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FACULTE DE MEDECINE UNIVERSITE ANTANANARIVO Cours de DU en EEG clinique du 23/09/15 Les artéfacts en EEG LA Rajaonarison, JG Lemahafaka, J Razafimahefa, AD Tehindrazanarivelo USFR Neurologie HU JRB 1 Plan • Introduction • Artéfacts : – Instrumentaux – Électrodes – Environnementaux – Bioélectrique – Potentielle évoquée • conclusion 2 Introduction • Définition : – Activité électrique d’origine non cérébrale – 2 groupes : • Physiologique (mouvements, bioélectriques, résistance cutanée…) • Non physiologique (interférence électrique externe ou interne) • Intérêts : – Fait partie du quotidien – Risque de mauvaise interprétation 3 Introduction • objectifs : – Identifier la source de l’artéfact – Reconnaitre les caractéristiques des différents types d’artéfacts 4 Source d’artefact Artefact physiologique (activités du corps) 1-Mouvements • Tête • Corps • Scalp (battement artériel, contraction musculaire) 2-Potentiel bioélectrique • Changement (mouvements yeux, langue, pharynx) • Production (muscles scalp, cœur, sueur) Artefact non physiologique 1-Interference électrique externe (autres énergie) • Ligne électrique • Équipements électriques 2- Dysfonctionnement électrique interne • • • • Électrodes Câble Amplificateur crayon, papier d’enregistrement 3-Changement de la résistance cutanée • Activité glandes sudoripares • Activité vasomotrice • Transpiration 5 Type d’artefact • Instrumentaux • Électrodes • Environnementaux • Bioélectrique • Potentiel évoqué 6 Artefacts instrumentaux Source d’artefact Caractéristiques -circuit d’amplification -apparait lors détection de silence cérébrale (1-2µV) -grapho-élément inhabituel (non physiologique) -corrosion / oxydation métal -problème mécanique divers • Poids pencil • alignement -distorsion de la morphologie et fréquence des ondes cérébrales -circuit tableau de bord (vibration, choque) -pas d’enregistrement -erreur de calibrage canal / paramètre de filtrage 7 Artefacts instrumentaux 8 Artefacts d’électrode Type Caractéristiques -limité à une électrode -bref et transitoire : • Électrode « pop », décharge spontanée • artefact de pince (aile de papillon) • mouvement du plomb -une partie du scalp -rythme de basse fréquence : • Transpiration, ondulation d’onde lente > 2s • Salt bridge, basse amplitude • Artéfact de mouvement 9 Electrode pop The nearly vertical rise followed by the slower fall at the F3 electrode is typical of electrode pop artifact. Also typical is an amplitude that is much greater than the surrounding activity, a field that is limited to one electrode, and repeated recurrence within a short time Electrode Movement artifact The focal slowing in the T4-T6 and T6-O2 channels has no field beyond T6 electrode and has the oscillations typical of rhythmic electrode movement Lead movement Multiple channels demonstrate the artifact through activity that is both unusually high amplitude and low frequency and also disorganized without a plausible field Sweat artifact The decreased amplitude and very low frequency oscillations are present diffusely, which is consistent with the whole scalp’s involvement. The recurring sharp waves across most channels are ECG artifact. Salt bridge artifact Activity in channels that include left frontal electrodes is much lower in amplitude and frequency than the remaining background. The lack of these findings when viewed in a referential montage confirms that an electrolyte bridge is present among the electrodes involved. Artefacts environnementaux • Bruits électriques ambiants de 50 à 60 Hz • Pousse seringue électrique • appareils électriques : pompe électrique, téléphone • effets mécaniques : ventilation mécanique, pompe électrique 15 60 Hz artifact The very high frequency artifact does not vary and is present in the posterior central region, which does not typically manifest muscle artifact. This example was generated by eliminating the 60Hz notch filter. IV goutte Triphasic and polyphasic transients are occurring simultaneous to the falling of drops in an IV infusion. This EEG corresponds to electrocerebral inactivity. Electrical motor The very high frequency activity suggests an electrical source, and the fixed morphology and repetition rate indicate an external device. This was caused by an electric motor within the pump. Circulatory pump Sharply contoured, b/l frontal repetitions occur with a fixed interval and are due to a pump providing circulatory support and extracorporeal membrane oxygenation. Pulse artifact is present in multiple channels and most apparent in the A2-T4 channel 21 Artefacts bioélectriques Type Origine -artéfact cardiaque -cardiaque (cœur / pacemaker) -pulsation arterielle -artefact oculaire -paupières -OY / FY -mouvement lent des yeux -saccade occulaire -artefact musculaire -Glossokinétique -Photomyogénique -EMG (scalp / muscle faciale) 22 Artefacts cardiaques 23 cardiac artifact ECG artifact is identified by its fixed period and morphology and is limited to T3-A1 channel in this bipolar montage Pacemaker artifact Transients comprising very fast activity recur in channels with the A1 and A2 electrodes. The transients are simultaneous to similar discharges in the ECG channel and correspond to a permanent pacemaker’s output Pulsation Focal slow waves at the left occiput follow each heart beat, as indicated in the ECG channel. The slow waves are artifact due to electrode movement and were eliminated by repositioning the O1 electrode Artefacts oculaire 27 Blink artifact Bifrontal, diphasic potentials with this morphology and field are reliably eye blink artifact. Eye flutter artifact Medium amplitude, low frequency activity that is confined to the frontal poles is identified as ocular artifact through its morphology. Compared to blink artifact, flutter artifact typically has a lower amplitude and a more rhythmic appearance 30 Artefacts musculaire 31 Muscle artifact The high amplitude, fast activity across the b/l ant. region is due to facial muscle contraction and has a distribution that reflects the locations of the muscles generating it. Typical of muscle artifact, it begins and ends abruptly. Photomyogenic artifact Simultaneous to the 6Hz strobe stimulations are transients across the frontal region that reflect an involuntary muscle contraction. 34 Conclusion • Pas facile à éliminer • Liste non exhaustive • Collaboration : – du technicien +++ – EEGer (expérience+++) • Intérêt polygraphie 35 Merci de votre aimable attention 36