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Assoc Prof Harry Mond
February 23, 2026
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Well at the end of this one you will have a headache, so take two aspirin now!
Our last ECG topic was reversed arm leads and dextrocardia.
This topic also looks at twisted leads, but this time involving all limbs.
I have discussed this before (Fun with ECGs 28), but I would like to take it further.
Let us twist the arm and leg leads with “leg leads on arms” and “arm leads on legs”.
To summarize:
Major footprint: Lead I is now on the feet well away from the heart and thus isoelectric (red highlight).
There are three minor footprints:
Here it is again (no limb lead attenuation):
Because the limb leads are reversed superior/inferior, it is not surprising that the P waves may also be reversed in leads II, III and aVF:
A right bundle branch block (blue highlight) makes no difference.
Sometimes reversed limb leads are overlooked because other abnormalities overwhelm you!
There is a prolonged QT interval (blue highlight).
Reversed limb leads are not always as easy to diagnose as these ECGs suggest.
There is growing popularity in placing the leg lead electrodes on the abdomen.
This makes no difference as far as conventional ECG are concerned.
Does this affect reversed limb leads? RA and LA leads are now near the heart.
The QRS emerges in lead I.
The clues are there, but very easy to miss.
Here is an example which is probably a normal variant and not reversed limb leads.
Axis to the right (red highlight). We have previously said that aVL is negative (green highlight) in this situation (Fun with ECGs 41). This mimics reversed limb leads.
Note the notched T wave in V3. We will discuss this further one day.
Now take two aspirin as we will look further with twisted leads next time!
Remember, keep your eyes open when reporting ECGs!
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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