ECG ECG Waveform Measurements and Intervals 2 — Questions and Answers
Question 1: How many small squares represent 0.04 seconds at standard ECG paper speed (25 mm/sec)?
- 1 small square (Correct answer)
- 2 small squares
- 5 small squares
- 10 small squares
Correct answer: 1 small square
At 25 mm/sec, each small square is 1 mm wide = 0.04 seconds, so 1 small square = 0.04 sec.
Question 2: Which measurement in the ECG is most commonly used to detect left ventricular hypertrophy?
- PR interval duration
- QRS voltage amplitude in precordial leads (Sokolow-Lyon criteria) (Correct answer)
- T-wave height
- P-wave duration
Correct answer: QRS voltage amplitude in precordial leads (Sokolow-Lyon criteria)
The Sokolow-Lyon criteria (S in V1 + R in V5 or V6 ≥35 mm) uses QRS voltage amplitude to suggest left ventricular hypertrophy.
Question 3: ST elevation ≥1 mm in two contiguous leads is significant because it suggests:
- Bundle branch block
- Acute myocardial infarction (STEMI) until proven otherwise (Correct answer)
- Normal variant
- Pericarditis with diffuse changes only
Correct answer: Acute myocardial infarction (STEMI) until proven otherwise
ST elevation ≥1 mm in two or more contiguous leads is the hallmark ECG finding of STEMI (ST-elevation myocardial infarction), requiring urgent intervention.
Question 4: The normal axis of the QRS complex in adults falls between:
- -90° to -30°
- -30° to +90° (Correct answer)
- +90° to +180°
- 0° to +30° only
Correct answer: -30° to +90°
Normal QRS axis is -30° to +90°, reflecting the predominant left and inferior direction of ventricular depolarization through the His-Purkinje system.
Question 5: A delta wave on the ECG is associated with:
- Left bundle branch block
- Wolff-Parkinson-White (WPW) syndrome pre-excitation (Correct answer)
- Hyperkalemia
- Right ventricular hypertrophy
Correct answer: Wolff-Parkinson-White (WPW) syndrome pre-excitation
A delta wave is the slurred upstroke at the start of the QRS caused by accessory pathway pre-excitation in WPW syndrome, bypassing the AV node.
Question 6: T-wave inversion in leads V1–V4 in an adult is most concerning for:
- Normal variant
- Anterior ischemia or right heart strain (Correct answer)
- First-degree AV block
- Atrial enlargement
Correct answer: Anterior ischemia or right heart strain
T-wave inversions in the anterior precordial leads (V1–V4) can indicate anterior wall ischemia, non-STEMI, or right ventricular strain and require clinical correlation.
ECG ECG Waveform Measurements and Intervals 2
How many small squares represent 0.04 seconds at standard ECG paper speed (25 mm/sec)?