Pseudoblock: Concealed Extrasystoles
Report:
Sinus rhythm & arrhythmia
Junctional premature beats
Antegrade block in first and third manifest beats (blocked SVEBs)
Concealed junctional extrasystole
AV pseudoblock
Incomplete RBBB
Comment:
Some junctional (presumably, main-stem, or bundle of His) extrasystoles are only conducted retrogradely, evidenced by inverted P’ waves in all three standard leads. One is conducted in both directions (last complex before the pause). It is followed by a blocked sinus P wave, which shows no reason to be blocked. There is a strong likelihood that it is blocked by a completely concealed junctional extrasystole - blocked both antegradely and retrogradely in the bundle of His, but there to prevent the next P wave from being propagated down the bundle. This situation is known as pseudoblock.
Whenever a pseudoblock is suspected (as it should be whenever there are unexplained instances of blocked P waves), one should look for (manifest) junctional or ventricular extrasystoles. They add weight to the diagnosis. However, AV block may also, rarely, be engendered by any atrial premature discharge.21
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