What Do You Think 21

This ECG was reported as sinus rhythm with a short run of atrial fibrillation.

What do you think?

The first part is correct. There are sinus P waves present (red vertical arrows).

The short irregular run(red highlight) has rapid regular P waves (blue arrows) rate  about 170 bpm and is an atrial tachycardia. There is 2:1 AV block with alternating non-conducting P waves (blue stippled arrows). The conducted P waves have a Wenckebach AV sequence (red vertical arrows) and the tachycardia is terminated before a dropped beat. These two AV blocks are called alternating Wenckebach.

How often do these bizarre blocks occur with atrial tachyarrhythmias?  

I went through my file on atrial tachyarrhythmias and found the following:

Sinus rhythm (red arrows) with a short run of atrial tachycardia, rate 170 bpm (blue arrows). The blue stippled arrows do not conduct, but those that do have an AV Wenckebach PR prolongation appearance, which ignores the dropped beats.

As the atrial rate and block increases, so do the bizarre AV block patterns:

The atrial rate is now over200 bpm and the block increases. There is a pattern of 2:1, 3:1, 4:1 block with solid arrows conducted and stippled, not conducted. A single sequence (red highlight) once again shows a Wenckebach AV sequence with an increasing PR interval before a dropped beat (green stippled arrow).

There are consistent patterns of non-conducted P waves.

Rapid atrial tachycardia or flutter (vertical arrows) with variable conduction and non-conducted beats(stippled arrows) which fall into a pattern. When two sequential waves are not conducted (yellow highlight), a new sequence commences. A long sequence (red highlight), demonstrates Wenckebach AV block with conducted beats (red horizontal arrows). The second dropped beat (green stippled arrow) terminates the sequence, which starts again, but now without an intervening dropped beat. This termination of a Wenckebach sequence with two dropped beats and a new sequence commencing with a conducted beat is characteristic of alternating Wenckebach.

Don’t believe me! Here is another. Work it out yourself.

In the literature, clinical alternating Wenckebach is usually sinus rhythm and marked bradycardia.

See if you can work out what is going on. It looks like complete heart block, but the ventricular response is irregular.

• Two blocks; one at the AV node and the other maybe lower, with the combination referred to as a multi-level block. This was an early explanation.
• Typical Wenckebach AV block (arrows labelled 1to 4) alternating with
• Complete AV block (green stippled arrows).
•  The next sequence commences without an intervening distal blocked beat.

This can also present with a bundle branch block, syncope, and sudden death.

Are the tachycardia and bradycardia sequences the same mechanism? I am aware that such blocks can occur with rapid atrial pacing at electrophysiology studies.

If someone would like to add any more information does please email me.