ACLS ACLS Cardiac Rhythm Recognition 2 — Questions and Answers
Question 1: In third-degree (complete) heart block, what is the relationship between P waves and QRS complexes?
- P waves and QRS complexes are completely dissociated with no consistent relationship (Correct answer)
- Every P wave is followed by a QRS complex with a prolonged PR interval
- P waves are absent and only QRS complexes are visible
- The PR interval progressively lengthens until a QRS is dropped
Correct answer: P waves and QRS complexes are completely dissociated with no consistent relationship
In complete heart block, the atria and ventricles beat independently with no relationship between P waves and QRS complexes — the PR interval varies randomly.
Question 2: Which ECG finding is most consistent with hyperkalemia in a symptomatic patient?
- Tall peaked T waves and widened QRS complexes (Correct answer)
- Prolonged QT interval with U waves
- Shortened PR interval and delta waves
- ST depression in lateral leads only
Correct answer: Tall peaked T waves and widened QRS complexes
Hyperkalemia classically produces tall, peaked T waves followed by widening of the QRS and, if untreated, can progress to a sine-wave pattern and cardiac arrest.
Question 3: A patient presents with a regular narrow-complex tachycardia at 150 bpm. Vagal maneuvers fail. Which drug is given first?
- Adenosine 6 mg IV rapid push (Correct answer)
- Amiodarone 150 mg IV over 10 minutes
- Metoprolol 5 mg IV
- Verapamil 2.5 mg IV
Correct answer: Adenosine 6 mg IV rapid push
Adenosine 6 mg given as a rapid IV push is the first-line drug for stable narrow-complex SVT after failed vagal maneuvers.
Question 4: On the ECG, a PR interval greater than 200 ms that is constant with all P waves conducted defines:
- First-degree AV block (Correct answer)
- Second-degree AV block Mobitz type I
- Second-degree AV block Mobitz type II
- Third-degree AV block
Correct answer: First-degree AV block
First-degree AV block is defined by a PR interval >200 ms (one large box) that is constant, with every P wave followed by a QRS complex.
Question 5: Which of the following best describes Mobitz Type II second-degree AV block?
- Constant PR interval with sudden dropped QRS complexes without warning (Correct answer)
- Progressive PR lengthening followed by a dropped QRS
- Complete P-QRS dissociation
- Alternating bundle branch block patterns
Correct answer: Constant PR interval with sudden dropped QRS complexes without warning
Mobitz Type II shows a constant PR interval with intermittent, unpredictable failure of conduction — a QRS complex simply drops without progressive PR lengthening.
Question 6: What ECG pattern is classically associated with right ventricular MI and should prompt right-sided lead placement?
- ST elevation in leads II, III, aVF — especially with ST elevation in V1 (Correct answer)
- ST elevation in V1–V4 with left axis deviation
- ST depression in aVL with tall R in V1
- New left bundle branch block with ST elevation in V5–V6
Correct answer: ST elevation in leads II, III, aVF — especially with ST elevation in V1
ST elevation in the inferior leads with ST elevation in V1 (or V4R on right-sided leads) suggests right ventricular MI, which complicates inferior STEMI.
ACLS ACLS Cardiac Rhythm Recognition 2
In third-degree (complete) heart block, what is the relationship between P waves and QRS complexes?