Sensing but not Pacing

Report:

Sinus rhythm 100/min 2

2:1 AV block 3

Left atrial abnormality (LAA) 1

Failure to pace in atrial-sensing pacemaker 3

Prolonged QT interval 0.56” 1

Comment:

The unit is almost certainly a DDD one, with preserved atrial sensing but no ventricular pacing. There is a pacemaker spike after each P wave, with P-V interval about 0.22”. Luckily the patient got by with 2:1 AV block in his native rhythm. The sinus rate 100/min indicates that he may not have been fully comfortable.

The pacing spikes vary considerably in both direction and amplitude, but no inference can be drawn from that: it can still be due to respiratory movement alone. Their AV interval is longer than the PR interval of the conducted sinus beats: 0.26”. This must have been programmed to allow narrow-QRS beats to replace broad paced ones.

Below is another trace, with 1:1 conduction of a slower (71/min) sinus rhythm. The pacemaker responds to the P waves well after the native QRS, producing pseudofusion beats throughout. Whether it could pace at the time remains unknown.

Fig 80a.

Fig 81. The funny-looking beats (FLBs) are of ventricular origin, at 118/min. Or are they?