DC Cardiac Pacemaker Therapy & Management 2 — Questions and Answers
Question 1: Which ECG finding is most consistent with pacemaker failure to capture?
- Pacemaker spikes followed by wide QRS complexes
- Pacemaker spikes with no following QRS complex (Correct answer)
- Absence of pacemaker spikes despite bradycardia
- Pacemaker spikes occurring at irregular intervals
Correct answer: Pacemaker spikes with no following QRS complex
Failure to capture is identified on ECG by pacemaker spikes that are not followed by a QRS complex, indicating the stimulus failed to depolarize the myocardium.
Question 2: A demand pacemaker fires during periods of adequate intrinsic heart rate. This finding most likely indicates:
- Failure to capture
- Oversensing
- Failure to sense (undersensing) (Correct answer)
- Pacemaker-mediated tachycardia
Correct answer: Failure to sense (undersensing)
Undersensing occurs when the pacemaker fails to detect intrinsic cardiac activity, causing it to fire inappropriately and compete with the patient's own rhythm.
Question 3: Oversensing in a permanent pacemaker most commonly results in:
- Inappropriate pacing at an accelerated rate
- Inhibition of pacing, potentially causing symptomatic bradycardia (Correct answer)
- Loss of AV synchrony
- Upper rate limit behavior
Correct answer: Inhibition of pacing, potentially causing symptomatic bradycardia
Oversensing causes the pacemaker to misinterpret non-cardiac signals (e.g., T-waves, myopotentials) as intrinsic events and inhibit its output, which can lead to pauses or bradycardia.
Question 4: What is the most common cause of pacemaker failure to capture in the early post-implant period?
- Battery depletion
- Electromagnetic interference
- Lead dislodgement (Correct answer)
- Oversensing of T-waves
Correct answer: Lead dislodgement
Lead dislodgement is the most common cause of failure to capture in the early post-implant period, as leads are not yet fully anchored in the myocardium.
Question 5: Pacemaker-mediated tachycardia (PMT) in a dual-chamber pacemaker is caused by:
- Electromagnetic interference triggering rapid pacing
- Battery depletion causing erratic pacing behavior
- Retrograde atrial activation being sensed and triggering repetitive ventricular pacing (Correct answer)
- Lead fracture producing repetitive electrical signals
Correct answer: Retrograde atrial activation being sensed and triggering repetitive ventricular pacing
PMT occurs when ventricular pacing causes retrograde conduction to the atria; the atrial lead senses this signal and triggers another ventricular pace, creating a reentrant loop.
Question 6: A chest X-ray is most useful in evaluating which pacemaker malfunction?
- Battery depletion
- Undersensing due to low-amplitude signals
- Lead displacement or fracture (Correct answer)
- Oversensing of skeletal muscle potentials
Correct answer: Lead displacement or fracture
Chest X-ray can directly visualize lead position and integrity, making it the most useful initial test for suspected lead displacement or fracture.
Question 7: A pacemaker-dependent patient experiences repeated pauses due to oversensing of myopotentials. The most appropriate programming change is to:
- Increase the pacing rate
- Decrease sensitivity by increasing the sensing threshold (mV) (Correct answer)
- Increase sensitivity by decreasing the sensing threshold (mV)
- Shorten the refractory period
Correct answer: Decrease sensitivity by increasing the sensing threshold (mV)
Decreasing sensitivity (increasing the mV threshold) makes the pacemaker less responsive to low-amplitude signals like skeletal muscle potentials, preventing inappropriate inhibition.
DC Cardiac Pacemaker Therapy & Management 2
Which ECG finding is most consistent with pacemaker failure to capture?