Ectopic Pacemaker

Report:

AV pacemaker rhythm 59/min; AV interval 020” (as programmed) 0.5

Displaced ventricular lead 3

Intermittent failure to pace & native QRS conduction at spike-R interval 0.36” 4

Failure to sense (the delayed atrial-paced native QRS) 2

ST/T changes 0.5

Comment:

The paced QRS morphology, instead of resembling LBBB with LAD, resembles RBBB with RAD, reflecting left ventricular pacing from somewhere over left ventricle. The native QRS is late, but the overall heart rate is still same as the paced rate, 59/min, since the pacemaker is not reset by the native beats – it fails to sense them.

Remarkably, this preoperative ECG was either misunderstood or unread and was not even stored in the permanent ECG database, where the Cardiology technicians would have seen it.. The patient went on to induction, thoracotomy and cardiopulmonary bypass with the RV lead of his permanent pacemaker in the pericardial sac! Fortunately the perforation was sealed around the ventricular lead and there was no pericardial blood. The surgeons cut its tip off and put their own temporary wires in place. It all ended well. Had the patient suffered any adverse events due to what should have been an obvious pacemaker problem, it would have been very difficult to explain away in a court of law.

Below (Fig 121a) is a post-implantation ECG taken 6 months previously, mistakenly reported as atrial pacemaker rhythm 77/min. The P waves have an atrial spike superimposed about 0.04” after their onset and are conducted with 1o AV block (0.24”). They could be called atrial pseudofusion beats. The atrial spikes in this location do not imply atrial undersensing – they would if they actually followed the P waves. Their contribution to the tracing is, in a sense, entirely negative: they inhibit the ventricular pacing spike for 0.20” (pacing AV interval), by which time the sinus P waves capture the ventricles and abolish the pacing spike altogether. The sensing AV interval of 0.17” is thus aborted by the atrial spike component of the pseudofusion beats.