CRAT ECG Waveform Measurements and Intervals 1 — Questions and Answers
Question 1: What is the normal duration of the PR interval on a standard ECG?
- 0.06–0.10 seconds
- 0.12–0.20 seconds (Correct answer)
- 0.22–0.30 seconds
- 0.30–0.40 seconds
Correct answer: 0.12–0.20 seconds
The normal PR interval ranges from 0.12 to 0.20 seconds (3–5 small squares).
Question 2: On standard ECG paper, one large square represents how many seconds?
- 0.04 seconds
- 0.10 seconds
- 0.20 seconds (Correct answer)
- 0.40 seconds
Correct answer: 0.20 seconds
One large square on standard ECG paper equals 0.20 seconds (200 ms) at the standard paper speed of 25 mm/sec.
Question 3: A QRS complex measuring 0.14 seconds is considered:
- Normal
- Slightly prolonged
- Wide or abnormal (Correct answer)
- Absent
Correct answer: Wide or abnormal
A QRS duration greater than 0.12 seconds is considered wide and suggests a bundle branch block or ventricular origin.
Question 4: The QT interval is measured from:
- Start of P wave to end of T wave
- Start of Q wave to end of T wave (Correct answer)
- Start of QRS to peak of T wave
- End of QRS to start of T wave
Correct answer: Start of Q wave to end of T wave
The QT interval is measured from the beginning of the QRS complex to the end of the T wave and represents total ventricular depolarization and repolarization.
Question 5: Which waveform on the ECG represents ventricular repolarization?
- P wave
- QRS complex
- T wave (Correct answer)
- U wave
Correct answer: T wave
The T wave represents ventricular repolarization — the recovery phase of the ventricles after contraction.
Question 6: A corrected QT (QTc) interval greater than 500 ms is clinically significant because it:
- Indicates a first-degree AV block
- Signals atrial fibrillation
- Increases the risk of Torsades de Pointes (Correct answer)
- Indicates a normal variant
Correct answer: Increases the risk of Torsades de Pointes
A prolonged QTc >500 ms significantly increases the risk of Torsades de Pointes, a potentially fatal ventricular arrhythmia.
CRAT ECG Waveform Measurements and Intervals 1
What is the normal duration of the PR interval on a standard ECG?