Pacemaker Completing the RBBB
Report:
Sinus rhythm 70/min 1
Atrial pacemaker rhythm 55/min 2
Failure to sense 3
Capture beats 2
Right axis deviation +95o 1
Right bundle branch block 1
Comment:
The atrial pacemaker discharges with complete regularity at 55/min, obviously heedless of the underlying rhythm. It does not sense, but still paces whenever not thwarted by a preceding P wave or refractory ventricle. Its four captures, with an AV interval of 0.24 sec, draw attention to themselves by producing the broadest QRS complexes in the tracing.
In the sinus beats, the RBBB is almost complete, at 0.12 sec; the long-short sequence and the faster rate of pacemaker captures extend the QRS duration to 0.14 sec – complete RBBB. Even this may be a misnomer: it’s not exactly rare for a “complete” bundle branch block to become even more complete! Still, reporting is guided by convention.
Below is a 100% paced ECG, all in (borderline) incomplete RBBB.
If you have any suggestions for or feedback on this report, please let us know.
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