CVT Cardiac Rhythm Management Devices 2 — Questions and Answers
Question 1: Which pacemaker parameter defines the minimum interval between a sensed or paced event and the next pacing output?
- Refractory period (Correct answer)
- Lower rate limit
- AV delay
- Upper rate limit
Correct answer: Refractory period
The refractory period prevents the pacemaker from responding to signals (such as T-waves) immediately after a paced or sensed event.
Question 2: In a dual-chamber pacemaker, what occurs during crosstalk inhibition?
- The atrial output inhibits the ventricular channel, causing ventricular asystole
- The ventricular lead senses atrial pacing output and inhibits ventricular pacing (Correct answer)
- Both chambers pace simultaneously
- The device switches to VOO mode
Correct answer: The ventricular lead senses atrial pacing output and inhibits ventricular pacing
Crosstalk occurs when the ventricular sensing channel detects the atrial pacing stimulus, potentially inhibiting ventricular output and causing dangerous pauses.
Question 3: Which ICD therapy is delivered first in a standard tiered-therapy protocol for ventricular fibrillation?
- Antitachycardia pacing (ATP)
- Synchronized cardioversion at low energy
- High-energy defibrillation shock (Correct answer)
- Overdrive suppression pacing
Correct answer: High-energy defibrillation shock
Ventricular fibrillation is not amenable to ATP or synchronized cardioversion, so devices deliver high-energy unsynchronized defibrillation as first-line therapy.
Question 4: A patient's ICD interrogation shows 'T-wave oversensing.' What is the most likely consequence?
- Failure to sense VF
- Inappropriate shock delivery (Correct answer)
- Pacemaker-mediated tachycardia
- Loss of capture
Correct answer: Inappropriate shock delivery
T-wave oversensing causes the device to double-count cardiac events, potentially satisfying tachycardia detection criteria and delivering inappropriate therapy.
Question 5: What does the term 'cardiac resynchronization therapy (CRT)' specifically aim to correct?
- Sinus node dysfunction
- Interventricular and intraventricular mechanical dyssynchrony (Correct answer)
- Atrioventricular block
- Atrial fibrillation with rapid ventricular response
Correct answer: Interventricular and intraventricular mechanical dyssynchrony
CRT uses biventricular pacing to resynchronize the contraction of the left and right ventricles, improving cardiac output in patients with heart failure and conduction delay.
Question 6: Which radiographic finding on chest X-ray suggests a right ventricular lead perforation?
- Lead tip projecting beyond the cardiac silhouette into the lung field (Correct answer)
- Lead tip at the RV apex with normal curvature
- Lead tip at the coronary sinus
- Lead tip at the superior vena cava junction
Correct answer: Lead tip projecting beyond the cardiac silhouette into the lung field
Perforation is suggested when the lead tip projects beyond the cardiac border, indicating penetration through the myocardium into the pericardial space or beyond.
Question 7: During threshold testing, pacing at 2× the chronic threshold is recommended to ensure what safety margin?
- Prevention of pacemaker syndrome
- Adequate capture with tolerance for lead maturation impedance changes (Correct answer)
- Avoidance of diaphragmatic stimulation
- Prevention of oversensing
Correct answer: Adequate capture with tolerance for lead maturation impedance changes
Programming output at 2× the pacing threshold provides a safety margin to maintain capture despite the normal rise in threshold that occurs during lead maturation (weeks post-implant).
CVT Cardiac Rhythm Management Devices 2
Which pacemaker parameter defines the minimum interval between a sensed or paced event and the next pacing output?