Rhythmic and periodic patterns (RPPs) are frequently reported in intensive care EEG and should be described by main term 1, defined as localization, and main term 2, defined as periodic discharges, rhythmic delta activity, spike-and-wave or sharp-and-wave EEG patterns, as well as appropriate major and minor modifiers(1). RPPs are detected in 10 to 35% of comatose patients after cardiac arrest.
In a RCT, van Putten et al. characterized RPPs on EEG in patients in a coma after cardiac arrest in relation to neurologic outcomes(2). Rhythmic and periodic EEG patterns were defined as periodic discharges, rhythmic delta activity, spike-and-wave or sharp-and-wave EEG patterns, each at a rate of 0.5 Hz or more, irrespective of their spatial evolution across EEG montages or temporal evolution. The minimum duration of continuous activity of these patterns for inclusion in the trial was 30 minutes or, if intermittent, 5 minutes, recurring at least twice at intervals of less than 60 minutes. The RCT assessed 172 patients with quantitative EEG, analyzing background continuity index, relative discharge power, discharge frequency, and shape similarity. Neurologic outcomes were evaluated using the Cerebral Performance Category scale at 3 months after arrest. Later RPPs onset, EEG background continuity before and during RPPs were associated with better outcomes and may therefore guide clinicians in selecting patients with higher chances of recovery and the appropriate treatment.
A previous open-label trial (TELSTAR trial) conducted on the same cohort of patients evaluated the neurological outcomes at 3 months in relation to suppressing rhythmic and periodic EEG patterns detected on continuous EEG monitoring(3).
Patients in the antiseizure-treatment group received intensive antiseizure treatment plus standard care, and patients in the control group received standard care alone. The incidence of a poor neurologic outcome at 3 months did not differ significantly between the two groups, hence intensive treatment of RPPs during at least 48 hours was not associated with improved recovery. Exploratory subgroup analyses suggested that patients with generalized periodic discharges may have presented fewer good outcomes with the antiseizure intervention when compared with patients with other patterns. Nonetheless, it wasn’t possible to draw any conclusion since the trial was underpowered for these analyses. The warning regarding overtreatment should be considered, but nevertheless be considered with caution. Two third of the patients investigated in the trial showed myoclonus and myoclonic status is indeed frequently associated with poor outcome(4). Furthermore, the study was not limited to EEG patterns reflecting status epilepticus (SE), but included any RPP, also patterns that could reflect a severe encephalopathic and irreversible condition. That’s relevant because, despite the results in post-CA comatose patients showing RPPs, patients with SE could still benefit from treatment - especially NCSE, in which favorable outcomes have been reported in one every fourth patients(5). It’s tempting to speculate that a brain being able to elicit NCSE, i.e., permanent neuronal (hyper-)activity, is less damaged than the severely affected patients with substantial global cerebral dysfunction/ breakdown, associated with often generalized myoclonus resulting from brainstem and subcortical disinhibition.
Key Points:
- Rhythmic and periodic patterns (RPPs) are detected in 10 to 35% of comatose patients after cardiac arrest
- Sufficient EEG background continuity before and during RPPs may be relevant for higher chance of recovery in intensive care
- Further studies are needed to guide the neurointensivists care: overtreatment of RPPs may be unwarranted, but it is still a matter of discussion since patients with NCSE may still benefit from treatment.
References:
- Hirsch LJ, Fong MWK, Leitinger M, et al. American Clinical Neurophysiology Society’s standardized critical care EEG terminology: 2021 version. J Clin Neurophysiol 2021; 38: 1-29.
- van Putten MJAM, Ruijter BJ, Horn J, van Rootselaar AF, Tromp SC, van Kranen-Mastenbroek V, Gaspard N, Hofmeijer J; TELSTAR Investigators. Quantitative Characterization of Rhythmic and Periodic EEG Patterns in Patients in a Coma After Cardiac Arrest and Association With Outcome. Neurology. 2024 Aug 13;103(3):e209608. doi: 10.1212/WNL.0000000000209608. Epub 2024 Jul 11. PMID: 38991197.
- Ruijter BJ, Keijzer HM, Tjepkema-Cloostermans MC, Blans MJ, Beishuizen A, Tromp SC, Scholten E, Horn J, van Rootselaar AF, Admiraal MM, van den Bergh WM, Elting JJ, Foudraine NA, Kornips FHM, van Kranen-Mastenbroek VHJM, Rouhl RPW, Thomeer EC, Moudrous W, Nijhuis FAP, Booij SJ, Hoedemaekers CWE, Doorduin J, Taccone FS, van der Palen J, van Putten MJAM, Hofmeijer J; TELSTAR Investigators. Treating Rhythmic and Periodic EEG Patterns in Comatose Survivors of Cardiac Arrest. N Engl J Med. 2022 Feb 24;386(8):724-734. doi: 10.1056/NEJMoa2115998. PMID: 35196426.
- Wijdicks EFM. Futility of Suppressing Seizurelike Activity in Postresuscitation Coma. N Engl J Med. 2022 Feb 24;386(8):791-792. doi: 10.1056/NEJMe2118851. PMID: 35196432.
- De Stefano, P., Kaplan, P.W., Quintard, H. et al. Nonconvulsive status epilepticus following cardiac arrest: overlooked, untreated and misjudged. J Neurol 270, 130–138 (2023). doi.org/10.1007/s00415-022-11368-5
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