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
Alex
100 yof CC: Rib pain and intermittent spasms
>>Too perfectly lined up with the T-waves, while the isoelectric line is relatively stable, to be strictly movement artifact. Can these spasms be sync-d with (or caused by) mechanical movement of the heart walls?
2014-11-25 23:20:19
Erich
What it Looks Like: Cardiac Arrest
Fantastic post, must see stuff for junior paramedics, medical students, residents and nurses that could potentially see cardiac arrest on a regular basis.
2014-11-25 16:22:28
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[…] ischaemia? Check out this case from the EMS 12 Lead blog. For more effective learning, read the original case first. […]
2014-11-25 09:09:03
ECG Axis Interpretation
The 360 Degree Heart – Part I
[…] http://www.ems12lead.com/2014/09/11/the-360-degree-heart-part-i/ […]
2014-11-25 09:01:37
LITFL Review 152 - LITFL
The 360 Degree Heart – Part I
[…] you understand axis as well as you’d like? The EMS 12-Lead blog gives us the first in a new series on understanding axis on the ECG. […]
2014-11-25 08:55:15

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