Adenosine Response Differentiating SVT — EECC MCQ

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EasyArrhythmia & ElectrophysiologyAdenosine Response Differentiating SVTEECC

A 40-year-old woman with no structural heart disease presents with a regular narrow-complex tachycardia at 190 bpm. Vagal manoeuvres fail. IV adenosine 6 mg is given. The tachycardia terminates abruptly revealing P waves after the last QRS. What is the diagnosis?

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Correct answer: E — AVNRT (AV nodal re-entrant tachycardia) — abrupt termination with adenosine confirms an AV-node-dependent tachycardia; the most common regular SVT; the re-entrant circuit uses the fast and slow AV nodal pathways

The response to adenosine helps differentiate SVT mechanisms: (1) ABRUPT TERMINATION (tachycardia stops): AV-node-dependent tachycardias — AVNRT (most common) or AVRT (orthodromic) — adenosine blocks the AV node, breaking the re-entrant circuit; (2) TRANSIENT AV BLOCK revealing atrial activity: atrial flutter (sawtooth waves), atrial tachycardia (discrete P waves at different morphology) — adenosine slows AV conduction, unmasking the atrial arrhythmia, which continues; (3) NO EFFECT: VT (not AV-node-dependent), some atrial tachycardias. AVNRT features: (1) regular, narrow-complex; (2) rate 140-250 bpm; (3) P waves often buried in QRS (pseudo-R' in V1, pseudo-S in inferior leads); (4) abrupt onset/offset. The ESC 2019 SVT Guidelines recommend catheter ablation (slow pathway modification) for recurrent symptomatic AVNRT (Class I, >95% success rate).

Reference: ESC (2019): SVT Guidelines