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5.2 Abnormal Patterns

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ABRET Registered EEG Technologist R.EEG.T.

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1 Introduction & R.EEG.T. Exam Overview

1.1 R.EEG.T. Exam Facts 1.2 Eligibility & Pathways 1.3 Content Outline & Study Strategy

2 Neurophysiology & Instrumentation

2.1 Neuroanatomy & Neurophysiology 2.2 Electronics & Instrumentation 2.3 Montages & Derivations

3 Pre-Study & Patient Preparation

3.1 Patient History, Assessment & Safety 3.2 Electrode Application & the 10-20 System 3.3 Equipment Setup & Calibration

4 Performing the Study

4.1 Recording Technique & Documentation 4.2 Activation Procedures 4.3 Special Studies & Populations

5 EEG Patterns, Artifacts & Recognition

5.1 Normal EEG Patterns 5.2 Abnormal Patterns 5.3 Artifact Recognition & Elimination

6 Clinical Correlation & Seizure Disorders

7.1 Seizures, Epilepsy & Syndromes 7.2 Neonatal & Pediatric EEG Patterns 7.3 Neurological Disorders & EEG Correlation

7 Post-Study Procedures & Professional Practice

8.1 Post-Study Procedures & Documentation 8.2 Ethics, Safety & Professional Issues

8 Final Review & Test-Day Strategy

6.1 High-Yield Recap 6.2 Localization & Pattern Drills 6.3 Test-Day Strategy & Pitfalls

5.2 Abnormal Patterns

Key Takeaways Explain This Topic AI

An epileptiform discharge is defined by a sharp transient (spike <70 ms or sharp wave 70-200 ms) that disrupts the background and is usually followed by an after-coming slow wave.

The generalized 3-Hz spike-and-wave complex is the classic correlate of childhood absence epilepsy, activated by hyperventilation.

Focal slowing (polymorphic delta) localizes a structural lesion, whereas generalized slowing indicates a diffuse process such as toxic-metabolic encephalopathy.

Burst-suppression alternates high-voltage bursts with near-flat suppression and indicates severe diffuse dysfunction or deep anesthetic/coma states.

Electrocerebral silence (ECS) requires a strict ACNS protocol: full montage, double interelectrode distance, raised sensitivity to 2 uV/mm, and integrity checks before any inactivity statement.

Last updated: May 2026

Why Abnormal Pattern Recognition Is Tested Heavily

Under the Performing the Study domain, ABRET expects the technologist to recognize abnormal patterns in real time so the recording can be optimized — adding montages, annotating events, or invoking the electrocerebral silence (ECS) protocol when indicated. The technologist does not diagnose, but the quality and annotation of the record determine whether the interpreting physician can.

Epileptiform Discharges

An interictal epileptiform discharge (IED) is a paroxysmal waveform that stands out from and disrupts the background and is typically followed by an after-coming slow wave .

  • Discharge Duration / Feature Typical Association
  • Spike <70 ms, pointed Focal cortical irritability
  • Sharp wave 70-200 ms, pointed Focal epileptogenic zone
  • Spike-and-wave complex Spike + after-coming slow wave Generalized or focal epilepsy
  • Polyspike Multiple spikes in a run Myoclonic / juvenile myoclonic epilepsy
  • 3-Hz spike-and-wave Generalized, regular 3 Hz Childhood absence epilepsy (HV-activated)
  • Hypsarrhythmia Chaotic high-voltage multifocal spikes and slowing Infantile (epileptic) spasms / West syndrome

The 3-Hz generalized spike-and-wave burst, frontally maximal and provoked by hyperventilation , is the highest-yield epileptiform pattern on the exam. Hypsarrhythmia is a disorganized, high-amplitude, asynchronous pattern of an infant and is an indication to extend the recording to capture sleep.

Periodic Patterns (ACNS Critical Care Terminology)

Periodic patterns recur at regular intervals and are reported with the current American Clinical Neurophysiology Society (ACNS) terms. Older names are still tested, so know both.

ACNS Term Older Name Typical Clinical Setting

LPDs (Lateralized Periodic Discharges) PLEDs Acute focal lesion (stroke, herpes encephalitis), often peri-ictal

GPDs (Generalized Periodic Discharges) GPEDs Anoxic injury, toxic-metabolic states; triphasic-appearing GPDs in hepatic/renal failure

BIPDs (Bilateral Independent PDs) BiPLEDs Bilateral independent acute injury; poorer prognosis

LPDs/PLEDs are repetitive lateralized sharp or spike discharges, classically every 0.5-2 seconds, signaling an acute focal process and a high risk of seizures. They are an interictal-to-ictal continuum pattern and should be carefully annotated.

Slowing: Focal vs Generalized

Slowing is the most common EEG abnormality and the technologist's job is to capture it cleanly and note its distribution.

Focal polymorphic delta activity (PDA): continuous, irregular, non-reactive delta over one region — suggests an underlying structural lesion (tumor, infarct).

Focal intermittent rhythmic delta: suggests focal dysfunction without necessarily a destructive lesion.

Generalized slowing: diffuse theta/delta replacing the normal background — indicates a diffuse encephalopathy (toxic, metabolic, anoxic, degenerative). Grade roughly by how much the normal background is replaced.

FIRDA / OIRDA: Frontal or Occipital Intermittent Rhythmic Delta Activity — nonspecific markers of diffuse dysfunction or deep midline involvement.

Burst-Suppression

Burst-suppression is a pattern of high-voltage mixed-frequency bursts alternating with periods of marked suppression (near-flat) background . It indicates severe diffuse cerebral dysfunction (severe anoxic injury) or a deep pharmacologic state (high-dose anesthesia, induced for refractory status epilepticus). When titrating anesthetics, the technologist may be asked to report the burst-suppression ratio or interburst interval.

Triphasic Waves

Triphasic waves are broad, high-amplitude waves with three phases (negative-positive-negative), frontally predominant, often showing an anterior-to-posterior or posterior-to-anterior lag . They are classically associated with metabolic encephalopathies (hepatic, renal/uremic, anoxic) but are not specific. Under ACNS terminology, triphasic-appearing periodic activity is often classified as GPDs with triphasic morphology . They are typically not epileptiform but can resemble generalized spike-wave; reactivity to stimulation supports a metabolic process.

Electrocerebral Silence (ECS) and the ACNS Recording Protocol

Electrocerebral silence (ECS) , also called electrocerebral inactivity (ECI), is the absence of cerebral activity over 2 uV during a technically valid recording. Because an ECS recording can support an ancillary determination of brain death, the technologist must follow the ACNS minimum technical standards exactly. Failing the protocol invalidates the study.

  • ACNS ECS Requirement Standard
  • Number of electrodes A full montage of scalp electrodes (minimum 8 scalp electrodes plus ground/reference)
  • Interelectrode distance Doubled (>=10 cm) to maximize sensitivity
  • Sensitivity Increased to 2 uV/mm during the inactivity assessment
  • Filters Low-frequency filter <=1 Hz; high-frequency filter >=30 Hz; document any 60-Hz notch
  • Impedances Between 100 and 10,000 ohms and balanced
  • Integrity test Demonstrate system integrity (touch/tap an electrode to prove the system records)
  • Recording time At least 30 minutes of technically adequate recording
  • Extracerebral monitors Record ECG and other artifact generators to exclude artifact mimicking activity

The technologist never declares brain death — that is a clinical determination. The technologist guarantees the recording is technically valid so a true flat record cannot be confused with artifact, and a real (artifactual) signal is not mistaken for cerebral activity.

Clinical Application

Annotate, do not interpret. Mark events, note state and stimulation, add montages to localize, and invoke the ECS protocol when the ordering physician requests an inactivity study. Your description — "left temporal sharp waves with after-coming slow waves, no clinical change" or "generalized triphasic-morphology GPDs, reactive to noxious stimulation" — is the clinical product ABRET evaluates.