Beginning of an Endless Loop

Report:

Sinus rhythm 79/min 1

VEB 1

Ventricular escape beat, preceded by attempt at atrial pacemaker escape 1

VEBs, dimorphic couplet 1

Retrograde conduction 2

Retrograde P sensing and generating pacemaker tachycardia 103/min 4

Comment:

The retrograde P starting the run is clearly seen after the second VEB of the dimorphic couplet. This is how the run starts, sensing the atrial activity, as programmed. But it can only be perpetuated by continued generation of retrograde P waves, the bane of “physiological” pacemakers12.

The rate of the endless loop (circus movement) tachycardia is limited by the programmed upper rate limit for the pacemaker, but this is often quite far from the patient’s physiological requirement. Worse still, the retrograde atrial activation increases the pulmonary and decreases the systemic pressure. The patient typically suffers from dyspnœa, weakness and dizziness – the pacemaker syndrome13 - as in this case.

It is unusual, even in Canberra, for a patient to have endless loop tachycardia actually recorded on 12-lead ECG on two separate admissions for pacemaker syndrome without even attempting to reprogram the pacemaker itself. Yet, it happened: this patient was discharged home twice without the pacemaker syndrome being recognised by his Cardiologist. Below (Fig 13a) is the ECG from the patient’s first admission, in circus movement tachycardia throughout.