A 32-year-old woman presents with palpitations. Her ECG shows a regular narrow complex tachycardia at 175 bpm with retrograde P waves visible in the ST segment. Adenosine terminates the episode. Electrophysiology study is planned. What is the most likely mechanism?
- A Orthodromic AVRT via a manifest accessory pathway
- B AV nodal re-entrant tachycardia (AVNRT) — slow-fast (typical) type ✓
- C Atrial tachycardia with AV conduction
- D Accelerated junctional rhythm
Explanation
AVNRT (slow-fast or typical form) is the most common cause of paroxysmal supraventricular tachycardia in young women. In typical AVNRT, anterograde conduction occurs via the slow AV nodal pathway and retrograde via the fast pathway, producing retrograde P waves very close to the QRS (in the ST segment or pseudo-S wave in V1/pseudo-R' in V1). Adenosine terminates re-entrant tachycardias using the AV node. Orthodromic AVRT would show retrograde P waves further after the QRS due to longer VA conduction time. Atrial tachycardia is not adenosine-sensitive in the same way. Accelerated junctional rhythm is not re-entrant and is not paroxysmal.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.