An ECG artefact is an inscription on an ECG tracing that does not originate from a cardiac source. Surface ECG electrodes record signals from a number of sources with cardiac electrical signals, the most important. Other signals include skeletal muscle, brain, respiratory interference, noise at the skin-electrode interface and external sources. For convenience, the appearance of ECG interference will be regarded as obvious or subtle and it is important to recognise interference to prevent ECG misdiagnosis.
ECG interference may be:
– extracorporeal (alternating current)
ECG machines have four types of filters:
An example of high-pass filtering:
What are the causes of electrical interference?
What are the causes of mechanical interference?
How do we recognise artefact on the ECG?
Electrical artefact; constant repetitive “fuzz” and more common with a 12-lead ECG
mechanical artefact; non-constant with a variable amplitude and more common with ambulatory Holter monitoring recordings.
Obvious ECG artefact:
With electrical artefact, the P, QRS and T waves are usually easy to identify.
Here are some examples:
Electrical: High frequency alternating current (AC):
Electrical: Regular, high frequency electromagnetic (EM).
On occasion, the P, QRS and T waves may be obscured.
Electrical: High frequency alternating current (AC).
With mechanical artefact, the P, QRS and T waves may be hard to identify.
Here are some examples:
Mechanical: ECG; dry electrodes, fractured cable, or connection issue
Mechanical: Dry ECG electrodes, skin preparation and marked respiration.
With a single ECG lead or electrode, it is possible to determine which is at fault.
In this example, the artefact is in leads I (red highlight) and III (yellow highlight) and therefore the common lead is the left arm.
All leads are involved. There is a serious ECG cable issue.
Frequently, we can’t tell if it is electrical or mechanical.
Other times, it is mixed.
Here is an example of gross Parkinson tremor.
The rhythm appears very irregular and a short period of absent tremor (red highlight) suggests it is atrial fibrillation, despite the possible artefactual P waves.
Another medical cause of obvious artefact is neuromodulation artefact. These are due to non-cardiac implanted pulse generators and lead I gives a clue as to what part of the body is being stimulated.
Brain: Involves lead I (red highlight) which is upper torso.
Bladder: Lower torso and lead I (red highlight) not involved.
Bowel: Lower body and lead I (red highlight) not involved.
Subtle artefact will be covered in the next “Fun with ECGs”.
Harry Mond .
In 49+ years as a practicing cardiologist, Dr Harry Mond has published 260+ published manuscripts & books. A co-founder of CardioScan, he remains Medical Director and oversees 500K+ heart studies each year.
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