CPR ECG Rhythm Interpretation 3 — Questions and Answers
Question 1: In Mobitz Type II second-degree AV block, which ECG finding differentiates it from Mobitz Type I?
- Progressively lengthening PR interval before a dropped beat
- Constant PR interval with sudden non-conducted P wave (Correct answer)
- Variable P-to-P intervals
- Widened QRS preceding the dropped beat
Correct answer: Constant PR interval with sudden non-conducted P wave
Mobitz Type II features a constant PR interval followed by a sudden dropped QRS, whereas Mobitz Type I has progressive PR lengthening (Wenckebach).
Question 2: A patient's ECG shows P waves and QRS complexes occurring independently with no relationship to each other. The ventricular rate is 38 bpm with wide QRS complexes. What is the rhythm?
- Second-degree AV block Mobitz II
- Accelerated idioventricular rhythm
- Complete (third-degree) AV block (Correct answer)
- Junctional escape rhythm
Correct answer: Complete (third-degree) AV block
Complete (third-degree) AV block is characterized by complete AV dissociation where the atria and ventricles beat independently, and a wide QRS with slow rate indicates a ventricular escape pacemaker.
Question 3: Which of the following best describes torsades de pointes on ECG?
- Monomorphic wide-complex tachycardia at 200 bpm
- Polymorphic VT where QRS axis twists around the isoelectric line (Correct answer)
- Irregular wide-complex rhythm with delta waves
- Rapid regular narrow-complex tachycardia
Correct answer: Polymorphic VT where QRS axis twists around the isoelectric line
Torsades de pointes is a polymorphic ventricular tachycardia in which the QRS amplitude and axis appear to rotate or twist around the baseline.
Question 4: A 45-year-old presents with palpitations. ECG shows a short PR interval of 0.10 seconds, a slurred upstroke on the QRS (delta wave), and a wide QRS. What syndrome does this suggest?
- Brugada syndrome
- Long QT syndrome
- Wolff-Parkinson-White syndrome (Correct answer)
- Lown-Ganong-Levine syndrome
Correct answer: Wolff-Parkinson-White syndrome
WPW syndrome is characterized by a short PR interval, delta wave (slurred QRS upstroke), and widened QRS due to pre-excitation via an accessory pathway.
Question 5: On an ECG, which lead configuration is best for identifying P wave morphology and diagnosing atrial rhythms?
- Lead aVR
- Lead V1
- Lead II (Correct answer)
- Lead V6
Correct answer: Lead II
Lead II is most commonly used to evaluate P wave morphology because it is oriented along the main atrial vector, producing the tallest and most upright P waves.
Question 6: A patient's rhythm strip shows a P wave before every QRS, but the PR interval progressively lengthens until a QRS is dropped, then the cycle repeats. What is this rhythm?
- Mobitz Type II second-degree AV block
- Third-degree AV block
- Mobitz Type I (Wenckebach) second-degree AV block (Correct answer)
- Junctional tachycardia
Correct answer: Mobitz Type I (Wenckebach) second-degree AV block
Wenckebach (Mobitz Type I) is characterized by progressive PR prolongation until a P wave fails to conduct, then the PR interval resets and the pattern repeats.
Question 7: ST segment depression in leads V1-V4 during a posterior MI is a reciprocal change. What would direct posterior leads (V7-V9) show?
- ST depression and T wave inversion
- ST elevation and upright T waves (Correct answer)
- Tall R waves and Q waves
- Flat isoelectric ST segments
Correct answer: ST elevation and upright T waves
True posterior MI produces ST elevation and upright T waves in posterior leads (V7-V9), which appear as mirror-image ST depression in V1-V4.
CPR ECG Rhythm Interpretation 3
In Mobitz Type II second-degree AV block, which ECG finding differentiates it from Mobitz Type I?