Fusion Beats in Idioventricular Escape Rhythm
Report:
Sinus bradycardia 27/min
First degree AV block
Right bundle branch block (by inference)
Right bundle branch escape rhythm 28/min
Fusion beats
Comment:
As the PR interval shortens the QRS gets fatter. This means that the P waves are conducted. The escape rhythm has LBBB morphology, presumably coming from right bundle branch beyond the block.
It may seem difficult to diagnose RBBB in its absence. Yet it has to be there to normalise the LBBB idioventricular complexes. Below (Fig 38a) is the proof. Note that the three conducted complexes (including the fusion beat in the middle of the trace) have the same rate as sinus bradycardia while the dissociated LBBB complexes are slightly but definitely faster. Why call the latter escape rhythm? Because of the setting of profound bradycardia.
Fig 38a.
Fig 39. 50 year old lady with primary congestive cardiomyopathy (COCM).
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