DC Dysrhythmia Cardiac Rhythm Interpretation 3 — Questions and Answers
Question 1: Which characteristic finding differentiates torsades de pointes from monomorphic ventricular tachycardia?
- Rate greater than 200 bpm
- Twisting of the QRS axis around the baseline with varying amplitude (Correct answer)
- Presence of P waves before each QRS
- Wide QRS complexes greater than 0.12 seconds
Correct answer: Twisting of the QRS axis around the baseline with varying amplitude
Torsades de pointes is identified by the characteristic twisting of QRS polarity around the isoelectric baseline, distinguishing it from monomorphic VT.
Question 2: A patient presents with sudden palpitations. The ECG shows an abrupt onset narrow-complex tachycardia at 180 bpm that terminates suddenly with vagal maneuvers. Which dysrhythmia best fits this presentation?
- Atrial fibrillation
- AV nodal reentrant tachycardia (AVNRT) (Correct answer)
- Multifocal atrial tachycardia
- Accelerated junctional rhythm
Correct answer: AV nodal reentrant tachycardia (AVNRT)
AVNRT is a reentrant tachycardia within or near the AV node, producing a sudden-onset narrow-complex tachycardia that responds to vagal maneuvers or adenosine.
Question 3: On a 12-lead ECG you see right bundle branch block (RBBB) morphology with an RSR' pattern in V1 and deep S waves in leads I and V6. Which QRS duration is consistent with a complete RBBB?
- 0.08–0.10 seconds
- 0.10–0.12 seconds
- Greater than or equal to 0.12 seconds (Correct answer)
- Greater than 0.20 seconds
Correct answer: Greater than or equal to 0.12 seconds
A complete RBBB requires a QRS duration of ≥0.12 seconds (3 small boxes on standard ECG paper), whereas an incomplete RBBB is 0.10–0.12 seconds.
Question 4: A critically ill patient's monitor shows wide, bizarre QRS complexes at a rate of 30 bpm with no discernible P waves. The patient is pulseless. What rhythm should you identify?
- Accelerated idioventricular rhythm
- Pulseless electrical activity (PEA)
- Idioventricular escape rhythm with cardiac arrest (Correct answer)
- Third-degree AV block
Correct answer: Idioventricular escape rhythm with cardiac arrest
A slow idioventricular rhythm (20–40 bpm) without a pulse indicates cardiac arrest; immediate CPR and resuscitation are required.
Question 5: You observe an ECG with a QTc interval of 520 milliseconds. Which clinical condition is most directly associated with this finding?
- Hyperkalemia
- Long QT syndrome predisposing to torsades de pointes (Correct answer)
- Wolff-Parkinson-White syndrome
- Right bundle branch block
Correct answer: Long QT syndrome predisposing to torsades de pointes
A corrected QT interval (QTc) ≥500 ms significantly increases risk of torsades de pointes, a life-threatening ventricular dysrhythmia.
Question 6: Which electrolyte abnormality is most commonly associated with the development of ventricular dysrhythmias including PVCs and VT?
- Hypernatremia
- Hypocalcemia
- Hypokalemia (Correct answer)
- Hypermagnesemia
Correct answer: Hypokalemia
Hypokalemia reduces the resting membrane potential threshold, increasing myocardial excitability and susceptibility to ventricular dysrhythmias.
Question 7: A rhythm strip shows premature beats with wide, bizarre QRS complexes that look different from the patient's normal beats, followed by a full compensatory pause. What are these beats called?
- Premature atrial contractions (PACs)
- Premature junctional contractions (PJCs)
- Premature ventricular contractions (PVCs) (Correct answer)
- Escape beats
Correct answer: Premature ventricular contractions (PVCs)
PVCs are ectopic ventricular impulses producing wide, bizarre QRS complexes with T waves opposite in polarity, usually followed by a full compensatory pause.
DC Dysrhythmia Cardiac Rhythm Interpretation 3
Which characteristic finding differentiates torsades de pointes from monomorphic ventricular tachycardia?