Failure to Pace

Failure to pace is usually divided into failure of output or failure to capture. In these dysfunctions, the pacemaker appropriately does not sense adequate native conduction; however, it does not provide the artificial stimulus for depolarization.

Output failure is when there is decreased or absent pacemaker function. In other words, the pacemaker does not attempt to provide adequate artificial electrical activity. There can be many reasons for this, including oversensing (most common), wire displacement (ie Twiddler's syndrome) or fracture, dead battery, or interference. The EKG will show inadequate native electrical activity (commonly the rhythm that was the indication for the pacemaker in the first place-ie 3* AV block) without any pacemaker spikes.

Failure to capture is a form of pacemaker dysfunction where the pacemaker appropriately does not sense adequate native conduction and attempts to provide a depolarization, but the pacemaker's firing does not result in myocardial depolarization. There are, again, many potential causes for this, including lead displacement, wire fracture, electrolyte disturbance, MI, or fibrosis around the lead tip (ie scar tissue).

One important point to differentiate is if the patient truly has failure to pace. If the patient has adequate native electrical activity, there is no 'pacemaker failure'; the pacemaker is following its programming to not fire when the patient's heart is able to carry out adequate depolarization. The computer sometimes reads these EKG's as pacemaker failure, though this is simply not true.

Further Reading:

https://litfl.com/pacemaker-malfunction-ecg-library/

http://hqmeded-ecg.blogspot.com/search/label/pacing

https://rebelem.com/pacemaker-basics/