Determining ICU EEG periodic patterns and why it matters

Historically, periodic EEG patterns were described as any pattern with stereotyped paroxysmal complexes occurring at regular intervals, i.e., the period (T). T is the sum of the duration of the waveform (t1) and, eventually, the duration of the interval between two consecutive waves (t2). The American Clinical Neurophysiology Society introduced the concept of a clearly discernible inter-discharge interval between consecutive waveforms (i.e., t2). As this definition was not applied to what have previously been termed triphasic waves and in some cases of lateralized periodic discharges, we propose reconsideration of terminology that includes historical use of definitions. This will allow the development and usage of the concept for periodic EEG patterns as any runs of stereotyped paroxysmal waveforms separated by nearly identical intervals and prolonged repetitive complexes on the EEG. Prolonged expression means EEG is recorded for a sufficient period of time to prove that the pattern is repetitive, thus resulting in a monomorphic/monotonous pattern. More important than the inter-discharge interval (t2), periodic EEG patterns occur at time regular intervals (T). As a result, periodic EEG activity should be considered along a continuum and not the opposite of rhythmic EEG activity where no interval activity exists between consecutive waveforms.

Automated summary

Historically, periodic EEG patterns referred to stereotyped paroxysmal waveforms occurring at regular intervals (period T), which includes the duration of the waveform (t1) and the interval between two consecutive waveforms (t2). The American Clinical Neurophysiology Society introduced the concept of a clearly discernible inter-discharge interval (t2). In order to include previously termed triphasic waves and lateralized periodic discharges, it is proposed to reconsider the terminology and allow for the development and usage of the concept for periodic EEG patterns as repetitive waveforms separated by nearly identical intervals (T).