Unusual AV Wenckebach

Over the last few weeks, I have presented a variety of Wenckebach sequences. Some may think I am obsessed with the subject and they are probably correct. However, there is so much that can be learnt by looking at the sequences.Broadly, they can be divided into atrioventricular (AV) and non-AV groups.We usually envisage AV Wenckebach with boring sinus rhythm and imagine the block at the AV node. It is, however, much more visually stimulating than that.Here is a short run of atrial tachycardia with 3:2 and 2:1 AV Wenckebach.

This represents upper rate physiology.If the rate is slower (<100 bpm) and nocturnal, then consider vagal hypertonia.

With very fast atrial rates such as atrial flutter, there is what I call a “regular irregularity”.

In this case, there are “regular” minor pauses with dropped beats (red highlight) making the overall rhythm “irregular”.Not all AV Wenckebach sequences are as a result of block at the AV node.Consider the bundle branches. Think of the ECG pattern, before you read further!Wenckebach AV sequences in the bundle branches was first described by the Royal Melbourne Hospital in 1976. It can be either the left or right bundle and is a sequence of increasing bundle branch block until complete and the sequence starts again.   This is what the ECG looks like.

This is hard to recognise unless you amplify one or more leads.

I am unsure if this is physiologic or pathologic. My usual answer to that question is look at the rate: Fast then “aberration”. Slow then disease.I have seen it combined with AV nodal Wenckebach.

I suspect there is pathology here.

Remember it’s all in the timing.

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Harry Mond