What bothered me about this being an accelerated junctional rhythm (interrupted each 3rd beat by sinus capture) - was that the R-R interval for the 1st junctional beat in each sequence (= the R-R between beats #3-4; 6-7; 9-10; and 12-13) is slightly different (shorter) than the R-R interval of the subsequent beat (= the R-R between beats #4-5; 7-8; 10-11; and 13-14) - whereas if this was AV dissociation by usurpation with junctional acceleration I would have expected them to be the same ....
Why couldn't the mechanism be the one I drew - whereby there are PJCs (beats #4,7, 10, 13) that conduct retrograde enough to slow down forward conduction of the next sinus impulse. Admittedly - that next sinus impulse is slowed down to a greater extent than usually occurs with such concealed conduction (perhaps due to switching to some alternate slow conduction pathway ... ).
Just wondering if Dr. Wang might consider my alternate mechanism plausible. In any case - GREAT TRACING - and what IS agreed is that there is AV dissociation from some junctional intervention and no evidence of any AV block.
Here is K. Wang's Respsonse:
An interesting comment and a legitimate argument by observing slight difference in the R-R intervals of what I claim to be junctional beats, an astute observation. Yes, junctional rhythm is very regular rhythm, and I would have been happier if they occurred with exactly the same interval. The slight difference in this case may be due to some degree of penetration of the impulse from P2,4 and 6 into the junction (some degree of concealed conduction). In my view, the argument against your diagram is that that long P2-R3 interval will become too short (P3-R4) too quickly. Also, a premature junctional beat would have occurred more prematurely. His bundle recording would have settled the issue, which this patient did not have. It is an important issue because an accelerated junctional rhythm and junctional trigeminy (which is what you are advocating) have different clinical implications (see the discussion of the case). It is also interesting that we two are applying concealed conduction at different places of the same tracing.
Thank you for showing interest in our program and generating interesting discussion.
My impression is that Ken's interpretation is very viable, but that the differences in R-R interval are tiny and that K.'s interpretation is more likely.
As Ken says, the important thing is not which of these is correct, but that in both interpretations, there is no AV block, only AV Dissociation.