Concept Tested:
This question assesses the mechanism of action of intravenous adenosine and its role in terminating specific tachyarrhythmias. The focus is on identifying AV node dependent rhythms.
What CMS is assessing here:
- Understanding that adenosine produces transient AV nodal block
- Differentiating AV node dependent from non AV node dependent arrhythmias
- Recognizing the correct acute management of paroxysmal supraventricular tachycardia
Adenosine acts on A1 receptors in the AV node, increasing potassium efflux and decreasing calcium influx. This results in a brief but complete AV nodal conduction block. Arrhythmias that rely on AV nodal reentry, particularly AV nodal reentrant tachycardia (AVNRT), terminate abruptly with this intervention.
It does not permanently terminate atrial fibrillation or atrial flutter, as these originate above the AV node and continue despite transient AV block. It is also ineffective in ventricular tachycardia.
Why this matters for the exam:
CMS frequently tests emergency arrhythmia management. Identifying AVNRT as an AV node dependent tachycardia is essential to avoid confusing it with atrial fibrillation, flutter, or ventricular tachycardia.
Quick revision takeaway:
- Drug of choice for acute AVNRT and AVRT
- Causes transient asystole lasting a few seconds
- Very short half life (less than 10 seconds)
- Not effective for ventricular tachycardia
- Does not terminate atrial fibrillation or flutter
- Safe in pregnancy