Assoc Prof Harry Mond
February 23, 2026
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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
whereas,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.
Wandering baseline.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”.
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Harry Mond.
October 28, 2026
As its name implies, AVNRT is a reentrant junctional or supraventricular tachyarrhythmia which involves the fast and slow pathways within the AV node creating a self-perpetuating circus movement. It can be divided into typical (slow-fast) or atypical (fast-slow) as well as several rarer forms related to more than one slow or fast pathway with similar electrophysiological properties. On the ECG, they can be identified and differentiated by the positioning of the P wave in relation to the QRS complex, which in turn is related to the direction of the re-entrant AV nodal circuit. However, in about 60% of cases, the P wave is buried in the QRS/T and cannot be identified on the surface ECG.
October 16, 2026
Retrograde conduction is defined as conduction from an ectopic site to the atrium via the AV node or accessory pathway and referred to as VA conduction. II results in a P wave configuration which differs from an anterograde P wave, and in most ECG leads is inverted. The site from where the impulse originates can be the AV node, Bundle of His, distal conducting system or the body of the ventricles including ventricular pacing. On the ECG, the QRS complex usually precedes the inverted retrograde P wave but on occasion may follow it.
October 1, 2026
In 1970, I commenced work as a “novice” cardiologist at The Royal Melbourne Hospital. Training at that time was learning how to recognise the diastolic murmur of mitral stenosis and making sure the ECG and chest x-rays were the correct way up. As this was prior to coronary artery surgery, stenting and echocardiography, the ECG was a highly respected tool for the diagnosis of many conditions. I was fortunate to befriend a number of the gurus of ECG interpretation who taught me to look into the soul of an ECG. Today, even though the ECG is the first investigation performed by a cardiologist, the art of ECG interpretation has been lost because we depend on the new tools for cardiac diagnosis.Â
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