Report:

Pacemaker rhythm 1

Variable rate 1

First degree AV (0.2 - 0.4”) and VA (0.47 - 0.51”) block 1

Bigeminy due to reentry (echo) beats of pacemaker origin 6

Ventricular conduction delay (unspecified) 1

Comment:

All the complexes shown - atrial and ventricular - are of pacemaker origin34! At first, one would assume the presence of typical escape-capture bigeminy, a rhythm commonly associated with electronic pacemakers set at slow rates. This would, however, dissipate if the pacemaker rate were changed. In this case, it did not. The native complexes remained “married” to the paced ones, albeit with different RP and PR intervals. Note the reciprocal relationship between these intervals.

It is always uncertain whether the atrium actually participates in the reentry circuit. It probably does in this case, but atrial depolarisation is certainly not necessary for the echo circuit: it could go through the AV junction alone.

After the PAT with block on admission and the reciprocal rhythm shown above, the patient continued to oblige when his pacemaker was turned off (Fig 55a). There were episodes of sinus bradycardia and arrest, with junctional escape. The remarkable thing was that all the escape beats produced reentry, with LBBB aberrancy in their echo beats – almost a mirror image of what happened during ventricular pacing! Sinus beats never produced an echo, the P wave stopping retrograde conduction through the AV bode.