Pacemaker Syndrome: Paced Bigeminy

Report:

Pacemaker rhythm 71/min 1

AV sequential (probably DDD) pacemaker 2

Reentry paced beats of pacemaker origin 5

Bigeminy 1

No evidence of paced atrial capture 1

Comment:

The trace should be compared to the previous one, where each atrial pacing spike is followed by a P wave. In this patient, not only is the atrial transport absent, but retrograde conduction from the ventricles may be causing hæmodynamically costly cannon waves from the atria. The retrograde impulses can be seen notching the ST segments just at the onset of the T waves. The VA interval (from pacemaker spike to onset of retrograde P wave) is approximately 0.22”.

The ventricular contraction may also be compromised during ventricular pacing; the slight impairment is due to disordered contraction sequence - replicating a native LBBB conduction - seen echocardiographically as paradoxical septal movement. In borderline patients this alone may be significant enough to precipitate overt heart failure.

The DDD unit thus functions as a VVI one in this patient; she in fact had the pacemaker syndrome20. Attempts to produce atrial capture by increasing the output and converting the atrial lead to a unipolar one (observe higher voltages than in an earlier tracing, below) were unsuccessful. The paced bigeminy occurs because the pacemaker is programmed to track atrial P waves - and it does precisely that. The only problem is that the only atrial waves are the retrograde ones. The bigeminal sequence involves the atria and the ventricles and is equivalent to any bigeminy due to reentry beats of ventricular origin - a pseudoreentry, to coin a phrase! Unlike true reentry, this variety has an atrial electrode for its returning limb21.[!xe "Pacemaker syndrome" \t "See Pacemaker, electronic"!]

Fig 27a below shows “straight” pacemaker rhythm with 1:1 retrograde conduction, but no reentry.

Fig 27a. Still no atrial capture, but retrograde conduction with every beat.

Fig 28. 80 year old lady with discreet bigeminy.