Adenosine - mechanism and contraindications
Core concept
- Endogenous purine nucleoside. Acts at the A1 receptor in the AV node.
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A1 receptor (Gi-coupled)
- dec adenylate cyclase, dec cAMP
- inc K+ efflux (IKACh/GIRK) -> hyperpolarisation
- dec L-type Ca2+ current
- -> transient complete AV nodal block
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- A2A receptors -> vasodilation (flushing, coronary steal in stress testing, hypotension)
- A2B/A3 on mast cells -> bronchoconstriction
Two distinct uses
| Use | Logic |
|---|---|
| Terminate AVNRT/AVRT | The AV node is part of the re-entrant circuit -> block it and the circuit stops |
| Diagnose the rhythm | Transient block unmasks atrial activity - flutter waves, atrial tachycardia |
- *Adenosine does not terminate AF, flutter or VT* - it reveals them
- Give it with a continuous ECG rhythm strip running, or you have wasted the dose
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