Interpolated Ventricular Ectopy

The ventricular ectopic compensatory pause is a lesson in timing!

To summarise:

The ventricular compensatory pause extends from the onset of the ventricular ectopic to the next P wave (red horizontal arrow and highlight). Within the ectopic, there is usually a concealed non-conducted sinus P wave (stippled red vertical arrow). As the sinus cycle lengthens and the rate slows, the sinus P wave may emerge into the ST segment or even beyond the T wave and is no longer concealed. At one point, ventricular conduction may be re-established and the ventricular ectopic is said to be interpolated; a ventricular ectopic without a space.

This is an ECG from the same Holter tracing, showing what happened when the sinus rate slowed.

The sinus P wave immediately following the ventricular ectopic (blue vertical arrow) now conducts to the ventricle, albeit with a prolonged PR interval (red horizontal arrows and red highlight). There is NO concealed nor non-conducted sinus P wave and NO compensatory pause. Although the sinus cycle lengths remain constant(apart from sinus arrhythmia), the R to R interval with the embedded ventricular ectopic is longer, by the extension of the PR interval.                               Sometimes the PR interval is normal without alteration of the R to R interval.

If the PR interval following an interpolated ventricular ectopic is very prolonged(blue highlight and blue horizontal arrow), an illusionary compensatory pause results(blue and red highlight), but because the P wave is in the middle of the pause, it is a pseudo-compensatory pause.

Because interpolated ventricular ectopics are very dependent on timing, the resultant ECG patterns create lots of fun!

Here is a bizarre looking ECG! How would you interpret this?

Interpolated ventricular bigeminy (red highlight).

The PR interval is again prolonged.

If we can have bigeminy, then we can have other combinations of ventricular ectopy.

In this example, the PR intervals are constant and there are three intervening sinus cycles for each ventricular ectopic:  Interpolated ventricular quadrigeminy.

 Interpolated ventricular couplets can have a number of concealed sinus P wave combinations: Firstly let us look at a unifocal ventricular couplet but with a compensatory pause.

There are two non-conducted concealed sinus P waves.

In the following example, the ventricular couplet is multifocal, interpolated and only one non-conducted concealed sinus P wave (red stippled vertical arrow).

Here is another unifocal interpolated ventricular couplet with no non-conducted sinus P waves:

The concealed sinus P wave(blue vertical arrow) conducts to the ventricle with a prolonged PR interval(blue horizontal arrow).

Not all “so called couplets” are couplets!

Here is an interpolated ventricular ectopic (red highlight) followed by aberrant ventricular conduction (yellow highlight).

The clues:

• The concealed P wave (blue vertical arrow)conducts to the ventricle (blue horizontal arrow)
• V1 demonstrates a rabbit’s ears “rsR’ pattern”,classical of aberration
• The initial QRS vector is identical to the sinus QRS complexes. 

One of the earlier illustrations showed a multifocal ventricular couplet. This could also have been aberration, but the QRS was left bundle branch block (V1), which makes it less likely.  

Another confusing “interpolated” scenario is shown below:

On careful inspection, the P wave beyond the ventricular ectopic is correct in timing but inverted and thisis probably due to retrograde conduction to the atrium resulting in an echo beat. By definition, the ventricular ectopic lies “without a space” and is therefore interpolated.

It is very easy to miss echo beats if the retrograde P wave is concealed!

There is a ventricular ectopic with a compensatory pause (red highlight) and one that is interpolated (yellow highlight). The sinus P waves are shown with red vertical arrows. The two that are stippled are assumed concealed and non-conducted. However, these P waves don’t exist as there are probably earlier retrograde P waves (blue arrows)which inhibit them.

This is ventricular ectopic interpolation due to an echo beat.

Another interpolation scenario occurs with dual chamber pacing.

There are atrial stimulus artefacts within the T waves (red vertical arrows) followed by a period of latency where the conduction is slowed by infiltrated foreign material such as amyloid (yellow highlight). Following this is a paced P wave (green vertical arrow) and a very broad conducted QRS. The AV delay is 360 ms and this suggests very severe heart disease. The ventricular ectopic (red highlight) is interpolated.

Here is another example of an interpolated ventricular ectopic.                                    

Spend some time and work out what is going on? Remember it is all in the timing!

The ventricular ectopic is in red highlight.

Here is my interpretation:

The sinus P waves (vertical arrows) are slow, regular and not concealed. The blue vertical arrows show sinus P waves at the end of the T waves. The first conducts with a prolonged PR interval (yellow highlight) and despite the apparent pause after the ventricular ectopic, it is interpolated. The timing also allows the next sinus cycle to conduct with a prolonged PR interval (blue highlight), before returning to a normal PR interval.  I called this:                                                                                                  Interpolated ventricular ectopic with pseudo-reversed Wenckebach AV block.

The next ECG was reported as an interpolated ventricular ectopic.

There is no compensatory pause after the ventricular ectopic (red highlight). The rhythm, however, is atrial fibrillation and therefore not interpolation.

Here is another ECG which was reported as two ventricular ectopics; one interpolated and other not.

One is real with a compensatory pause (yellow highlight) and the other artefact (red highlight).The answer lies in the bottom two tracings and stresses the importance of three channel Holter monitoring.

Now that you know everything about ventricular ectopic interpolation, you will have no problem with this ECG!

• Sinus bradycardia
• Sinus arrhythmia‍
• Interpolated ventricular ectopic despite the pseudo-compensatory pause

Remember it is all in the timing.