Cardiovascular | ECG Basics

All right, engineers. So, what we're going to do in this video is we're going to talk about the basics of EKG. This is a really important diagnostic tool that we should use as clinicians. It's important for being able to look for arhythmias, being able to look for possible myioardial inffections. So, it's a great tool that we as clinicians should be able to understand. In order for us to do that, we have to really kind of dig in just to the the basics of the electrical activity of the heart. Talk about how that represents vectors. Talk about how those vectors are basically interpreted um and generated through a graphical representation that we see on EKGs. So let's go ahead and first start on the cardiac conduction system. All right. So let's go ahead and talk about a little bit about the cardiac action potentials. Right. So whenever we re in order for us to really understand how the electrical activity of the heart correlates with the uh corresponding EKG we have to understand just a little bit about electrodes. Okay just the basics basics on electrodes. So let me give you an example of what I'm talking about here. So in order for there to be like this graphical representation because that's what Nikkag is. It's a graphical representation of the electrical activity of the heart. the electrical activity of the heart is actually going to be transmitted onto specific electrodes and those electrodes will pick up at that electrical activity and present it with either a positive deflection, a negative deflection or it might just be like a flatline. So, let me explain just a little bit about that. Let me say here I take a piece of cardiac tissue here. Here's a piece of cardiac tissue and here's a piece of cardiac tissue. Okay. What I'm going to do is let's say that this cardiac tissue is going to it has the ability to conduct electricity. All right? And what I'm going to do is I'm going to put an electrode on one end of the tissue. Let's say that here I put a positive electrode at one end of the cardiac tissue. Okay. So here's a positive electrode. It's linked in with this tissue here. Then over here I'm going to put a negative electrode on the other end of this cardiac tissue. Now what happens is let's say that the cardiac tissue right it has the ability to generate its own electrical activity and that electrical activity when it's generated it moves in a direction towards the positive electrode. When the electrical activity of that tissue moves towards the positive electrode the positive electrode actually picks that up as a positive deflection. So when electrical activity which is being conducted through a tissue is moving towards the positive electrode which are going to be these different things that we're going to put on the patient's body it is actually going to have a positive deflection. Okay? So this will give you a positive deflection. If again I do the same thing over here I put a positive electrode on this end of the cardiac tissue. I put a negative electrode on this end of the cardiac tissue. You probably already know where I'm going with this, right? So same thing let's say that the electrical activity that's being generated is actually moving from this side to this side. So it's moving from the positive to the negative electrode. Well now if it's moving away from the positive electrode because that's who's actually picking up the electrical activity. It's the positive electrode. If the electrical activity is moving away from the positive electrode, it'll actually produce a negative deflection. So that's what I really want you to guys to remember here when we're kind of just talking about, oh, this is a positive deflection. This is a negative deflection. This is a flat kind of line. So that's the next thing. Well, how do I know if something is just going to be maybe there is no deflection? Well, that means that maybe that if you're having something like that, it could be that the action potential is actually being conduct uh so the the electricity that is being conducted through that tissue is being conducted very very very slowly or another thing that could indicate a flat line is that you have an electrical activity that's moving perpendicular to the axis of this lead this electrodes. Okay. So basic thing that I really want you to understand here for these EKGs is you have a negative positive electrode. If the electrical activity of the cardiac tissue, which we're going to use in this example, is moving towards the positive electrode, it's going to produce a positive deflection. If the electrical activity of this tissue, in this case we're talking about cardiac tissue, is moving away from the positive electrode, it's going to produce a negative deflection. All right, that's what I want you guys to remember for right now. I just want you guys to trust me and we'll talk about all these different leads. I just want you guys to trust me that we're going to be looking at each one of these hearts from one specific lead. Okay? And that's going to be lead two. And again, we'll talk about what the heck lead two is. I just want you guys for right now to trust me that this is going to be lead two. So, in order to make a lead, right, a lead two, you're going to have to have a positive and negative electrode. So lead two, we're going to put the positive electrode here at the apex of the heart. And we're going to put the negative electrode here at the base of the heart. And now you have this this lead this axis of the lead which is going to be moving in this direction here. Okay. Now let's try to imagine that this is kind of a straight line right here. Okay. So negative to positive electrode. The electrical activity of the heart starts where? It starts at the SA node which is up in the right atrium. Right? When the electrical activity of the SA node is triggered, it triggers action potentials that move throughout the atria. But where is it moving towards? It's moving towards the AV node, right? So it could be moving all the way out this way. It could be moving this way and moving towards the middle. the mean vector of atrial depolarization is going to be pointing directly towards the AV node. So that's where the mean vector of atrial depolarization should be going. What am I talking about? Let's make it very simple here. Let's say that I'm talking here's the heart. Okay, here's just a very generic thing. Here's going to be the essay node. Let's say here I put the essay node. Here I put the AV node. Okay, here's my bundle branches and perkenis. Very simple here. Electrical activity is generated and it might move this way. It might move this way, this way and this way. If you take all of these vectors and develop a net vector, the net vector should be directed towards the AV node. That's what I'm talking about. Okay. So, atrial depolarization starting from the SA node going towards the AV node is moving this way, moving kind of downwards and to the left. Where's it moving towards the positive electrode? If the electrical activity of the heart is actually moving towards the positive electrode and again what lead is this that we're kind of using this example here for here. Let's make kind of like a dotted line here. This is going to be lead two. Again, we're I just want you to trust me for right now that this is going to be lead two. I'll explain what that means in a second. But which way is it moving? The electrical activity is moving towards the positive electrode. So what should that produce on the EKG on lead two? A positive deflection. Right? So on lead two, if we were looking at lead two here, you should get a positive deflection. Well, guess what that positive deflection is? That's the Pwave. That's representing atrial depolarization. So the Pwave is indicative of atrial depolarization. All right. All right. Cool. Next thing we move on. Okay, electrical activity was generated right essay node to the AV node. Then what happens? Remember I told you that the electrical activity goes to the AV node and remember this back from all the other physiology videos. The AV node is a slow conductor of electrical potentials. So it has about a 0.1 second delay before it sends the action potentials from the AV node into the bundle of hits. So what mean what that means is that there's no actual vector that's being generated. The electrical potential isn't moving. If no electrical potential is actually being generated and moving, is there going to be a direction of the electrical potential? In other words, I want you to think about like this. The electrical potentials was being generated from the SA node towards the AV node. The AV node is now stimulated, right? So it's positive, but it's depolarizing and it's conducting the action potentials through it very very slowly. So it hasn't developed an actual action potentials to move down to the bundle of H yet. It's stuck in that AV node. So therefore the electrical potentials, the actual electrical activity isn't moving anywhere in this direction. It's staying in the AV node for about 0.1 second. So if there's no electrical activity being generated or moving, imagine here your negative electrode, positive electrode. Again, here's your lead 2. There's no electrical activity that's moving from the AV node to the bundle of his yet. There's about a 0.1 second delay. Is there going to be any deflection? No. So this should actually be a flat line. So this is your Pwave. Again, we already discussed that that was actually going to be atrial depolarization, right? And that's generated by this vector. But now you're going to have this period where there's an isoelectric line. In other words, there's no deflection from this point. This is actually going to be the PR interval. And the PR interval is basically when action potentials are being conducted through the AV node but very very slowly. And because of that, no action potentials and move from the AV node into the bundle of H. So there's no direction of the action potential. Why is this important? The PR interval is important because when it comes to heart blocks, in other words, if someone has a firstderee heart block, what does that mean? That means that the AV node is taking a while before it's actually conducting action potentials down to the bundle of his down to the ventricles. If it's a second degree heart block, sometimes there's action potentials coming down to the AV node, but it just doesn't send some of the action potentials. And then third degree is the AV node doesn't even have any connection anymore between the atria and the ventricles. So that's why the PR interval is very important. Okay, so Pwave, PR interval. Move on to the next one. Again, SA node action potential to the AV node. AV node is now going to generate action potentials that are going to move into the bundle of H and down these bundle branches. Right? So what are you going to have here? You're going to have SA node to the AV node. AV node is going to generate this conduction, but again it's a very slow conduction. So it's not going to have a direction of the electrical vector yet. Then it's going to move down into the bundle of H and into the right bundle branch and left bundle branch. Well, we have to deolarize the septum. Here's what's really interesting. When electrical activity moves down the bundle of H and down the right bundle branch and down the left bundle branch, the left bundle branch is the actual branch that depolarizes the interventricular septum. So, imagine it like this. Let's come over here to this little diagram. You have here your left bundle branch, right? So left bundle branch and over here you're going to have your right bundle branch electrical activity is going to be generated through the AV node into the bundle of H and then down into these bundle branches. When the left bundle branch is generating these action potentials, he is actually sending these action potentials in the direction of the interventricular septum. So it's actually going to be deolarizing the septum and it's going to be moving towards the right side of the heart. So when you're deolarizing the septum, it's only going to be from the left bundle branch. Okay? So left bundle branch is actually going to be stimulating the interventricular septum moving this way. So what kind of vector would that generate? If you're moving this way, you're going to generate that type of vector, right? It's a simple thing. So again, left bundle branch is stimulating the interventricular septum. Just remember the heart's kind of shifted two/irds of the left. So it's going to be kind of at an angle moving towards the right and upwards. So they go back to your lead system here, lead two, right? Negative electrode, positive electrode. And then here's going to be the axis of that lead. Which way is that actual uh action potential, the positive um the the conduction of electrical potentials moving towards? was moving from the left bundle branch towards the right bundle branch, right? But it's going to be going through the interventricular septum. So that's moving in what direction? The opposite direction. So what should that generate? That should generate a negative deflection. Okay? So you're going to have your Pwave, which is going to be a positive deflection from the atrial deolarization. Your PR interval right there, right? P R interval which is going to be whenever the AV node is slowly conducting action potentials but there's no net direction of an electrical vector. Okay. Then you're going to have this negative deflection and that's going to be indicative of intervententricular septum depolarization. What is this wave here called? This wave is called your Qwave. Now remember this, there is pathological Q waves and we'll talk about what these mean. But all I want you to remember for right now is that the Qwave in this normal QRS complex is indicative of septal depolarization. Okay, simple thing here. I just want you to remember that the Q wave is indicative of septal deolarization. Okay, so we got our Pwave here, right? That's going to be indicative. Let's draw the net vector. Let's keep again being consistent with this. So where's the net vector going from the SA node to the AV node? It's generated like this. Okay. So there's that vector. Then we have the period PR interval. This is where the AV node is stimulated. It's conducting action potentials through it very very slowly. Then we have the net vector for the Qwave. Where's that pointing? It's pointing from the left bundle branch right towards the right. So it's going to be pointing rightwards and slightly upwards. Now we're going to move down the left bundle branch down the right bundle branch. So we've already depolarized the septum. Now what do we got to start doing? Let's have these action potentials that are now going to be from the bundle branches go to the perkingis. And from here we're going to start depolarizing like this. It's going to move. So imagine here I kind of took a a tissue. I took like a piece of tissue there. Imagine here I take this piece of tissue, right? And this is going to be the inner cavity. This is going to be the outer wall. Okay? So imagine here just to be simple here. This is going to be the inner wall. This is the outer wall. Inner wall, outer wall. Imagine here you're going to have a bunch of cells, right? So this is made up of a bunch of cells. The action potentials are going to be generated moving through those cells. Okay? So it's going to be moving through those cells. So these action potentials are going to be generated. They're going to start moving outwards like this. Okay. So it's going to turn the negative membrane to a positive, negative, positive, negative, positive. So the direction of the action potentials are moving towards the right, towards the left, and straight down. Let's think about this. Right ventricle, is it thicker or is it thinner than the left ventricle? Left ventricle is pretty thick, isn't it? is thick. So if the left ventricle is thicker than the right ventricle, who is going to have more electrical activity, more of a larger magnitude of electrical activity? The left ventricle. So let's do this. Let's say that we get a net vector for the right ventricle. Let's draw it like this. Okay, there's our net vector for the right ventricle. But then you're going to have the net vector for the left ventricle. And this should actually be have a larger magnitude. So there's one vector. There's another vector. This is the right ventricular vector. Left ventricular vector. Why is the left ventricular vector larger? Because it's thick. You got a thick left ventricle. So now where is the resultant vector going to be? Between these two, right? But it should point a little bit more towards the left. Right? Why? because the left ventricle is going to generate more electrical activity than the right side. So if you're going resultant vector just basic physics right you have here here one vector one vector the net vector is supposed to go between but it's going to be a little bit more towards the left. So now the net vector here should be going like this. Okay. So if the net vector is pointing down that way, let's imagine this then what do we have here? What do we have at this point? Down here we have our positive electrode. Positive electrode of lead 2. Over here we have the negative electrode of lead 2. The mean vector which we're going to circle here. Let's circle this vector here in brown. This is the mean vector between the left and right ventricle. Where is it pointing? That sucker is pointing straight down at the positive electrode and it's going to be a big vector. Okay, this is going to be the mean QRS vector, right? And it's pointing towards downwards towards the left hip, right? Towards that positive electrode. So, it's going to produce a very nice large positive deflection. Okay, the mean QRS vector which is the sum of the left ventricular vector and the right ventricular vector should point downwards and a little bit more towards the left. Why? Because the left ventricle is has a thicker myioardium so it generates more electrical activity larger magnitude that's going to produce a positive deflection. So again this positive deflection again what do we got here? Pwave. Then we have here this point is the PR interval. Then we have here we have the Q-wave negative deflection. What's this big mama? That big mama jama right here is going to be the Rwave. And the Rwave is indicative of what? Ventricular depolarization. Right? So it's indicative of ventricular depolarization. Now let's move on to the next step. So you're depolarizing the ventricles. You're you're basically flipping the membrane from negative to positive. That's what this Rwave is is indicating, right? So, the net vectors are being generated. Now, we go to the next step, which is going to be this S-wave. Okay? So, again, keep going off of your vectors just to be consistent. Where's the the direction SA node to AV node? That's your Pwave, right? That's the first vector. Then AV node is becoming positive. Y is conducting action potentials very slowly, but no net direction. Okay? Then the net vector from the left bundle branch stimulating the septum is going to be moving to the right and slightly upwards. Then you're going to have a right vector coming to the right ventricular mioardium. Left ventricular mioardium is going to be a larger vector. When you sum the two up and get your resulting vector because the left is larger than the right, it's going to be pointing downwards and slightly leftward. Okay, let's keep her going then. Now we said that you were deolarizing outward right in this stage here where you were generating the Rwave. Well now guess what happens as you stimulate outwards you then have to move where? So you're going to have to move upwards. And now the electrical activity is going to start moving upwards. And as it starts moving upwards towards these actual bases of the um the ventricles, where's the vector moving? So imagine now I draw a vector. This is moving upwards. This is moving upwards towards the bases of the ventricles. Where is this pointing with respect to lead two? Here's your positive electrode. Here's your negative electrode. And again, here's the axis of that lead. Mama, where is these guys pointing? They're pointing in the opposite direction of the positive electrode. So what does that mean? If it's going in the opposite direction of the positive electrode, it's a negative deflection. So that's going to be our negative deflection right there. And that is our S-wave. So again, you have the Pwave, you have the PR interval, you have the Qwave, Rwave, and the S-wave. What is the S-wave indicative of? It's indicative of the depolarization at the bases of the ventricles. Okay? So, it's the deolarization of the bases of the ventricles. So, the Rwave is you were depolarizing the apex of the ventricles and then the base of the ventricles is going to be too polarized for the S-wave. Okay? All right. So, now let's think about this. SA node, you guys are going to hate me by the end, but this is going to make sense, right? So, this is the net vector from SA node to AV node. AV node is deolarized afterwards. It stays positive. Conducts action potentials very very slowly. Doesn't generate a net electrical vector. Left bundle branch is going to be deolarizing the septum and it moves from the left to the right and slightly upwards. Mean QRS vector formed as the resultant between the right ventricular vector and left ventricular vector for the apes is going to be slightly downward and leftward. And then you're going to have after that after it deolarizes the apex it's going to turn around and go upwards towards the bases of the ventricles and you're going to get the depolarization of the right and left basil part of the ventricles and that's going to generate your S-wave. All right. So now the entire ventricular mioardium is depolarized. Okay. But there's no net direction. It's just depolarized. It hasn't repolarized yet. So that is what our ST segment represents. So the ST segment is going to be the period of time in which the ventricular mioardium is still depolarized. Okay? It hasn't gone into a repolarization state just yet. Okay? So that's what I want you to remember about the ST segment. The ST segment there's no net electrical vector. Okay? So that's why it's going to be isoctric. the entire ventricular myio myioardium is deolarized for that instant of time and it hasn't repolarized just yet that is the ST segment okay we got to go to the last part which is actually going to be our T-wave right so again if you guys remember the vectors right SA node to AV node pointing downward here towards the AV node positive AV node due to conducting the electrical potential slowly septal depolarization pointing uh rightwards and slightly upwards Right? And then you have your mean QRS vector pointing downwards and to the left. And then you have the base of the ventricles deolarizing because of the moving from the apex and upwards. Right? Then the entire ventricular myioardium is deolarized. Right? So it's entirely positive. Now when you flip the charge, right? So it was entirely positive. Now it's going to go from positive and you're going to flip it to negative right when you flip the charge. So now this entire ventricular myioardium imaging this entire thing on the outwards is positive. I'm going to go positive flip it to negative positive flip it to negative. So I'm trying to make my entire I'm trying to bring a negative charge moving back and upwards. So that negative charge is moving away from the positive electrode. And so what you're going to want to remember for this is because the negative charge is moving away from the positive electrode, it's just going to give you a positive deflection. Okay? So again here, positive electrode here for lead 2, negative electrode here, right? Here's going to be this axis of that lead. Again, lead two. If you guys are remembering, the negative charges are going to be moving and it's going to be moving upwards, right? So, negative charges are going to be moving. You're going to be going flipping it from positive to negative, positive to negative, positive to negative. Because the negative charges are moving in the opposite direction of this positive electrode, it's going to cause this deflection to be upwards. So you're going to get an upwards deflection and that is going to be the T-wave. So to wrap it up for this part here, Pwave is going to be this part here. Again, that's going to be the deolarization from the SA node to the AV node. PR interval is going to be the period where the AV node is actually conducting electrical potentials very slowly. Qwave is going to be the septal depolarization. Rwave is going to be the mean QRS vector generated between the resultant of the left and right ventricle. S-wave is going to be the base of the ventricle deolarization. ST segment is going to be when the entire ventricles are deolarized and haven't repolarized just yet. And the T-wave is going to be when the entire membrane flips its charge and it becomes from positive to negative. Okay, that is going to be your entire EKG strip there. Now, we've gone through the electrical vectors and correlated that with their corresponding EKG deflections. What we have to do now is get a little bit more information on how these leads work. Okay, what are the different types of leads and how all these leads make up a 12 lead EKG system that gives you a very very significant three-dimensional view of the heart in both a frontal and horizontal plane. All right. So now that we understand how the cardiac vectors that are generated from the electrical activity of the heart represent these kind of deflections positive negative or isoelectric lines on the EKG and we kind of just kind of bombarded you with the this idea of oh you're only looking at it in this lead to system. That's not true. Again that's one way that you can look at it. So whenever you see EKGs you just see like a one component of an EKG. Usually it's a lead 2 EKG. Um, and and again, we'll talk about what that means, but what I want you to remember is that whenever we're doing these things in a clinical setting, they're usually 12 lead EKGs. So, 12 leads, what does that mean? That means that you have Okay, so we have 12 leads. Out of these 12 leads that make up the EKG, three of them are going to be what's called bipolar limb leads. Okay? And these are going to be what we call one lead one, lead two, and lead three. Okay, we'll talk about these first. The next one is going to be three augmented, we call them augmented unipolar limb leads. And these were kind of derived from Antoven's triangle by a guy named Wilson. He made what's called Wilson central terminal. And then another guy named Goldberg, he kind of modified that to where you got this really cool way of having an augmented uniolar limb lead. And we'll talk we'll talk a little bit more about what that means. But again, this is going to be AVF, ARVR, and AVL. And again, we'll discuss this a little bit more. The last thing is going to be your six precordial or we just chest leads. Okay? or we can call them chest leads. Okay? And this is going to be V1 all the way to V6. And again, we'll talk about these. Here's one thing I want you to remember though, the bipolar and the augmented uniolar limb leads, they look at the heart in a frontal plane. So, if you were to imagine what that means, a frontal plane is, it's also another word for it called coronal. So in other words, you're taking a slice of me like this. You're slicing me like this and you're putting me into an anterior and posterior piece. Okay? So an anterior and posterior piece is a frontal plane. That's how these are looking at the heart. Okay? The chest leads are going to be looking at it in a horizontal or transverse. So imagine you're cutting through me right in the middle of the heart and you're looking at the heart in that direction. So a superior and inferior piece is what I'm going to be in. but you're looking at the heart in a transverse type of way. Okay? Transverse or horizontal sectioning. So that's another thing I want you to remember. All right? So the first ones that we're going to talk about is bipolar limb leads. Bipolar limb leads is you're going to have a negative electrode and a positive electrode. So there's two poles, a negative electrode, positive electrode. What you're going to be doing is you're going to have three of them. And you're going to need one electrode on one side, one electrode on the other one. and that's going to develop a lead. Okay, so imagine here we have this guy. He's coming in. He's got to get an EKG. We got to get him hooked up. Okay, so we're gonna apply the bipolar limb leads on him. All right, so the first thing we have to do is we have to take and put some electrodes on him. What we want to do is we're going to put on his right arm. So, this is going to be right arm, left arm, left leg, right leg. On his right arm or right shoulder, we're going to put a specific electrode here. We're going to put a negative electrode on this guy. We're going to stick that on his right arm. Okay. Then, what I'm going to do is that's my negative electrode. I have to put another electrode on the other side, the left side. And if it's a positive electrode, that's going to give me one lead. So this is going to be a lead right here. There's one lead. That's the axis of my lead. This one right here is called lead one. So I'm going to put a a negative electrode on right arm, a positive electrode on the left arm, and that's going to create the axis of lead one. Okay? That's the first thing I want you to remember. Then what we're going to do is we're going to take another electrode and we're going to put a positive electrode on the left leg. So let's put a positive electrode on the left leg. Now I have a negative electrode from the right arm and a positive electrode from the left leg. Look that generates an axis here. Now I have an axis of a lead. This is the axis of this lead. This lead right here is going to be lead two. So negative electrode on the right arm. Right? So what I'm going to do is here I'm actually going to put another because I actually have to create I'm going to put a negative electrode another negative electrode on this guy's right arm. And then I'm going to put a positive electrode on his left leg. That creates this axis. This is going to be the axis of lead two. Okay, let me do another one. I'm going to put another positive electrode on this guy's left leg. And then what I'm going to do is I'm going to put a negative electrode on his left arm. If I do that now, I'm going to have another axis right here going from the left arm to the left leg. This is going to be the axis of lead three. Now, this right here is going to be my bipolar limb leads. All right. So, now we're just going to take and kind of superimpose this onto here, right? So, very simply, what do we have on this side? Right arm, left arm, left leg. Right. Right arm. What are we going to have? We're going to have a negative electrode here. Positive electrode over here. That's going to give you lead one. Then we're going to put another electrode on the right arm. Positive electrode on the left leg. That's going to give you lead two. We're going to put a negative electrode on the left arm. And another positive electrode on the left leg. That's going to give you lead three. All right. So, this makes up this triangle which is a Tven's triangle. And he has a law and Antoven's law uh says that if you take lead one, right, and you add it to lead three, it's going to equal lead two. And this is just coming based off of the vectors. We'll explain this very, very briefly in a second. Here's what I want you to remember, though. The axis of this lead, right? You have a negative electrode and a positive electrode here. Okay, that's going to be making up lead one. The positive electrode is the exploring electrode. Here's the way I want you to think about this. Imagine the positive electrode is your eye. Okay, imagine it's your eye and you're looking towards the negative electrode. Okay, so if we were to kind of think about it like this, this is me. I'm on the positive end and I'm looking this way. This is what lead one is doing. It's looking at the heart from which way? From the left side. Okay. So that's the way you want to remember this is that lead one is looking at the electrical activity of the heart but from the left side of the heart. Okay, that is important. Now lead two, where does it looking from? Okay, well the positive is here. Remember I told you put your eye where the positive electrode is and look towards the negative electrode. Okay. Well, he's looking from down here. So now I have positive electrode looking up towards the negative electrode. So it's looking at the heart from the bottom. Okay. What about three? Three is doing the same thing. He's just looking at a different angle, but he's looking at the bottom of the heart looking upwards. Isn't that so cool? So now what these leads are doing is is they're looking at the electrical activity activity of the heart from different angles. So which way is one looking? One is looking at the electrical activity of the heart from the we're going to say left lateral. So left and lateral heart. So it's looking at the left and lateral view of the heart. What about two and three? It's looking inferiorly. Okay. And we'll talk about angles later. This two is usually positive 60. three is actually going to be um like positive 120 degrees. And again, we'll get into that stuff when we talk about axis. But what I want you to remember is that two and three are looking at the inferior view of the heart. Why is that important? Because if someone is having a myioardial infarction in the inferior view of the heart, which leads are you going to be wanting to look at? Two, three. And there's another one, AVF. If you want to look to see if there's a infuction on the left lateral portion of the heart, what are you going to be looking to one as well as another one we'll talk about AVL and V5 and V6. So that is the significance of these leads. That's what I want you to remember from this. Not all of the physics and stuff behind it and all the electrodes, but really just to understand what is lead one doing and how is it looking at the heart? What is lead two and three doing and how is it looking at the heart? And again, you should know where to put the negative and positive electrodes. That should be important. But know the axis of the lead and where the how you're looking at the electrical activity of the heart with respect to those electrodes. Okay. So that's our bipolar. Let's go on to the augmented uniolar. All right. So now let's talk about the augmented uniolar limb leads. So this guy named Wilson, he kind of developed this like different way. Again, you don't really need to know all the history and background and physics behind it. What I just want you to understand is augmented uniolar limb leads. I want you to really know how they're looking at the heart, what these electrodes are supposed to be doing, okay? Which one's negative, which one's positive, in what direction. The EKG machine is doing all of this really for you. So, you don't really have to know a lot about the physics and the electrodes on this one. It's more just about the direction that this is looking at the heart. That's what I want you to really understand more of. So augmented uniolar limb leads what happens is the e the machine the EKG machine it has this ability right to generate negative charges at two points right so imagine here here's going to be the right arm here's the left arm here's the left leg right let's say that the EKG machine so we're going to be have we want to look at the heart from a specific way let's say that we want to look at the heart from the right side okay So what it'll do is if we want to look at the heart from the right side, it's actually going to take and put a negative electrode on the left arm. Okay? It then correlates a negative electrode on the left leg. Now what happens is whenever you have negative negative, this is going to have to be the positive electrode here at the right arm. Now the direction in which this vector is actually moving is between the negative electrodes. Right? So now it's actually pointing which way? It's pointing this way towards the positive electrode. Okay? So now here's what I want you to remember then. This right here, right? So the augmented uniolar limb leads you put the EKG machine puts a negative electron on the left arm left leg and then it generates a positive electrode on the right arm. Okay. What that does is is that creates a vector between these two negative points these two electrodes, right? Because it can't you're going to have the net between this one and this one. So it's going to be right in the middle there. Remember positive is looking towards the negative which is going to be in between these two negative electrodes. So if you're looking, how is the how is this electrode looking at the heart? It's looking at it from kind of upward. So it's above it and it's looking at it on the right side. So it's getting a view of the heart from the right side and a little bit above it. This right here is called augmented uniolar limb lead, right? But we don't like to put all that crap. So we just put AVR, augmented uniolar limb lead R. So AVR, how is it looking at the heart? Again, here's your eye. You're looking at the heart from the right side and a little bit from the superior view. So a little bit more of the upper and righter right part of the heart. But if you want to be simple, it's looking at the right side of the heart. Okay? So that's the big thing there. All right. So now you want to look at the heart from the bottom, right? So again, here we're going to have right arm, left arm, left leg. Okay. What we're going to do is we're going to put a negative electrode on the right arm, a negative electrode on the left arm. And again, the EKG machine is doing all of this, and then it's going to generate a positive electrode here on the left leg. Where is the resultant vector going to be? Remember, this is pointing this way. This will be going this way. But the resultant is going to be straight down, slap dab in the middle, right? So, it's going to be pointing this way towards that positive vector. But again remember the positive electrode is going to be looking towards the negative electrode which is going to be smack dab in the middle. So how is it looking at the heart? It's looking at the heart from the inferior view the bottom. So it's looking at it from the bottom. So which one is this one? This is going to be augmented uniolar limb lead foot. Well we don't want to write all that. So we just put AVF. So this one is actually going to be AVF. So this is what I want you to remember. AVF looking at the heart from the inferior view. AVR looking at the heart from the right sided view. So what do you think we're going to have left guys? AVL. Right. So again, let's come over here. Right arm, left arm, left leg. So we want it to be obviously the positive electrode at the left arm and the EKG machine will generate negative electrodes on the right arm and left leg. So which way is the resultant vector? Because remember it's moving from negative to positive, negative to positive. Smack dab in the middle is the resultant. So it's going to be pointing this way. So now how is this one looking? It's looking at the heart from the left and lateral view. Isn't that a beautiful thing? So which one's this one? It's augmented uniolar limb lead left arm. So this is going to be AVL. So here's what I want you to remember. AVR looks at the right side of the heart. The AVL is looking at the left and lateral side of heart. And then the AVF is looking at the inferior view of the heart. That is really important. All right. So, let's imagine here that we're going to be putting the these chest leads on the chest wall. Right? So, what you're going to be doing is you're going to go in feel the patient's chest, right? And right like about here, you're going to have this little prominence, a little bump, okay? Call the sternal angle or the angle of Louis. You're going to palpate that. Then, what you're going to do is you're going to kind of move over to the right. When you move over to the right, you should be at the level of the second rib. And then, what you're going to do is you're going to count down. Right. Second rib, second intercostal space, third rib, third intercostal space, fourth rib, fourth intercostal space. Okay, that's where we want to go first. So, right, fourth intercostal space just on the right side of the sternum. We're going to put our first chest lead there. And let's put on here. Let's do first one here. So again, first, so second, third, fourth, we're going to put V1. That's going to be our first chest lead. Okay, it's going to be right fourth intercostal space on the paristernal side. Okay, then what we're going to do is we're going to just go on the opposite side of that. So just go symmetrically to the other side. So now you should be on the left fourth intercostal space on the parernal side. Right? So now put your second chest lead right there. Okay. Then we're going to skip V3 for a second. Okay. We're going to go to V4. V4 is going to go to the fifth intercostal space. Okay, but we're going to have to make sure that it's kind of like right in the middle part of the clavicle. So, what we're going to do is we're going to skip V3. We're going to go from the fourth to the fifth intercostal space and we're going to go to about maybe right here. And let's say that about right there, that's mid-clavicular line. We're going to put V4. V3 is going to go right between them. Okay? Okay. So, right smack dab in the middle here, I'm going to put V3. So, V1, right fourth intercostal space. V2, left fourth intercostal space, paristernal line. V3, hold on a second. V4, mid-clavicular line, fifth intercostal space. Then put V3 right between it. Then you're going to go to about the anterior axillary line. And again, fifth intercostal space, you're going to put V5 there. there. So let's say that V5 we're going to put right here. Then after you go to the anter axillary line, you're going to go mid axillary line. And that mid axillary line, fifth intercostal space is going to be V6. So let's put that one a little bit over here. This is going to be the placement of the chest leads. Okay? Now, this doesn't do justice on how these are actually looking at them, but here's one thing I want you to understand. This is really pretty really pretty pretty pretty cool with the bipolar and the augmented uniolar limb leadings. You had negative and positive electrodes. These are really cool because they're just a positive electrode. So all that they are are pos So imagine like a little suction cup here. Imagine here we have like a little suction cup. Okay, it's connected to a wire. This right here is just a positive electrode. That's all it is. So, it's picking up electrical activity to generate it by the heart. It doesn't need a negative electrode. It only just needs this one positive electrode. That's pretty darn cool. So, there's they're they're actually picking up electrical potentials that are moving through the heart and into the chest wall, right? So, let's look at this and let's imagine here that I take the heart, right? We're going to take the heart out and then we're going to slice it in half and we're going to look at it and we're going to pull it out like this. Okay. So again, imagine here I'm taking the heart like this. Okay. And all I'm going to do here is I'm going to slice it and I want to look at this heart in a sliced view. Okay. So here we're going to have the interventricular septum. Right? Here's our interventricular septum. This is going to be the left ventricle and this is going to be the right ventricle. Okay? Here's the apex of the heart and here's going to be the bases of the ventricles. So if you imagine here, let's put our first lead on here. So again, V1 is going to go about right here. So imagine here we're putting V1. Then we're going to put our next one here, V2. We'll put our next one over here, V3. Put our next one over here, V4. And then again, we'll put over here, V5. And then over here, we're going to put V6. All right. So how these work is again this is going to be positive electrodes here. These are all positive electrodes. They're uniolar. What they're able to do is pick up electrical activity of the ventricles. So V1 and V2, these ones are mainly picking up activity within the septum. So well here's what I want you to remember. V1 and V2 is picking up mainly the electrical activity within the intervententricular septum. So we're going to put septum here. V3 and V4 are going to be picking up most of the anterior part the anterior part of the ventricles. Okay? So this is going to be the anterior wall. And then you're going to have V5 and V6. And this is going to be picking up most from the left side of the heart, the left lateral part of the heart. So left slash lateral wall. So whenever someone is having um infarks, right, you're going to be looking and depending upon where it is, you can determine. So for example, if someone is having some changes in their ST segment in V5 and V6, what would that tell us? It would tell us that, oh man, this is maybe be picking up some uh infarction within the left lateral wall. Oh, it's V3 V4. Well, maybe there's something going on here in the anterior component. Oh, it's V1 V2. Maybe there's something going on with the septum. Or maybe sometimes V1 V2. It can indicate possible septum. But guess what else it could indicate? It could be a possible sometimes posterior MI. And remember what you need for that one is sometimes what you'll see is you'll see ST segment depression in V1 and V2. So ST segment depression T-wave inversion of V1 V2. You put on posterior chest leads. So V7, V8, V9 and it should be able to pick up ST segment elevation which could be possible for a posterior M. So that's something to also remember. So look at V1 V2 because it's also important for posterior wall. So that's the basics of the the chest lead. So again chest leads are picking up a view of the heart and I want to make sure that we write this down here. It's looking at the heart in the horizontal plane. So horizontal plane or transverse plane. And again what I want you to remember V1 V2 it's picking up electrical potentials from the septum right and it also can tell us about posterior wall remember if you f SD segment depression T-wave inversion anterior wall V3 V4 if you want to combine V1 to V4 it's pretty much all anterceptyl okay and then V5 and V6 is left lateral wall all right so that tells us about the chest leads all of This if you combine together you get an insane view of the heart. Your bipolars can give you a view of what? From inferior. It can tell you a view of what else? From the left. Your augmented uniolar can tell you the right. It can tell you the left. And it can tell you the inferior view. and V1 and V2, V3, V4, V5, V6 can tell you the entire horizontal plane from the left ventricle, right ventricle and the interventricular septum as well as even the posterior part of the ventricles as well. So that's an amazing thing that these EKGs are able to do. So that's giving us everything we need to know about the basics of EKGs. All right, engineers. So that covers pretty much everything you guys need to know about the basics of EKG boiling down to cardiac action potentials, their electrical vectors, how that correlates with the graphical representation on EKG, mainly looking at it from a lead 2 position. And then after that we talked about the multiple different chest leads uh V1 through V6. We talked about the augmented uniolar limb leads AVF, AVR and AVL. And then we also talked about bipolar limb leads one two three and their significance in being able to get a very significant large view of the heart from multiple different planes including the frontal and horizontal plane. I hope all of this made sense. I really hope that you guys did enjoy it. That's what we really want for you guys is to understand this stuff. I know it was a really long video. I'm sorry. I hope that you guys it's really able to help you guys. If you guys did like this video, please hit that like button, comment down in the comment section, and please subscribe. Also, if you guys want to check out our uh Instagram, our Facebook, even our Patreon account, you guys can go down to the description box and check that out as well. All right, Ninja Nerds, as always, until next time. [Music]