Failure to Sense (Undersensing) — ECG Academy Lesson

Recognize failure to sense (undersensing) — the pacemaker fails to detect native cardiac activity and delivers pacing stimuli at inappropriate times. Learn to identify the dangerous pattern of spikes landing near native beats, understand the R-on-T risk, and respond appropriately.

Learning Objectives

• Define failure to sense (undersensing) and explain the underlying mechanism
• Identify the hallmark ECG pattern: pacemaker spikes at inappropriate times relative to native beats
• Explain the R-on-T phenomenon and why undersensing can trigger ventricular tachycardia or fibrillation
• List the most common causes of undersensing
• Describe the appropriate monitor tech response to undersensing
• Differentiate undersensing from failure to capture and failure to pace (oversensing)