In the context of pacemakers, what does ‘underpacing’ refer to?

Underpacing refers to a specific scenario in cardiac pacing where the device fails to deliver pacing impulses at the appropriate times, which can result in insufficient stimulation of the heart muscle. This can lead to inadequate heart rates or even the failure to pace the heart when it is necessary, such as during periods of intrinsic electrical activity that fall below a certain threshold. Underpacing is a significant concern because it can compromise the effectiveness of the pacemaker, potentially causing symptoms of bradycardia and other complications related to poor cardiac output.

In contrast, underpacing does not involve pacing too frequently or maintaining an optimal rate. Those scenarios involve pacing that could be either excessive or appropriate, respectively, but underpacing specifically addresses the failure to provide pacing when it is actually required to maintain a safe and effective heart rhythm.