ECG Clinical Applications 3 — Questions and Answers
Question 1: A patient with WPW syndrome develops atrial fibrillation. Which drug is contraindicated?
- Procainamide
- Ibutilide
- Adenosine (Correct answer)
- Flecainide
Correct answer: Adenosine
Adenosine blocks the AV node but not the accessory pathway in WPW, potentially accelerating conduction and causing ventricular fibrillation.
Question 2: Which ECG finding is associated with right ventricular infarction?
- ST elevation in V1-V4
- ST elevation in right-sided leads (V3R-V4R) (Correct answer)
- Q waves in leads I and aVL
- ST depression in V5-V6
Correct answer: ST elevation in right-sided leads (V3R-V4R)
Right ventricular MI is diagnosed by ST elevation in right-sided leads (V3R-V4R), which are not part of standard 12-lead ECGs.
Question 3: A patient's ECG shows a prolonged PR interval of 280 ms with all P waves conducting normally. This is classified as:
- First-degree AV block (Correct answer)
- Mobitz Type I
- Mobitz Type II
- Third-degree AV block
Correct answer: First-degree AV block
A PR interval >200 ms with every P wave conducting to the ventricles defines first-degree AV block.
Question 4: During treadmill stress testing, which ECG finding is considered a positive result?
- 1 mm ST elevation in aVR
- ≥1 mm horizontal or downsloping ST depression (Correct answer)
- Junctional ST depression <1 mm
- T wave inversion in V1 only
Correct answer: ≥1 mm horizontal or downsloping ST depression
≥1 mm of horizontal or downsloping ST depression during exercise stress testing indicates myocardial ischemia.
Question 5: A patient has complete left bundle branch block (LBBB). Why is diagnosing acute MI difficult?
- LBBB masks P waves
- LBBB causes diffuse ST elevation mimicking pericarditis
- LBBB causes secondary ST-T changes that obscure ischemic patterns (Correct answer)
- LBBB prolongs the QT interval artificially
Correct answer: LBBB causes secondary ST-T changes that obscure ischemic patterns
LBBB produces secondary ST-T wave changes (discordant from QRS) that interfere with the standard ECG interpretation of ischemia.
Question 6: Which rhythm shows regularly irregular RR intervals with a pattern of progressive RR shortening followed by a pause?
- Atrial fibrillation
- Sinus arrhythmia
- Wenckebach (Mobitz I) block (Correct answer)
- Junctional rhythm
Correct answer: Wenckebach (Mobitz I) block
Wenckebach block shows progressive PR lengthening and RR shortening until a P wave is not conducted, creating the characteristic grouped beating.
Question 7: A patient has ST elevation in leads V1-V4 with reciprocal ST depression in the inferior leads. Which vessel is most likely involved?
- Right coronary artery (proximal)
- Left circumflex artery
- Left anterior descending artery (Correct answer)
- Posterior descending artery
Correct answer: Left anterior descending artery
ST elevation in V1-V4 indicates anterior STEMI, most commonly due to LAD occlusion, with reciprocal changes often in inferior leads.
ECG Clinical Applications 3
A patient with WPW syndrome develops atrial fibrillation.
Which drug is contraindicated?