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Assoc Prof Harry Mond
February 23, 2026
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When I describe Wenckebach AV sequences occurring from a non-sinus focus, I often see facial bewilderment. Remember, most Wenckebach AV sequences occur at the AV node, so it is not surprising that other supraventricular foci can also result in typical Wenckebach AV block sequences.Let us look at some examples with relevant nocturnal times in blue highlight.Nocturnal low atrial rhythm:
Accelerated low atrial rhythm with Wenckebach AV block (red highlight). The effects of low atrial slowing and vagal hypertonia are seen.With low atrial rhythm (yellow highlight), Wenckebach AV block sequence termination during vagal hypertonia may allow sinus rhythm to re-emerge (green highlight).
Accelerated low atrial run with Wenckebach AV block.
The background nocturnal rhythm is sinus (red highlight). Upon termination of the sequence, the rhythm returns to sinus.Similar appearances occur with other supraventricular runs:
The rate is about 95 bpm. There is a Wenckebach AV block sequence (arrows and red highlight), terminating in two dropped beats (blue arrows). A junctional escape beat occurs before the next P wave can emerge (red stippled arrow).An atrial run may terminate before a beat is dropped.
The atrial run has an increasing PR interval (red highlight) but terminates before a beat is droppedOnce the atrial rate increases, the tracings become more difficult to interpret:
Short run of atrial tachycardia rate 170 bpm. There is 3:2 (red highlight) and 2:1 (yellow highlight) Wenckebach AV block.The near impossible!
Atrial flutter with block. Short length sequences (red and yellow highlight) which show an increasing PR interval (red arrows) and a dropped beat (blue solid arrows). There are also alternating P waves, which do not conduct (blue stippled arrows). Hence, two dropped beats terminate a sequence, and the next sequence commences, but without a preceding “alternating P wave” blocked beat. The red highlight is a 5:4 sequence (5 atrial:4 ventricular), whereas the yellow highlight is 3:2.This complex appearance is called alternating Wenckebach AV block.Here is an example of sinus rhythm with 3:2 alternating Wenckebach AV block sequence (red highlight):
Two blocks; one at the AV node and the other lower, with the combination referred to as a multi-level block:
This can also present with a bundle branch block, syncope, and sudden death.I just heard someone say, “this must be very rare?”.I don’t think so. It is just that we don’t look for it!Another atrial flutter example of 4:3 alternating Wenckebach AV block (red highlight).
Just when you thought it couldn’t get any more complex!
Atrial flutter with 3:2 alternating Wenckebach AV block sequence (red highlight). However, the alternating complete block extends for two P waves (blue stippled arrows). The dropped Wenckebach P wave may be fused with the distal block (green arrow)?There may be more than one explanation?What about ectopic atrial groupings:Nocturnal sinus rhythm and first degree AV block (red arrows) with an atrial couplet demonstrating 2:1 Wenckebach AV block (blue arrows).
Here is another which is difficult to explain!
The lower Holter tracing shows Wenckebach AV block (red highlight). The above tracing shows a Wenckebach AV sequence within a run of atrial bigeminy (yellow highlight).Because atrial pacing (AAI) conducts to the ventricle, it is not surprising that physiologic Wenckebach AV block can occur overnight (red highlight).
Many observers would regard this as an indication to upgrade to a dual chamber pacemaker. However, if asymptomatic it should be regarded as physiologic similar to nocturnal Wenckebach.Let us finish with an nocturnal “accelerated junctional rhythm” (yellow highlight) with a Wenckebach AV sequence.
Careful inspection reveals that this is actually sinus rhythm (red arrows) with long PR intervals (red highlight) and termination of the sequence with a dropped beat (blue arrow) which allows the normal sinus PR interval to be seen. There is no alteration in the sinus rhythm.Now take an aspirin and lie down!Until next timeHarry 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.Â
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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