What Do You Think 65

This ECG was sent to me by Hathaikarn (Ann), CardioScan, Thailand.

Thank you Hathaikarn.

What do you think?

This is one of those complex looking ECGs identified by “instant recognition”.

The clues:

• Rapid ventricular rate.
• Pauses where P waves are recognised at a rate between 250 to 300 bpm.
• The pauses divide the ventricular response into sequences.

In order to make the diagnosis, a poorly understood, albeit important idiosyncrasy of AV conduction, needs to be reviewed.

Alternating Wenckebach AV block.

Alternating Wenckebach AV block is usually called complete AV block, but the ventricular rate is irregular with regular Wenckebach sequences.

How do we explain this rhythm?

• Supraventricular (sinus) rhythm (arrows).
• Two blocks; one at the AV node and the other maybe lower, with the combination referred to as a multi-level block.
• 4:3 Wenckebach (red arrows, red highlight) alternating with complete AV block (light blue stippled arrows).
• A new sequence commences without an intervening blue blocked P wave (Two non-conducted sinus P waves rather than three occur when the rhythm is relatively slow (green highlight).
• With sinus rhythm, this can occur with a bundle branch block, syncope, and sudden death.
• Alternating Wenckebach is also seen with atrial tachyarrhythmias including atrial tachycardia and atrial flutter with a rapid ventricular response.

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Let us return to our case study and select a sequence to investigate (yellow highlight).

The pauses confirm atrial flutter, which by extrapolation can also be identified (not seen) during the sequence (blue arrows). There is a Wenckebach relationship between the P waves and the broad QRS complexes (green stippled arrows), terminating in a non-conducted P wave (blue stippled arrow) and the next sequence commences. The PR interval before the pause is the longest, whereas the first PR interval of the sequence is the shortest (red highlights).

There are also alternating non-conducted P waves(pink stippled arrows) with the sequence terminating in three non-conducted P waves (red open circle).

This is therefore atrial flutter with alternating Wenckebach AV block.

Here is another example with short 3:2 Wenckebach sequences and three non-conducted P waves.

Atrial flutter (blue and pink arrows), rate 250 bpm with sequences of two ventricular responses (yellow highlight), each with an increasing PR interval (green stippled arrows) until a dropped beat (blue stippled arrow). There are alternate non-conducting P waves(pink stippled arrows) and the sequence is terminated by three  non-conducted P waves (red open oval). There are two levels of AV block, one Wenckebach and the other complete.

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An example where there are only two dropped beats (red open oval).

Another atrial re-entry tachycardia is a macro-reentrant atrial tachycardia. It occurs in patients with structural heart disease including previous atrial cardiac surgery such as with congenital heart disease, electrophysiological ablation in the atria or any condition causing atrial scarring. It resembles atypical atrial flutter, particularly if the flutter rate is relatively slow due to drug therapy. It is frequently persistent but can be paroxysmal and may be asymptomatic if there is a significant AV block. These AV blocks can result in bizarre ECG appearances and most ECG reporters do not bother to establish the relationship between the P waves and the QRS complexes.

Macro-reentrant atrial tachycardia or slow atrial flutter, atrial rate 195 bpm (blue arrows). 4:3 Wenckebach AV block (blue arrows and stippled for dropped beats) with alternating non-conducted P waves (pink stippled arrows) comprising the sequence (yellow highlight). There are only two dropped beats terminating the sequence (red open oval).

An example with incessantatrial tachycardia (220 bpm) demonstrating two and three non-conducted P waves terminating the sequences.

The incessant atrial tachyarrhythmia terminates, has a pause and recommences after one sinus beat (red arrow). There are varying Wenckebach AV block sequences (yellow highlight, blue arrows) alternating with non-conducted P waves (pink stippled arrows). Immediately prior to termination of the arrhythmia, there are two sequences resulting in two and three sequential dropped beats (red open oval).  

Harry Mond