What Do You Think 43

What do you think?

Clue:

Last week, I stated that maybe I would talk about interpolated ventricular ectopics this week.

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In the tracing there is an obvious ventricular ectopic, so let us start there.

The ventricular ectopic:

• Sinus rhythm (red arrows)
• Premature broad QRS (red highlight)
• No preceding P wave
• Concealed within the ectopic QRS is the next sinus P wave (blue arrow), which does not conduct to the ventricle because the conducting system is  refractory -referred to as concealed retrograde conduction
• Full compensatory pause, determined by the concealed, non-conducting P wave (green stippled arrow)

If the sinus rhythm is slower (red arrows) and the ventricular ectopic very premature (red highlight), then the P wave may follow the T wave (blue arrow). Now the P wave is not concealed, but the AV conducting system is still refractory.

What happens if the AV conducting system is not refractory?                                            

AV conduction will occur and by definition, there will be no compensatory pause.

This is called an interpolated ventricular ectopic.

• Usually sinus bradycardia (red arrows)
• Premature ventricular ectopic (red highlight)
• The next sinus P wave is usually visible (blue arrow) and can conduct to the ventricle, but because of concealed retrograde conduction, the PR interval is extended from 200 ms to 400 ms.
• There is no compensatory pause.
• The R-R interval containing the embedded ventricular ectopic is usually longer than the R- intervals without an embedded ventricular ectopic due to the PR extension increment, which is 200 ms

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Holter monitor tracings.

Left: Sinus rhythm (red arrows), rate 64 bpm and a ventricular ectopic (red highlight) with a compensatory pause. There is a concealed P wave at the foot of the T wave, which does not conduct to the ventricle (blue arrow).

Right: The sinus rate has now slowed to 55 bpm and the sinus P wave lies beyond the T wave. The P wave now conducts to the ventricle, albeit with a prolonged PR interval.

On occasion the PR interval extension is marked (yellow highlight).

With marked bradycardia, even a very late ventricular ectopic can still be interpolated if the timing is correct.

Sinus bradycardia (red arrows)with a ventricular ectopic (red highlight). The sinus P wave is embedded in theT wave, and there is no/minimal concealed retrograde conduction, allowing conduction again with a prolonged PR interval.

The tracings become confusing if aberrant ventricular conduction also occurs.

Sinus rhythm (red arrows) and a ventricular ectopic (red highlight) closely followed by a broad complex QRS(blue highlight). This was called a multifocal ventricular couplet. There is a concealed sinus P wave (blue arrow) which conducts to the ventricle with a prolonged PR interval and an rsR’ in V1, highly suggestive of aberrant ventricular conduction, again resultant from concealed retrograde conduction.

Even monomorphic ventricular couplets can be interpolated, if the timing is correct.

Sinus rhythm (red arrows) with a ventricular couplet (red highlight) with the concealed sinus P wave within the T wave of the second ectopic (blue arrow). Once again, it conducts to the ventricle with a prolonged PR interval.

Of course, ventricular interpolation may occur with ventricular trigeminy (red highlight).

And quadrigeminy (red highlight).

When the sinus rate is fast, the compensatory pause may disappear, and the tracing may be mistaken for ventricular interpolation.

Mapping the sinus P waves (red arrows) identifies the concealed, non-conducting sinus P wave (blue arrow),embedded in the ventricular ectopic (red highlight).

A ventricular ectopic during single chamber atrial pacing (AAI) can result in ventricular interpolation.

AAI pacing (red arrow) with a very long AV delay. There is NO ventricular sensing, and thus the atrial pacing cycle is not interrupted. Following the ventricular ectopic (red highlight),the next atrial paced beat (blue arrow) conducts to the ventricle, with a pseudo-compensatory pause, because of prolonged AV conduction.

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Not all interpolation is interpolation. If the P-P or R-R interval with the embedded ventricular ectopic is shorter than without, then think of echo beats.

Sinus bradycardia 50 bpm (red arrows). A ventricular ectopic is followed by a premature inverted P wave(green arrow) resultant from concealed retrograde conduction to atria and then anterograde to ventricle. The sinus cycle is interrupted (red ghost stippled arrow), and P-P/R-R interval shorter with the embedded ectopic.

However, not all echo beats result in a shortened R-R interval, because the timing depends on both retrograde and anterograde conduction, which may be delayed.  

Sinus rhythm (red arrows) with a ventricular ectopic (red highlight) followed by an echo beat with an invertedP wave (green arrow). The P-P/R-R interval with the embedded ectopic is longer than the sinus cycle.

Knowing everything about interpolated ventricular ectopics, how do we interpret our initial ECG?

• Sinus rhythm (vertical arrows) with a ventricular ectopic (red highlight) and a sinus P wave at the foot of the ectopic T wave (blue arrow).
• This P wave conducts to the ventricle, albeit with a very long PR interval of 700 ms, due concealed retrograde conduction.
• Because of the timing, the next P wave also falls at the foot of the T wave (red stippled arrow) and conducts with a shorter, but nevertheless, prolonged PR interval of 600 ms.
• The next PR interval is near normal at 260 ms.

This gradual sequential shortening is referred by me as pseudo-reversed AV Wenckebach.

Does reversed AV Wenckebach exist?

Of course.

Here is an example!

In summary:

• Sinus rhythm (red arrows)
• Sequential shortening of PR interval (yellow boxes)
• There is NO dropped beat
• The R-R interval is longest with longest PR interval (green stippled arrow)
• The varying R-R intervals exclude complete heart block
• Usually not symptomatic

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Our final diagnosis:

Interpolated ventricular ectopic with sequential reducing concealed retrograde conduction, masquerading as reversed AV Wenckebach.

It’s all in the timing.

Harry Mond