Standardized EEG interpretation accurately predicts prognosis after cardiac arrest

Abstract

Objective: To identify reliable predictors of outcome in comatose patients after cardiac arrest using a single routine EEG and standardized interpretation according to the terminology proposed by the American Clinical Neurophysiology Society.

Methods: In this cohort study, 4 EEG specialists, blinded to outcome, evaluated prospectively recorded EEGs in the Target Temperature Management trial (TTM trial) that randomized patients to 33°C vs 36°C. Routine EEG was performed in patients still comatose after rewarming. EEGs were classified into highly malignant (suppression, suppression with periodic discharges, burst-suppression), malignant (periodic or rhythmic patterns, pathological or nonreactive background), and benign EEG (absence of malignant features). Poor outcome was defined as best Cerebral Performance Category score 3-5 until 180 days.

Results: Eight TTM sites randomized 202 patients. EEGs were recorded in 103 patients at a median 77 hours after cardiac arrest; 37% had a highly malignant EEG and all had a poor outcome (specificity 100%, sensitivity 50%). Any malignant EEG feature had a low specificity to predict poor prognosis (48%) but if 2 malignant EEG features were present specificity increased to 96% (p < 0.001). Specificity and sensitivity were not significantly affected by targeted temperature or sedation. A benign EEG was found in 1% of the patients with a poor outcome.

Conclusions: Highly malignant EEG after rewarming reliably predicted poor outcome in half of patients without false predictions. An isolated finding of a single malignant feature did not predict poor outcome whereas a benign EEG was highly predictive of a good outcome.

Figure 1. Highly malignant EEG patterns

Highly malignant patterns used in the study defined according to the standardized EEG terminology by the American Clinical Neurophysiology Society. (A) Suppressed background (amplitude <10 μV, 100% of the recording) without discharges. (B) Suppressed background with superimposed continuous periodic discharges. (C) Burst-suppression (periods of suppression with amplitude <10 μV constituting >50% of the recording) without discharges. (D) Burst-suppression with superimposed discharges.

Figure 2. Study flow chart of exclusion from and inclusion into the study

The recommended time point of prognostication was 72 hours after rewarming, corresponding to approximately 108 hours after the cardiac arrest. The most probable cause of death according to the treating physician is reported (cerebral, multiorgan failure, or cardiovascular). Eight study sites were included since they had an EEG system that allowed export of EEG data that included notations regarding testing of reactivity.