Failure to Pace

Report:

Sinus rhythm approximately 75/min 1

AV dissociation 3

Pacemaker rhythm 88/min 4

Intermittent failure to capture (pace) 2

Comment:

Large pacemaker spikes march regularly throughout, but the 10th spike is not followed by a QRS. The morphology of the successfully paced beats is the expected LBBB one, but the frontal plane axis indicates a superior displacement of the right ventricular electrode. Such placement or displacement – toward the RV outflow tract - often causes ventricular ectopic activity as well as unstable pacing.

Dissociated sinus beats are seen in several places and their rate is in fact slower than that of the electronic pacemaker. One cannot, therefore, diagnose 3o AV block here – only AV dissociation. Even the P wave following the non-capture could, conceivably, be conducted (with 1o block) if the next paced beat did not occur where it did.

The reason for the pacemaker rate 88/min is not known; the programmable parameters’ settings must be established before a comment can be made. Possibly, the patient’s ventricle was already operating at maximum contractility and the only way to increase cardiac output was through the paced rate. Most likely, it was a rate-responsive VVI unit, a VVIR one.

Fig 23. 54 year old man with left-sided chest pain on inspiration. Casualty trace.