ACNS Standardized Critical Care EEG Terminology 2021 - Reference Chart - A. EEG Background

Sep 28, 2026

Uploaded by hdkawk

ACNS Standardized Critical Care EEG Terminology 2021 provides a reference chart for systematically describing critical care EEG features. It details EEG background symmetry and frequency bands, including delta, theta, and alpha-related findings, plus continuity, reactivity, state changes, voltage thresholds, AP gradient, and breach effects. The chart also defines epileptiform findings such as sporadic discharges prevalence and rhythmic or periodic patterns, with main terms and modifiers covering prevalence, duration, frequency, phases, sharpness, amplitude measures, stimulus response, and evolution.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages2

Reading Time5 min

AccessFree to download

A. EEG Background

Symmetry and background frequency

Epileptiform findings (including rhythmic and periodic patterns)

B. Sporadic epileptiform discharges

C. Rhythmic and periodic patterns (RPPs)

Major modifiers

Minor modifiers

Plus (+) modifiers

D. Electrographic and electroclinical seizures

ACNS Standardized Critical Care EEG Terminology 2021: Reference Chart A. EEG Background | Symmetry | Background EEG frequency | | PDR | Continuity | Reactivity | State Changes | Cyclic Alternating Pattern of Encephalopathy (CAPE) | Voltage | AP Gradient | Breach effect | | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Symmetric | Delta | | Present
Specify
frequency | Continuous:<1% periods of suppression (<10 µV) or attenuation (>10µV but <50% of background voltage) | Present | Present with normal stage N2 sleep transients | | Normal
>20 µV | Present | Present | | | | | | | | | Present | | | | | Mild
asymmetry
<50% Amp.
0.5-1/s Freq. | Theta | | Absent | | SIRPIDs
only | Present but with abnormal stage N2 sleep transients | | Low
10 to <20
µV | Absent | Absent | | | | | | | | | Absent | | | | | | | | | Nearly continuous: 1-9% periods of suppression attenuation | | | | | | | | | >Alpha | | | | Absent | Present but without stage N2 sleep transients | | Suppressed
<10 µV | Reverse | Unclear | | Marked
asymmetry
≥50% Amp.
>1/s Freq. | | | | | | | | | | | | | | | | | | | Unknown/unclear | | | | | | | If Burstsuppression or Burst-attenuation then specify if:
| | Discontinuous:
10-49% periods of
suppression or
attenuation | Unclear | Absent | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Highly Epileptiform
Bursts (Present or
Absent) | | | | | | | | | | | | | | | | Burst-suppression
or
Burst-attenuation:
50-99% periods of
suppression or
attenuation | | | | | | | | Identical Bursts
(Present or Absent) | | | | | | | | | | | | | | | | Suppression:
>99% periods of
suppression or
attenuation | | | | | | | | | | | | | | | | | | | Epileptiform Findings (including Rhythmic and Periodic Patterns) | B. Sporadic Epileptiform Discharges | | --- | | Prevalence | | Abundant
>1/10s | | Frequent
≥1/min but <1/10s | | Occasional
≥1/h but <1/min | | Rare
<1/h | C. Rhythmic and Periodic Patterns (RPPs) | Main term 1 | | --- | | G
Generalized
- Optional : Specify frontally, midline or occipitally predominant; or generalized, not otherwise specified. | | L
Lateralized
-Optional: Specify unilateral or bilateral asymmetric
-Optional: Specify lobe(s) most involved or hemispheric | | BI
Bilateral Independent
-Optional: Specify symmetric or asymmetric
-Optional: Specify lobe(s) most involved or hemispheric | | UI
Unilateral Independent
- Optional: Specify unilateral or bilateral asymmetric for each pattern
-Optional: Specify lobe(s) most involved | | Mf
Multifocal
-Optional: Specify symmetric or asymmetric
-Optional: Specify lobe(s) most involved or hemispheric | | Main term 2 | | --- | | PD
Periodic Discharges | | RDA
Rhythmic Delta Activity | | SW
Spike and Wave OR
Polyspike and Wave OR
Sharp and Wave | Major modifiers | Prevalence | Duration | Frequency | Phases1 | Sharpness2 | Absolute Amplitude | Relative Amplitude3 | Stimulus Induced or Stimulus Terminated | Evolution4 | | --- | --- | --- | --- | --- | --- | --- | --- | --- | | Continuous
>90% | Very long
>1 h | 4/s | >3 | Spiky
<70 ms | High
>150 µV | >2 | SI
Stimulus Induced | Evolving | | | | 3.5/s | | | | | | | | | | | 3 | | | | | | | | | | | | | <2 | ST
Stimulus
Terminated | Fluctuating | | Abundant
50-89% | Long
10-59 min | | | Sharp
70-200 ms | Medium
50-149 µV | | | | | | | 3/s | | | | | | | | | | | 2 | | | | | | | | | | | | | | | Static | | | | 2.5/s | | | | | | | | | | | | | | | Spontaneous only | | | Frequent
10-49% | Intermediate
duration
1-9.9 min | 2/s | 1 | Sharply
contoured
>200 ms | Low
20-49 µV | | | | | | | | | | | |

FAQs

How does the reference chart categorize EEG background symmetry and frequency?

It uses symmetry (symmetric, mild or marked asymmetry) combined with background frequency bands such as delta, theta, and alpha, and links these to presence or absence of features like PDR and continuity.

What are the main terms for rhythmic and periodic patterns (RPPs)?

The chart provides main term groupings including generalized (G), lateralized (L), bilateral independent (BI), unilateral independent (UI), and multifocal (Mf), each with optional localization details.

How are electrographic seizures and electrographic status epilepticus defined?

Electrographic seizure requires epileptiform discharges averaging above a frequency threshold for at least 10 seconds, or any definite-evolving pattern lasting at least 10 seconds; electrographic status epilepticus requires an electrographic seizure lasting at least 10 continuous minutes or exceeding 20% of any 60-minute recording period.

Sep 28, 2026

Uploaded by hdkawk