Table 3 Definitions and prognostic value of each EEG patterns, adapted from ACNS terminology and Westhall et al. classification [32, 58]

Highly malignant  ≥ 24 h after CA

Suppression

Suppressed background (< 10 µV) during all the recording

No discharge

0% CI95(0–11.7) [41, 42, 58, 61,62,63, 65, 123]

Suppressed background  + periodic discharges

Suppressed background (< 10 µV) during all the recording, with periodic discharges

0% CI95(0–23.1) [41, 42, 58, 63]

Burst suppression

Alternance of:

- Suppressed background (suppression period  > 50% and  < 99% of the recording) with identical burst

Or alternance of:

- Suppressed background (suppression period  > 50% and  < 99% of the recording) with non-identical burst

Suppressed with identical burst: 0% CI95(0–20.6) [41, 42, 58, 61,62,63, 65, 123]

Suppressed with non-identical burst: 0–1.4% CI95(0–3.1) [42]

Malignant ≥ 12 h after CA

False positive rate (%) CI95(%) for poor outcome prediction (CPC 3–4–5)

Malignant periodic or rhythmic patterns

Periodic discharges

Also called epileptiform features

Abundant non-evolving* and low frequency (0.5–2.5 Hz) periodic discharges (spike, sharp or wave) during  > 50% of the recording

No suppressed background

Early (< 24 h after CA): 0–3% CI95(0–34.8) [62, 65, 67,68,69, 164, 165]

Late (≥ 24 h after CA): 0–33.3% CI95(0–70.1) [42,43,44, 61, 166]

Rhythmic discharges

Also called epileptiform features

Abundant non-evolving* rhythmic discharges during  > 50% of the recording

No suppressed background

Early (< 24 h after CA): 0–3% CI95(0–34.8) [62, 65, 67,68,69, 164, 165]

Late (≥ 24 h after CA): 0–33.3% CI95(0–70.1) [42,43,44, 61, 166]

Unequivocal electrographic seizure or electrographic status epilepticus

Epileptiform discharges  > 2.5 Hz for  ≥ 10 s

or

Any pattern with definite temporo-spatial evolution and lasting  ≥ 10 s

Electrographic seizures for  ≥ 10 continuous minutes or for a total duration of  ≥ 20% of any 60-min period of recording

0–17.4% CI95(0–26.7) [41, 43, 50, 71, 74, 167,168,169]

Malignant backgound

Discontinuous background

Suppression periods (< 10 µV) constituting  > 10% but  < 49% of the recording

0–13.8% CI95(0.1–48.2) [42, 62, 82][65]

Low voltage background

Amplitude  < 20 µV

0–12.1% CI95(0–29.2) [42, 58, 63, 76, 170]

Unreactive background

Absence of reproductible modification for both sound, visual and sensory stimuli

0–50% CI95(0–70.9) [41, 58, 61, 67, 71, 76, 84, 86, 166]

Benign  ≥ 12 h after CA

Specificity (%) CI95(%)

for good outcome prediction (CPC1–2)

Continuous normal-voltage background or nearly continuous normal-voltage background without discharges and reactive EEG

Continuous background during all the recording

Nearly-continuous: Suppression periods (< 10 µV) constituting  < 10% of the recording

reactive EEG: Change in cerebral EEG activity to stimulation, include change in voltage or frequency (including attenuation of activity)

Continuous or nearly continuous EEG: 56.5–100% CI95(45.3–100) [26, 44, 56, 58, 61, 78]

Reactive EEG: 57.1–85% CI95(37.2–93) [26, 42, 44, 78, 86, 105, 171]