BBBB[!xe "Bilateral bundle branch block (BBBB):LBBB + RBBB" \b \i!]
Report:
Sinus rhythm
Interpolated junctional (main-stem) extrasystoles[!xe "VEBs:main-stem (bundle of His) extrasystoles" \b \i!]
Right bundle branch block[!xe "Right bundle branch block:LBBB" \b \i!]
Left bundle branch block[!xe "Left bundle branch block:with RBBB" \b \i!]
Pacemaker escape beats
Comment:
Carotid sinus massage was performed in order to demonstrate absence of its effect on the AV block in this patient with established diagnosis of Möbitz 2 block. It did that: the sinus rate slowed without any concomitant effect on AV conduction.[!xe "Carotid sinus massage:BBBB" \b \i!]
It also affected, in some way, the intraventricular conduction, since some of the complexes became LBBB in morphology. This is the only time I have seen both LBBB and LBBB during 1:1 conduction of sinus rhythm in the same strip.
Another rare phenomenon occurred: intercalated main-stem extrasystoles. At first one takes them for SVEBs, perhaps in couplets. However, the would-be second SVEB has a P wave not only identical in contour to normal sinus beats, but is also on time for a sinus beat. It is a sinus beat. And then, if it is a sinus beat, its escape interval from the would-be first SVEB is preternaturally short. And, looking closer, the PR interval following the first SVEB is slightly longer than others (in RBBB conduction). The only explanation that fits is that the complex is interpolated, arising below the AV node; its morphology, virtually the same as sinus beats with RBBB conduction, designates it as a bundle of His (main-stem) VEB!
This made me look at other rhythm strips, recorded at other times. Sure enough, he had those valuable (for a collector) main-stem extrasystoles on many other occasions; one is shown below. The intercalation-related increment in the PR increment is easier to see now, without the carotid sinus massage.
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