Single Failure to Capture

Report:

Sinus rhythm 63/min 2

Complete AV dissociation 4

Pacemaker rhythm 80/min 2

Single failure to pace 4

Comment:

AV block cannot be accurately diagnosed here: the atrial (sinus) rate is too slow and the ventricular (pacemaker) rate too fast. Just before the pacemaker insertion, the patient was in 2:1 AV block (Fig 104a) with the ventricular rate 34/min and the atrial 68/min. Alternate P waves there were blocked even further from the preceding QRS complex than the blocked P wave seen preceding the pause created by the temporary failure to pace.

That P wave resembles, superficially, a blocked atrial ectopic, the well-known Marriott’s commonest cause of a pause. It is the reason for including this trace in this collection: so many have misdiagnosed it!

The paced complexes show typical QS morphology in the inferior and all the precordial leads.

An AV block in the setting of inferior infarction would be expected to resolve within days. The only action required here would be to continue monitoring or, perhaps, increase the temporaryunit’s output.