A 28-year-old woman presents with recurrent paroxysmal SVT. ECG during tachycardia shows a narrow complex tachycardia at 185 bpm with no visible P waves (P waves buried in QRS). Baseline ECG is normal. Carotid sinus massage terminates the episode. The most likely mechanism and first-line long-term prophylactic treatment are:

• A Orthodromic AVRT via accessory pathway — flecainide
• B AV nodal re-entrant tachycardia (AVNRT) — radiofrequency catheter ablation for recurrent symptomatic episodes ✓
• C Atrial flutter — electrical cardioversion
• D Junctional ectopic tachycardia — amiodarone

Explanation

AVNRT is the most common cause of paroxysmal SVT in young women, characterised by narrow complex tachycardia with P waves buried in or just after the QRS (pseudo-S waves in inferior leads, pseudo-R' in V1). It is terminated by carotid sinus massage or adenosine (vagal manoeuvres). Radiofrequency catheter ablation of the slow AV nodal pathway achieves cure rates >95% and is the first-line definitive treatment for recurrent symptomatic AVNRT per current guidelines.

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

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Written and medically reviewed by the StethoPrep medical team.