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Adenosine Mechanism of Action — EECC MCQ

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EasyCardiac PharmacologyAdenosine Mechanism of ActionEECC

A medical student asks about the mechanism of action of adenosine in terminating SVT. Which statement best describes how adenosine works?

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Correct answer: C — Adenosine activates A1 receptors in the AV node, increasing potassium conductance and hyperpolarising AV nodal cells, causing transient AV block

Adenosine is an endogenous purine nucleoside that acts on A1 receptors in the AV node. Binding to A1 receptors activates IKAdo (an inward-rectifier potassium channel, GIRK), causing hyperpolarisation of AV nodal cells and slowing conduction through the AV node. This transient AV block (lasting 10-20 seconds) interrupts re-entrant circuits that utilise the AV node (AVNRT, AVRT). Adenosine has an ultra-short half-life (<10 seconds) and must be given as a rapid IV bolus followed by a saline flush. Side effects include transient chest tightness, flushing, breathlessness, and brief asystole. It is contraindicated in severe asthma and in patients on dipyridamole (which inhibits adenosine uptake, potentiating its effects). Caffeine and theophylline are competitive antagonists.

Reference: BNF; ESC (2019): Guidelines on SVT Management