RBBB & Contralateral Escape Beats
Report:
Atrial fibrillation with slow response
Right bundle branch block
Borderline left axis deviation –30o
Ventricular escape beats with left bundle branch block morphology
Nonspecific ST/T changes
Comment:
One instinctively looks (or should look) at lead V1 as soon as intraventricular conduction is thought of. In this case, further thought is required, to recognise that both the LBBB beat there and its neighbour in V4 are actually escape complexes; all the other beats, terminating shorter and irregular cycles, are conducted supraventricular RBBB complexes. The rhythm strip is, unfortunately, on lead 2 – of little help here.
The LBBB escape beats probably arise from the distal, unblocked part of the right bundle branch. In patients with either bundle branch block and AV block or bradycardia, escape beats tend to have the morphology of the contralateral bundle branch block.
Below (Fig 44a) is another sample, with V1 showing both the LBBB escape and the conducted RBBB beats. A fusion beat in this situation could look completely normal.
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