Which statement best differentiates oversensing from undersensing?

Which statement best differentiates oversensing from undersensing?

• A. Oversensing inhibits pacing due to sensing of noncardiac signals; undersensing fails to detect depolarization
• B. Oversensing causes tachycardia; undersensing causes bradycardia
• C. Both require lead replacement
• D. Both always result in increased heart rate

Answer: (A)

Sensing in pacing devices can go wrong in two ways that produce opposite problems: oversensing and undersensing. Oversensing happens when the device detects signals that are not real cardiac depolarizations—such as myopotentials, electromagnetic interference, or the T wave—so it mistakes the heart’s activity for already having occurred. The result is pacing inhibition or inappropriate therapy because the device thinks a beat has already happened or that there is a rhythm to treat, which can lead to pauses or mis-timed pacing. Undersensing is when the device fails to pick up the actual depolarizations of the heart, so it doesn’t pace when it’s needed. This can occur with poor lead contact, lead fracture, or low signal amplitude, and it risks bradycardia or pauses because the device doesn’t recognize intrinsic heartbeats that require pacing or therapy. The other statements don’t fit because oversensing isn’t restricted to causing tachycardia, and undersensing isn’t limited to causing bradycardia in every case. Additionally, not all sensing problems require lead replacement—they can often be addressed by reprogramming or troubleshooting—so that option isn’t universally true.

Sensing in pacing devices can go wrong in two ways that produce opposite problems: oversensing and undersensing. Oversensing happens when the device detects signals that are not real cardiac depolarizations—such as myopotentials, electromagnetic interference, or the T wave—so it mistakes the heart’s activity for already having occurred. The result is pacing inhibition or inappropriate therapy because the device thinks a beat has already happened or that there is a rhythm to treat, which can lead to pauses or mis-timed pacing.

Undersensing is when the device fails to pick up the actual depolarizations of the heart, so it doesn’t pace when it’s needed. This can occur with poor lead contact, lead fracture, or low signal amplitude, and it risks bradycardia or pauses because the device doesn’t recognize intrinsic heartbeats that require pacing or therapy.

The other statements don’t fit because oversensing isn’t restricted to causing tachycardia, and undersensing isn’t limited to causing bradycardia in every case. Additionally, not all sensing problems require lead replacement—they can often be addressed by reprogramming or troubleshooting—so that option isn’t universally true.