Conducted LPHB and Escaping LAHB

Report:

Sinus rhythm 82/min

Left atrial abnormality (LAA)

2:1 AV block

Right bundle branch block

Left posterior hemiblock

Junctional escape (first two) beats

RBBB + LAHB morphology

Nonspecific ST/T changes

Comment:

Most commonly, the escape rhythm has the contralateral bundle branch block morphology: it’s what’s beyond the block that escapes. Here the conducted beats all have a LPHB morphology, with a modest RBBB. The first two beats are obviously dissociated and have the LAHB morphology, again with a tad of RBBB. Below (Fig 62a), there are no conducted beats; the atria are in dissociated sinus and junctional rhythm throughout, with one atrial fusion beat. The escape rhythm, like the two initial beats in the original trace, has RBBB/LAHB morphology.

The site of the 2:1 block is almost certainly ventricular. Since there are no two consecutively conducted P waves, there is no way of assigning Möbitz 1 or 2 status to this block. If the conduction improved (to, e.g., 3:2 block) it would, again almost certainly, reveal its Möbitz 2 nature.