Assoc Prof Harry Mond
February 23, 2026
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I have presented this before, but it continues to bewilder people.
Is this heart block?
What do you think?
In each tracing, all recorded overnight, there is sinus bradycardia (red arrows), ventricular ectopics (red highlight) and non-conducted P waves (blue arrow) at the end of the ectopic T wave. This often called, in error, a non-conducted atrial ectopic.
These non-conducted beats are timed with the sinus cycle and are therefore, not ectopics, but rather sinus beats that do not conduct to the ventricle. For those fussy with measurements, there is also ventriculo-phasic sinus arrhythmia.
To explain the non-conducted P waves, we need to revisit the ventricular ectopic.
As the sinus rate slows (red arrows), the non-conducted sinus P waves (blue arrows) creep beyond the QRS of the ventricular ectopic (red highlight) and are now “non-concealed” within the ST segment of the ventricular ectopic.The conducting system is still refractory, and the P waves do not conduct to the ventricle (blue arrows, yellow highlight).
As the sinus rate (red arrows) slows further (blue highlight), the non-conducted sinus P waves becomes concealed within the ectopic T wave and eventually emerges once again at the end of the T wave (red highlight) or beyond it (blue arrows).
With marked sinus bradycardia, the ECG appearance is that of AV block referred to as “pseudo-AV block”.
Sinus bradycardia (red arrows) with first degree AV block and an early ventricular ectopic (red highlight).The next sinus P wave occurs well beyond the ectopic T wave (blue arrow) and would be expected to conduct to the ventricle. However, the conducting system is still refractory from the retrograde concealed conduction. This suggests that this is more than timing and there is also conducting tissue disease.
What happens if the AV conducting system is not refractory?
AV conduction will occur and by definition there will be no compensatory pause.
This is called an interpolated ventricular ectopic.
Now you know the exciting next “What do you think?”
Or maybe not!!
It’s all in the timing.
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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