CCS Cardiac Rhythm Interpretation & ECG Analysis 2 — Questions and Answers
Question 1: Which ECG finding is most characteristic of a left bundle branch block (LBBB)?
- QRS >0.12 s with RSR' pattern in V1
- QRS >0.12 s with broad monophasic R wave in V5–V6 (Correct answer)
- QRS >0.12 s with deep S wave in V5–V6
- QRS >0.12 s with right axis deviation
Correct answer: QRS >0.12 s with broad monophasic R wave in V5–V6
LBBB shows a broad, slurred, or notched monophasic R wave in lateral leads (I, aVL, V5–V6) with QRS duration >0.12 seconds and absence of septal Q waves.
Question 2: What ECG triad is associated with Wolff-Parkinson-White (WPW) syndrome?
- Prolonged PR interval, wide QRS, and ST elevation
- Short PR interval, delta wave, and wide QRS complex (Correct answer)
- Normal PR interval with intermittently dropped QRS complexes
- Prolonged QT interval and biphasic T waves
Correct answer: Short PR interval, delta wave, and wide QRS complex
WPW is characterized by a short PR interval (<0.12 s), a delta wave (slurred initial QRS upstroke), and wide QRS due to ventricular pre-excitation via an accessory pathway.
Question 3: Atrial flutter typically presents with what atrial rate?
- 100–150 bpm
- 150–250 bpm
- 250–350 bpm (Correct answer)
- 350–600 bpm
Correct answer: 250–350 bpm
Atrial flutter has a characteristic atrial rate of 250–350 bpm, producing sawtooth-pattern flutter waves most visible in inferior leads (II, III, aVF).
Question 4: Which ECG change is classically seen early in hyperkalemia?
- Prolonged QT interval and prominent U waves
- Peaked narrow symmetrical T waves and QRS widening (Correct answer)
- ST elevation and short QT interval
- PR prolongation with delta waves
Correct answer: Peaked narrow symmetrical T waves and QRS widening
Early hyperkalemia produces tall, narrow, peaked (tented) T waves; as potassium rises further, PR prolongation, QRS widening, and eventually a sine wave pattern emerge.
Question 5: Which ECG finding most strongly supports ventricular tachycardia (VT) over SVT with aberrancy?
- Narrow complex tachycardia at 180 bpm with retrograde P waves
- Wide complex tachycardia with AV dissociation and QRS >0.14 seconds (Correct answer)
- Irregularly irregular wide complex tachycardia
- Regular narrow complex tachycardia terminating with vagal maneuvers
Correct answer: Wide complex tachycardia with AV dissociation and QRS >0.14 seconds
AV dissociation (independent P waves and QRS complexes), along with QRS width >0.14 seconds, fusion beats, and capture beats, are hallmark features of ventricular tachycardia.
Question 6: ST elevation in leads V1–V4 most commonly indicates occlusion of which coronary artery?
- Right coronary artery (RCA)
- Left circumflex artery (LCx)
- Left anterior descending artery (LAD) (Correct answer)
- Posterior descending artery (PDA)
Correct answer: Left anterior descending artery (LAD)
Anterior STEMI with ST elevation in V1–V4 is most commonly caused by occlusion of the LAD, which supplies the anterior wall and septum of the left ventricle.
Question 7: What is the defining ECG appearance of torsades de pointes?
- Regular monomorphic wide complex tachycardia at a constant rate
- Polymorphic ventricular tachycardia with QRS complexes that appear to twist around the isoelectric baseline (Correct answer)
- Narrow complex tachycardia with alternating QRS amplitude
- Wide complex bradycardia with variable PR intervals
Correct answer: Polymorphic ventricular tachycardia with QRS complexes that appear to twist around the isoelectric baseline
Torsades de pointes is a polymorphic VT where the QRS complexes progressively shift in axis, appearing to rotate around the isoelectric line, typically occurring in the setting of prolonged QT.
CCS Cardiac Rhythm Interpretation & ECG Analysis 2
Which ECG finding is most characteristic of a left bundle branch block (LBBB)?