Artefact and error Flashcards
Indications for an ECG
- Dizziness * Irregular pulse/palps
Loss of consciousness * Hypotension - Shortness of breath * Fall
- Heart murmur * Screening
- Suspected MI * Research
- Chest Pain * Pre-operative assessment
Contraindications
Relative – Sensitivity/allergy to electrodes
Absolute – Patient refusal
Performing a 12 Lead ECG
Introduction and explanation
Patient identification
Consent
Chaperones
Dignity (This may be uncomfortable for women so offer gowns, paper towel to respect privacy and dignity makes sure doors are closed curtains are drawn ect.)
Hand hygiene/PPE
Patient Preparation
Skin prep is vital for a clear, accurate reading. Several techniques you can use to ensure adequate contact between skin and electrode: shaving, skin abrasion, sweaty or oily skin may need wiping
Abrasion
Shaving
Positioning - supine positioning
Mobility - can be performed in chair but positions may be inaccurate. Will need to be recorded on ECG.
Dressings
Limbs - amputations - try for optimal positioning as anatomy will allow, write on ECG anything outside of normal practice
Chest lead position
Place fingers at bottom of throat, move them down until you feel a bony lump - angle of Louis. From here, move fingers to the right to feel a gap between ribs- 2nd ICS.
V1 - 4th intercostal space on RHS, on sternal border
V2 - 4th ICS, left sternal border
V3 - between V2 and V4
V4 - mid-clavicular line 5th ICS
V5 - anterior axillary line, positioned on same horizontal line as V4
V6 - mid axillary line, same horizontal plane as V4
What is Einthoven’s triangle?
Einthoven’s triangledescribes the relationship between the limb leads and electrodes. 3 bipolar limb leads: Lead 1 looks at the voltage difference between the RA and LA. Lead 2 between RA and LL, and Lead III between LA and LL. Then you have your 3 unipolar limb leads –aVr, aVl and aVf.
Features of a good ECG?
Flat isoelectric baseline
No artefact on any leads
Correct pt details
Any deviations from standard practice are recorded
Correct paper settings - 25mm/s, 10mm/mV
Different types of artefact
Baseline wander
Poor connection
Muscle tremor
Electromagnetic interference
Baseline Wander
Oily or sweaty skin? – Rub with an alcowipe and reapply fresh electrodes.
Is patient too flat? – Respiration can cause this problem, sit patient up higher with pillows or bed adjustment.
Air underneath electrodes? – Press electrode more firmly. If patient very hairy, may need to shave.
Muscle Artefact
Caused by muscle tension – ask patient to relax, especially arms and legs.
Make sure the patient is comfortable, not cold or embarrassed – cover women up.
Be careful about electrode placement – if moving electrodes towards body make sure they are 15cm away from the heart.
Electrical Interference
Rare with battery powered machines.
Can sometimes occur with patients who are attached to lots of other electrical equipment.
Try to move the machine as far away from the patient as possible and also if possible unplug any equipment
Poor Connection
Is the electrode applied properly to patient’s skin?
Is the electrode gel dry? – If so it won’t record properly.
Is the crocodile clip attached to the lead and electrode properly?
Is the acquisition module properly attached to the machine?
Are the leads pushed properly into the acquisition module?
No waveform
Check all connections.
Is a particular lead broken? If so replace it.
Check electrodes – dry gel, stuck on properly?
Make sure it isn’t asystole!
Properties of filters
Aim of a filter is to eliminate unwanted artefact. Standard initial recording, filter off made at 150Hz
Filter will reduce interference but will also distort the ECG.
To be used only when all efforts to remove artefact have been attempted.
Use of “Filter” should be clearly
written on ECG.
SCST - Evidence of somatic muscle interference:
Repeat recording – filter on – recording made at 0.67 - 40Hz
The filter reduces interference but also distorts the ECG
Paper speed and gain can also be altered if needed.
This should also be clearly written on ECG.
Posterior leads
V7 – Left posterior axillary line, in the same horizontal plane as V6.
V8 – Tip of the left scapula, in the same horizontal plane as V6.
V9 – Left paraspinal region, in the same horizontal plane as V6.
The Paediatric ECG
V4R:5th intercostal space, right mid-clavicular line.Use this lead for V4R, must label as such on ECG.
Dextrocardia
Dextrocardia is the most common form of cardiac malposition and refers to any situation where the heart is located within the right side of the chest rather than the left. It may be associated with the condition situs inversus where other organs are in a mirror image relation to the usual position. Dextrocardia may be suspected if a resting 12-lead ECG reveals negative P waves and QRS complexes in lead I in the absence of any technical error such
as reversal of the right and left arm connections. Poor R-wave progression observed in leads V1 through V6 supports this interpretation.
CS3: Recording a Standard 12-lead ECG Page | 19
A second ECG should be recorded with the chest electrodes (V3 to V6) positioned on the right side of the chest using the same intercostal spacing and anatomic landmarks as previously described but on the right side. V1 and V2 should remain in the usual position.
This approach should provide a ‘true’ ECG representation. The limb lead complexes will continue to appear inverted, demonstrating the abnormal location of the heart. However, the repositioned chest leads (V3R to V6R) will now show appropriate R-wave progression.
There should be clear annotation on the recording to describe the repositioned electrodes, for example “V3R”, “V4R” etc.
An alternative approach is to swap the right and left arm connections. This will ‘normalise’ the appearance of the limb leads. If this approach is preferred it is
imperative that the ECG be very clearly annotated to prevent the possibility of dextrocardia being overlooked
