A 62-year-old woman presents with palpitations. ECG shows a regular tachycardia at 165 bpm with narrow QRS complexes and a pseudo-R' wave visible in lead V1 (retrograde P wave). Vagal manoeuvres terminate the tachycardia transiently. What is the most likely mechanism?
- A AVRT (orthodromic): antegrade conduction via AV node, retrograde via accessory pathway
- B AVNRT (typical slow-fast): antegrade conduction via slow pathway, retrograde via fast pathway ✓
- C Atrial tachycardia with 1:1 conduction and aberrant conduction
- D Junctional ectopic tachycardia
Explanation
Typical AVNRT (slow-fast) is the most common paroxysmal SVT mechanism, characterized by: narrow QRS complex tachycardia, retrograde P waves either buried in the QRS (making P invisible) or causing pseudo-R' in V1 (retrograde atrial activation is near-simultaneous with ventricular activation due to common AV nodal circuit). The RP interval is very short (<80 ms). AVRT shows a slightly longer RP interval with P waves visible just after the QRS in the ST segment. Atrial tachycardia shows P waves before QRS (long RP tachycardia). Vagal manoeuvres terminate AVNRT by blocking the AV node, interrupting the reentry circuit.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.