USMLE PRACTICE QUESTION OF THE WEEK

Question for August 8, 2025

A 34-year-old man presents with palpitations and dizziness. ECG shows a shortened PR interval, a slurred initial upstroke of the QRS complex (delta wave), and episodes of supraventricular tachycardia.

Which of the following is the underlying cause of his condition?

A. Abnormal AV node conduction

B. Ectopic atrial focus

C. Reentrant circuit through an accessory pathway

D. Reentrant circuit within the AV node

E. Slowed conduction in the His-Purkinje system

Get Detailed Explanation

Correct Answer:

C. Reentrant circuit through an accessory pathway

Step-by-Step Explanation:

Step 1: A short PR interval and delta wave are diagnostic of Wolff-Parkinson-White (WPW) syndrome.

Step 2: WPW occurs due to an accessory pathway (Bundle of Kent) that allows pre-excitation of the ventricles, leading to reentrant tachyarrhythmias.

Why These Are Incorrect:

A. Abnormal AV node conduction would lengthen the PR interval.
B. Ectopic atrial focus causes focal atrial tachycardia, not WPW.
D. AV nodal reentry tachycardia (AVNRT) uses dual pathways within the node, without delta waves.
E. His-Purkinje slowing results in bundle branch blocks.