Assoc Prof Harry Mond
February 23, 2026
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An exercise in thinking outside the box.
What do you think?
There is obvious Wenckebach AV block.
Some people believe that sinus rhythm holds the sole rights to Wenckebach AV block! However, it can occur with any supraventricular rhythm and in this case an ectopic atrial rhythm.The P waves are inverted (blue arrows) and there is a progressive increase in the PR interval with a non-conducted beat (stippled blue arrow). You can also call this low atrial rhythm. However, on Holter tracings the leads are not defined, and it is more correct to call the rhythm, ectopic atrial.
Here is another non-sinus P wave generated sequence.
Sinus rhythm with a short run of supraventricular tachycardia (yellow highlight). Within the run is a Wenckebach AV sequence (blue arrows) and a non-conducted P wave (blue stippled arrow). The P waves are similar but not identical to the sinus generated P waves. This is because the ectopic focus is close to the sinus node and probably in the crista-terminalis, which is a fibromuscular ridge in the right atrium immediately below the sinus node and a common site for atrial ectopy.
Is there anything else with this tracing?
Following the pause, sinus rhythm emerges for two cycles only (red arrows).
The first sinus P wave is premature! Why?
Simple physiology. As there isa ventricular pause, sympathetic drive as well as other volume and pressure sensors increase the underlying sinus rhythm faster than the ectopic atrial rhythm. This is called ventriculo-phasic sinus arrhythmia and often overlooked when reporting ECGs. It is simply variations in the sinus rate, depending on whether there are QRS complexes during the P-P intervals and is seen in about 50% of cases of second degree or complete AV block.
To summarize:
The P-P interval with the embedded QRS complex is shorter than the P-P interval without the QRS complex.
Wenckebach AV block.
2:1 AV block.
Complete heart block.
Anything more?
There are three pacemaker foci in the tracing.
By definition this is a wandering atrial pacemaker.
When two or more atrial ectopics are present in a rhythm strip together with sinus rhythm, it is called a wandering atrial pacemaker or chaotic atrial mechanism. When the rate exceeds 100 bpm, then the rhythm is referred to as a multifocal atrial tachycardia. There are often fusion beats as well.
Sinus rhythm (red highlight, red arrows) with atrial ectopics from two sites (yellow and blue highlight, blue arrows). Two of the beats are atrial fusion (green highlight) where the timing results in the P waves being isoelectric or sinusoidal.
Harry Mond
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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