What Do You Think 53

Elderly male.

Holter monitor. All tracings overnight.

Reported as high degree AV block Two or more dropped beats).

What do you think?

‍

There is first degree AV block.

Sinus rhythm 60 bpm with PR interval of 540 ms.

As well, there is Wenckebach AV block.

The absolute criteria for Wenckebach AV block have been fulfilled. There is also a conducted atrial ectopic (blue arrow) with a long PR interval confirming conduction tissue disease most likely in the AV node.

To summarize the absolute criteria for Wenckebach AV block.

With infrequent dropped beats, in order to be sure that this is not type II AV block, the following absolute criteria for Wenckebach AV block are required:

• The PR interval before the dropped beat is the longest (540 ms).
• Non-conducted sinus P wave (red stippled arrows).
• The first PR interval after the dropped beat is the shortest (210 ms).

With our case the differences in the PR intervals are minimal (40 ms). This is often the case with prolonged PR intervals and long sequences without a dropped beat.

The third strip demonstrates two dropped beats and a significant pause of about 3seconds.

Is this high degree AV block (Wenckebach AV block with two non-conducted sinus P waves?

Timing out the P waves confirms that the second dropped beat is a non-conducted atrial ectopic with a compensatory pause, which extends the Wenckebach AV pause.

Although Wenckebach AV block is usually regarded as a benign vagal mediated nocturnal arrhythmia in the young, in the elderly it is usually due to degenerative  AV nodal disease or even more distal disease in the bundle of His or bundle branches. Wenckebach is seen at any time and is often associated with conduction system disease such as first degree AV block and bundle branch blocks. If symptomatic, cardiac pacing may be required.

Because of the disease in theAV node, atrial ectopics are frequently non-conducted, giving rise to aplethora of interesting and sometimes confusing ECG appearances when they occur with Wenckebach AV block.

During nocturnal Wenckebach sequences the dropped beat is sinus generated (red stippled arrow), whereas during non-Wenckebach periods it may be a non-conducted atrial ectopic (blue stippled arrow). There is also first degree AV block and a bundle branch block, suggesting degenerative conduction system disease.

The Wenckebach sequence is terminated with a non-conducted atrial ectopic (blue stippled arrow).

Both non-conducting sinus P waves and atrial ectopics in the same tracing.

With sequential dropped P waves the order may change.

Above: The non-conducted atrial ectopic follows the non-conducted sinus P wave with the compensatory pause extending the Wenckebach pause.

‍Below: The non-conducted atrial ectopic from a different site in the atrium precedes the dropped sinus P wave of a Wenckebach AV sequence, thus terminating the sequence.

How to differentiate Wenckebach AV block from non-conducted atrial ectopics?

A very common error encountered with Holter monitoring reporting is misinterpreting non-conducted atrial ectopics as the non-conducted sinus P wave of a Wenckebach AV sequence or visa-versa. Both non-conducted atrial ectopics and Wenckebach AV block arevery common, so it is not surprising that they occur in the same ECG tracing.

To summarize:

The absolute footprints of a Wenckebach AV block sequence:

• The PR interval is longest immediately before the dropped beat.
• The non-conducted sinus P wave(blue arrow) is not premature.
• The PR interval is shortest immediately after the dropped beat.
• The sinus cycle is not reset.

‍

The footprints of a non-conducted atrial ectopic:

• The non-conducted P wave is premature (blue stippled arrow).
• The P wave is usually different in morphology from the sinus P wave.
• The PR intervals are the same (red highlight).
• The sinus cycle is reset by the atrial ectopic which has a compensatory pause (green stippled arrow) unless interpolated.

Harry Mond