO of 0.76-0.83 and sensitivity of up to 0.80, with 17-24% of patients experiencing a favorable outcome. Time-dependent analysis further demonstrated that PPO for suppression increased over time, while sensitivity declined for burst-suppression and flat EEG. Conclusion: The prognostic uncertainty of EEG patterns post-CA is highly variable, and evolves within the first 72 hours. Flat EEG, and SE are highly specific prognosticators of poor outcome, but, importantly, they are rare and not infallible. Suppression identifies the most patients with poor outcomes but has moderately high FPRs and variable prognostic certainty over time. Future large-scale prospective studies that incorporate long-term outcomes are needed to validate these findings.

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