Onset of Atrial Fibrillation: Mode Switch

Report:

Sinus rhythm 76/min 1

Atrial-sensing ventricular pacemaker 3

SVEB, onset of atrial fibrillation 4

Atrial fibrillation with ventricular response 118-124/min 1

Pacemaker inhibition 0

Incomplete left bundle branch block 1

Comment:

At first, the pacemaker tracks the atrial activity in AF, up to its pre-set upper rate limit of 120/min; then it is overtaken and suppressed by the conducted native complexes, switching its mode to VVI. Slowing the ventricular rate pharmacologically may be difficult now, as the pacemaker is ready for anything (atrial) up to 120/min (ventricular). It may have to be converted to a VVI unit permanently if sinus rhythm cannot be restored.

The incomplete LBBB is diagnosed from precordial leads only: the QRS is just over 0.10 sec in duration and there is no septal q wave in V6; the complexes are relatively large. LVH with ST/T changes would also be an acceptable diagnosis.

If you have any suggestions for or feedback on this report, please let us know.