Understanding Atropine

As requested, during our previous Adenosine discussion, we will briefly review, Parasympathetic stimulation and Atropine pharmacodynamics on the heart.

ACETYLCHOLINE (ACh) is one of the Neurotransmitters, a chemical signal, used by the Central Nervous System, which has many effects on the body, from stimulating muscle contraction, inducing peristalsis (digestion), Bile release by the liver, and as discussed here, decreasing Sinoatrial Node (SAN) and Atrioventricular Node (AVN) stimulation. When the later occurs, often we encounter its effect recorded on the ECG, seen as:

  • Sinus Bradycardia
  • SA Blocks
  • AV Blocks

The most common symptoms of Vagal stimulation include:

  • Vasovagal Syncope
  • Nausea and vomiting
  • Dizziness

ACh is released during Vagus Nerve (Cranial Nerve X) stimulation ,which in the heart, binds to M2 Muscarinic Receptors, one of the 5 types of Muscarinic Receptors, which mainly work in CNS and skeletal muscle. Out of all these receptors, binding of ACh to M2 receptors affects the heart and its overall conductivity.

How does this work?

  • Decrease Cyclic Adenosine Monophosphate (cAMP) intracellular
  • This slows down L-type Calcium Channel opening, leading to decreased automaticity and slightly decreasing contractility
  • Potassium (K+) efflux (leaving the cell) is delayed, which prolongs repolarization, delaying the next action potential

The combination of all these actions, hyperpolarize the cells, increasing SA Nodal and AV Nodal threshold, which decreases the overall conduction, mainly through the AVN. This is known as Negative Dromotropic Effect.

 

ATROPINE

atropine

Atropine, an antichollinergic, derived from the plant, Atropa Belladonna, or “Deadly Nightshade flower”,  blocks ACh binding to M2 receptors, giving it the “Parasympatholytic” property. The goal is not necessarily to increase SAN function, but rather, block the parasympathetic  response produced by M2 receptor stimulation, leading to normal SAN and AVN function.

 Now that we understand how Vagal Stimulation affects our cardiac function, the use of Atropine makes a bit more sense during suspected bradycardia induced symptoms.

 

2 Comments

  • James M says:

    I love these drug summaries. Thanks a lot, Ivan, for taking the time to do them. I look forward to seeing more! Perhaps amiodarone?

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EMS 12-Lead

Cardiac Rhythm Analysis, 12-Lead ECG Interpretation, Resuscitation
Comments
Brooks Walsh MD
“Bad heartburn” – 82 y.o. female without chest pain.
The option was indeed turned on! As for non-CP presentations of ACS, I absolutely believe that these warrant the same level of urgency as the "typical" presentations. Both men and women, young and old, all commonly present without classic chest pain. Besides, how much difference is there between "burning in the epigastrium," and "pain in…
2014-08-21 17:10:37
Austin
“Bad heartburn” – 82 y.o. female without chest pain.
You took the words right off of my keyboard, Jason! A little bit of critical thinking works wonders when faced with "protocol versus best interests of the patient" type decisions. Not to encourage deviation from protocols and such, but it is a much less severe trespass if you bend the rules a bit as long…
2014-08-21 16:33:27
Brooks Walsh MD
“Bad heartburn” – 82 y.o. female without chest pain.
My uninformed opinion? I pretty much agree with AHA - if they aren't hypoxic, no need. I'm not sure how terrible superoxia really is, short-term, but why bother if it doesn't help?
2014-08-21 16:31:05
jason
“Bad heartburn” – 82 y.o. female without chest pain.
Chris Watford- as you probably know the "acute MI suspected" detection function in the LP12/15 is a programable option. I suspect the software didn't miss this but rather it wasn't turned on. As for treatment everyone has pretty much got it down. Finally as for activation. Absolutely! Don't real care if the protocol allows for…
2014-08-21 16:30:34
Austin
“Bad heartburn” – 82 y.o. female without chest pain.
There's not much I think I can add at this point, but I will comment on a couple of things. The reciprocal changes indicate to me that there is likely RCA involvement. Also, I've recently been hearing quite a bit about withholding O2 in ACS patients like this. Dr. Walsh, do you have any opinions…
2014-08-21 16:23:21

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