Pacemaker Ventricular Block

Last week, I showed this ECG which was interpreted as ventricular tachycardia with 3:2 Wenckebach block at the ectopic-myocardial junction.

I immediately had a number of emails, requesting evidence that such a block exists.

Here is a reference: Oreto G, Luzza F, Satullo G, Arrigo F.Non-sustained ventricular tachycardia with Wenckebach exit block. Journal of Electrocardiology 1987;20:51–4.

However, let us try and prove this for ourselves on the surface ECG!!

Is this possible? The answer is yes yes yes!

Think of the ectopic focus asa ventricular pacing stimulus artefact:

You can see the stimulus artefact (ectopic focus) on the surface ECG.

Following each stimulus artefact is a latency period between the stimulus artefact and the paced QRS(red highlight), which increases for each complex until there is exit block.

This is a 4:3 pacemaker Wenckebach exit block sequence in a dying heart at the stimulus artefact-myocardial junction.

I have called this type 1, second degree pacemaker-ventricular block.              

(Kistler, Mond and Vohra. Pacemaker Ventricular Block. PACE 2003: 23; 1997-1999).

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Definition:

A pacemaker-ventricular block is an altering temporal relationship between the stimulus artefact and the subsequent QRS.

So there must be a first degree pacemaker-ventricular block.

The latency is fixed (red highlight). We have previously seen this in the atrium.

(Someone will ask if pacemaker seconddegree block occurs in the atrium. I have never seen it, but here is a reference: Narula et al. B Heart J1972;34:1127).

What about type 2, second degree pacemaker-ventricular block?

There is latency, but alternate stimulus artefacts show exit block.

This could be type 1 or type 2, 2:1 pacemaker ventricular block!

As you would expect the mortality is very high and these tracings are usually immediately prior to death.

This case was an antidepressant overdose and the patient survived.  

Not all cases demonstrate latency.

Again this is in the patient with the dying heart.

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In summary:

The block is progressive until death, which is third degree pacemaker ventricular block, and this is where it all ends!!

Remember, it’s all in the timing.