What Do You Think 7

72 year-old astronaut with acrophobia.

What do you think?

Looks bizarre but is not difficult.

Like I have said many times “break it down to its basic elements”!

Write down an answer before you proceed.

• Underlying rhythm; sinus bradycardia, 43 bpm(red arrows) with varying PR intervals and a narrow QRS (red highlight).
• Ventricular ectopic (yellow highlight) with an almost concealed P wave (red stippled arrow) lying on the ectopic T wave.  

Let us review how, with bradycardia, “concealed” sinus P waves (red stippled arrows) emerge from within ventricular ectopics (red highlight):

The sinus P waves related to the ectopics (red stippled arrows) do not conduct, and because the conducting system is refractory, there are compensatory pauses.

Our tracing has what appears to be a compensatory pause, but this is due to PR interval extension from 200ms to 700 ms and therefore the ectopic is interpolated.‍

Summary: Ventricular interpolation

Ventricular ectopic (yellow highlight) with a non-concealed sinus P wave (red stippled arrow) lying outside the absolute refractory period and therefore can conduct to the ventricle, albeit with a prolonged PR interval. Although no compensatory pause, the R-R interval with the embedded ectopic is longer (1340 ms) than without (1140 ms)by an amount equal to the lengthening of the PR interval (200 to 400 ms).

Let us return to our ECG.

• The next sinus p wave (blue arrow) lies after the T wave, but within the relative refractory period and conducts with a PR interval of 600 ms.
• The following PR interval is 260 ms, and then thePR intervals return to normal (200 ms).

The appearance is a “reversed” Wenckebach AV block without a dropped beat.              

Does it exist?

Yes it exists!

Regular sinus rhythm (red vertical arrows). There are repeated reversed Wenckebach AV block sequences(shortening red horizontal arrows) without a dropped beat. The changes in the R-R intervals exclude complete heart block.    

This has been reported without a dropped beat together with a bundle branch block and syncope.

The one above is real, but in our case, it is not and is therefore a pseudo-reversed Wenckebach AV block.

‍

In summary, our ECG showed:

Sinus bradycardia with an interpolated ventricular ectopic resulting in very long PR intervals, a pseudo-compensatory pause and a pseudo-reversed Wenckebach AV sequence.                  

It’s all in the timing.