ACNS Standardized Critical Care EEG Terminology (2012)


Standardized terminology of periodic and rhythmic EEG patterns in the critically ill has been proposed by the ACNS and is reproduced in outline form below. This terminology is designed for research purposes, not for clinical use. Terms were chosen to avoid clinical connotations and to ensure adequate inter-rater reliability.

The full text of the article: American Clinical Neurophysiology Society’s Standardized Critical Care EEG Terminology: 2012 version can be found at the ACNS website, here:

Rhythmic or periodic patterns

All terms consist of main term # 1 followed by #2, with modifiers added as appropriate.

Main Term 1

  • Generalized (G)
  • Lateralized (L)
  • Bilateral Independent (BI)
  • Multifocal (Mf)
  • Main Term 2

  • Periodic Discharges (PD)
  • Rhythmic Delta Activity (RDA)
  • Spike or Sharp and Wave (SW)
  • Modifiers

  • Prevalence
  • Duration
  • Frequency
  • Number of phases
  • Sharpness
  • Amplitude
  • Polarity
  • Stimulus-Inducing (SI)
  • Evolving OR Fluctuating
  • Plus (+)
  • Minor Modifiers

  • Quasi-
  • Sudden OR gradual onset
  • Triphasic morphology
  • A-P or P-A lag
  • Sporadic epileptiform
  • Abundant
  • Frequent
  • Occasional
  • Rare
  • Background EEG


    Posterior Dominant Rhythm

    Predominant frequency

    Anterior-Posterior Gradient




    Stage II sleep transients


  • Continuous
  • Nearly continuous
  • Discontinuous
  • Burst attenuation / suppression
  • Suppression