What Do You Think 25

Referred for opinion regarding heart block

What do you think?

There is sinus rhythm (arrows) and a ventricular ectopic (red highlight).

Embedded in the terminal portion of the T wave is a sinus P wave (blue arrow). Because of the timing of ventricular ectopic, the P wave falls within the refractory period of the ventricle and therefore is not conducted.

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With ventricular ectopics, a sinus P wave is usually concealed (blue highlight) within the ectopic and obviously does not conduct, unlike the other P waves (red arrows).

A poorly understood feature of ventricular ectopics is that the non-conducted sinus P wave (blue arrow) may not be concealed within the ectopic QRS (yellow highlight).

With appropriate timing (including sinus rate, ectopic prematurity) as well as QRS width and shape, the sinus P wave may emerge from the tail of the QRS or even the T wave.

Left ECG: The sinus rate is ~60 bpm (blue highlight) and the non-conducted sinus P wave (blue arrow) lies at the end of the T wave.

Right ECG: The sinus rate is ~50 bpm (blue highlight) and the non-conducted sinus P wave is later (blue arrow), but still within the refractory period of the ectopic. This mimics second degree AV block. I call this pseudo AV block and remember it is physiologic and dependent on the timing.