Atropine Pharmacodymanics
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 c...
Source: EMS 12-Lead - Category: Cardiology Authors: Ivan Rios Tags: Pharmacology Training atropine bradycardia Source Type: research
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