Two Dropped Beats

A Holter monitor I reported had Wenckebach AV block overnight.

Within a few minutes, there were two examples of two sequential dropped beats in the sequence (yellow highlight)

How would you interpret this and are they the same mechanism?

Look closely before you answer.

In Holter monitor reporting, the most common error by far is confusing Wenckebach AV block with non-conducted atrial ectopics.

To summarize:

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Now let us return to our two dropped beats

The first is a Wenckebach AV sequence with a dropped beat (all sinus P waves red circles) followed by an atrial ectopic (blue circle) which does not conduct as conduction is still refractory. The next sinus beat (pale red circle) does not occur as the atrium is still refractory from the atrial ectopic (see Fun with ECGs 5).

‍The non-conducted atrial ectopic extends the Wenckebach AV pause.

In the second ECG, all the sinus P waves are present. The non-conducted atrial ectopic is very early and results in the next sinus P wave not conducting thus completing the sequence with a second dropped beat.                                                     The Wenckebach AV pause is not extended!

Its all in the timing!

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