A 32-year-old woman with structurally normal heart has recurrent palpitations with sudden onset and offset. ECG during palpitation shows regular narrow-complex tachycardia at 180 bpm with RP interval shorter than PR interval and pseudo-S waves in inferior leads. She has no delta waves on resting ECG. What is the most likely mechanism?
- A Typical (slow-fast) AV nodal re-entrant tachycardia (AVNRT) ✓
- B Atrial flutter with 2:1 block
- C Orthodromic AVRT in Wolff-Parkinson-White syndrome
- D Atrial tachycardia from a focal trigger
Explanation
Typical (slow-fast) AVNRT is the most common paroxysmal supraventricular tachycardia in adults, especially young women. It uses the slow pathway (AV node) for anterograde conduction and the fast pathway for retrograde conduction, resulting in near-simultaneous atrial and ventricular activation. ECG shows a short RP interval (<70 ms), pseudo-S waves in inferior leads (retrograde P waves inscribed at end of QRS), and pseudo-R' in V1. No delta waves exclude WPW. Orthodromic AVRT has P waves visible after the QRS (RP >70 ms). Catheter ablation of the slow pathway is curative.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.