ACLS Drugs – Adenosine
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Article at a Glance
- Indicated for narrow-complex SVT, Adenosine is used to differentiate between SVT and VT or AF with RVR.
- Adenosine is contraindicated for wide, polymorphic VT.
- Adenosine affects the SA and AV nodes in the heart, causing temporary paralysis of these areas.
- The team should expect temporary asystole following administration.
- The first dose of adenosine is 6 mg IV and the second dose is 12 mg.
- The medication should be administered with a rapid IV push.
A Quick Overview of Adenosine
First, let’s review adenosine’s pharmacology and mechanism of action. Adenosine may sound familiar. If you’re thinking of adenosine from ATP (adenosine triphosphate), you’re exactly correct. Adenosine is found naturally within the body. When adenosine is synthesized, turned into a drug, and injected intravenously in large doses, several interesting events occur.
Adenosine injection
As it pertains to ACLS, adenosine affects the sinoatrial (SA) and the atrioventricular (AV) node. Adenosine pumps potassium (K+) into the cells and inhibits calcium (Ca2+), in effect hyperpolarizing those areas of the heart. Adenosine temporarily paralyzes the SA node and the AV node. If one were to temporarily paralyze the whole top half of the heart, it would display on the cardiac monitor as a characteristic, yet temporary, asystole.
Asystole on a cardiac monitor.
In summary, adenosine impacts the SA node by inhibiting the SA node firing, which limits the conduction through the AV node.
Indications of Adenosine
The following are ways adenosine is used in medical settings.
Therapeutic Use
Adenosine is the first drug of choice for narrow complex supraventricular tachycardias (SVT). Adenosine “stops” the heart just long enough to terminate SVTs.
Related Video – One Quick Question: What are the SVT (Supraventricular Tachycardia) Criteria?
These tachycardias are usually caused by a re-entry problem. The conduction travels through the atrium, arrives around the AV node, and then part of the conduction loops back into the atrium. It re-enters the heart. It “cuts in line” and begins another impulse.
The re-entry point for most narrow complex SVTs is at the AV node. Fortunately, adenosine works right at the AV node. That’s why it’s so effective in treating supraventricular tachycardias.
Related Video – Adenosine – SVT Treatment
Suppose your patient has a heart rate clipping along at 182–220 bpm. Maybe you’re having a hard time discerning whether this is regular or irregular. Is this a regular supraventricular tachycardia or an atrial fibrillation with a rapid ventricular response? It’s hard to distinguish because the R waves occur so rapidly.
Related Video – ECG Rhythm Review – Atrial Fibrillation with Rapid Ventricular Response (RVR)
Now, suppose you administer adenosine, and it doesn’t work. Adenosine is ineffective in treating atrial fibrillation. In atrial fibrillation, other re-entry pathways are being used besides the AV node. If adenosine works on the AV node, it’s not going to impact the other re-entry ports used during atrial fibrillation with a rapid ventricular response (RVR).
Read: 10 Cardiac Drugs to Know for the Pharmacology Test
The SVT reentry pathway is typically the AV node, while re-entry pathways vary in atrial fibrillation.
Diagnostic Use
Adenosine is a first-line drug for narrow complex, regular supraventricular tachycardias (SVT). Adenosine is also used as a diagnostic drug for ventricular tachycardia (VT).
Remember, adenosine won’t treat the cause of VT. It impacts the SA node while VT originates in the ventricular chambers, so adenosine won’t work. However, you can use adenosine as a diagnostic tool to discern between VT or SVT with an aberrant ventricular conduction.
Additionally, if your patient is stable, obtain a 12-lead EKG rather than administering adenosine. The EKG provides the same information.
Dosing
The first dose of adenosine for SVT is a 6mg rapid IV push. If the heart rate does not convert within a minute or so, administer an additional 12 mg. So, you’ll initially administer 6 mg followed by a 12 mg IV push.
Supraventricular Tachycardia Adenosine Dosing
Special Considerations
Physicians must remember some special considerations when administering adenosine. First, the drug has a very short half-life. Second, you must administer a liberal amount for it to be effective. 6 mg is a huge dose of adenosine. The drug is going to go into the closest IV port to the patient. Downstream in the next port, you’ll have a syringe full of saline ready for rapid administration after the adenosine.
Finally, adenosine should not be administered in any wide polymorphic ventricular tachycardias because it has been shown to cause deterioration of the patient’s hypotension and ventricular fibrillation.
Related Video – ECG Rhythm Review – Polymorphic Ventricular Tachycardia (Torsades de Pointes)
Summary
Adenosine inhibits the SA node firing and conduction through the AV node. It’s used to treat SVTs. It may also be used as a diagnostic tool in the case of ventricular tachycardias. Remember to administer a liberal amount due to its short half-life.
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