all right I want to welcome everybody back to another video lesson from ICU advantage and this is going to be part 1 in our new series of lessons covering ECG or EKG rhythm interpretation and in this lesson we're going to cover the conduction system of the heart [Music] you all right welcome back everybody like I said this is going to be the first lesson in a new series of lessons that we're doing covering ECG or EKG rhythm interpretation and so for those of you that this is your first time to the channel and you want to see more in-depth critical care education content such as this please do subscribe below and make sure and hit that notification bell to ensure that you're alerted as soon as new lessons become available your support really does mean a lot and it helps to support the channel and the videos such as this one and so for that I really do thank you and for those of you who don't know me my name is Eddie Watson and I'm gonna be presenting this lesson for you alright so let's go ahead and dive on in and so like I said in this lesson we're gonna be talking about the conduction system of the heart and in order to really be able to understand what's going on with your patient in terms of what you're seeing on their ECG rhythm strip it helps to really have a good foundation and understanding the conduction system that really makes that all possible and so we have a diagram of the heart here and I'm really gonna use this to show you where this conduction system is explained about it and helped you to have a good understanding of what's going on in the heart with this system and so I'm gonna go ahead and label some parts on here so that we make sure we're looking at this in the same way and so the first thing I'm gonna label is our right atrium our right ventricle our left atrium and our left ventricle now as we know these are the four major chambers of the heart and the blood flows through these chambers out to various parts of the body in addition to that the blood flow also will flow through our tricuspid valve our mitral valve our pulmonic valve and our aorta valve now I'm not going to spend much time here and really talk about the flow of blood through this system in fact we have a really great lesson that actually goes through all of this in detail within our hemodynamic series which i'm going to go ahead and link to up above but it does help to have a good understanding of that blood flow as well because ultimately the conduction system the whole point of that is to ensure that that blood flows through the system now one last thing I do want to get into before we really get into the meat and potatoes of what we're gonna talk about here is I do want to cover some basic terminology that's going to be important and for this we're really just gonna be talking about two things the first of these is what we call depolarization and depolarization is the key process that makes this whole system work and so real quick I'm gonna take a dive back into our biology anatomy physiology days and we're gonna talk about muscle cells and so to really give you that Cliff Notes version the muscle cells operate off of what's called an action potential and so if you remember we have all of those ions sodium potassium calcium all of these which have a positive charge and these ions have an ability to move in and out of the cell in order to change the charge of the cell and so if you remember inside the cell we have all the myosin and actin and when it receives this action potential or this change in charge it causes these muscle fibers to shrink down reducing the size of the cell and what essentially creates that contraction and so as these cells depolarize essentially they contract and so really we can think of depolarization as our contraction now the other bit of terminology that I want to talk about here is going to be our repolarization and so after that action potential has happened the ions have shifted and the cells have contracted eventually those ions start working their way back in the actin and myosin release causing the cell to move back out to its original size and this is what we call our relaxation and so like I said these terms are going to be very important as we get to talking about what's happening within this conduction system but just remember depolarization means we have contraction happening and repolarization means we have relaxation happening and so it's also important to note that when this is happening in the ventricle this contraction is what we call systole and again within the ventricle when we have this real taxation going on this is what we refer to as diastole all right so we've got that stuff out of the way so let's go ahead and jump into really talking about the pathways and how this conduction system works and so the first of these things that we're going to talk about is a special collection of cells that are located over here in the right atrium and this collection of cells is what we refer to as the sinoatrial node or oftentimes you'll just hear it called the SA node and this SA node you're gonna hear it referred to as the pacemaker of the heart and the reason for this is these specialized cells actually have the ability to depolarize on their own and this depolarization causes an action potential that moves out away from them and this is something that we refer to that's called automaticity and so like I said when that action potential happens this is gonna spread out to all the surrounding cells causing all of those cells to depolarize as well and in fact most cells in the heart will only depolarize when a neighboring cell depolarizes and so that's what makes these cells so special is they have the ability to depolarize entirely by themselves and to even make this cooler this depolarization happens at a pretty consistent rate and in fact the cells in the SA node will depolarize all by themselves at a rate of about sixty to a hundred times per minute and this rate can change as a result of various influences you can have influence from the sympathetic or the parasympathetic nervous system which we do cover quite thoroughly within our lessons on chalk again I'm gonna link to up above but also this rate can be influenced by some sort of problem or condition and ultimately change the rate in which these cells are depolarizing and so as those cells depolarize you get that wave of depolarization that flows throughout the rest of the atrium causing the cells of the atrium to contract and thus ejecting blood down into the ventricle now one thing to note though is this spreading of depolarization between cells is not the fastest process it works great spreading that signal from the proper direction slowly throughout those cells that you have a nice coordinated contraction but sometimes you need to get that signal to other places a little bit quicker and an example of this is here we have the SA node is over in the right atrium but we also need the left atrium to be firing at the same time and so there's actually a special pathway that kind of goes from the SA node and comes into the left atrium over here and helps to spread this signal out and the specialized cells that make up this pathway carry that signal very fast and this pathway that we have here is what we call Bachmann's bundle again think of this as a highway for that signal to spread from the SA node in the right atrium over to the left atrium in order to begin that process of depolarization and thus contraction so now moving from there there's another area of specialized cells and these cells are found down here in the atrial septal wall and these cells are what we call the atrial ventricular node or you'll often hear it referred to as the AV node and the AV node oftentimes you're gonna hear this referred to as the gatekeeper and the reason for this is the AV nodes job is to take that signal that originated in the SA node and pass that signal along throughout the rest of the conduction system and the way that it gets this signal from the SA node is through the use of three pathways and we call these the internodal pathways essentially all these do is take that depolarization that's happened within the SA node and ensure that it gets to the AV node so that the AV node can continue to pass that along now the cells that make up the AV node they're actually pretty specialized cells too and they have that same automaticity that the cells in the SA node have as well although these ones fire at a slightly differ rate so in the off chance that they aren't receiving signal from the SA node and they can fire with their own intrinsic rate of 40 to 60 but like we talked about really the AV nodes primary job is to be that gatekeeper of the signal from the SA node and so there's one really important thing that this node does is when it gets that signal from the SA node it's actually going to delay the conduction and so it's gonna receive that signal and it's gonna hold on to it for just a little bit before it passes it on to the rest of the system and it usually delays this about a hundred and twenty milliseconds or 0.12 seconds and this delay is absolutely vital in the functioning of this system the reason for that is by having this delay it allows for the full contraction of the atria as well as the closure of the tricuspid and the mitral valve before sending that signal along to the ventricles to contract and it's pretty amazing that this happens because by having this little bit of delay it prevents the atria and the ventricles from really working against each other and it keeps that blood moving in the right direction first from the atria to the ventricles and then from the ventricle out to either the lungs or the rest of the body and so really without this delay this flow of blood wouldn't work and so after we've had this delay the AV node is gonna pass that depolarization down into something that we call the bundle of hiss and the bundle of hiss is located within that ventricular septum and you can think of the bundle of hiss as this high speed transport system that we had just talked about it allows the conduction of those signals to happen very fast and it will take the same signal of depolarization that started all the way up in the SA node which has come through the intra nowtell pathways to the AV node and will now carry those throughout the ventricles and again it does this very quickly and the bundle branch is actually gonna split into two separate pathways we have our right bundle branch and our left bundle branch and then from there the left bundle branch is actually gonna split some more and take this into our left posterior fascicle and our left anterior fascicle so it's going to ensure that this signal gets to both the back or the posterior side as well as the front or the anterior side of that left ventricle and so we have those bundle branches which come down and again they really provide that fast transport of that action potential and then so finally from there we're gonna have these extensions off of these bundle branches and fascicles which we call the Purkinje fibers and so the whole point of these Purkinje fibers is to take that signal to the correct area their correct part of the ventricle in the correct order and this is what allows for that organized contraction of the ventricle ejecting that blood either out into the pulmonary artery or the aorta and so by sending the signal down that bundle of his into our left and right bundle branches and out through these Purkinje fibers you get that very uniform proper contraction again keeping that blood flowing in the right direction and finally once again the cells that are within the bundle of hysts or the Purkinje fibers they are also specialized cells and if they're not receiving a signal from the AV node they also have that same automaticity to be able to have their own intrinsic rate and so here if we're not receiving that rate from the AV node we're gonna have an intrinsic rate of 20 to 40 all right so that there is the overview of the conduction system of the heart and how it works as a quick review we have that signal that originates that depolarization that originates from the SA node is carried out through the atria aided by Bachmann's bundle to get over from the right atrium to the left atrium causing contraction in those atria pumping blood into the ventricles at the same time that signal is moving across those intra nodal pathways and reaching the AV node or the gatekeeper in which this delay is going to happen to that signal and after that delay that signal is gonna go out into the bundle of his into our left and right bundle branches are left branching into the left posterior fascicle on the left anterior fascicle and from there it's going to carry out into those Purkinje fibers and get to all the parts of the ventricle very quickly in the right timing and right order to cause that organized contraction ejecting that blood out the ventricle into either the the pulmonary circuit to go to the lungs or into the aorta to go out to the rest of the body it's really a pretty amazing system that we have here in the way it all comes together in order to just make everything work and keep that blood flow going in the right direction and moving throughout our body I hope this all made sense for you guys I hope that you have a better understanding of what's happening in this electrical system because like I said in order to really know what's happening when you're looking at your patients rhythm strip you have to know what's happening underlying to give you those electrical signals and so with that said I do want to thank you guys for watching I really hope that this lesson was informative to you guys if you like this video and you found it useful please make sure and hit that like button down below as it really helps to spread the word about our channel we're so appreciative of it we also love to hear your comments and feedback or any questions you have in regards to this video so feel free to leave those down below as well now coming up in the next lesson in part two of this series we're gonna dive into the actual rhythm interpretation and how you break down that electrical signal that you see on your patients rhythm strip so make sure and stay tuned for that next episode and the meantime feel free to check out another one of our great series of lessons on arterial blood gases as always thank you guys so much for watching and we'll see in the next lesson [Music]