What Do You Think 47

Dr Kianseng Ng from Malaysia recently sent me this ECG and the only information was that he thought the patient had a pacemaker.

This is a continuous rhythm strip for 60 seconds and the format is extremely difficult to visualize.

To make it easier for you, I have selected relevant sections.

What do you think?

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Did I hear too hard!

You are correct.

Then how do we interpret this ECG?

Let us start by:

• Analysing the different rhythms separately.
• Using arrows and highlight.

Is sinus rhythm present?

Yes (red highlight).

Sinus rhythm at a rate of 60bpm and marked first degree AV block (400 ms). The PR interval appears fixed and if there were dropped beats, we may be able to call this type II AV block.A dropped beat is present (purple highlight) but follows immediately after a funny looking beat (FLB) and AV conduction is probably still refractory.  

What about the FLBs?

The FLBs (yellow highlight, red arrows) are very regular every 2.2 seconds and bear no relationship to thebeat before. Indeed the beat before does not reset the timing of the FLBs whichcompete independently of the other rhythms, completely ignoring they are there.

This is ventricular parasystole and because the QRS complexes are narrow, we call these fascicular ectopics and hence fascicular parasystole. Although there is no inhibition of these beats, fusion occurs with the sinus generated QRS (blue highlight), which is a strong feature of parasystole.  

To summarize ventricular parasystole:

A parasystolic focus is an ectopic focus that competes with the sinus focus, so there are two intrinsic pacemakers each having different cycle lengths. Ventricular parasystole has varying coupling intervals between sinus beats and the ventricular ectopics.Think of a ventricular pacemaker, programmed asynchronous VOO at a rate of about 40 bpm in competition with sinus rhythm. The primary rhythm is sinus and there is an entrance block protecting the secondary ectopic “parasystolic”focus, so conducted sinus impulses cannot enter and thus reset the timing of the parasystolic focus. The parasystolic block is unidirectional and whenever the secondary ectopic focus depolarizes, it will conduct to the surrounding myocardium, provided the myocardium is not refractory.  

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Here is an example of ventricular parasystole with the ectopics in the PR interval (red highlight), a fusion beat (blue highlight) and a “concealed” ectopic  (green highlight) where the focus depolarizes, but the surrounding myocardium is refractory.

The differential diagnosis isa ventricular geminy such as quadrigeminy (red highlight), where every fourth beat is a ventricular ectopic and the coupling intervals between the previous sinus beat and the ectopic are fixed.

But wait, there is more!

There are broad QRS complexes (green highlight, blue arrows).

None of these broad complexes are sequential, so the rate is measured from the previous beat and is 40 bpm.Although there are no stimulus artefacts, these are clearly ventricular paced beats and because the timing is continually being reset, this is single chamberVVI. This pacemaker setting is used when pacing is to be avoided, particularly with implantable defibrillators. Once again there are fusion beats (blue highlight).

Finally there is a lone ventricular ectopic (grey highlight).

It is not difficult to interpret this complicated ECG using Mond’s interpretive tools.

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In summary:

• Sinus rhythm with marked first degree AV block.
• Fascicular parasystole.
• VVI pacing.
• Fusion beats.
• Ventricular ectopic.

Now go back and interpret the rhythm yourself.

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Harry Mond