What's up Ninja Nerds? In this video today we're going to be talking about the basics of EKGs. Let's go ahead and get started. Hi Ningenerds, so when we talk about EKGs we obviously have to start with the basics.
Understanding the physics, understanding the physiology before we actually start going through and reading 12 lead EKG cases and determining what's going on. So what I want to do is I want us to take us a stroll really quick through some basic physics and physiology which will really prepare us when we start going through a systematic approach of EKGs. In order for us to understand and to start this process What I want us to do is I want you to imagine. Imagine I have this ventricular myocardium here, and I'm just going to take and cut like a chunk of tissue out and place those chunks of tissue here in this box layer, okay? Then what I'm going to do is I'm going to get a little evil, and I'm going to put some electrodes on each end of this tissue, right?
I'm going to put a positive electrode on that side, a negative electrode on that side. Then what I'm going to do is I'm going to stimulate. I'm going to come at this end of this tissue, and I'm going to stimulate. I'm going to provide some electrons.
electrical stimulus. When this tissue becomes stimulated, it actually, you know, cells, they undergo depolarization, right? Positive ions like calcium and sodium ions will flood into these cells, cause them to flip, become positive, depolarize them, right?
And you know, there's little junctions, right? If I had like a little hole between this cell and this cell, there's little gap junctions. And so those sodium ions and calcium ions can move through those gap junctions from cell to cell to cell to cell.
creating kind of this electrical signal that's being propagated from this end of the tissue to this end of the tissue. And what kind of charge is being propagated? Well, remember, this cell is resting.
So originally, it's kind of slightly negative, right? Then it becomes positive, positive, positive, positive. So there's a flow of positive charges moving in which direction if I go ahead and apply a stimulus at this end.
There's going to be a flow. positive charge moving towards this positive electrode. Now why is that important? If I take the positive electrode and I hook it up to an EKG machine it should cause a particular type of deflection right when you look at EKG all they look like is you see upward deflections, downward deflections, you see flat lines. What does that mean?
I'll tell you what it means. If a particular tissue is generating action potentials, depolarizing waves that are moving towards a positive electrode, it'll get red from that electrode, send it to the EKG machine, and produce a positive deflection that shows up on the EKG. So I want you to remember that. A flow of positive charges moving towards the positive electrode of any kind of lead of the 12 lead system should produce a.
Upward deflection, okay? Let's take the opposite scenario. Let's say I take and I put a negative electrode here on that same side, a positive electrode on this side, but now what I want to do is I want to stimulate this end of the tissue. okay so I'm gonna go ahead and stimulate this into the tissue stimulate it it'll depolarize positive charges will then flow from this cell to this cell to this cell to this cell via the gap junctions right and it'll move in which direction towards the negative electrode or what we like to say is away from the positive electrode right and again what kind of charges is flowing here positive charges whenever this flow of positive charges is moving away very very important away from the positive electrode it'll then get picked up by the electrode send it to the ekg machine and produce a downward deflection so again downward deflection all right so to quickly recap positive charges or flow electrical activity moving towards positive electrode upward deflection If there's a positive charge moving away from the positive electrode, downward deflection. Okay.
Let's switch it up a little bit. So we'll change it up a little bit. Because this is going to become very important when we go through this entire EKG waveform and explaining what all these deflections are indicating. What if I do one more thing?
I put a negative electrode here on one side of the tissue. I put a positive electrode here on this side of the tissue, right? And now what I'm going to do is I'm going to... going to actually have these cells, you know whenever cells depolarize, right?
For example, let's say that we took this one, it depolarized. After it depolarizes, it then has to start to repolarize. So let's pretend for a second that these cells will repolarize, right? And let's say that they're repolarizing just for the sake of this argument here.
Let's say that they're repolarizing going in this direction, right? So for example, This cell will become negative. This cell will become negatively charged, negatively charged, negatively charged.
It's going to be moving in this direction, just for as an example, right? So I have a flow of negative charges that is moving from the positive electrode towards the negative electrode, right? When negative charges are flowing towards the negative electrode, electrode, guess what it does?
The same thing that would happen if positive charges are moving towards the positive electrode. Produces an upward deflection. So in this case negative charges to negative electrode will produce a upward deflection.
So very important. You'll see why whenever we start going through this. The last thing I want you to remember. Is that there's parts where there is no deflection, whether it be upward or downward. Sometimes it's just flat, right?
An isoelectric line. What could that be indicative of? Let's say here I take this tissue, negative electrode on this side, positive electrode on this side. But now the tissue's oriented.
into kind of in a different direction. You know this is an axis, right? If you kind of imagined an imaginary line going from this electrode to this electrode, there's an axis of that lead, okay? If I were to stimulate this end of the tissue. Which way is it going to go?
Upwards, right? So if I stimulate this into the tissue and I cause this to depolarize, this to depolarize, this to depolarize, and so on and so forth, what is the direction of positive charge is going to look like? It's going to start moving towards the axis of this lead and then after it passes through the axis it'll move away from the axis of that lead.
You know what actually happens but your EKG is so smart, your EKG machines are so smart, generally whenever this kind of charge, this positive charge, positive charge that we have flowing here, down this tissue perpendicular to the axis of the lead. Originally, as it's going towards the axis, it actually produces a positive deflection. And then it moves away from the axis of that lead. But since it's the same amplitude on both sides of the axis of that lead, the deflections will be equal to one another, equi-phasic, and then guess what happens? The EKG machine actually will cancel.
cancel them out and make a kind of an isoelectric line. So you can remember two things. Whenever there's like no net movement of electrical activity, there'll be kind of a flat line.
Or whenever the electrical activity of the heart is moving perpendicular to the axis of whatever lead we may be looking at, okay? I think we have a pretty strong idea now about what causes a positive, negative deflection, or a straight line. Now what I want us to do is let's take one lead That's the most commonly used lead in the rhythm strips of 12 lead EKGs. Lead two and map out the entire EKG waveform.
All right, engineers. So now let's go ahead and take, and I want you to trust me for right now. We'll go through all the 12 different leads and understand them a little bit more. But for right now, just trust me that the lead that we are looking at in this kind of example that we're going to follow throughout the entire EKG cycle is lead two.
Lead two, usually the negative electrode is kind of on the right arm or right side. And then the. the positive electrode will be on the left leg.
Okay? And so it creates this axis. If you imagine an imaginary dotted line, the axis is going in this direction from negative to positive. Okay? So remember, for the most part, where's the flow of positive charges going with respect to the positive electrode?
Think about the positive electrode as an eye looking towards the negative electrode. It's looking for those positive charges. If it's coming to it, it's going to be a positive. If it's going away from it, it's going to be a negative. it's going to be a negative.
Okay. So let's start off. Let's start off with the first part of the EKG.
Whenever the atrial cells, you know, all this entire EKG activity starts within the atria. The atria, they have this structure called the SA node. You know the SA node? It's located within the upper kind of top right portion of the atria near the entry of the superior vena cava.
So that would be our SA node, correct? That tissue has special types of pacemakers. cells that have the ability to generate action potentials and spread those action potentials throughout the atria going towards a particular direction.
And the ultimate direction that these electrical potentials want to go towards is this big fat structure here sitting at the top of the interventricular septum. And that is called our AV node. Okay. So let's say here that we have our SA node. It decides, Hey baby, I'm going fire.
I'm going to send some action potential. So it starts sending action potentials originating in the right atrium. So it'll send action potentials kind of all throughout this direction, kind of spreading from the right atrium all the way towards the left atrium. Here's what's interesting, though. If you were to take the mean of all or the average of all of these vectors that are spread throughout the atria, the mean vector that is generated...
...generated by the depolarization of the atria from the SA node to the AV node, one big vector would really kind of look like it's going straight to the AV node. So really, if I took the mean of all of these little vectors that was generated by the SA node spreading out to the atria, the mean vector that's generated... the SA node to depolarize the H-rate is going downward and leftward towards the AV node. Now, that's the positive voltage right there, right?
So here, let's get rid of all these like little guys so that we can completely understand here that this right here, just this arrow here. This is a flow of positive charge moving from the SA node to the AV node, but remember it's the mean vector of all atrial depolarization. Which direction is that positive charge flowing with respect to the positive electrode of lead II?
It's moving in the direction of the positive electrode of lead II. What does that mean? Positive charges flowing towards the positive electrode, upward deflection.
We got ourselves a P wave baby. So there is our P wave. So we have our P wave and what does that indicate? This indicates atrial depolarization. Now, more particularly, if we really, really want to be particular though, that P wave, if it looks just the way it's supposed to, which I know it may sound a little odd, what else could it look like?
It can look very different sometimes, and we'll explain that throughout later videos. If the P wave looks the way it's supposed to, in other words, it's a sinus P wave, that means that that P wave was generated by the SA node. So if you have an upright P wave looking like the same morphology throughout, that atrial depolarization, it actually occurs. heard because the SA node was the one that generated the electrical activity to depolarize the entire atria.
Very, very important. Okay. So we already started with the first part of our EKG.
Let's move on to the next part. If you look here, we have our P wave, right? So this is our P wave, but then we have this portion of the EKG where there's this flat line.
Okay. Well, I want you guys to remember, what does the flat line indicate? The flat line indicates that there's either no net movement of electrical activity or that the electrical activity is being directed perpendicular to the axis of that lead. That's what it means, right? So let's understand why there is this flat isoelectric line here.
Let's go back to where we were before. Here we have our SA node at the top of the atria. It generated a bunch of depolarization vectors. And where was that directed toward?
Do you remember the end point that we want all of this electrical activity to kind of come to? We wanted to go to the AV. node at the top of the interventricular septum.
We said that there's a bunch of different depolarization vectors but the primary main depolarization, the mean vector from all of those, is directed downward and leftwards towards the AV node. So that's our atrial depolarization vector. We said that gave us a positive type of deflection, right, the P wave. Now let's say that the electrolyte finally gets to the AV node. The AV node becomes depolarized so it's starting to become positive, positive.
positive but guess what the AV node is a very nice little waiter it takes its time with the electrical activity it slows down the conduction a little bit sometimes like about a point one second delay that the AV node just hogs all the electrical activity and says hey stay here with me baby and then I'll send you down to the ventricles so what happens is the electrical activity hits the AV node the AV node starts kind of taking all this electrical activity it becomes depolarized but it holds that electrical activity within it before it decides to send the action potentials down to the ventricles. So it is positive charge but that positive flow of charge is not actually moving in a particular direction to produce the action. produce any upward or downward deflection.
So that's how we have this isoelectric line. Now very important to understand here that if we take from here that point of where the P wave ends onto where this line is going to end, we're going to have a line that's kind of ends because there's going to be another little jaggedy point that we'll talk about here with the EKG. This right here is a very specific type of name here.
This is called our PR segment. Okay, that's the PR segment. The next part that we really need to differentiate here, if I were to draw like another, let's say I drew another one. Here's my P wave and my PR segment there.
If I drew the distance from the beginning of the P wave all the way... until where that PR segment ends, that is referred to as the PR interval. So make sure you understand that, okay? So it's very important to remember the difference between these two.
But what do we know? We know why we have this isoelectric line. It's because the depolarization that moved from the SA node got to the AV node.
AV node is a very slow conductor hold that electrical charges for a certain amount of time about a point one second delay then it says okay I'll send the electrical activity down to the ventricles. Now we understand the P wave in the PR segment. Now The next thing that we're going to do is move on to the next part All right So now we understand the P wave the PR segment and we kind of formed at this point our PR interval Now we start going to this next part of the EKG. Do you guys remember what that part is?
So if you guys remember we have our P wave we already understand what but that is indicating. Then we have our PR segment, together the P wave and the PR segment make our PR interval. Then we go into this next part, which is kind of a downward deflection.
Let's kind of quickly, very, very quickly recap. P wave is what again? SA node firing.
generating a mean vector towards what structure? The AV node, right? AV node holds on to that electrical activity because it's kind of a slow conductor, has and receives all that positive charge but does not conduct it down the bundle of hiss and bundle branch system yet.
So that causes that PR segment. Now, here's where it gets cool. We have from the AV node, the bundle of hiss, right?
Or the AV bundle, which then splits called the right bundle branch and then through your left bundle branch. Now your left bundle branch actually has two other small branches, left anterior and left posterior fasciculars, but we're not going to, we'll talk about that a little bit later, okay, when it comes to axis and deviation. But for right now, I want you to remember simply there's a right bundle branch and a left bundle branch, okay? Here's what's really, really interesting.
Whenever that depolarization finally moves from the AV node down to the bundle of his and then through your bundle branches, Do you know what's really interesting? Your left bundle, this is the left bundle branch, it is actually responsible for depolarizing the interventricular septum. Not really the right bundle branch.
It's primarily the left bundle branch that depolarizes your interventricular septum. So if you think about that, if it's causing these small little depolarization vectors that are moving towards the right and maybe even a little bit kind of upwards superiorly, then what would the mean vector of all of those little guys, guys look like on this diagram? It would look like this.
Right? So like I said, you should have all of these vectors that are pointing towards the right, because it's going to be the left bundle branch depolarizing the interventricular septum from the left towards the right. And it even is oriented a little bit upwards because of the shift of the heart. Two-thirds. of the left of the mid-sternal line.
So this should be the net depolarization vector of the interventricular septum or septal depolarization. Okay, if that's the case then, what direction is that? that flow of positive charge moving with respect to the positive electrode of lead II. It's moving in the opposite direction. So if it's moving in the opposite direction or away from the positive electrode of lead II, what does that do?
Causes a negative deflection. So that's where we get our negative deflection. That negative deflection has a very specific type of name.
So we know we have P wave. That's our P wave. Then here, what do we have? We have our Q. Q wave.
That's our Q wave. And what does the Q wave indicate? That's very, very important. It is indicative of septal depolarization.
So what is the Q wave indicative of? It's best represented in this diagram, but the Q wave is indicative of septal depolarization. Okay.
One more thing that I really want to kind of get across here, because sometimes when we go further throughout these EKG lectures, you guys will see that there's something called pathological Q waves. Q waves are normal. They're a physiological part of our EKGs. Whenever they become larger, so in other words, they become very wide, and we'll talk about what that actual distance is. Or whenever they become very deep, they have a very long kind of depth that they really have a negative downward deflection.
And a couple. other things and particularly like what kinds of locations you really don't want to see them in then they can be called pathological Q waves. So again remember Q waves are a normal physiological part of the EKG it's just the size of it really determines whether it is physiological or pathological.
And sometimes what's very interesting is you may not even see the Q waves within a 12-lead EKG. Alright so we have the basic understanding here we know that the P wave is indicative of atrial depolarization vector pointing down to the left, PR segment. indicative of atrial depolarization but no net movement, Q wave indicative of septal depolarization moving upward and to the right away from the positive electrode. Let's go to the next part of the EKG. Alright so now let's go into the next part here.
So we have our P wave right we know what that indicates. We have our PR segment we know what that indicates right so here we'll put down here PR segment. We have our Q wave, we know what that now indicates.
But now we go from this negative deflection into an upward deflection. What the heck does that indicate? Don't worry guys, I got you. So again, SA node, this is going to be building.
like just buried into your brains. You guys will never forget this now. The SA node sends an atrial kind of depolarization vector that's directed downward in what direction? Towards kind of the left.
Okay, let me just draw your bundle branch system here. So again, which direction? would that be moving?
It'll be moving atrial depolarization downward and to the left as you're going towards the AV node. So that's going to produce that positive deflection. Atria stay depolarized, don't have any net movement because they're slow conductors, PR segment. Goes down through the bundle branch system, but remember that the left bundle branch is what really depolarizes the septum and that creates this net vector that moves in which direction? Moves to the right and then upward, which creates a again that negative deflection.
Alright now let's go to the next part here. The electrical activity will then continue to move down the bundle branches so it eventually got a you know from here down the left bundle branch it'll start to spread outwards like this from the bundle branches through the Purkinje system you kind of get this kind of direction here so then we'll go through the right bundle branch and then through the right Purkinje system and you guys get the point. We're generating these vectors as we're going down through the interventricular septum towards the apex and then up up towards kind of the bases. Here's what I want you guys to think.
They're like, holy crap, there's so many arrows. Where the heck is the net vector? All right, remember, which ventricle is supposed to be thicker?
It has more myocardium, meaning that it's going to conduct more action potentials, meaning that it'll generate higher voltages, meaning it'll generate a larger positive deflection. Which side? The left ventricle. That left ventricle will be thick, right?
So the left ventricle is going to generate more... intents of a net vector, right? So if we were to kind of say, let's say an imaginary line here, cut in half, right ventricle on this side, left ventricle on this side, all of these net vectors here will create, I mean, so all of these little vectors here will create one net vector, all right, from here to here.
What will that look like? It'll be pointing like this, okay? So that's going to be the vector from the left ventricle.
So this is, again, a flow of positive charge. Then let's say over here you have the right ventricle. The right ventricle is generating all these electrical activity that's moving in this direction, right?
So it's going to have a smaller, okay, it's not as thick. So its electrical vector may be a little bit tinier, okay, and it may kind of look like this. Because again, the left ventricle is way thicker than the right ventricle. And again, this is going to be a flow of positive charge. So here's what our different vectors would look like if we only imagined it generating the left ventricle or the right ventricle.
But we want the mean QRS vector. we want the equivalent of what the vectors would be additive of the left ventricular vector and the right ventricular vector. So it should be if I take this one and this one, which one's bigger? Usually you want to kind of go in the middle if they're equal, but they're not equal right? That left side is way bigger.
So because of that it's going to start the mean of these two will lean a little bit more towards the left. So your net vector here between these two is going to look like this. So this is our net QRS vector and again it's a flow of positive charge and I erased it before but let's say here's our positive electrode of lead 2. If this is our mean QRS vector which is the net sum of the left ventricular vector and the right ventricular vector which direction is that flow of positive charge moving towards with respect to the positive electrode?
It's moving towards it right? If it's moving towards the positive electrode What does that cause? A nice positive deflection.
What do we get? A positive deflection. What does this mean vector indicate?
We know it's going to cause a positive deflection. Why? Because there's a flow of positive charges from this mean vector moving towards the positive electrode of lead. And we know that based upon our discussion that causes a positive deflection.
What is that positive deflection here called? That is called our R wave. So that's your R wave.
So if you want to think about it, this would be the vector particularly for the R wave in the left ventricle and this would be the vector for the R wave in the right ventricle. So this is the mean of them. So we could kind of say if we want to, this is the mean R wave. vector.
Okay? Alright, so that discusses that part of the EKG. Now let's move on to the next part.
So we have our P wave that we generated, which was again what? That was when the SA node was firing, generating a atrial depolarization vector aimed towards what structure? The AV node, right?
And the AV node, once it's actually depolarized, it holds on to that electrical activity for a bit. It doesn't let it move down through the ventricular bundle system. And that is going to be the PR segment, right?
Collectively. The P wave and the PR segment is called what? That is called your PR interval.
Then what happens is these AV bundle will then finally say, okay, time to send this stuff down to the bundle system. So send it through the AV bundle, the right bundle branch, and the left bundle branch. If you guys remember, the left bundle branch will generate depolarization vectors that are aimed towards the right and upwards, moving away from the positive electrode, and that causes this downward deflection.
here called the Q wave. So now we have our Q wave. Then what happens is the depolarization vectors will then move down into the left and down into the right. They'll create a vector moving towards the right, a vector moving towards the left. We want the mean of those two but because the left ventricle is thicker it's going to cause the mean r-wave vector to be pointed downwards and to the left more.
So you should get a downward vector like this. and that's what caused our R wave. Well now we go to the next part.
The next part here is we had the depolarization spreading from the inner part of the myocardium all the way to the outer part of the myocardium. After it depolarizes the inner to outer part of the myocardium, it's not only going down in this way, so it goes down. and it goes from inwards to outwards, but it also moves superiorly towards the base of the heart. As it does that, look at the direction here.
Let's use our purple marker here. This kind of depolarization as we're saying here, it moves down like this. it also moves like this and it starts moving towards the actual base of the heart and the same thing for this side it moves downwards like this but it also move upwards like this.
As it does that there's going to be this kind of like basal ventricular kind of depolarization and if you look at it which direction is it actually kind of pointing it's pointing upwards and then towards the left for both of them. So if I were to draw kind of a little depolarization vector on this side it should go this way and a little depolarization vector on this side should go this way. Okay so these are going to be the depolarization of the ventricles towards the bases and again it's because they're moving down and upwards so if it's moving upwards and generally towards the left and it's a flow of positive charge what direction is that moving with respect to the positive electrode of lead 2? It's moving away from it what does that cause? cause?
A downward deflection. What do we get? A downward deflection.
What in the world is that downward deflection called? This is called the S-wave. We'll actually put that in here, S-wave for this part.
Okay, so what is the S-wave indicating? It is still ventricular depolarization, but at this point it's more towards the base part of the ventricles rather than the entire kind of thickness of the ventricular myocardium, right and left ventricle. thickness part from inner to outer that was more the r wave okay and then the q wave is more septal depolarization all right we've covered that let's pop right over into the next part here all right quick recap we're not going to go through all of this intensely again we're not going to draw the vectors i think by now that you guys should know it all but we'll draw here our kind of our bundle system here to just be consistent okay here's our right bundle branch you Here's our left bundle branch.
Okay. So we know now, we definitely, we're professionals, I think, right? And engineers at this point, we know the P wave.
We know what it means. We know the PR segment. We know what that means. We know the Q wave.
We know what that means. We know the R wave. We know what that means. And we know the S wave.
And we know what that means. Okay, here we go. You get to this next part, which is very interesting, which is going to be kind of like this. flat segment here.
There's kind of a little upstroke here, but really it's this isoelectric line that we really need to focus on. This isoelectric point here, where it's staying kind of in a flat line, just like the PR segment was, this is called the ST segment. Now, ST segment is basically when the The entire ventricular myocardium is completely depolarized. Remember how in the AV node, the AV node was depolarized and it stayed depolarized, but it didn't actually kind of like cause a movement of charge down into the AV bundle. It kind of just stayed in that AV node.
In the same way, the entire... Ventricular myocardium has already been completely depolarized. It's super positive.
It hasn't begun to repolarize yet. And there's no more movement of any kind of charge. It's just been depolarized.
And it's just about getting ready to repolarize. But it's stuck in this depolarization state. But there is no net movement of any of that electrical charge. If there's no net movement of electrical charge, what will that do to the EKG?
Is there a positive? is a negative, it's an isoelectric line. So that's where we get this part here which is called our ST segment. And this is a very very important segment when it comes to pathology, so we'll talk about this in future videos, okay? Alright, so we understand that.
Let's go into the last part of the EKG analysis here. Alright, so the last part of... the EKG, okay, so we know this by now.
Engineers, we should be professionals at this whole waveform stuff. We know the P wave, okay? We know our PR segment. We know what all of this stuff indicates by now.
We know our Q wave. We know our R wave. We know our S wave. Let's lengthen this ST segment here a little bit more though so we can make sure it's a super profound ST segment there.
And then we have one more wave that we have to talk about here. And again, what is this port here that we just finished discussing? This is our ST segment. Okay. Alright, here we go.
So the first thing that we need to do is understand how the heck we get this upward deflection which is the T wave. Okay, let's make sense of everything that we've done so far. So far, without going through all of those vectors, here's our AV node. We'll just draw SA node here, SA node, AV node, we got our bundle of his, we got our right bundle branch, we got our left bundle branch, right?
What did we leave off with? At the last point here, this entire ventricular myocardium, the entire thick, of the ventricular myocardium was depolarized. Now here's where it gets good baby. Whenever a tissue depolarizes in order for it to relax, in order for it to be stimulated again, it has to repolarize.
In other words, has to go back to its resting membrane potential, which is what kind of voltage inside of the cell? Negative voltage. So at one point it was all positive charge throughout this entire ventricular myocardium. But what happened is imagine the charges flipping from the outside of the myocardium to the inside of the myocardium.
So it's positive here then it goes negative and then it was positive here negative. So imagine like this let's say that we kind of use it as an example here positive positive positive positive that entire ventricular myocardium was positive right and during the ST segment. I'm gonna flip each one but I'm gonna move in this direction I'm gonna repolarize that one repolarize that part of the myocardium.
Repolarize that one and repolarize that one. The negative charge is flipping in which direction? It's going backwards in the direction that the mean r-wave vector was, right? Because if you think about it, it's going to be the same thing. It's going to be negative charge flowing this way from the right ventricles, negative charge flowing this way from the left ventricles.
So this is gonna create a nice vector, a thick vector, right, that would be pointing upwards and towards the right. And this would be kind of creating like a little baby. negative charge vector that's going to be pointing upwards and towards the left.
But again we want kind of the net vector between those two. So what's the net vector? Well again this one's the bigger net vector, this one has the bigger vector of the bigger amplitude.
So we want between, we want in the middle, we want the net of those two, but it's going to be leaning more towards this side. So what happens is in this case this vector will kind of look like this. This is going to be the net vector between these two. And what kind of charge does it actually have?
What flow of charge is moving in this direction from the outer part of the myocardium to the inner part of the myocardium? Negative charge. Now, here's where we've got to go back to remember what we talked about.
If positive flows towards positive, it's an upward deflection. If positive moves away from positive, It's a downward deflection. What do we say happens when negative charge moves towards negative charge or negative electrode? It's going to produce an upward deflection. Negative charge oriented upwards towards that negative electrode.
That is where we get our upward deflection and that upward deflection is indicative of this is our T wave. And what does the T wave indicate? It indicates the ventricles repolarizing. So what does it indicate?
It is indicative of ventricular repolarization. Beautiful. So at the end of this, to really quickly recap this, what does the P wave indicate?
Atrial depolarization. What does the QRS indicate? Ventricular depolarization.
What does the P wave indicate? Ventricular repolarization. Now that we've understood where these waveforms come, how they're actually, why it's up, why it's down, why it's isoelectric, let's do the same thing with all the other 12 leads that are a part of our EKG. Alright, engineers, so at this point, At this point in time, we've covered what the EKG kind of waves and segments and all the different components of that should look like in one lead, right?
Lead two, I told you. Usually lead two is the most common lead used in a rhythm strip of a 12 lead EKG. But we only looked at one out of a total of 12 total leads that you can have in an EKG. And so that's important to remember that what are these different 12 leads?
We'll talk about them individually, but there's what's called three limb leads, lead one, two, three, not too bad. And there's three all. augmented unipolar limb leads, and that's AVR, AVL, and AVF. And then there's six precordial or chest leads, V1 to V6.
So if you add all of that up, that's three plus three, six, six plus six, 12. 12 total leads. So we should, we don't have to, but we should see what all of these waves would look like if we utilize the vector format that we talked about above in each of those 12 leads. Now, These are tiny little arrows and there's a lot of them so it's going to be kind of like confusing so we're going to go through each one by one but we're going to kind of all use my hands to kind of gesture when what direction it's moving within as well. Before we start going through this you should know what the heck lead am I looking at where the negative electrode is on this side the positive electrode is here same thing with these. So let's quickly take there was this guy who made up this lead system Eindhoven he came up with it's called Eindhoven's triangle right so In Tovan's triangle is this simple kind of method where the heart is kind of situated here in the center and we create these axis of particular leads with lead one two and three.
So what happens is we take an electrode and we put that on the right arm, we put one on the left arm, we put one on the left leg and then we put a neutral one usually on the right. So let's say here I recommend this is right arm, left arm, left leg. There's three total leads.
This is going to be lead one, this is going to be lead two, and this is going to be lead three. And you can kind of already see that. If I were to take kind of a look with the respect of the heart, this one's kind of going horizontal here. be lead one.
This one's kind of going diagonal in this way, that's lead two. And this one's kind of going diagonal in this way, that's lead three. But let's say it makes sense of where the negative and the positive is. For the axis of lead one, there's a negative electrode that's placed on the right arm.
and a positive electrode that we have on the left arm. Then that creates an axis, and that's that axis that we see right here. That's the axis of lead 1 that we kind of situated on the heart there.
Lead 2, the axis of lead 2, you have a negative electrode on the right arm and a positive electrode on the left leg, and that creates this axis that's coming down diagonally. And again, if you imagine I took this kind of dotted line and put it over the heart, you can see there, negative electrode here at the top, positive electrode here at the bottom towards the left. Same thing.
lead three, put the negative electrode here on the left arm, positive electrode here on the left leg. What does that create? It kind of creates this axis here that's going down this way.
If I were to take this, put that over the heart, negative electrode should be over here, positive electrode should be down here. So that's where I'm getting all of these electrodes. I don't want you to just think I just made them up and put them there willy-nilly, right?
So this is lead one, this is lead two, this is lead three. The beauty of all of this is is that we already know what lead two should look like, right? We should already know. So if I were to draw out that, utilizing all those vectors that we talked about, we should already know that there should be an upright P wave, a PR segment, QRS, ST segment, and then our T wave, right? Here, for right now, I want you to trust me.
But guess what? Lead 1, lead 2, lead 3, all of them are pointing in the same direction. So for right now, I want you to trust me, but we'll go through it. There may be slight variations because of the axis of those leads with respect to the vectors.
But for the most part... You're going to get the same kind of waveform here that you would get in lead 2, that you would get in lead 1 and lead 3. So let's go ahead and look at this. Here's my positive electrode.
Let's start with the P wave. Which way is it going? I have this arrow up here, but which way is it going? downwards into the left is it going towards the positive electrode? Yeah.
Upward deflection. Then I go septal depolarization right that's my Q wave. It's going upwards and kind of towards the right.
Is it which way is it going with respect to the positive electrode? It's going away from it so that's going to be be a downward deflection. Then I go to my actual entire kind of like mean r-wave vector.
It's going down and to the left. It might not look like it's going straight towards the positive electrode, but in general, the direction of where it's going is moving towards the positive electrode. So that's going to produce a positive deflection. Then you have the depolarization at the bases of the ventricles. That's moving upwards and towards the right.
That's moving away from the positive electrode. That's going to be the S-wave. wave and then again your T wave is this negative depolarization that's moving in which direction?
It's going this way. What is it moving towards? The negative electrode. So it should be a positive deflection. The same exact thing happens with lead 3. So if you look at it the positive charge is down there.
So if you were to do this, we don't have to do this because it's gonna make the exact same sense, if you were to follow all of these vectors you would get the same kind of of situation there for lead three, okay? So what I want you to remember is lead one, two, and three, their waveforms should be pretty much the same on a 12 lead. Here's the next thing I really, really need you guys to know. Imagine the positive charge as an eyeball, okay?
Imagine it as an eye, and you are looking at the heart from that view. Wherever that positive charge, imagine that is where you're looking at the heart. If that's the case, then lead one is looking at what part of the heart directly.
What's the first thing that that eyeball sees? This portion here. It sees that left ventricle, but particularly like the lateral wall, more towards the top.
So we call that a high lateral wall of the left ventricle. So if I were to highlight over here, let's highlight it in a very nice color here. Let's use this beautiful like turquoise color.
This portion right here would be what one lead. one sees. So lead one would give us an idea of what kind of electrical activity is taking place in which part of the heart?
The high lateral wall of the left ventricle. Okay? That's very very important especially when we get to STEMIs.
Okay? The next one, lead two and lead three. You know what?
We're so lucky because if you look here lead two and lead three are both looking at the heart from the bottom. So the first part that they see is this part here and this part there. That's the inferior portion of the actual what?
That's the inferior portion of the ventricles. So it looks at the inferior portion of the heart. So this would be what portion would be looking at this? This would be leads.
two and lead three would be looking at the inferior wall of the heart. Okay? And that includes the right ventricle and even a little bit of the left ventricle.
All right? So that's important to remember that. So now we have a pretty good idea of what lead one, lead two, lead three, EKG waveform should look like. like and what part of the heart they tell us where the electrical activity is kind of altered in some way.
Alright, now let's talk about the augmented unipolar limb leads, do the same kind of thing with these vectors and then talk about what views or what portions of the heart they tell us about. Alright, so we finished our limb leads, now let's talk about the augmented unipolar limb leads. Now the thing is is that these can be kind of annoying and complicated if you really get into the physics of them, we're not gonna do that, we don't need to, it's not necessary because you know what, your EKG machines are so smart.
that they have the ability to kind of switch the electrodes kind of simultaneously. And so it's really kind of cool what they can do. We'll go into a brief discussion of what I'm talking about. So remember, I told you that there is three types of augmented unipolar limb leads. So what are those?
The first one that we'll talk about is AVR. So this is going to be AVR, augmented unipolar limb leads. That's going to be for the right side.
And AVL. and AVF. Okay.
So what happens is you're still kind of using that same lead system, the same triangle. There was another guy named Wilson who came up with this idea. But it's the same kind of concept from the limb leads.
Okay. The only thing that's different is is that what happens is that the EKG machine will switch the negative electrodes on two corners like on the like further in this case there'll be a negative electrode on that left arm and a negative electrode on the left leg and it'll put a positive electrode on that right arm. And what happens is, that means that if you were to kind of again follow the axis, where does that mean the axis of AVR is?
Whenever you have two negative charges, the actual kind of mean point is actually situated here in the center. So actually, when you look at this, the vector is actually going to be kind of pointing this way towards that right side. So that's where that kind of AVR comes from. So if you were to imagine here for a second, imagine that's where that...
that vector starts, this is where I would imagine I had this negative electrode situated, this is the axis of that AVR. Okay, so I want you to again imagine here this is the eyeball, you're looking at the heart from this direction. Let's follow all the waveforms.
P wave. Where is it going? I know it's right there, but there's a lot of these waves very close. But again, this top one right there, that's your P wave.
It's going downwards and to the left. With respect to the positive electrode of AVR, where is it moving? Away from the positive electrode.
What does that mean? That is a downward deflection. So that means you're going to get something like this. Oh, shoot.
Then we go here. We got this next part. What is this?
That's septal depolarization. That moves towards the right and upwards. That means it's going to the positive charge. That's going to be a upward deflection.
Maybe a little guy like that. Then the ventricles, right? You have your mean R wave vector that's pointing downwards to the left. that's moving away from the positive electrode.
That's a downward deflection. And then you have this depolarization that's occurring at the bases of the ventricles. That's moving towards the positive electrode. That's a upward deflection, okay? And then from there, you go into your ST segment, right?
Which is where the entire ventricles are depolarized. They aren't having a net movement. And then what happens?
Ventricular repolarization. I know you can't really see it, but this was the positive. charge that was for the R wave. What do you think that negative charge is? That's for the T wave, right?
So then after the ventricles depolarize, what happened? You guys remember what happened from above? Then what happens is you start to have this ventricular repolarization which is a negative charge, a negative charge moving towards the positive electrode, okay?
In other words if you were to imagine, remember we imagine that this is our negative, our imaginary negative electrode between these two points here. This is moving in which direction with respect to that negative electrode? Away from it. And so because it's moving away from it, that is going to produce a negative deflection.
And this is what you would get here for your actual EKG waveform with respect to this AVR. All right, so now if you think about this, we now kind of see what our waveform would look like, our EKG and AVR. Do you know what's really interesting about this? It's literally the exact opposite of lead 2 and technically lead 1 and lead 3 but lead 2 is kind of like our poster child of what the EKG would really look like.
So if you imagine remember what lead 2 did at an upward P wave. Remember what the the Q wave was? It was a downward deflection. Remember what the R wave was? Upward deflection.
Remember what the S wave was? A downward deflection. Do you remember what the T wave was?
An upward deflection. This is the exact opposite. That is going to become so so important later when we start talking about how to determine rate and rhythm if something is in sinus rhythm or not if there's ectopic foci that are developed we'll go into all of that later so it's very important out of all of this stuff that we're just talking about leads remember that avr and lead 2 should be opposite of one another in their waveforms Now, we can go through this all again.
I think it's going to be kind of repetitive, but if you follow the same thing, AVL, again, the EKG machine is smart, creates negative electrodes on the right arm and left leg, and then what happens is the imaginary negative charge then would form between those two going towards the positive electrode that way, so you would have an axis like this, right? So that means that the AVL, the I, that positive charge will be looking at the heart like this, okay? And if you followed every single waveform from that point on, ...on utilizing everything we talked about, guess what?
It's the exact same as lead 1, lead 2, lead 3. Hey, let's take it another step. Guess what? The next one below this, it's the exact same. The only one that really should be opposite is AVR.
Every single other one of them, lead 1, 2, 3, AVL, AVF, should all pretty much look the exact same. The only one that should really look different... is AVR.
There may be variations from EKG to EKG, but for the most part, in a perfect world, lead one, two, three, AVL, AVF should look the same. Okay, so we should have an upright P wave, QRS, T. upright P wave, QRS, T. If you wanted to go through these, definitely stop the video and follow each of these depolarization vectors and try to map all of them out.
And again, you'll get pretty much this. Again, there may be a small variance from either one, from all of these, but for the most part, same for AVL, AVF as one, two, and three. AVR should be the one that's completely different.
All right, we now understand that. Before we go. into the heart, showing the portions of the heart, we should actually finish explaining this AVF though.
So again, same thing as we talked about before with AVR and AVL. The machine's very smart, right? So what it does is it turns a negative electrode on the right arm, negative electrode on the left arm, and creates a positive electrode here on the left leg.
And again, if you imagine kind of the null electrode would form where? Somewhere in the center between those two, directed towards that positive electrode in this direction here. And so it would would be like this positive electrode is the eye looking at the heart from below. That already kind of tells you what we need to know the next part. What portion of the heart do these leads tell us about or they really are good at?
So take a look here if you imagine AVR it's kind of like a positive charge kind of situated like right here and it's looking at the heart kind of down this way. It really is good at telling us about two parts of the heart. The one part is it it tells us about the very beginning part of the interventricular septum and it tells us about parts of the right ventricle as well.
So again what does AVR tell us about? It tells us about the activity of the right ventricle and what's called the basal septum. Okey-dokey. So that would be for, let's write that up here, this is for AVR.
The next one here is for AVL. AVL, where is the eye kind of situated? The eye is situated right over here, right?
So the positive charge would be here kind of looking down at the heart this way. So that's going to tell us about what part here. Well, if you can kind of follow this down here, it's going to tell us kind of about the same thing that one did. Do you remember what one told us about? That high lateral...
wall of the left ventricle, it's the same thing for AVL. So AVL will tell us about what? AVL will tell us about the high lateral wall of the left ventricle. Okay? And last but not least is AVF.
AVF is going to be, again, imagine the eyeball is on the bottom, so you're gonna have the positive charge and it's looking upwards at the heart. What part does that hit? If you kind of draw an imaginary line.
You're going to get kind of this portion here. What's this portion? We already kind of seen this before. It's going to kind of hit like from here to here.
Do you remember what that looked like before with the limb leads? Leads two and three. So leads two and three and AVF tell us about the inferior wall, okay, of the heart.
So this is going to be about inferior wall. heart. So if we were to combine some of these to kind of tell us about what we know already, we can add on to help us to remember all of this in one thing not in separate pieces right.
So we know that AVF sees the inferior wall of the heart, but what else sees the inferior wall of the heart or kind of gives us an idea of what's going on with the inferior wall of the heart? You can add on two, three, and AVF. That's gonna tell us about the inferior wall of the heart. We already know that though.
And then again what tells us about that high lateral wall of the left ventricle? AVL. but remember what else told us about it? One. So one and AVL tell us about the high lateral wall of the left ventricle, 2,3-AVF tells about the inferior wall of the heart, and AVR is just kind of like a lone rider that tells us about the right ventricle in the basal septum.
All right, let's go to the next part. Now that we got limb leads down, we got augmented unipolar limb leads down, we know now that all of the limb leads are having an upright kind of direction. We know that all of the augmented except for AVR have all of an upright direction. And we now appreciate the portions of the heart that those leads tell us about. Now let's do the same.
Same thing for the precordial leads. Alright Ninja Nerds, so now at this point in time we've covered our limb leads, we've covered our augmented unipolar limb leads, and we've talked about a lot of these deflections and what their EKG should look like, what portions of the heart these leads tell us about. to do the same thing for the precordial leads. Now the precordial leads are probably one of the more important leads out of all of the 12 limb leads because they can tell us a lot about pathology.
Okay these are interesting ones. So these are unipolar limb leads. So they only have one kind of positive electrode that we put on the chest at different portions.
So these are unipolar leads and we put them on the chest at different regions. So let's actually kind of annotate where those ones would go. Alright, first thing here, you put one of these V1, we call it, the first one, which again is a positive electrode.
All of them will have a positive electrode that we place on the chest wall. V1, we actually go to the sternal angle, okay? That's you.
usually around the second intercostal space, and you feel down, you go to about the right fourth intercostal space, and that's where you'll put V1. Then you go to the next one, so go back over to the left side, and you go to the left fourth intercostal space. parasternal line, that's going to be V2.
You skip V3 for a second because you come back to him a little bit later. Then you go to V4. V4, you go down to the fifth intercostal space on the left and you go to about mid clavicular line.
You place V4 there. V5, you stay in the left fifth intercostal space, but you move to the anterior axillary line, which is about right here. Okay, so that's going to be V4.
V5. And the last one is you again stay in that left fifth intercostal space but keep moving, moving, moving until you get into the middle of the armpit and that's called mid axillary line. So that's V6. Now we got to come back though and place V3.
Where do we place V3? We just make sure it fits between somewhere between V2 which is that left fourth intercostal space parasternal angle or parasternal region. between V4 which was left fifth intercostal space midclavicular line. So as long as you just place it between them doesn't really matter. So that's V3.
Okay so these are our precordial or our chest leads. We know kind of now where they go right. Right fourth, left fourth, both pair sternal. This one goes between V2 to V4.
V4 is left fifth, midclavicular. V5, left fifth, anterior axillary line. V6, left fifth, midaxillary line. We know that these are... are unipolar they only have a positive electrode that we place on the chest so they only can pick up kind of the vectors that are moving either towards them or away from them and what plane that's what's really important this is what's really cool about them so they tell us about the electrical activity and it was called a horizontal or kind of a transverse plane which is very very cool so what we did here is we took a cross section okay of the thorax to where you're gonna see the heart you can't obviously this is where you're your lungs would be here on the sides.
But we're taking a kind of a cross section or a transverse section of the thorax and looking at it. Now, these leads, we kind of try to have them all converge on a point here like that AV node basal septal portion. But each one of these tells us about a particular portion of the heart. Before we start getting into that though, we should have an understanding very, very importantly about what's called the progression of the.
the R wave and the S wave as we go from V1 all the way to V6. I'm not too concerned about the P and Ts. It's very important we understand the R wave progression as well as the S wave as we go from V1 to V6. When you talk about the EKG, right? So if we were to kind of just draw out the EKG wave form, we kind of know all the parts by now.
Definitely, we're good at it now. P wave, Q, R, S, T wave. There's two waves that I primarily want us to focus on throughout the process here. That's the R wave and the S wave. That's the ones I want us to really, really discuss about.
The reason why is that Q waves, sometimes you see them, sometimes you don't. And really, you shouldn't really see them, at least big ones in V1 to V3. So again, we're going to focus primarily on the R wave and the S wave and the ratio as you go from V1 to V6.
Very, very important. We have to understand this as a basic concept of EKGs. So, remember the first positive deflection in the QRS is the R wave.
The second deflection, if it comes after any positive deflection, that is going to be the S wave. So, let's say that we take here and we kind of look at the ventricles. I like to look at them a little bit separately with respect to the R wave. If you think about it, remember whenever the ventricles are depolarizing, right? This phase you create a small right ventricular vector for the r-wave and you create a large ventricular vector, a bigger one, for the left ventricle right and you know that you would create a mean one that would be a little bit more directed between the two of them but it would definitely be leaning more towards that larger left ventricular r-wave vector.
For right now before we even look at the mean one I like to look at just the individual ones I think it helps me to make sense of this. So let's look at at that. V1, if you kind of follow the lines here, you obviously can tell that V1 tells us about the right ventricle, V2 tells us about the right ventricle, V3 it does a little bit of the right ventricle as well, but V1, V2, V3 they should tell us a little bit about that right ventricle, but primarily V1 and V2.
So if that's the case then, if I have a r-wave vector that's coming from that right ventricle, and it's little because it's not going to be as big as the left ventricle one because of the thickness. What kind of r-wave would I get for v1, v2, and maybe even v3? Would I get a big r-wave or would I get like a smaller r-wave? I get a smaller r-wave, right? Because that's a smaller r-wave vector.
So if that's the case then my first upward deflection has to be little, right? Like this, and then like this. And then like maybe a little bit, maybe a little bit bigger as you go to V3 because look where V3 is starting to kind of look at.
It's starting to get more towards that left ventricle. So if you kind of look at it, V1, V2, maybe the same size, but V3. that R wave should be getting a little bit bigger at that point in time. Okay, let's keep following that over here to V4. V4 is actually what's called our transition point.
Because now we have that leftward kind of vector. here that left ventricular r-wave vector that's pointing towards the left side here and v4 is getting a good shot of it v5 is getting a really good shot at it and so is v6 so what do you think should the r-wave be big for four five and six or should it be small that's a big r-wave vector coming from the left ventricle so it should be a big r-wave right so guess what we do we get a nice r-wave even bigger here in v5 and then a decent size one here in V6, right? Actually don't need that yet, we're gonna get to the S wave in a second.
But you get the point here, look at what's happening with the R waves as we go from V1 to V6. For the most part they should be getting smaller, a little bit bigger, a little bit bigger, bigger, bigger, DANG! That's kind of a whole process of the R wave as you start to transition throughout these.
Let's do the same thing but with the S wave. S wave. So the S wave is usually indicating what?
So you're going to have this kind of depolarization of the bases and then this kind of depolarization of the bases as well. Same thing if you're kind of looking at these it's the same kind of concept here right that these are moving away from the positive electrodes. Okay so this is what happens is it's moving away from the positive electrodes So this will produce a downward deflection. Okay because again if you're looking at this one here it's going to be moving again away from the positive electrode that should produce a downward deflection.
If you look in V2 same thing it should produce a downward deflection. In V3 it should produce a downward deflection, but guess what? That downward deflection starts to decrease as you move from V3 all the way till V6.
So now watch... Watch what happens now. This should kind of become like a little bit smaller, like a little bit there. And then here, this one will kind of almost become like isoelectric.
This one will be really tiny and this one will kind of be almost non-existent. So do you see what's happening? now with the R to S ratio here is that as you progress the R wave should be getting bigger as you go from V1 to V6 and the S wave should be getting smaller as you go from V1 to V6.
That's very very important especially when we start talking about axis deviation and other types of pathologies like ventricular hypertrophy so on and so forth. Okay so again what do I want you to get out of this? R wave progression.
As you go from V1 to V6, what happens to the R wave? It should get bigger. As you follow the S wave from V1 to V6, what should happen? It should get smaller.
Okay? That's very important to remember. All right. So I think we now have a pretty good idea of what the R wave is.
Heart-ass ratio should look like through V1 to V6 and what these kind of precordial leads are telling us about. Alright, so now at this point in time we should have a pretty strong idea about where do we place the precordial chest leads, right? We should understand what kind of a way they're looking at the heart from horizontal or transverse plane.
We should very very importantly understand the progression of the R wave as we go from V1 to V6 is increasing. and that the S-wave as we go from V1 to V6 is decreasing. So the R to S ratios, usually less than 1 for V1 to V3, greater than 1 for V5 to V6. And the next thing that we need to understand here is what portion... of the heart do V1 all the way to V6 tell us about?
Because that's very important, again, when it comes to STEMIs. So to make it easy, there's the different parts that we're going to color in here for us, right? So this first one here, right ventricle.
Right ventricle is definitely going to be told to us by V1, V2, and even a little bit of V3. So I want you to remember here, V1 to V3 will tell us about the activity of what? It'll tell us about the activity of the right ventricle. Now do you guys remember what other lead that we talked about like the limb leads or augmented unipolar limb leads tell us about the right ventricle which one? AVR.
So AVR you can also add into this if you want to also gives us an idea about that right ventricle. Pretty cool right? So if you wanted to add in from what we remember you can also add in there a VR like we did before.
All right so we know that VR V1 to V3, and we can add on that little AVR there as well to help us remember stuff, recognition there. That kind of tells us a little bit about the right ventricle. Now, the basal septum, though, the top part of the interventricular septum, if you will, that is going to be pretty much picked up by the electrodes V2 and V3. So V2 to V3 tell us about that basal septum.
But what else told us about the basal septum? Remember AVR told us about the right ventricle and the basal septum? So if we want to, we can also add in AVR. Okay?
Let's come over to the next part. So now we have the anterior portion of the heart. So the anterior wall of the heart.
So the anterior wall of the heart is a very good big chunk of the heart and that's going to be from V2 all the way to V4. So V2 to V4 tell us about the anterior wall of the heart, very very important one. The last one here, which is going to be telling us about the kind of the lateral wall of the left ventricle.
So again, which part of the left ventricle here, the lateral wall of the LV, which is your left ventricle, that's going to be the lateral wall. to be what V5 and V6 which will be giving us a good representation of that part of the heart so V5 to V6. Now if you wanted to add on here and think a little bit about this remember the lateral wall of the left ventricle is V5 to V6 but do you remember what kind of the higher part of the left lateral wall of the lateral wall of the left ventricle was covered by?
One in AVL. So sometimes if some people develop STEMIs and V5 V6 they may also they have elevations. in V5 and V6, they may also have some elevations in one in AVL if it's those higher parts. So sometimes you can also combine one AVL. V5 and V6 together because they really give you a good idea about that entire lateral wall of the left ventricle.
Okay? All right. I think we have a pretty good idea now about these precordial leads. And I think we have a pretty good idea about all of these different waveforms and vectors and physics, which I know is mind-numbing sometimes.
What I want us to do is now start taking everything, all this basics kind of topics that we've gone over and start applying that to EKGs now. What I really want to do is give you the very basics about what an EKG kind of strip or paper looks like. What are some of the bare minimum things that you really need to know whenever we start reading them? And then also talk about a quick little recap of the different deflections and maybe what the actual parameters or distance of those intervals or waves what how wide they should be how long they should be so on and so forth.
So let's now come over here finish off our lecture with that. Alright so we've really built up our foundation now. We have a very strong foundation that we've built. Let's go ahead and really quickly before we really start getting into looking at lectures and reading real EKGs, have a basic idea of some of the components of the EKG strip itself. So if I were to take here I want you guys to know first thing you see this big large red box.
This big large kind of red box right here there's a couple things I want you you to know about it. So large box. First thing I want you to know is I want you to know a couple things about its width.
Less significant with respect to these I want you to know the height. So the width and the height thankfully are the same. It's five millimeters in width, five millimeters in height. You're probably like, okay what the heck is that supposed to mean? I'll tell you, don't worry.
Width is a little bit more of the important one, okay. So I like to turn width particularly and because this is measured over time so width is really helpful when it comes to time Height is determining kind of the amplitude or the voltage that the wave is actually kind of generating So the more dependent upon the voltage or the amplitude So when it comes to width I look at that with respect to time So I want I need to have some kind of conversion factor if you will between five millimeters and some type of seconds or milliseconds I like seconds. So what actually happens here is 5 millimeters is actually equal to 0.20 seconds.
So one large box means that 0.20 seconds has gone by with some electrical activity that's occurred right there on the EKG strip. Height wise, that's 5 millimeters, right? So 5 millimeters tells us a little bit about the voltage, like I told you.
So voltage for this is generally going to be about 0.5 millivolts. So 0.5 millivolts is how much 5 millimeters is equal to. So one large box and height tells us that there's a voltage of about 0.5 millivolts. Is that important?
Not necessarily. We'll see later that sometimes you can have low QRS voltages in certain conditions. But the real important one that I really want you to remember, I think it's very important to remember, is the width. Because that's going to become very significant when we start talking about is the PR interval too long?
Is it too short? Is the QT interval too long? Is the, another thing, is the QRS waves wide?
Are they narrow? So on and so forth. The next thing is if you look in these large boxes, there is so many small boxes. And you know how many there is?
So within one large box. There's actually equivalent to 25 small boxes. Okay? So there's kind of like five rows, five in each one. So it's kind of like if you want to think about it, it's five millimeters squared for these actual, the small boxes.
Okay? So when we talk about the small boxes, what I really want you to know is the same thing. I want you to know width, important, and I want you to know height.
So for the small boxes, the width is actually very interesting here. You think about it, one, two, three, four, five. Five little boxes make up one large box.
It's five millimeters in width. What do you think the width would be? with a small box will be one millimeter.
So it's one millimeter. Then if you take five and divide it from so you take point two zero and you divide it by five that'll give you your time that it takes for that one small box and that's equal to equal to about 0.04 seconds. Also very important. Now height, same thing, it's equal to one millimeter, which is equal to 0.01 millivolt, because it's the same thing.
It's just off by a factor of, in this case, it's off by a factor of 10. So what do I really want you to know about the height stuff? I'm not really concerned about you knowing the millivoltages. I'm more concerned about you knowing that one small box is one millimeter, one large box is five millimeters.
The reason why is when we have to measure ST segments. Is the ST segment elevated? Well sometimes it needs to be one millimeter elevation. So you have to go in and see is the ST segment elevated more than one box? Or maybe it's super elevated and you see an ST segment that has elevation beyond one large box, five millimeters.
So the whole point is Why do I really want you to know the height? Not super important for the voltages, more important for measuring those ST segments. Okay, that's the basic concept.
If you really wanted to know a little bit more... So again, width is the big one. Height is gonna be a little bit more, it's particular for the small boxes, the one millimeter. Hopefully you don't see ST segments that are beyond five millimeters in elevation, but again, you can.
But again, I think we have a basic concept to that. The other thing I want you guys to know about this is whenever we look at this EKG, we see the various waves, right? We already kind of have a pretty strong idea about these, but if we were to quickly recap this is our P wave Q R S ST segment and our T wave right same thing but now let's talk about maybe some extra stuff this is our PR interval.
This, from this point here, to this point here, is our QT interval. And then this part here is our ST segment, right? And we already kind of talked a little bit about that ST segment there, but what I really want you to know is that these are going to become very important in certain types of pathologies.
Okay, so I want you to have a basic idea of I love some of these. So the first one that I want you to remember is your PR interval. So your PR interval, we already kind of talked a little bit about that.
It's from the beginning of the P wave all the way until we get to the beginning of the QRS complex, right? A PR interval should normally be from it should be less than 0.20 seconds. So it should be less than one large box.
That's kind of the goal if it's less than 0.20 seconds it's considered to be a normal PR interval. If it's greater than that it's prolonged. It's going to become important in different types of blocks. Okay so this is considered to be normal. The next one that I want you to remember is your QR QRS complex, so your QRS, the width of that, usually you want that to be less than 0.12 seconds.
Okay, which if you count that up, one little box is 0.04 seconds. So if I do 0.04 times three, that's 0.12 seconds. So I want it to be less than three little boxes. If it's greater than that, it's considered to be a wide QR. a pathologically wide QRS.
Now some textbooks will even go and be a little bit like stingy and they'll even say technically like greater than.10 seconds is considered to be a little bit wide of a QRS, but it's easier to remember and for the sake of it, if you're starting to like question it, is it wide, is it narrow, you're taking too much time. If it's greater than.12 seconds, three little boxes, it's wide. If it's less than that, it's narrow. Don't make it too complicated, right? So this is gonna be normal or.
or sometimes what we call, you'll see us, we refer to it a lot, kind of they're synonymous in a way, they're kind of referred to as narrow, which is normal. All right, the last one here is the QT interval that I want you to know. So the QT interval is important because whenever that sucker is prolonged, it increases the risk of a particular type of arrhythmia called torsades de pointes, which is a type of polymorphic VTAC. And so this number, literally, it can vary from textbook to textbook, it can vary from gender to gender, so male, females, there can be a lot of different. The consensus that's kind of been, I've seen here within the textbooks that I utilized was that if you're a male or a female, and if it's a male, less than 430 milliseconds.
Now this is utilizing rates particularly at like 60. It depends, if you're going a little bit faster you have to adjust. And we'll talk about those things later, you have to use like corrected QTC formulas and we'll get into all that stuff. But for the most part, less than 430 milliseconds is considered to be normal in males.
and then less than 460 milliseconds in females is considered to be normal. Now again, I don't want you to get too bogged down into that detail. I usually don't consider something to be super dangerously like prolonged QT until I start approaching 500. But again, to really kind of be thorough, these are the numbers that are generally thrown around, but we'll talk about this a lot more when we get into the arrhythmias, okay?