A pacemaker tracing shows pacing spikes with no subsequent P waves or QRS complexes. How is this condition best described?

A pacemaker tracing shows pacing spikes with no subsequent P waves or QRS complexes. How is this condition best described?

• A. Oversensing
• B. Undersensing
• C. Failure to pace
• D. Failure to capture

Answer: (D)

When a pacemaker delivers an impulse but the heart tissue does not respond with depolarization, you’re seeing a failure to capture. On the tracing, a pacing spike with no subsequent P wave or QRS complex means the impulse didn’t induce atrial or ventricular contraction. This is different from failure to pace (no pacing spike when one is expected) or sensing issues like oversensing/undersensing that alter when pacing occurs. Causes of capture failure include lead problems (dislodgement, fracture, poor contact), high capture thresholds from ischemia or electrolyte disturbances, or insufficient pacemaker output. Management focuses on ensuring a good lead connection, assessing lead integrity, increasing output or adjusting thresholds if appropriate, and addressing any underlying conditions that raise the capture threshold.

When a pacemaker delivers an impulse but the heart tissue does not respond with depolarization, you’re seeing a failure to capture. On the tracing, a pacing spike with no subsequent P wave or QRS complex means the impulse didn’t induce atrial or ventricular contraction. This is different from failure to pace (no pacing spike when one is expected) or sensing issues like oversensing/undersensing that alter when pacing occurs. Causes of capture failure include lead problems (dislodgement, fracture, poor contact), high capture thresholds from ischemia or electrolyte disturbances, or insufficient pacemaker output. Management focuses on ensuring a good lead connection, assessing lead integrity, increasing output or adjusting thresholds if appropriate, and addressing any underlying conditions that raise the capture threshold.