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Assoc Prof Harry Mond
February 23, 2026
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How would you report this ECG?
For those unfamiliar with ECGs, let us look at how a 12-lead ECG is generated.
Einthoven’s triangle is formed by three skin electrodes; right arm (RA), left arm (LA) and left leg (LL). It is an inverted equilateral triangle with the heart at its centre.Lead I is created between the negative potential RA electrode and the positive LA electrode and is usually positive as the current flows from R to L (red arrow). For leads II and III, the left leg is positive. The right leg electrode by convention is the earth. The three unipolar augmented leads (aV) are also dependent on the polarity with aVR negative. The chest leads V1 to V6 traverse the chest wall.We can now create a normal 12-Lead ECG:
Knowing this, our first ECG looked different because of reversed limb leads.For the example shown, the arm and leg leads are reversed.
When this occurs, lead I (blue arrow) is now on the legs and is therefore isoelectric (red highlight). This is a major footprint which should immediately catch the eye. The other changes are minor footprints and are not always reliable, apart from lead aVL being flipped (yellow highlight), as that lead is now on the left arm.Let us return to our original ECG:
Reverse the arm and leg leads and the ECG becomes normal.The diagnosis is not always that simple!Today, particularly in women (panty hose) the leg electrodes may be placed on the high abdomen. For leads in the normal position, this makes little or no difference. When the reversed leads are on the abdomen, lead I is almost at heart level and not surprisingly, lead I is no longer isoelectric and aVL becomes positive.
There is also a normal variant in young people, that can mimic these findings.
There are a number of other classical patterns with twisted leads.Once again think of the major footprints. Right arm-right leg reversed
Lead II (blue arrow) is now at leg level and is thus isoelectric. The minor footprints as listed above are reliable and helpful.
Left Arm-Right Leg Reversed
Now lead III lies on the legs (blue arrow) and is isoelectric. Although there is a major footprint, the remainder of the ECG has no characteristic features and cannot be diagnosed with certainty as lead III is often “near” isoelectric in the normal ECG. In reality, we are only moving the left arm as the right leg is the earth electrode. Finally there is the “double-twist” with only the left leg in the normal position.
Once again, lead III is isoelectric and the ECG looks abnormal! You really have to work hard to create this pattern. In summary, think of the major footprints as isoelectric patterns in the arm leads. Need the minor footprints to confirm. It’s what catches the eye.
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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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