CET 12-Lead ECG Interpretation 2 — Questions and Answers
Question 1: Which leads form the precordial (chest) leads on a standard 12-lead ECG?
- I, II, III, aVR, aVL, aVF
- V1 through V6 (Correct answer)
- aVR, aVL, and aVF only
- V1, V2, V3, and V4 only
Correct answer: V1 through V6
The precordial leads are V1 through V6, placed across the chest to view the heart in the horizontal plane.
Question 2: In a 12-lead ECG, what does a left axis deviation (LAD) most commonly indicate?
- Right ventricular hypertrophy
- Left anterior fascicular block (Correct answer)
- Right bundle branch block
- Hyperkalemia
Correct answer: Left anterior fascicular block
Left anterior fascicular block is the most common cause of left axis deviation, shifting the QRS axis to between -30° and -90°.
Question 3: ST elevation in leads V1–V4 is most consistent with which type of STEMI?
- Inferior STEMI
- Lateral STEMI
- Anterior STEMI (Correct answer)
- Posterior STEMI
Correct answer: Anterior STEMI
Leads V1–V4 overlie the anterior wall of the left ventricle, so ST elevation there indicates an anterior STEMI.
Question 4: A patient's ECG shows a QRS axis of +120°. This is classified as:
- Normal axis
- Left axis deviation
- Right axis deviation (Correct answer)
- Extreme axis deviation
Correct answer: Right axis deviation
A QRS axis beyond +90° (up to +180°) is classified as right axis deviation.
Question 5: Which of the following patterns on a 12-lead ECG is associated with Wolff-Parkinson-White syndrome?
- Prolonged PR interval and wide QRS
- Short PR interval, delta wave, and wide QRS (Correct answer)
- Normal PR with narrow QRS and ST depression
- Prolonged QT with notched T waves
Correct answer: Short PR interval, delta wave, and wide QRS
WPW is characterized by a short PR interval (<120 ms), a slurred delta wave at the onset of the QRS, and a widened QRS complex.
Question 6: Which lead is the primary lead for identifying atrial activity and P-wave morphology?
- V1
- aVR
- Lead II (Correct answer)
- V5
Correct answer: Lead II
Lead II is oriented along the heart's electrical axis and provides the clearest upright P waves for evaluating atrial activity.
Question 7: In right bundle branch block (RBBB), what is the classic finding in lead V1?
- Deep S wave and no R wave
- RSR' pattern (rabbit ears) (Correct answer)
- QS pattern with ST elevation
- Tall, peaked R wave only
Correct answer: RSR' pattern (rabbit ears)
RBBB produces an RSR' or 'M-shaped' (rabbit ears) pattern in V1 due to delayed right ventricular depolarization.
CET 12-Lead ECG Interpretation 2
Which leads form the precordial (chest) leads on a standard 12-lead ECG?