DC Dysrhythmia ECG Monitoring & Analysis 2 — Questions and Answers
Question 1: On a rhythm strip, the PR interval measures 0.28 seconds. This finding is most consistent with:
- First-degree AV block (Correct answer)
- Second-degree AV block Type I
- Third-degree AV block
- Normal conduction
Correct answer: First-degree AV block
A PR interval greater than 0.20 seconds indicates first-degree AV block, which is a consistent prolongation without dropped beats.
Question 2: A patient's ECG shows P waves that progressively lengthen their PR intervals until a QRS is dropped, then the cycle repeats. This pattern describes:
- Mobitz Type I (Wenckebach) (Correct answer)
- Mobitz Type II
- Complete heart block
- Junctional escape rhythm
Correct answer: Mobitz Type I (Wenckebach)
Progressive PR prolongation followed by a non-conducted P wave is the hallmark of Mobitz Type I (Wenckebach) second-degree AV block.
Question 3: Which ECG finding best differentiates ventricular tachycardia from supraventricular tachycardia with aberrant conduction?
- AV dissociation (Correct answer)
- Heart rate above 150 bpm
- Wide QRS complex
- ST segment depression
Correct answer: AV dissociation
AV dissociation, where P waves and QRS complexes fire independently, is the most reliable ECG differentiator of ventricular tachycardia.
Question 4: A rhythm strip shows no identifiable P waves, an irregularly irregular ventricular response, and a rate of 110 bpm. The most likely diagnosis is:
- Atrial flutter with variable block
- Atrial fibrillation (Correct answer)
- Multifocal atrial tachycardia
- Junctional tachycardia
Correct answer: Atrial fibrillation
Absent P waves with an irregularly irregular ventricular rate are the classic hallmarks of atrial fibrillation.
Question 5: The QT interval on a rhythm strip should be corrected for heart rate using Bazett's formula. A corrected QT (QTc) greater than what value is considered prolonged in adults?
- 0.36 seconds
- 0.44 seconds (Correct answer)
- 0.52 seconds
- 0.60 seconds
Correct answer: 0.44 seconds
A QTc exceeding 0.44 seconds (440 ms) is generally considered prolonged and associated with increased risk of torsades de pointes.
Question 6: During continuous ECG monitoring, you observe a pause of 3.2 seconds following a P wave with no subsequent QRS. Which conduction problem does this most likely represent?
- Sinus arrest
- Second-degree AV block Mobitz II (Correct answer)
- First-degree AV block
- Bundle branch block
Correct answer: Second-degree AV block Mobitz II
A sudden dropped QRS after a non-prolonged PR interval, especially with a long pause, is characteristic of Mobitz Type II second-degree AV block.
Question 7: A fusion beat on an ECG strip is significant because it indicates:
- Dual pacemaker activity with simultaneous ventricular activation (Correct answer)
- Complete failure of the SA node
- Junctional escape mechanism
- Normal variant in athletes
Correct answer: Dual pacemaker activity with simultaneous ventricular activation
A fusion beat occurs when a supraventricular and ventricular impulse simultaneously depolarize the ventricles, producing a hybrid QRS morphology.
DC Dysrhythmia ECG Monitoring & Analysis 2
On a rhythm strip, the PR interval measures 0.28 seconds.
This finding is most consistent with: