Rhythmic and Periodic Patterns and Seizures in Hypoxic-Ischemic Encephalopathy

Cardiac arrest is a major cause of hypoxic-ischemic brain injury, often resulting in coma even after the return of spontaneous circulation. In this severely ill population, accurate neurologic prognostication is essential for guiding treatment decisions. Continuous electroencephalography (EEG) has become a cornerstone of postcardiac arrest care, offering real-time monitoring of cerebral activity and facilitating early detection of electrographic seizures and other pathologic patterns. This narrative review focuses on the standardized interpretation of EEG findings using the 2021 American Clinical Neurophysiology Society Critical Care EEG terminology. Key EEG patterns-such as generalized periodic discharges, suppression-burst, and status epilepticus (SE)-are discussed in the context of their prognostic significance and therapeutic implications. Particular attention is given to the progressive restoration of background EEG continuity and amplitude over the first 24 hours after the arrest, which is increasingly recognized as a marker of the extent of neuronal damage and potential for recovery. Seizure and SE management remains complex in comatose postcardiac arrest patients, with recent studies highlighting variable outcomes and the potential risks of both under- and overtreatment. We underscore the importance of individualized treatment strategies informed by EEG characteristics and integrated with clinical examination, neuroimaging, and serum biomarkers. Multimodal prognostication helps identify patients with a potential for meaningful recovery while avoiding unnecessary interventions in those with poor neurologic prognosis. EEG-guided care is crucial in optimizing outcomes after cardiac arrest and enhancing the precision of neurocritical care.