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Ventricular Sensing failure

Patient

An 81-year-old asymptomatic woman underwent implantation of an Adapta dual chamber pacemaker for management of atrial disease, which evolved toward well controlled chronic AF; programming in VVIR mode at 60-120 bpm; she was seen on routine follow-up.


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Trace

The first channel is lead III of the surface ECG with the markers superimposed, the second shows the ventricular EGM and the third is lead II with the intervals superimposed;

  1. ventricular event not sensed despite appropriate amplitude on the ventricular EGM channel; ventricular pacing in the vulnerable period of the previous QRS and effective ventricular capture;
  2. rate responsive ventricular pacing;
  3. re-emergence of spontaneous, non-sensed ventricular events with pacing at regular intervals;
  4. further pacing in the vulnerable period without capture.

Comments

This tracing shows ventricular undersensing due to faulty programming. The bipolar ventricular EGM measured 3.8 mV, and the device was programmed with a 5-mV sensitivity. In absence of proper sensing, the pacemaker operates as in VOO mode, with no inhibition by the spontaneous ventricular events, as they are not sensed.
In these circumstances 1) a large amount of energy is expended unnecessarily (ventricular pacing without capture or with useless and dangerous capture) 2) it creates a risk of proarrhythmia when the ventricle is paced during the vulnerable period. Programming of an appropriate sensitivity rectified the problem.

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