A 35-year-old woman presents with sudden palpitations and light-headedness. ECG during the episode shows a regular narrow-complex tachycardia at 185 bpm with no clearly visible P waves between QRS complexes; a pseudo-R' in lead V1 is noted. Vagal maneuvers terminate the tachycardia. The MOST likely diagnosis is:
- A Atrial flutter with 2:1 block
- B Typical AV nodal re-entrant tachycardia (AVNRT) ✓
- C Atrial tachycardia
- D Atrioventricular re-entrant tachycardia (AVRT) via accessory pathway
Correct answer: B. Typical AV nodal re-entrant tachycardia (AVNRT)
Explanation
Typical AVNRT (slow-fast) shows a narrow-complex tachycardia with retrograde P waves buried in or immediately after the QRS, creating a pseudo-S wave in inferior leads and pseudo-R' in V1. The RP interval is very short (<70 ms). Atrial flutter typically shows sawtooth flutter waves at 300 bpm with 2:1 block giving 150 bpm. AVRT (Wolff-Parkinson-White) has P waves further behind the QRS (long RP) with typical delta waves during sinus rhythm. Atrial tachycardia shows P waves before QRS.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.