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”.

4 Comments

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Comments
Jake
47 year old male CC: Crushing chest pain
I know this is old, but it just popped up on facebook so I'll go ahead and put in my $0.02 worth. With that hx and that 12-lead, there's no question this is an acute STEMI. I'm comfortable calling that third strip Torsades (assuming I've verified it's not an equipment issue). The defib pads are…
2015-03-24 14:14:19
Ngan Thanh
17 year old male CC: Syncope
I thinks about WPWs on ECG!
2015-03-21 23:27:41
bob
Adenosine for sinus tachycardia: Try to avoid this!
I have a better answer for Shay's patient (and Mel) and it's called lone a-flutter because I just had it diagnosed in me. I'm looking at my ekg showing a rate of 230 which fooled the doc who thought it was svt's until I told him I had no history of anything and talked him…
2015-03-21 21:57:17
darren
17 year old male CC: Syncope
Voltage criteria for LVH. ? Hypertrophic Cardiomyopathy?
2015-03-21 21:12:57
Kyle H
Transcutaneous Pacing Success!!! Part 2
Great article. I love the use of US. This is another (in a growing list) of reasons why we should have prehospital US.
2015-03-21 16:10:38

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