This week, I saw two similar unusual ECG appearances on consecutive days.

Is this artefact?What do you think?The pauses are real and there is a non-conducted atrial tachyarrhythmia, which terminates abruptly after a few beats.I see similar appearances about once a month, so it is not rare.I will show a few more examples:

Because it doesn’t conduct, the asystolic pauses can be quite long and symptomatic.Why then, does the tachyarrhythmia stop abruptly?Clue: Remember, my obsession with Wenckebach.Some of you will say that is the reason…… and you would be correct!!!!!This is one of the non-atrioventricular Wenckebach blocks.Focal atrial tachycardia with Wenckebach block at the ectopic-myocardial junction. In summary:

• P waves are generated by impulses conducted to the atrium.
• These ectopic tachyarrhythmias must pass an electrical barrier in order to depolarize the surrounding muscle.
• The tachyarrhythmia eventually stops as there is a Wenckebach block sequence at this electrical barrier.
• Rarely discussed in the literature.
• The features of Wenckebach, as with sino-atrial block are
• Must recognise footprints.

The footprint is the same as with sino-atrial Wenckebach (fun with ECGs 21):The P to P cycle length shortens until there is block (red highlight).

Another example:

Can it occur in the ventricle? Of course!A fast-short run of a tachyarrhythmia, with the last cycle length, being the shortest.

If you look you will find it!Remember it’s all in the timing.Harry Mond