83 Questions
What is the minimum number of standard 10–20 electrode locations required for sequential spreading?
Two
How long must a single location persist to qualify as present?
3 cycles
What is the minimum number of changes in frequency required to qualify as fluctuating frequency?
3 changes
What is the maximum time allowed between changes in frequency to qualify as fluctuating frequency?
1 minute
What was the purpose of developing a database that incorporated the ACNS terminology?
To enable multicenter investigations into the clinical significance of rhythmic and periodic patterns
What is the primary goal of the 'ACNS Standardized Critical Care EEG Terminology 2021: Reference Chart'?
To provide a detailed reference for EEG terminology
What is the purpose of the schematic diagrams provided in the content?
To provide educational purposes and conceptual clarity
What is the term used to describe the 'ictal-interictal continuum'?
IIC
What is the term used to describe 'cyclic alternating pattern of encephalopathy'?
CAPE
What is the term used to describe 'extreme delta brush'?
EDB
What is the term used to describe 'potentially ictal rhythmic discharges'?
BIRDs
If a pattern qualifies as both PDs and RDA simultaneously, how should it be coded?
PDs1R
What is the duration of an intermediate pattern?
1 to 9.9 minutes
How should the typical frequency of a pattern be specified?
Specifying typical, minimum, and maximum frequency
What is the correct category for a pattern with a duration of 5 seconds?
Brief
How should the prevalence of a pattern be calculated?
Based on the proportion of the epoch that includes the pattern
What is the significance of a typical frequency of 2.5 Hz for PDs or SW?
It is a criterion for electrographic seizures
What should be done when categorizing or using qualitative terms for prevalence?
Follow the cutoffs listed for each term
How should the frequency of a pattern be recorded?
Specifying typical, minimum, and maximum frequency
What is the term used to refer to an EEG pattern seen during an epileptic seizure?
Ictal
What is the unit of measurement used for all types of periodic or rhythmic patterns?
Hertz (Hz)
How are voltage measurements in this document based?
Peak to trough
What is the term used to describe a consistent feature that is present in at least 80% of instances?
Consistent
What type of recording is preferred for assessing voltage symmetry?
Referential
What is the criteria for marked asymmetry in voltage?
$ 50% asymmetry
What is the frequency range for the Beta frequency band?
.13 Hz
In which type of recording is mild asymmetry in voltage typically seen?
Referential recording
What is a characteristic of unilateral independent periodic discharges?
Two independent patterns occurring simultaneously in the same hemisphere
What is an example of unilateral independent periodic discharges?
PDs at 1 Hz in the left hemisphere and focal midline PDs at 0.5 Hz
What is the main difference between unilateral independent periodic discharges and multifocal periodic discharges?
The timing of the patterns
What is a characteristic of multifocal periodic discharges?
At least three independent lateralized patterns, with at least one in each hemisphere
What would be classified as two populations of LPDs on the left, but not unilateral independent periodic discharges?
Two independent patterns occurring sequentially in the left hemisphere
What is true about focal midline patterns in unilateral independent periodic discharges?
They are considered as part of the independent pattern in the same hemisphere
What is the term used to describe bilateral periodic discharges that are synchronously but consistently asymmetric?
Lateralized, bilateral asymmetric
What is a characteristic of lateralized periodic discharges (LPDs)?
Periodic discharges only seen in one hemisphere
What is the minimum duration required for a pattern to qualify as a state change?
60 seconds
What is the term used to describe the primary reported background EEG pattern for the patient?
Primary background pattern
How should K-complexes and spindles be described separately?
As separate entities with specific characteristics
What is the voltage range for high activity in longitudinal bipolar with standard 10–20 electrodes?
Most or all activity $ 150 mV
What is the significance of the presence of state changes?
It corresponds with cycling of other functions such as respirations, heart rate, blood pressure, movements, muscle artifact, and pupil size
What is the term used to describe a pattern that lasts less than 60 seconds?
None of the above
How should abnormal stage N2 sleep transients be specified?
Specify abnormality (e.g., asymmetry, location, frequency, poorly formed)
What is the significance of the absence of state changes?
It corresponds with a lack of cycling of other functions such as respirations, heart rate, blood pressure, movements, muscle artifact, and pupil size
What is the minimum number of cycles required for a pattern to qualify as spike-and-wave or sharp-and-wave?
6 cycles
What is the characteristic of the relationship between the spike (or polyspike or sharp wave) component and the slow wave in a spike-and-wave pattern?
Consistent and repeating
What is the maximum interval allowed between one spike-wave complex and the next for it to qualify as spike-and-wave?
No interval
How long must a pattern continue to qualify as rhythmic or periodic?
At least 6 consecutive cycles
What is the minimum duration required for a pattern to qualify as very long?
1 hour
What is the characteristic of the spike-wave complex in a spike-and-wave pattern?
A spike or polyspike or sharp wave consistently followed by a slow wave
What is the requirement for the pattern to qualify as spike-and-wave or sharp-and-wave?
A consistent relationship between the spike and slow wave for at least 6 cycles
What is the significance of the duration of a pattern in determining its classification?
It determines the type of pattern
What is the duration of a sharp wave in EEG?
70 to 200 ms
What is the characteristic of a polyspike?
2 or more spikes occurring in a row with an interdischarge interval
What is the direction of the voltage and frequency gradient in an anterior-posterior (AP) gradient?
Lower voltage, faster frequencies in anterior derivations and higher voltage, slower frequencies in posterior derivations
How is the duration of a spike or sharp wave measured?
From the peak of the spike or sharp wave to the EEG baseline
What is the characteristic shape of a spike or sharp wave?
Diphasic or triphasic, apiculate (pointed peak)
What is the definition of an AP gradient?
A clear and persistent gradient of voltages and frequencies in at least 1 continuous minute
What is the significance of a spike or sharp wave in EEG?
It is a sign of abnormal brain activity
What is the definition of a reverse AP gradient?
A clear and persistent gradient of voltages and frequencies with lower voltage, faster frequencies in anterior derivations
What is the minimum frequency for a pattern to qualify as an electrographic seizure if the duration is 10 seconds or more?
2.5 Hz
What is the term used to describe a pattern that has a frequency of 0.5 Hz or more and lasts 10 seconds or more but does not meet criteria for an electrographic seizure?
Brief potentially ictal rhythmic discharges (BIRDs)
What is the term used to describe a pattern that has a frequency of 4 Hz and lasts 0.5 seconds or more but less than 10 seconds?
Brief potentially ictal rhythmic discharges (BIRDs)
What is the significance of a typical frequency of 2.5 Hz for PDs or SW?
It is the frequency above which a pattern must last 10 seconds or more to qualify as an electrographic seizure
What is the term used to describe an EEG pattern seen during an epileptic seizure?
Electrographic seizure
What is the term used to describe a pattern that has a frequency of 4 Hz or more and lasts 10 seconds or more?
Electrographic seizure
What is the primary characteristic of Rhythmic Delta Activity (RDA)?
Repetition of a waveform with relatively uniform morphology and duration
What is the minimum duration required for a pattern to qualify as an electrographic status epilepticus?
10 minutes
What is the minimum duration of a discharge?
0.5 seconds
What is the term used to describe a pattern that has a frequency of 0.5 Hz or more and lasts 10 seconds or more but does not meet criteria for an electrographic seizure or electrographic status epilepticus?
Brief potentially ictal rhythmic discharges (BIRDs)
What is the characteristic of a Spike-and-Wave pattern?
Spike consistently followed by a slow wave
What is the minimum number of cycles required for a pattern to qualify as Spike-and-Wave or Sharp-and-Wave?
6 cycles
What is the difference between a Discharge and a Burst?
A Discharge has less than 3 phases, while a Burst has more than 3 phases
What is the primary difference between a Discharge and a Burst?
Number of phases in the pattern
What is the requirement for a pattern to qualify as Rhythmic?
Repetition of a waveform with relatively uniform morphology and duration
What is the characteristic of a Spike-and-Wave pattern in terms of the interval between one spike-wave complex and the next?
There is never an interval between one spike-wave complex and the next
What is the voltage range for a pattern to be categorized as 'Medium'?
50 to 149 mV
How should voltage measurements be taken in EEG pattern analysis?
From peak to trough
What is the minimum change in frequency required to qualify as evolution in frequency?
At least 0.5 Hz
What is the requirement for a pattern to qualify as evolution in location?
Sequentially spreading into or out of at least two standard 10-20 electrode locations
What is the definition of evolution in morphology?
At least two consecutive changes to a novel morphology
What is the categorization of a pattern with a voltage of 160 mV?
High
What is the requirement for a pattern to qualify as evolution in frequency, morphology, or location?
At least two consecutive changes in the same direction
What is the definition of a pattern with a voltage of 15 mV?
Very low
Study Notes
Standardized Critical Care EEG Terminology
- The terminology is defined as sequentially spreading into or out of at least two different standard 10-20 electrode locations.
- A single location must persist for at least 3 cycles to qualify as present.
EEG Patterns
- Fluctuating frequency is defined as 3 changes in frequency (by at least 1 Hz) not more than one minute apart.
Rhythmic and Periodic Patterns (RPPs)
- RPPs in critically ill patients have been investigated for their clinical significance.
- Patterns include LPDs (lateralized periodic discharges), PDs (periodic discharges), SW (slow waves), and others.
Pattern Classification
- Patterns can be classified by duration:
- Brief: 10 to 59 seconds
- Very brief: <10 seconds
- Intermediate duration: 1 to 9.9 minutes
- Long: 10 to 59 minutes
- Patterns can also be classified by frequency:
- Specify typical rate and range (e.g., LPDs with typical frequency of 1 Hz and range of 0.5-2 Hz)
- Use categories: <0.5, 0.5, 1, 1.5, 2, and 2.5 Hz; and if very brief duration: 3, 3.5, and 4 Hz
Modifiers
- Prevalence: Specify percent of record or epoch that includes the pattern.
- Main modifiers can be applied to any EEG phenomenon.
- Modifiers include prevalence, frequency, and duration.
Educational Resources
- The ACNS Standardized Critical Care EEG Terminology 2021: Condensed Version is available.
- The ACNS Standardized Critical Care EEG Terminology 2021: Reference Chart is available.
- Extensive schematic diagrams of most patterns are provided for educational purposes.
State Changes in EEG
- State changes in EEG correspond with cycling of other functions such as respiration, heart rate, blood pressure, movements, muscle artifact, and pupil size.
- Each state change must persist at least 60 seconds to qualify as a "state".
- State changes can occur spontaneously or with stimulation.
- The more alert/stimulated pattern is considered the primary reported "background" EEG pattern for the patient.
Categorizing State Changes
- State changes can be categorized as:
- Present with normal stage N2 sleep transients (K-complexes and spindles)
- Present but with abnormal stage N2 sleep transients
- Present but without stage N2 sleep transients
Voltage Measurements
- Voltage measurements are based on peak-to-trough measurements in a standard 10-20 longitudinal bipolar recording.
- High voltage: most or all activity ≥ 150 mV in longitudinal bipolar recording.
- Normal voltage: most or all activity between 20-150 mV in longitudinal bipolar recording.
- Low voltage: most or all activity ≤ 20 mV in longitudinal bipolar recording.
EEG Background
- Symmetry of EEG background can be:
- Symmetric
- Mildly asymmetric (consistent asymmetry in voltage ≤ 50% or consistent asymmetry in frequency of 0.5-1 Hz)
- Markedly asymmetric (≥ 50% voltage or ≥ 1 Hz frequency asymmetry)
Predominant Background Frequency
- Predominant background frequency when most awake or after stimulation can be:
- Beta (≥ 13 Hz)
- Alpha
- Theta
- Unilateral independent (UI): two independent periodic or rhythmic patterns in the same hemisphere, occurring simultaneously.
Periodic Discharges
- Periodic discharges can be:
- Lateralized (LPDs): periodic discharges only seen in one hemisphere.
- Unilateral independent (UI): two independent periodic or rhythmic patterns in the same hemisphere, occurring simultaneously.
- Multifocal (Mf): at least three independent lateralized patterns, with at least one in each hemisphere, with all three or more patterns occurring simultaneously.
Spike-and-Wave or Sharp-and-Wave Patterns
- Spike-and-wave or sharp-and-wave patterns are characterized by a polyspike, spike, or sharp wave consistently followed by a slow wave in a regularly repeating and alternating pattern, with a consistent relationship between the spike (or polyspike or sharp wave) component and the slow wave for at least 6 cycles.
Conflicts of Interest and Funding
- Trinka received fees from multiple pharmaceutical companies and research grants from various organizations
- Other authors have no funding or conflicts of interest to disclose
EEG Frequencies and Patterns
- 2.5 Hz frequency can only be applied to Rhythmic Pattern Discharges (RPPs) with a duration of 10 seconds or less
- Patterns with a frequency of 2.5 Hz and a duration of 10 seconds or more qualify as electrographic seizures
- No RPP can have a typical frequency of 0.4 Hz; if a pattern is 0.4 Hz and lasts 0.5 seconds, it would qualify as a polyspike
- Patterns with a frequency of 0.4 Hz and a duration of 10 seconds or more would meet criteria for either Brief Potentially Ictal Rhythmic Discharges (BIRDs) or an electrographic seizure
Evolution of RPPs
- Evolution of an RPP is limited to patterns that are 4 Hz or slower and last 10 seconds or more
- RPPs with evolution lasting 10 seconds or more meet criterion B of an electrographic seizure and should be coded as such
New Terms and Definitions
- Electrographic seizure (ESz)
- Electrographic status epilepticus (ESE)
- Electroclinical seizure (ECSz)
- Electroclinical status epilepticus (ECSE)
- Possible electroclinical status epilepticus
- Brief Potentially Ictal Rhythmic Discharges (BIRDs)
- Ictal-Interictal Continuum (IIC)
EEG Background
- Predominant background frequency now includes beta (13 Hz)
- Continuity categories:
- Nearly continuous: 1-9% attenuation/suppression
- Burst suppression: 50-99% attenuation/suppression
- Suppression/attenuation: 99% or more of the record
- Burst attenuation/suppression can be described using location descriptions
Highly Epileptiform Bursts
- Defined as multiple epileptiform discharges within the majority (50%) of bursts, occurring at an average of 1/s or faster
- Can also be defined as a rhythmic, potentially ictal-appearing pattern within the majority (50%) of bursts
Spike and Sharp Wave Definitions
- A spike is a transient, clearly distinguished from background activity, with a pointed peak at a conventional time scale and duration of 20-70 ms
- A sharp wave is defined identically, but with a duration of 70-200 ms
- A polyspike refers to 2 or more spikes occurring in a row with no interdischarge interval and lasting less than 0.5 seconds
Learn about the standardized terminology for EEG patterns in critically ill patients, including sequentially spreading patterns, fluctuating frequencies, and rhythmic and periodic patterns.
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