CMT Pacemaker Monitoring and Function 2 — Questions and Answers
Question 1: A cardiac monitor technician observes that the pacemaker is not firing even though the patient's heart rate has dropped below the programmed lower rate limit. This is most consistent with:
- Failure to capture
- Failure to sense (undersensing)
- Failure to pace (oversensing) (Correct answer)
- Normal pacemaker inhibition
Correct answer: Failure to pace (oversensing)
Oversensing causes the pacemaker to incorrectly detect non-cardiac signals as native beats, inappropriately inhibiting pacing output.
Question 2: A pacemaker rhythm strip shows pacemaker spikes occurring in competition with the patient's own intrinsic beats. This pattern suggests:
- Failure to capture
- Failure to sense (undersensing) (Correct answer)
- Pacemaker-mediated tachycardia
- Rate modulation response
Correct answer: Failure to sense (undersensing)
Undersensing occurs when the pacemaker fails to detect the patient's own intrinsic electrical activity, causing it to fire inappropriately.
Question 3: What is pacemaker-mediated tachycardia (PMT)?
- A tachycardia triggered when the magnet rate exceeds 100 bpm
- A reentrant tachycardia in dual-chamber pacemakers triggered by retrograde P waves (Correct answer)
- Rapid pacing caused by a depleted pacemaker battery
- Tachycardia resulting from pacemaker oversensing of T waves
Correct answer: A reentrant tachycardia in dual-chamber pacemakers triggered by retrograde P waves
PMT is a reentrant loop in dual-chamber pacemakers where retrograde atrial conduction from a ventricular beat is sensed, triggering continuous ventricular pacing.
Question 4: Which finding on a rhythm strip would MOST likely indicate pacemaker battery depletion?
- Pacing rate increases above programmed rate
- Pacing rate drops or converts to backup (EOL) rate (Correct answer)
- Pacemaker spikes disappear entirely
- QRS complexes become progressively narrower
Correct answer: Pacing rate drops or converts to backup (EOL) rate
As pacemaker battery approaches end-of-life (EOL), the pacing rate typically drops to a manufacturer-designated elective replacement indicator (ERI) rate.
Question 5: In a dual-chamber pacemaker, what does the programmed AV delay (AV interval) simulate?
- The time between two ventricular paced beats
- The normal PR interval seen in sinus rhythm (Correct answer)
- The refractory period of the atrial lead
- The upper rate limit behavior
Correct answer: The normal PR interval seen in sinus rhythm
The programmed AV delay mimics the natural PR interval, allowing appropriate time for atrial emptying before ventricular contraction to preserve AV synchrony.
Question 6: What does the term 'lower rate limit' refer to in pacemaker programming?
- The minimum sensing threshold for intrinsic beats
- The slowest rate at which the pacemaker will allow the heart to fall before pacing (Correct answer)
- The battery voltage required to activate pacing
- The minimum AV delay setting
Correct answer: The slowest rate at which the pacemaker will allow the heart to fall before pacing
The lower rate limit (LRL) is the programmed rate below which the pacemaker will fire to prevent bradycardia.
Question 7: What is the primary purpose of a rate-responsive (DDDR or VVIR) pacemaker?
- To pace faster than the programmed upper rate limit
- To automatically increase pacing rate in response to physical activity (Correct answer)
- To switch between atrial and ventricular pacing as needed
- To detect and treat ventricular fibrillation
Correct answer: To automatically increase pacing rate in response to physical activity
Rate-responsive pacemakers use sensors (e.g., accelerometer or minute ventilation) to increase pacing rate during physical activity to match metabolic demand.
CMT Pacemaker Monitoring and Function 2
A cardiac monitor technician observes that the pacemaker is not firing even though the patient's heart rate has dropped below the programmed lower rate limit.
This is most consistent with: