Jump to content

SA Node and AV Node Functionality


Recommended Posts

I need help understanding this: How are the SA node and AV node connected, yet still can function independently?

I know how the two nodes function in unison and how the signal is sent from the AV node--->SA node----> rest of the heart via purkinje fibers, bundle of his, and a network of myocardial muscle tissue. What I really want to understand here is if they can even function independently of each other if they are so interconnected. Any help is much appreciated. 

Thanks in advance

Link to comment
Share on other sites

I don't know the exact electrophysiology behind this but essentially every myocyte has the potential to act as a pacemaker. Generally the pace set by one of these cells is lower the further down the heart it is (so a cell in the atrium would pace faster than a cell in the ventricle).  My understanding is that if the AV node is not receiving an input for any reason it will begin to pace itself, potentially leaving you with two independently (mal)functioning pacemakers. But this is a pathological condition, even if people can survive with milder forms such as atrial fibrillation. Complete heart block would be the worst case before cardiac arrest.

Link to comment
Share on other sites

9 hours ago, Prometheus said:

I don't know the exact electrophysiology behind this but essentially every myocyte has the potential to act as a pacemaker. Generally the pace set by one of these cells is lower the further down the heart it is (so a cell in the atrium would pace faster than a cell in the ventricle).  My understanding is that if the AV node is not receiving an input for any reason it will begin to pace itself, potentially leaving you with two independently (mal)functioning pacemakers. But this is a pathological condition, even if people can survive with milder forms such as atrial fibrillation. Complete heart block would be the worst case before cardiac arrest.

Hmm. Thanks for your response. But, since the two nodes are heavily interconnected and no input is being sent to the AV node, wouldn't that mean that the SA node isn't receiving an input as well? So how would the heart have to independently beating segments if the pacemaking starts from the AV node. 

I could be understanding incorrectly and am slightly confused. Let me know your thoughts--thanks again in advance. 

Link to comment
Share on other sites

In normal physiology they fire in sequence as you say. But when things go wrong they can fire independently. Normally things start in the SA node and travel around the atrium, causing it to contract, before arriving at the AV node. But sometimes the signal does not reach the AV node. If this happens the AV node will fire independently of the SA node, causing the ventricles to contract. The AV node can do this because all cardiac cells have the ability to become pacemakers (which causes a lot of the different arrhythmias - but is better than having ventricles not contracting at all). 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.