Understanding Adenosine (Adenocard)

So, recently, I was involved in a conversation, where the topic of Adenosine administration came up. It seems like there is a misunderstanding regarding its use and mechanism of action. Although this is not our classic ECG interpretation topic, I believe its worth talking about for a bit.

adenosine (1)

Adenosine, a Class V antiarrhythmic from the Vaughan Williams Classification, is an Endogenous Neucloside, meaning, already present in the body. In the EMS system, Adenosine is known for the treatment of Supraventricular Tachycardias (SVT), however, the reality is that, Adenosine is responsible for many actions in the body at a cellular level, depending on which receptor it binds to. During excessive reentry tachycardias (SVT), Adenosine, in simple terms, is given to slow down the overall ventricular rate.

Pharmacodynamics: 

  •  Adenosine binds to A1, one of multiple Adenosine receptors, which in the SA Node, it blocks L-type Calcium Channels and reduces Calcium influx, which may lead to a decreased firing rate, known as Negative Chronotropic Effect
  • Same channels at the AV Node, decrease conductivity , known as Negative Dromotropic Effect, down to the ventricles. This is what we want to do during tachyarrhythmias, especially with reentry capabilities, to slow down the ventricular rate

However, at higher or infused doses, such as during Cardiac Stress Test, Adenosine is given often as 60 mg over 4 minutes, not the typical administration for a reentry SVT right?

When infused slowly, Adenosine may bind to A2 receptors which in the heart and vasculature, can decrease Cyclic Adenosine Monophosphate (cAMP)

What is cAMP?

cAMP is a second messenger used to send signals from the cell membrane to intracellular areas to release chemicals like Calcium or break down proteins. Since Calcium is required for contraction and constriction, this leads to vasodilation. Physiologic changes in response to reduced blood pressure from vasodilation lead to increase heart rate to compensate for it. Understanding this details can help recognize complications that can happen when administrating Adenosine like AV blocks, short Asystole or other problems.

Other Adenosine receptors like Purinergic Receptors, for example, P1 receptors, lead to smooth muscle relaxation in the GI tracts.

Bottom line, Adenosine has many purposes in the body, therefore, it does not “die” or “dissapears” fast, but rather, it is used rapidly by the body, which is why it should be pushed fast, and as closed to the heart as possible, in order to reach the targeted areas during a reentry tachycardia, or “SVT”.

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Comments
William Dillon
60 year old male CC: Sudden cardiac arrest
Great case but it stopped short. It should continue. The patient was transferred to an experienced PCI center. Focused medical evaluation was performed in the ED and emergent cardiology consultation was obtained. Although there is not clear ST elevation on the 12 lead the interventional cardiologist knows the data that over 70% of VF cardiac…
2015-03-03 12:53:20
Sharon Sinclair
The 12 Leads of Christmas: V3
As a technician, I absolutely love how comprehensive these posts are. Although I do not have the advanced knowledge or understanding of a licensed provider, I try to absorb as much as I can from posts like these. Maybe one day I will muster the courage to transition to a more advanced position in cardiac…
2015-02-28 20:40:17
A visit to Johns Hopkins #EMSToday2015 | EMS 12 Lead
Episode #11 – Are we harming patients with oxygen?
[…] might remember Mike from one of our most popular EMS 12-Lead podcasts Episode #11: Are we harming patients with oxygen? We finished up the night with food and adult beverages in the […]
2015-02-25 14:33:03
Rollo
The Trouble with Sinus Tachycardia
Had a pt today with a rate @ and around 160, it was indeed sinus tachycardia. The tachycardia was secondary to a stimulant which caused over stimulation of sympathetic nervous system ie sympathomimetic O.D. The treatment was fluid and a benzo. Problem solved.
2015-02-25 00:14:18
Jeff Reader
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When looking at how the heart sits in the chest and how things are named remember they were probabily named during autopsys when the cadaver was on its back.
2015-02-24 16:55:04

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