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Assoc Prof Harry Mond
February 23, 2026
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We have already discussed the two most common variations of reversed arm and leg leads. There are a number of other combinations and at least one more can be easily recognised on the 12-lead ECG; Right Arm-Right Leg Reversed.To summarise:
Major Footprint: Lead II is on the legs and thus isoelectric (red highlight).Minor Footprints: Leads I and III are mirror images (yellow highlight).Leads I and aVL are near identical (blue highlight)Leads aVR and aVL are near identical (green highlight)Lead III normal as leads are in normal position (brown highlight)Here is another example with the same colour scheme.
If the leg leads are placed on the abdomen, lead II is no longer isoelectric.
With abnormalities like right bundle branch block (note the ST changes)
and left bundle branch block, the changes are often missed.
Likewise for ventricular pacing:
Look carefully; biventricular pacing (brown highlight) with right ventricle paced before the left ventricle.Reversed limb leads are very easily confused with poor lead attachment:
Another combination which must be hard to create is reversing the left arm with the right leg.
Lead III is on the feet away from the heart.There are no other footprints.A low voltage or isoelectric lead III is not uncommon in the normal ECG and thus it is not possible to diagnose this abnormality without a previous ECG.There is another combination, I call the double twist, which is really a merry-go-round with all leads moving one clockwise position.Here is the result:
There are clues, but they are really minor footprints: Lead III is isoelectric because left leg and left arm are on the feet (red highlight). Lead I is really lead III (yellow highlight). Now go and take a tablet for that terrible headache!! Remember, keep your eyes open when reporting ECGs!
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.
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