A 28-year-old man presents with palpitations. ECG shows a short PR interval (0.1 s), delta waves, and wide QRS. He develops a regular narrow-complex tachycardia at 180 bpm. The mechanism of this tachycardia in Wolff-Parkinson-White (WPW) syndrome is:

• A Antidromic reentrant tachycardia (accessory pathway antegrade, AV node retrograde)
• B Atrial flutter with 2:1 conduction through accessory pathway
• C Ventricular tachycardia originating from bundle of Kent insertion
• D Orthodromic reentrant tachycardia (AV node antegrade, accessory pathway retrograde) ✓

Explanation

In WPW, 95% of SVT episodes are orthodromic reentrant tachycardia (ORT): antegrade conduction occurs through the AV node–His-Purkinje system (producing narrow QRS) and retrograde conduction through the accessory pathway back to the atria. Because conduction to the ventricles is via normal His-Purkinje system, the QRS is narrow (normal morphology) and the rate is regular (150–250 bpm). Antidromic tachycardia uses the accessory pathway antegrade, producing wide bizarre QRS (mimics VT). Pre-excited AF (irregular wide complex) is the most dangerous arrhythmia in WPW, where AV nodal blockers are contraindicated.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.