artifacts & normal variants in eeg

ARTIFACTS & NORMAL VARIANTS

DR.SHAHANAZ AHAMED.MPAEDIATRIC NEUROLOGIST

GMC,TVM

ArtifactsArtifacts are pen deflections not

caused by cerebral activity.They may be due to 1)physiological activity originating

from the patient2) Interference from power lines or

other electrical sources3)Malfunction of the recording system

which includes recording electrodes, amplifiers, pen motors & paper drive.

Artifacts from patient Blinking & other eye movements Muscle artifacts Movement artifacts Heart beat artifacts Pulse wave artifact. Perspiration artifact oropharyngeal artifacts

Interference artifacts

60 HzArtifact cardiac pacemaker artifact mobile phone artifact

Artifacts from Equipment

Electrode poping Paper stop artifact Impedence artifact

ALPHA

EPILEPTIFORM TRANSIENTS

SPIKES

SHARP WAVES

SLOW SHARP WAVES – not always epileptiform

Blinking & other eye movements These are picked up by frontal

electrodes Vertical eye movements cause

potentials in electrode pairs in paramedical positions-Fp1-F3, Fp2-f4 etc

Lateral eye movements Deflections in transverse chains=Fp1-F7, Fp2-F8, F7-F3

F8-F4 etc

Blinking or eye closure causes large down going deflections,

Eye opening produces upward deflections.

EYE BLINK

EYE OPENING

EYE CLOSURE

Lateral eye movements Lateral eye movements may be

preceded by a single sharp muscle potential which may resemble a cerebral spike & in combination with eye movements form a spike & wave artifact

LATERAL EYE MOVEMENTS

Eye movement artifacts Eye movement artifacts can be

identified by their frontal distribution, their symmetry on the 2 sides & their characteristic shape.

Slow repetitive rhythmic eye movements may closely resemble B/L synchronous frontal slow waves like FIRDA

They are stopped by asking the patient to place his fingertip on the eyes,tapping cotton balls over the eyes etc

Muscle artifacts Muscle activity causes very brief

potentials which usually recur. If they recur they resemble cerebral

discharges except that most cerebral spikes are of much longer duration than muscle potentials.

Moreover epileptiform activity usually has a aftercoming slow wave associated with a spike.

MUSCLE ARTIFACT

MUSCLE ARTIFACT They are usually recorded predominantly

from frontal/ temporal electrodes but can occur in any electrodes

They can be eliminated by asking the patient to relax, drop the jaw or open the mouth slightly/change position.

Repetititive movements such as chewing, blinking & tremor may give rise to fast & slow artifacts which resemble cerebral discharges

Movement artifacts Movement of head /body or other rhythmic

movements such as chewing & sucking can lead to irregular high amplitude wave forms which can be easily recognized.

They do not have consistency & characteristics of cerebral discharges

They can occur in instances such as restless/ confused patients,infants & children , patients having seizures,tremors/other movt disorders

Heart beat artifacts Mainly in recording with wide

interelectrode distances& in subjects with short necks.

Small artifacts reflect mainly the Rwave of ECG. Large artifacts may reflect additional components of ecg

EKG ARTIFACT

Heart beat artifacts If necessary heart beat can be

eliminated by using a balanced noncephalic reference.

They can be identified by the equal intervals & rate corresponding to heart rate.

Simultaneous recording of ecg can be done in doubtful cases

Pulse wave artifact Periodic waves of smooth

/triangular shape may be picked up by electrode on or near a scalp artery

.More likely to occur in frontal/temporal areas. It can be eliminated by reapplying electrode

Perspiration artifact Sweating causes very slow drifting

of electrodes lasting several seconds .

Usually common in frontal/temporal electrodes & occurs in several channels at the same time

Glossokinetic & oropharyngeal artifacts. They produce intermittent

/repetitive slow waves in a wide distribuition often with a maximum in the middle of the head

They occur in speaking, chewing, swallowing ,sucking,coughing,hiccoughs.

Palatal myoclonus causes rhythmical artifacts at the rates of 100-200 /mt.

Dental spike like artifacts are produced by dental fillings /dissimilar metals rubbing against each other

GLOSSOKINETIC ARTIFACT

Interference artifacts

Artifacts due to electrical interference from power lines & equipments.

60 Hz is the frequency. Appears in all channels.

Other types of interference include signals from nearby TV stations,

radiopaging,Mobile phones telephone ringing,cardiac pacemakers,

CARDIAC PACEMAKER

mobile phone artifact Another confusing artifact is

mobile phone artifact which may look like a epileptiform discharge but can be distinguished by the lack of aftercoming slow wave & positivity & raggedness of the artifact wave

Artifacts from Equipment

They are distinguished in that They differ radically from

previously recorded activity, Do not blend with other recorded

activity but seem to be superimposed on it &

Appear only in channels connected to the faulty electrode.

Electrode poping Electrode poping is due to sudden

changes in electrode contact causing spike artifact.

PAPER STOP ARTIFACT

A1/A2 ARTIFACT

NORMAL VARIANTS

Hyperventilation changes Hypnagogic hypersynchrony Mu rhythm Lambda Positive occipital sharp transients of sleep(POSTS} Posterior slow waves Ctenoids/14 & 6hz positive spikes 6 hz spike wave Rhythmic midtemporal theta-Psychomotor variant Small sharp spikes Frontal arousal rhythm

HYPERVENTILLATION

HV produces bursts of 2—3 HZ frontally dominant delta activity.

Normal background in between. Can be admixed with sharper

components.

“ V” WAVESVERTEX WAVES

Bilaterally synchronous Maximum amplitude at vertex Extend to central, frontal & parietal May appear in sequence Shifting asymmetries may occur Higher amplitude in youth Principal component is sharply contoured

electronegative wave. Occurs in light sleep

Hypnagogic hypersynchrony

Prominent bursts of rhythmic high amplitude delta slowing maximum in the parasagittal area are a normal finding in the drowsy state in the first few years of life

HYPNOGOGIC HYPERSYNCHRONY Appears during transition from

wakefulness to drowsiness Seen in age group 5 months to 10 yrs. Bursts of 3-5 Hz , moderate to high

amplitude activity. Lasts for 1.5 to 3 secs. Can be mistaken for spike –wave

activity,when intermixed with faster frequency components.

Mu rhythm It is a 7-11 hz saw tooth shaped

rhythm seen in 15 % recordings It can be unilateral/bilateral &

seen in central area It is attenuated by touch/

movement

Lambda Lambda is low amplitude (<

20micv) sharp transient bi/triphasic activity which is surface positive

It is seen in the waking state due to visual exploration & attenuated by closing the eyes

POSTS( Positive Occipital Sharp Transients of sleep)

Occur in NREM sleep ;Esp. stages - 2 & 3 Occur in occipital region. Monophasic, sharp contoured,

electropositive waves. Similar to Lamda waves; higher in

amplitude & longer in duration. Occur singly or in trains of 4-6 Hz. Usually bisynchronous, but may be

asymmetric

POSTS( Positive Occipital Sharp Transients of sleep)

Differentiating points from spikes:

Predominant phase is surface positive

Monophasic Occur in trains of 4-5 Hz. Bilateral occurrence of POSTS

Posterior slow waves They are 1-4 hz slow waves seen

spreading from occipital to tremporal to parietal which are prominent in first decade.

Ctenoids/14 & 6hz positive spikes Seen b/w 5-15 yrs in the posterior

head region as a surface positive comb shaped rhythm

6 hz spike wave It is a bisynchronous low

amplitude 5-7hz spike wave rhythm most prevalent in drowsiness & light sleep.

It is of gradual onset & offset & maximal in midcentral/parietal electrodes

Rhythmic midtemporal theta-Psychomotor variant

Theta rhythm of 5-7 hz seen in temporal region unilateral/biateral lasting 5-10 seconds.

Commonly seen in adoloscents. Attenuated in stage 2 sleep & alerting

Small sharp spikes Medium amplitude spikes of short

duration seen in anterior & midtemporal areas associated with drowsiness & light sleep

Frontal arousal rhythm

They are bursts of rhythmic notched theta with superadded beta in midfrontal regions on arising from sleep,seen in 2-14 yrs lasts upto 20 sec.

Can resemble ictal pattern. But there is no evolution