Neurophysiology State Dynamics Underlying Acute Neurologic Recovery After Cardiac Arrest

Background and Objectives:

Epileptiform activity and burst suppression are neurophysiology signatures reflective of severe brain injury following cardiac arrest. We aimed to delineate the evolution of coma neurophysiology features ensembles associated with recovery from coma after cardiac arrest.

Methods:

Adult subjects in acute coma following cardiac arrest were included in a retrospective database involving seven hospitals. The combination of three quantitative EEG features (burst suppression ratio [BSup], spike frequency [SpF], and Shannon's entropy [En]) was used to define five distinct neurophysiology states: Epileptiform High Entropy (EHE: SpF ≥4/minute and En ≥5); Epileptiform and Low Entropy (ELE: SpF ≥4/minute and <5 En); Non-Epileptiform High Entropy (NEHE: SpF <4/minute and ≥5 En); Non-Epileptiform Low Entropy (NELE: SpF<4/minute and <5 En), and Burst Suppression (BSup≥50% and SpF <4/minute). State transitions were measured at consecutive 6h blocks between 6-84h after return of spontaneous circulation. Good neurological outcome was defined as best Cerebral Performance Category (CPC) 1-2 at 3-6 months.

Results:

One-thousand thirty-eight subjects were included (50,224 hours of EEG), and 373 (36%) had good outcome. Subjects with EHE state had a 29% rate of good outcome while those with ELE had 11%. Transitions out of an EHE or BSup to a NEHE were associated with good outcome (45% and 20%, respectively). No subjects with ELE state lasting >15h had good recovery.

Discussion:

Transition to high entropy states is associated with increased likelihood of good outcome despite preceding epileptiform or burst suppression states. High entropy may reflect mechanisms of resilience to hypoxic-ischemic brain injury.