CVT Cardiac Rhythm Management Devices 3 — Questions and Answers
Question 1: A CRT device shows less than 98% biventricular pacing on follow-up. What is the most appropriate first intervention?
- Upgrade to a subcutaneous ICD
- Optimize AV delay and manage causes of native conduction (e.g., AF) (Correct answer)
- Replace the left ventricular lead
- Increase lower rate limit above the patient's intrinsic rate
Correct answer: Optimize AV delay and manage causes of native conduction (e.g., AF)
Maximizing biventricular pacing percentage—by programming AV delay shorter than intrinsic PR and treating AF that competes with pacing—is the first step before hardware revision.
Question 2: The subcutaneous ICD (S-ICD) is contraindicated in patients who require what function?
- Rate-responsive pacing
- Antitachycardia pacing or bradycardia pacing support (Correct answer)
- Remote monitoring
- High-energy defibrillation
Correct answer: Antitachycardia pacing or bradycardia pacing support
Because the S-ICD has no transvenous leads, it cannot provide antitachycardia pacing or chronic bradycardia pacing, limiting its use to patients with no pacing indication.
Question 3: Magnet application to a permanent pacemaker in a non-dependent patient typically results in which response?
- Asynchronous pacing at a fixed magnet rate (Correct answer)
- Complete inhibition of pacing output
- Device reset to factory settings
- ICD therapies enabled at maximum energy
Correct answer: Asynchronous pacing at a fixed magnet rate
Magnet application causes most pacemakers to switch to asynchronous (AOO, VOO, or DOO) pacing at a manufacturer-specific magnet rate, bypassing sensing functions.
Question 4: Which electrogram (EGM) characteristic best distinguishes supraventricular tachycardia (SVT) from VT in a dual-chamber ICD?
- Atrial rate slower than ventricular rate
- Atrial rate equal to or faster than ventricular rate with 1:1 AV relationship at onset (Correct answer)
- Ventricular EGM width narrower than 120 ms
- Presence of retrograde P-waves only
Correct answer: Atrial rate equal to or faster than ventricular rate with 1:1 AV relationship at onset
When the atrial rate meets or exceeds the ventricular rate with a 1:1 relationship, SVT is favored; VT typically shows VA dissociation or slower atrial rate than ventricular rate.
Question 5: What is the primary purpose of the post-ventricular atrial refractory period (PVARP) in a dual-chamber pacemaker?
- To prevent sensing of far-field R-waves on the atrial channel (Correct answer)
- To allow tracking of rapid atrial rates
- To extend the AV delay after ventricular pacing
- To prevent atrial pacing during the ventricular vulnerable period
Correct answer: To prevent sensing of far-field R-waves on the atrial channel
PVARP prevents the atrial channel from sensing the ventricular event or its far-field signal, thereby avoiding pacemaker-mediated tachycardia and inappropriate tracking.
Question 6: A patient with a transvenous ICD develops recurrent inappropriate shocks due to atrial fibrillation with rapid ventricular response. Which programming change is most appropriate?
- Decrease the VF detection rate
- Increase the VT/VF detection interval (number of intervals to detect) (Correct answer)
- Enable 'all therapies off' mode
- Shorten the ventricular refractory period
Correct answer: Increase the VT/VF detection interval (number of intervals to detect)
Increasing the number of intervals required to confirm tachycardia (NID) reduces inappropriate therapy by allowing time for spontaneous AF rate slowing or discrimination algorithms to operate.
Question 7: Impedance trending for an ICD lead shows a sudden rise from 500 Ω to >2000 Ω. This most likely indicates:
- Lead fracture or insulation breach near the connector (Correct answer)
- Normal post-implant threshold maturation
- Increased fluid around the lead
- Cardiac perforation
Correct answer: Lead fracture or insulation breach near the connector
A sudden, marked increase in impedance typically signals a lead fracture or conductor discontinuity, which can also cause oversensing and inappropriate shocks.
CVT Cardiac Rhythm Management Devices 3
A CRT device shows less than 98% biventricular pacing on follow-up.
What is the most appropriate first intervention?