CCS Cardiac Rhythm Interpretation & ECG Analysis 1 — Questions and Answers
Question 1: What is the normal PR interval on a standard 12-lead ECG?
- 0.04–0.08 seconds
- 0.12–0.20 seconds (Correct answer)
- 0.25–0.35 seconds
- 0.06–0.10 seconds
Correct answer: 0.12–0.20 seconds
The normal PR interval is 0.12–0.20 seconds, representing the time for an impulse to travel from the SA node through the AV node to the ventricles.
Question 2: Which ECG finding is characteristic of first-degree AV block?
- Dropped QRS complexes following P waves
- Progressive PR interval lengthening until a QRS is dropped
- Consistently prolonged PR interval greater than 0.20 seconds with all P waves conducted (Correct answer)
- Complete dissociation between P waves and QRS complexes
Correct answer: Consistently prolonged PR interval greater than 0.20 seconds with all P waves conducted
First-degree AV block is defined by a PR interval consistently >0.20 seconds, with every P wave still successfully conducted to the ventricles.
Question 3: What heart rate range defines sinus bradycardia in an adult?
- Less than 40 bpm
- Less than 60 bpm (Correct answer)
- 40–50 bpm only
- Less than 50 bpm
Correct answer: Less than 60 bpm
Sinus bradycardia is defined as a sinus rhythm with a heart rate less than 60 beats per minute originating from the SA node.
Question 4: On a standard ECG, what physiologic event does the QRS complex represent?
- Atrial depolarization
- Ventricular repolarization
- Ventricular depolarization (Correct answer)
- AV nodal conduction delay
Correct answer: Ventricular depolarization
The QRS complex represents ventricular depolarization, which triggers the mechanical contraction of both ventricles.
Question 5: What is the normal QRS duration on an ECG?
- 0.04–0.08 seconds
- 0.12–0.20 seconds
- 0.06–0.10 seconds (Correct answer)
- 0.20–0.40 seconds
Correct answer: 0.06–0.10 seconds
Normal QRS duration is 0.06–0.10 seconds (60–100 ms); a duration ≥0.12 seconds suggests a bundle branch block or ventricular origin.
Question 6: Which rhythm is characterized by an irregularly irregular ventricular response with no discernible P waves?
- Atrial flutter
- Atrial fibrillation (Correct answer)
- Junctional tachycardia
- Multifocal atrial tachycardia
Correct answer: Atrial fibrillation
Atrial fibrillation presents with an irregularly irregular ventricular rhythm and absent or chaotic P waves due to disorganized atrial electrical activity.
Question 7: What does the T wave on a surface ECG represent?
- Atrial depolarization
- Atrial repolarization
- Ventricular depolarization
- Ventricular repolarization (Correct answer)
Correct answer: Ventricular repolarization
The T wave represents ventricular repolarization, the electrical recovery phase of the ventricles in preparation for the next contraction.
CCS Cardiac Rhythm Interpretation & ECG Analysis 1
What is the normal PR interval on a standard 12-lead ECG?