Assoc Prof Harry Mond
February 23, 2026
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In my last “What do you think?”, I showed this ECG of junctional rhythm.
With “tongue in cheek”, I referred to the premature beat as a sinus node “ectopic” (red highlight).
I felt it prudent to investigate this “ectopic” further.
Here is another example (red highlight).
Is this really an ectopic?
What do you think?
Because the latter is a Holter monitor recording, we can investigate the rhythms further.
The rhythm is sinus. There isa pause due to sino-atrial block (ghosted red arrow) and an escape junctional beat (yellow highlight).
If the sino-atrial block (red ghosted arrows) is long enough, then an escape junctional rhythm dominates.
When we discuss sino-atrialblock, we usually recognise pauses in “groups” and forget about an escape rhythm.
Let us revisit sino-atrialblock!
How do we differentiate second and third degree sino-atrial block?
Type I, sino-atrial Wenckebach.
The P-P intervals shorten with the greatest increment between the first and second P waves (40 ms). The P-P interval before the dropped beat is the shortest (690 ms) and the one after the dropped beat is the longest (840 ms).
Type II sino-atrial block.
The pauses are multiples of the P-P intervals.
Sinus rhythm (red arrow) with pauses, which are twice the P-P intervals of the regular sinus beats. The dropped P waves are shown as ghosted red arrows.
Sinus pauses or arrest.
The pauses are not necessarily multiples of the P-P intervals.
Unlike our case (and those inthe literature, the above examples have no junctional escape beats or rhythm to“muddy the waters”.
Because of these escape rhythms, it is near impossible to determine the type of sino-atrial block.
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.
September 18, 2026
Dr Thura Thant asked for an opinion on this confusing ECG. By using arrows and highlight, the ECG bared its soul and gave me an answer. See if you can work it out? What do you think?
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