CET 12-Lead ECG Interpretation 3 — Questions and Answers
Question 1: Reciprocal ST depression in leads I and aVL, along with ST elevation in leads II, III, and aVF, suggests occlusion of which artery?
- Left anterior descending artery
- Left circumflex artery
- Right coronary artery (Correct answer)
- Left main coronary artery
Correct answer: Right coronary artery
Inferior STEMI (II, III, aVF) is most commonly caused by right coronary artery occlusion, with reciprocal changes in lateral leads.
Question 2: A 12-lead ECG shows a QTc of 520 ms. Which of the following is the most serious risk?
- Atrial fibrillation
- Torsades de pointes (Correct answer)
- First-degree AV block
- Sinus bradycardia
Correct answer: Torsades de pointes
A markedly prolonged QTc (>500 ms) greatly increases the risk of torsades de pointes, a potentially fatal polymorphic ventricular tachycardia.
Question 3: On a 12-lead ECG, which leads are considered the lateral leads?
- II, III, aVF
- V1, V2, V3
- I, aVL, V5, V6 (Correct answer)
- aVR, V1, V4
Correct answer: I, aVL, V5, V6
Leads I, aVL, V5, and V6 view the lateral wall of the left ventricle, supplied by the left circumflex artery.
Question 4: Tall, peaked, narrow (tented) T waves on a 12-lead ECG are a classic early sign of:
- Hypokalemia
- Hyperkalemia (Correct answer)
- Hypercalcemia
- Hypomagnesemia
Correct answer: Hyperkalemia
Early hyperkalemia causes tall, narrow, peaked (tent-shaped) T waves before progressing to wider QRS and sine wave pattern.
Question 5: What ECG finding best differentiates left ventricular hypertrophy (LVH) from anterior STEMI?
- LVH shows ST elevation in V1–V3 with deep S waves and large R waves elsewhere (Correct answer)
- LVH shows ST elevation in V4–V6 only
- LVH shows reciprocal ST depression in inferior leads
- LVH shows tall T waves in aVR
Correct answer: LVH shows ST elevation in V1–V3 with deep S waves and large R waves elsewhere
LVH produces a strain pattern with ST-T changes in V1–V3 (repolarization abnormality) accompanied by voltage criteria—deep S in V1 and tall R in V5/V6—unlike STEMI's acute injury pattern.
Question 6: A patient's 12-lead ECG shows no P waves, an irregular RR interval, and fibrillatory baseline. The diagnosis is:
- Atrial flutter with variable block
- Atrial fibrillation (Correct answer)
- Multifocal atrial tachycardia
- Wandering atrial pacemaker
Correct answer: Atrial fibrillation
Atrial fibrillation is characterized by the absence of distinct P waves, an irregularly irregular rhythm, and a chaotic fibrillatory baseline.
Question 7: In a 12-lead ECG, lead aVR views the heart from which direction?
- Inferior wall
- Right shoulder looking toward the heart (Correct answer)
- Lateral wall
- Anterior wall
Correct answer: Right shoulder looking toward the heart
Lead aVR is oriented from the right shoulder toward the heart's base, making it uniquely positioned to show the right atrium and outflow tracts.
CET 12-Lead ECG Interpretation 3
Reciprocal ST depression in leads I and aVL, along with ST elevation in leads II, III, and aVF, suggests occlusion of which artery?