Let’s start the year with an easy one. The quality isn’t as good as I’d like but it’s good enough for answering the question: what is the rhythm? This is one that might not be obvious at first glance but a careful analysis should yield the correct answer.


This one is not complex but it’s easy not to recognise straight away what is happening. The key, as so often with arrhythmias, is first to identify the atrial activity. I’ve shown the P waves below with arrows and it’s now clear that there is an underlying sinus rhythm/tachycardia and that not all P waves are followed by a QRS complex. I have also shown the PR intervals with blue bars, and it should now be apparent that there is 4:3 Wenckebach AV block. The red arrows show the blocked P waves.

This is a simple rhythm disturbance but what makes it perhaps difficult to recognise immediately is the length of the PR intervals: the shortest is 440 ms, the longest 600 ms. As we have seen before, when the PR interval is very long it is difficult for the human/eye brain combination to make the link between P wave and QRS. However, when the P waves are clearly marked, as here, the relationship between P and QRS is much easier to appreciate.

Well done to those who worked it out. As Scott Walton and Arron pointed out, there is also a left axis deviation that is most likely due to left anterior fascicular block.

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