Assoc Prof Harry Mond
March 18, 2025
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.
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.
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May 14, 2025
Fusion is another lesson in timing! Fusion beats are an amalgam of two competing rhythms. Both are responsible for partial depolarization of the respective chambers and depending on the contribution of each, result in progeny with similarities to one or both parents.
May 14, 2025
The ventricular ectopic compensatory pause is a lesson in timing!
