CCRN Cardiac Rhythm Interpretation and Management 1 — Questions and Answers
Question 1: An ICU patient's monitor shows a regular rhythm at 150 bpm with narrow QRS complexes and a classic sawtooth baseline pattern. What is the most likely rhythm?
- Sinus tachycardia
- Atrial flutter with 2:1 block (Correct answer)
- Junctional tachycardia
- Atrial fibrillation
Correct answer: Atrial flutter with 2:1 block
Atrial flutter typically fires at 300 bpm; with 2:1 block the ventricular rate is 150 bpm, and the sawtooth (flutter) waves are the hallmark finding.
Question 2: Which ECG change is the earliest indicator of hyperkalemia in a critically ill patient?
- Widened QRS complex
- Sine wave pattern
- Peaked (tall, narrow) T waves (Correct answer)
- Flat or absent P waves
Correct answer: Peaked (tall, narrow) T waves
Peaked T waves are the earliest ECG manifestation of hyperkalemia, appearing before PR prolongation, QRS widening, or the sine wave pattern seen in severe cases.
Question 3: Which ECG characteristic definitively identifies a third-degree (complete) AV block?
- PR interval consistently greater than 0.20 seconds
- Progressive PR prolongation followed by a dropped QRS complex
- Completely independent atrial and ventricular rates with no relationship (Correct answer)
- Alternating conducted and non-conducted P waves
Correct answer: Completely independent atrial and ventricular rates with no relationship
In complete heart block, the atria and ventricles fire independently because no impulses conduct through the AV node, producing dissociated P waves and QRS complexes.
Question 4: A normal PR interval on a standard ECG measures:
- 0.06–0.10 seconds
- 0.12–0.20 seconds (Correct answer)
- 0.20–0.24 seconds
- 0.24–0.30 seconds
Correct answer: 0.12–0.20 seconds
The normal PR interval ranges from 0.12 to 0.20 seconds (3–5 small boxes); values above 0.20 indicate first-degree AV block.
Question 5: A patient's rhythm strip shows an irregularly irregular ventricular response, absent distinct P waves, and an estimated atrial activity rate of 400–600 bpm. What is this rhythm?
- Atrial flutter
- Multifocal atrial tachycardia
- Junctional tachycardia
- Atrial fibrillation (Correct answer)
Correct answer: Atrial fibrillation
Atrial fibrillation is characterized by chaotic atrial activity at 400–600 bpm, absent organized P waves, and an irregularly irregular ventricular response.
Question 6: What is the normal range for QRS complex duration in an adult?
- Less than 0.06 seconds
- 0.06–0.12 seconds (Correct answer)
- 0.12–0.16 seconds
- 0.16–0.20 seconds
Correct answer: 0.06–0.12 seconds
A normal QRS duration is 0.06–0.12 seconds; a QRS wider than 0.12 seconds indicates intraventricular conduction delay such as bundle branch block or ventricular origin.
Question 7: Which ECG finding most strongly differentiates ventricular tachycardia from supraventricular tachycardia with aberrant conduction?
- Heart rate greater than 150 bpm
- Hemodynamic instability in the patient
- Left bundle branch block morphology of the QRS
- AV dissociation visible on the rhythm strip (Correct answer)
Correct answer: AV dissociation visible on the rhythm strip
AV dissociation — independent P waves unrelated to QRS complexes — is pathognomonic for ventricular tachycardia and cannot occur with SVT.
