ECG ECG Interpretation — Questions and Answers
Question 1: What does the P wave on an ECG represent?
- Atrial depolarization (Correct answer)
- Ventricular depolarization
- Atrial repolarization
- Ventricular repolarization
Correct answer: Atrial depolarization
The P wave represents the electrical depolarization spreading through the atria, triggering atrial contraction.
Question 2: A normal PR interval ranges from:
- 0.12 to 0.20 seconds (Correct answer)
- 0.06 to 0.10 seconds
- 0.24 to 0.36 seconds
- 0.40 to 0.60 seconds
Correct answer: 0.12 to 0.20 seconds
The normal PR interval is 0.12-0.20 seconds (3-5 small boxes), representing the time from atrial depolarization to ventricular depolarization.
Question 3: ST segment elevation most commonly indicates:
- Acute myocardial injury (Correct answer)
- Normal variant in all cases
- Chronic heart failure
- Pulmonary embolism
Correct answer: Acute myocardial injury
ST elevation is a hallmark finding of acute myocardial infarction (heart attack), indicating acute injury to the heart muscle.
Question 4: What does the QRS complex represent?
- Ventricular depolarization (Correct answer)
- Atrial depolarization
- Ventricular repolarization
- AV node conduction
Correct answer: Ventricular depolarization
The QRS complex represents the rapid depolarization of both ventricles, triggering ventricular contraction and ejection of blood.
Question 5: What is the standard paper speed for ECG recording?
- 25 mm/sec (Correct answer)
- 50 mm/sec
- 10 mm/sec
- 100 mm/sec
Correct answer: 25 mm/sec
Standard ECG paper speed is 25 mm/second, where each small box represents 0.04 seconds and each large box represents 0.20 seconds.
Question 6: Lead II records electrical activity between which electrodes?
- Right arm and left leg (Correct answer)
- Right arm and left arm
- Left arm and left leg
- Right leg and left arm
Correct answer: Right arm and left leg
Lead II measures the potential difference between the right arm (negative) and left leg (positive), roughly aligned with the heart's electrical axis.
ECG ECG Interpretation
What does the P wave on an ECG represent?