ECC Cardiac Rhythm Recognition & Interpretation 1 — Questions and Answers
Question 1: What is the normal heart rate range for an adult in normal sinus rhythm?
- 40–60 bpm
- 60–100 bpm (Correct answer)
- 100–120 bpm
- 120–160 bpm
Correct answer: 60–100 bpm
Normal sinus rhythm in adults is defined as a heart rate of 60–100 bpm with a regular rhythm and consistent P-wave morphology.
Question 2: Which ECG finding is characteristic of ventricular fibrillation (VF)?
- Regular narrow QRS complexes at 150 bpm
- Chaotic, irregular waveforms with no identifiable QRS complexes (Correct answer)
- Wide QRS complexes at a rate of 150–250 bpm
- Sawtooth flutter waves at 300 bpm
Correct answer: Chaotic, irregular waveforms with no identifiable QRS complexes
Ventricular fibrillation produces disorganized, chaotic electrical activity with no identifiable P waves, QRS complexes, or T waves.
Question 3: What does the PR interval on a 12-lead ECG represent?
- Time for ventricular depolarization
- Time for atrial repolarization only
- Time from onset of atrial depolarization to start of ventricular depolarization (Correct answer)
- Duration of the complete cardiac cycle
Correct answer: Time from onset of atrial depolarization to start of ventricular depolarization
The PR interval spans from the start of the P wave to the beginning of the QRS complex, reflecting conduction from the SA node through the AV node to the bundle of His.
Question 4: A regular narrow-complex tachycardia at 180 bpm with no visible P waves is most consistent with which rhythm?
- Atrial fibrillation
- Supraventricular tachycardia (SVT) (Correct answer)
- Ventricular tachycardia
- Sinus tachycardia
Correct answer: Supraventricular tachycardia (SVT)
SVT typically presents with a regular rate of 150–250 bpm, narrow QRS complexes, and P waves buried within or immediately following the QRS.
Question 5: What is the normal duration of a QRS complex on ECG?
- Less than 0.04 seconds
- 0.06–0.10 seconds (Correct answer)
- 0.12–0.20 seconds
- 0.20–0.30 seconds
Correct answer: 0.06–0.10 seconds
A normal QRS duration of 0.06–0.10 seconds reflects rapid ventricular depolarization via the intact His-Purkinje system.
Question 6: In atrial fibrillation, how is the ventricular response best characterized?
- Regular rhythm with rate of 60–100 bpm
- Irregularly irregular rhythm (Correct answer)
- Regular rhythm with rate greater than 150 bpm
- Regularly irregular rhythm with grouped beats
Correct answer: Irregularly irregular rhythm
Atrial fibrillation produces an irregularly irregular ventricular response because impulses conduct through the AV node randomly.
Question 7: Which ECG finding defines first-degree AV block?
- PR interval greater than 0.20 seconds with all P waves conducted (Correct answer)
- Progressive PR lengthening until a P wave is not conducted
- Fixed 2:1 ratio of P waves to QRS complexes
- Complete dissociation between P waves and QRS complexes
Correct answer: PR interval greater than 0.20 seconds with all P waves conducted
First-degree AV block is characterized by a PR interval exceeding 0.20 seconds (200 ms) with every P wave still successfully conducted to the ventricles.
ECC Cardiac Rhythm Recognition & Interpretation 1
What is the normal heart rate range for an adult in normal sinus rhythm?