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
Kevin
44 year old male CC: Palpitations
Why on earth would you risk VF, by giving Adenosine to rule out rhythms.. This is dangerous, and foolish. There might be a slight chance that this is WPW.. You might as well just give him Cardizem, they are both AV nodal blockers... I don't know why the AHA even added this stupid idea..
2014-10-22 13:31:06
Vince DiGiulio
The 360 Degree Heart – Part II
It is standard practice in electrocardiography to label the first 90 degrees counter-clockwise from "zero" that way. When you see a patient with "left axis deviation" you'll see that their measured QRS axis is somewhere between -30 and -90 degrees. Imagine if you saw someone with a mean QRS axis at 5 degrees. Now imagine…
2014-10-21 14:00:37
Bryan
The 360 Degree Heart – Part II
I don't understand why (-)III and aVL are be labeled -60 and -30 degrees instead of 300 and 330 degrees?
2014-10-21 13:43:29
The 360 Degree Heart – Part II | EMS 12 Lead
The 360 Degree Heart – Part I
[…] first post in our “360 Degree Heart” series attempted to visualize how the different frontal plane […]
2014-10-21 12:50:56
Eric Strong
Axis Determination – Part VI
This is a great discussion of axis determination. One minor suggestion: I think it's potentially misleading to refer to an axis between 0 and -30 as "physiologic left axis deviation", since "axis devitation" implies deviation from normal, and axes between 0 and -30 are perfectly normal, (depending on age and body habitus). It may be…
2014-10-05 17:09:00

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