Electrocardiogram (ECG) - Video Tutorials & Practice Problems
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concept
Electrocardiogram
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This is an electrocardiogram and almost certainly you are familiar with this sight and with this sound. Now we're gonna talk about electrocardiogram in a lot more detail. Now, before we do, I just wanna acknowledge, we don't normally talk about medical tests in a lot of detail. We're gonna talk about electrocardiogram because it tells you so much about the heart. They're so common and you are so very likely to see questions about it. All right, before we really dive in though, I just want to note, we have two words here that are very similar. We have electrocardiograph and electrocardiogram. Let's talk about the distinction between these two electrocardiograph. That's the instrument, that's the machine that measures the electrical activity in the heart using electrodes on the body. Now, the electrocardiogram, what we sometimes call that ECG or EKG, I'll come back to those letters in just one second. That's the recording of the cardiac electrical activity. So this distinction, it's a fine one and it's probably OK if you get it confused, what you really wanna be able to do is to be able to read an electrocardiogram and say what's going on in the heart but electrocardiograph, technically, that's the machine. The readout from that machine is the electrocardiogram. The way I remember it is, I think of a telegraph and a telegram. Now, that's that old timey way of sending messages that you may be familiar with from like movies about the old West, the telegram. That's the readout you get, that's the message you get, it's sent by a machine called a telegraph. So that distinction is the same that we're talking about here. So what we really want to talk about is that read out? What does it look like? And how do we read it? That's the electrocardiogram. Now, we said we can call this an ECG and that just comes from electrocardiogram or sometimes people call it an EKG that comes from the same word just if you spell it in German. Now I speak English. So I'm gonna be trying to say ECG. But for historical reasons, sometimes people still call it an EKG again. You probably don't need to really worry about that. If you get mixed up and you call it an EKG, just tell your professor you like to speak in German. All right, these again, we said these are the recording of the cardiac electrical activity. What you're really recording though. What you're measuring is the depolarization and the re polarization of the atria and the ventricles. We are looking at these cardiac contractile cells, remember that's the majority of the heart muscle and when we looked at the action potentials in these cardiac contractile cells. Remember the depolarization and the repolarization are separated by that plateau phase when it just sort of stays depolarized for a little while. So we can see those two things happen separately. Now, this means that we're actually gonna be looking for four things. When we look at this ecg we're looking for the depolarization and the repolarization of the atria and the depolarization and the repolarization of the ventricles. Now spoiler, you can't actually see all four of those, but I want you to keep those four things in mind as we're going through this. So we're gonna draw this out here and we have the voltage on the Y axis and time on the X axis. And we also have our heart there showing the electrical conduction system for reference. All right. So we start out, we go along and we get this first little blip that we have uh sort of color there and that yellow, orange color and we've labeled this the P wave. All right. So if you think what starts the electrical conduction system of the heart, well, that's when the sinoatrial node, the S A node depolarizes and that starts a wave of depolarization that spreads through the atria. So that's what we're seeing here. We're seeing those contractile cells in the atria depolarizing, right? So that P wave, we're gonna say the S A node fires and then what you're actually seeing here is that the atria depolarize. All right. Well, remember the atria depolarized and then they go into those cells go into that plateau phase and during that plateau phase, that's when those cells actually contract. So I've highlighted the atria there in red to illustrate now is when those atria are contracting. All right. Well, following that, now we get sort of the, the major feature of one of these electrocardiograms, we get this QR S complex. This QR S complex is gonna be really big compared to that P wave. Because these are when this is when the ventricles depolarize and the ventricles. Well, there's just so much more mass in the ventricles than there is in the atria. So when all those cells depolarize it basically the same time it is a massive electrical activity. So we're gonna say here, the QR S complex, we can see the ventricles depolarized. And I just want to note, you may wonder why does it go down for the Q way up for the R and then down again for the S. Well, the Q and the S specifically remember we're measuring electrical activity in the heart, but this electrical activity, these action potentials are spreading through the heart like a wave and the heart is this very complex three dimensional structure. And we're measuring this from nodes on different parts of the body, from electrodes on different parts of the body is what I meant to say. Excuse me. So sometimes those waves are sort of moving towards those electrodes, sometimes they're moving away from the electrodes. And so that sort of down for the Q and the down for the S, that's sort of just actually an artifact of how the, how this electrical activity is measured. What you really wanna see is just how big that, that R wave is this massive depolarization because you have a lot, a lot of mass in the heart all depolarizing at the same time in those ventricles. Now, we also want to know we're looking for four things here. We were looking for the atria and the ventricles to depolarize. We've seen that, but we also wanna see the repolarization. Well, our atria depolarized, but we're not gonna be able to see them rep polarized because it's happening now. So this is also atrial repolarization and the atria just are so small in terms of mass compared to the ventricles that, that repolarization of the atria, just sort of gets lost in the wash of this QR S complex. It's happening at the same time, but you can't really see it because the ventricles are just so much bigger. All right. Well, now the ventricles are contracted. So now we're remember we're in that plateau phase of these cells. That means that this is when the ventricles are really contracting. So the ventricles are contracting and then they need to re polarize. And we see that in the T wave. So the T wave, we can see the ventricles re polarize. All right. Now, as we look at this, there's gonna be different intervals and segments that people sometimes measure an interval is when you're measuring more than one part of this readout at the same time. And that is going to include at least one of these waves. A segment is going to be one of the times when the line is flat between the waves. So just to give you an some examples of this, we'll uh include one of each of those here, we can look at what's called the pr interval. Now, the pr interval starts with the P wave includes the P wave and it ends at the beginning of the QR S complex. Now you may say why isn't it called the PQ interval? Well, sometimes that Q wave is very small and you can't see it. So normally when we talk about something like that, we just refer to the R wave because the R wave is so big and so obvious. So the pr interval we said there that's when those Atria are contracting. But we also need to think why aren't the ventricles starting to contract right then too. Remember action potentials waves of depolarization that spread really fast. Remember this is what happens. This is the A V node delay. Remember that depolarization is gonna get to that A V node very quickly. It's the A V node is gonna get that signal during that first P wave. But the ventricles don't contract for a little while because that a V node puts that 100 millisecond pause on things. So let's just wait a second. Let's give a second for the atria to contract. Then we'll spread that action potential to the ventricles right now between the QR S complex and the T wave we can see here, this is called the ST segment. And so we've highlighted that on the um read out there as well on that electrocardiogram there. So the ST segment, well, we said this is when those ventricles are contracting. And this specifically, we can say this is definitely that ventricle plateau phase, right, the plateau phase when the ventricles are depolarized and they're just sort of staying there depolarized before theyre polarize again. All right. Now, this is a normal ECG. But of course, when people look at an ECG, they're looking for things that are wrong. So we're gonna practice looking at some things that are wrong with an ECG and trying to figure out how to read those as well. We don't need to be an expert at it. But honestly, if you get pretty good understanding what each one of these figures on the ECG represents. Well, if it doesn't look right, you should be able to figure out what part of that heart's electrical conduction system is causing a little bit of a problem. Again, we'll look at that more. Coming up first, we have an example in practice problems. I'll see you there.
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example
Electrocardiogram (ECG) Example 1
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3m
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Our example says on the ECG below, identify the following. And it has four things that we need to do with this ECG. So as I look at this ECG or electrocardiogram, I see those waves and complexes that we've been over. So let's see what we need to do with it. It says a correctly label one heart contraction with the letters P QR SNT. All right. So look at the CCG, pick out one heart contraction and think where would you put those letters P QR S and T? All right. Well, when I look at it, the first thing I wanna do is I wanna identify the different heart contractions because we can see the heart contracting a few times here. So this pattern that I'm circling here, that's one heart contraction, the depolarization of the atria, the depolarization of the ventricles and then the rep polarization of the ventricles. And I see that happen once, twice, three times. And then this fourth time we see it starting, we don't see the whole thing there because the end of it's cut off. All right. So now to label the P QR s and T, I'm gonna pick one of them. I'll pick the first one. Well, start with P, that's the first thing you see. That's that first little bump there. The P wave. Remember that's depolarization of the atria. Next we see the QR S so it goes down for the Q goes way up for the R and then goes down a little bit again for the S that QR S complex remember is depolarization of the ventricles. Now remember the rep polarization of the atria happens at the same time, but you can't see it on an ECG because the depolarization of the ventricles is such a bigger voltage change that just sort of gets lost in the wash. All right. That means finally we got one more thing here. We got one more bump right down here. That's our T wave. Remember the T wave is the rep polarization of the ventricles. All right. That means that I have done a, I'm gonna cross that out next. We want to put a box around the sections which measure the activity of the ventricles. All right. So where would you put your boxes on this? Ecg Well, I'm gonna put my boxes sort of starting at the beginning of that QR S complex and then ending right after the T wave. Remember QR S, that's the depolarization of the ventricles and the T wave, that's the repolarization. So everywhere in that box has to do with the ventricles. So I'm gonna keep going, I'm gonna put this down here a few times, there's another box, there's another box and then on the fourth one, well, we can see the activity of the ventricles. We don't see that T wave because it's cut off. But we can still put a box there. All right. That means I've done b and I'm gonna move on to C circle the sections that measure the activity of the atria. All right. Where are you gonna put your circles? Well, the Atria we can see on an ECG, we can see when they depolarize as part of that P wave. So I'm gonna circle my P waves. Now, technically speaking, the repolarization is happening during that QR S complex, but we can't see it on the ECG. So I'm not gonna circle that part. All right. So I've circled my four P waves. That was the activity of the Atria. I'm done with C. I'm gonna move on to D. He says in this section of readout, how many times can you observe the ventricles rep polarizing, right. So take a look how many repolarization of the ventricles do you see? I remember re polarization of the ventricle, that's the T wave. So really, we're just asking you to count the T waves and I see one T wave, two T waves, three T waves and you can't see the fourth T wave in that last contraction there. So I counted to three. That's gonna be my answer. I see three times that the ventricles rep polarize. All right, with that, I've answered the question. We got more practice problems to follow. Give them a try.
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Problem
Problem
When analyzing an ECG, you measure the time between the beginning of the QRS complex and the end of the T wave. Which physiological events are included in this interval?
A
Atrial depolarization and repolarization.
B
Ventricular depolarization and repolarization.
C
Atrial repolarization only.
D
Ventricular depolarization only.
4
Problem
Problem
During an ECG analysis of a patient, the doctor detects an abnormally prolonged PR interval. Which stage of cardiac conduction is most likely responsible for this delay?
A
Conduction through the SA node.
B
Atrial repolarization.
C
Conduction through the AV node.
D
Ventricular repolarization.
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concept
Electrocardiogram: Pathologies
Video duration:
9m
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We've been looking at electrocardiograms or ECGS and we've been seeing how these waves and complexes of the ECG correspond to normal heart function. But of course, normally, when someone's looking at an ECG, they're looking to see if there's something wrong with the heart, they're looking for pathologies. So we just want to start by saying that ecgs help health professions, diagnose heart pathologies and by pathologies, of course, we just mean anything that might be wrong with heart function. Now, I just wanna be clear here. Almost certainly, you are not expected to be an expert at diagnosing heart pathologies using ecgs in your class. But if you understand what a normal ECG is supposed to look like, and you understand what those different waves and complexes represent in the heart. When you see one that's abnormal, it's actually not that hard to usually uh figure out at least generally what might be going wrong in the heart. That's what we want to practice here. So to start that, we just want to look at this normal ECG in the top right here that we're using as a reference we can see here, it has this normal P wave, that's the atria depolarizing. We have the QR S complex. Remember that's the ventricles depolarizing followed by this T wave and that T wave is the ventricles rep polarizing. Well, now we see that this pattern just repeats nice and normally in a nice steady rhythm. Now, if an ECG doesn't look like that, we call it an arrhythmia and we can break this word down a means not an rhythm. Well, that refers to the rhythm. It doesn't have a rhythm or it doesn't have the right rhythm at least. So we're gonna say here, an arrhythmia or arrhythmias are abnormal heart rhythms and arrhythmias can vary from, you know, minor and very inconsequential to very serious and potentially fatal. Now to start this out and start looking at them, we just wanna first define what a normal heart rate is. And so we're gonna say here in a normal ECG, the resting heart rate is expected to be between 6100 beats per minute. And we call that out because the first thing, that sort of the easiest thing that jumps out when you look at an ECG is that heart rate? How fast is this pattern repeating? And one type of arrhythmia is gonna be if it's too slow and one is gonna be if it's too fast. So, if it's too slow, we call it bradycardia. Bradycardia is if that resting heart rate is too low or too slow. And we're gonna say that, that is a resting heart rate that is gonna be below that 60 beats per minute. Now, we can look at this ECG right here and we can see that in this ECG, we have a simple bradycardia. We can see a P wave, we can see the QR S complex. We can see the T wave that all looks normal. We can see it here. But then as it repeats, it's just kind of too spread out. Those heartbeats are just spread out and it's just beating too slowly. Now, a lot of times when you see a bradycardia, it's diagnosed as bradycardia with something else there. It's gonna be something else wrong here. We don't see that in this ECG here. We see a normal ECG just with a simple bradycardia, something like that. It can be concerning or it might not be concerning depending on the patient. People with excellent cardiovascular fitness will sometimes have or often have heart rates below that 60 beats per minute. In fact, you know, people, if you're a competitive marathoner or competitive cyclist, often they have heart rates down in the forties, beats per minute. Now, they have physiological changes going on in their heart that is puts them into an abnormal range, but it's not a, it's not unhealthy, they just have this abnormal cardiovascular fitness. All right. Now, in the other direction, we have tachycardia, tachycardia is gonna be if that resting heart rate is too fast. Now, that's gonna be a resting heart rate of uh above 100 beats per minute. And we can see here we have another ECG here. That is just a simple tachycardia. We can see the normal P wave that normal QR S complex and the normal T wave. But that pattern, while it pattern is normal, it just repeats too fast, that heart is just beating too fast. So again, this is a simple tachycardia. Often there will be something that's more complex where you have tachycardia with other things going on, other problems with those waves. Again, this is a normal tachycardia. But unlike bradycardia, there's really no time that someone's happy to have tachycardia. If your resting heart rate is above 100 beats per minute, that pretty much universally says there's something unhealthy going on, there's some pathology there. All right, our next one is going to be fibrillation, fibrillation is going to be uncoordinated contraction. And when we first started talking about the intrinsic cardiac conduction system, we said that co-ordinated contraction was one of the most important things that that conduction system does. For the heart, you need your atria to contract as one. You need the ventricles to contract as one so that it can push blood through the heart. Well, if it doesn't do that, if all these cells are contracting, but they're just kind of doing it on their own. You get this quivering fluttering heart that can't push blood. Now, fibrillation can be either atrial or ventricular atrial fibrillation is serious, but it's usually not fatal. At least not initially. In fact, plenty of people live a very long time with atrial fibrillation. As long as those ventricles are contracting at least somewhat regularly. You're able to push blood through the body and that's enough to keep you alive. In fact, it's so common that you'll see ads on TV for drugs that treat atrial fibrillation or as the ads often call it a FB, right? So that's atrial fibrillation. Now, in contrast, ventricular fibrillation, well, ventricular fibrillation is pretty much always fatal if not immediately treated. And we can see here this is an ecg of a ventricular fibrillation and you can see there's just completely uncoordinated polarization and depolarizations just going off all over the place. You can't see any recognizable waves. This is just a heart, just fluttering, not pumping blood in any, in any co-ordinated way. Now, when we say immediately treated, you've probably heard it the way you treat this. This is fibrillation, you treat it with a defibrillator. That's where you've seen in like TV shows with a clear, you get the paddles kun you put that big ho electric shock through. Now that electric shock coordinates the heart, it causes all of the heart cells to depolarize at one time and then I hopefully they rep polarize simultaneously and the S A node or the A V node can take back over and coordinate heart function again. All right, as we move on, I want to know those first three that we talked about bradycardia, tachycardia and fibrillation. Almost. Certainly, you should know those vocabulary words. Heart block is the next one we're gonna do. And it's less likely that you need to know what a heart block is. But like anything, check with your notes, know what your professor expects of you. We put this here again because just knowing what normal heart function is supposed to look like, it's not that hard to recognize when something goes wrong. And I want to point that out by using a heart block. So a heart block is going to be a disrupted signal and this is gonna be an issue with that conduction circuit. So to see what I mean, we can look at this ECG down here and you can see we have a normal P wave, we have a normal QR S complex. We have a normal T wave that all looks great. And now you expect it to repeat again. So we get a normal P wave and then nothing, right? So it looks to me like the atria depolarized and then the ventricles didn't follow you, follow it along some more. You get another P wave. Well, now this one follows correctly, QR S followed by the T wave and then you get another P wave and then again, nothing. So as I look at this ecg what it looks like to me is that sometimes those Atria are depolarizing and the ventricles aren't depolarizing afterwards. That's quite serious. So, if I were to say what's going on here, well, it's something with the conduction circuit, something in between the time the Atria depolarized and the ventricles depolarize something in there is stalling out. So maybe something with the A V node may be to blame. Ok. Again, you almost certainly don't need to be an expert at recognizing all sorts of different pathologies. I'd be familiar with those first three vocab words that we said here, the bradycardia, the tachycardia and the fibrillation. And I would also just practice seeing well, if it doesn't look normal, can I figure out what might possibly be wrong with it? We will practice that some more coming up. It'll be fun. I'll see you there.
6
concept
Electrocardiogram (ECG) Example 2
Video duration:
4m
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Here, we see that a normal ECG and two pathological ECGS are shown below. And we have this table down here that shows our 123 different ECGS or electrocardiograms that we're gonna need to analyze. And it says A for each ecg identify it as normal or pathological B if possible identify and label at least one P wave QR S complex and T wave on each diagram, we also note here, not all waves or complexes may be present in all ecgs. And then finally, it says in simple terms, what part of the heart's conduction system do you think may be failing each pathological ecg? All right. So as we look at this, I think for me, the easiest way to do this is just start labeling these complexes and waves. And if I can do it, it's gonna be normal. If I have trouble, it's gonna be abnormal. So in this first one, I see a P wave, I see a QR S complex and then I see a T wave. So that looks relatively normal. This does kind of look like a big space there, but we'll come back to that in a second now, as I keep going, I have a P wave and then nothing, it looks like I have another P wave and then nothing. I have another P wave and then we have another QR S complex, right? So I was able to label things there. But as you look at this, ecg does that look normal or pathological to you? Well, to me, it looks pathological. So I'm gonna put a P there and it looks pathological because it looks like I have these P waves that are not followed by QR S complexes. That's a problem. So, in simple terms, what part of this conduction system do you think may be failing? Well, the P wave is depolarization of the atria, the atria therefore, are depolarizing here, but the ventricles seem to not be depolarizing regularly. That means that that action potential stalls out somewhere going from the atria to the ventricles. So what does that action potential have to pass through? Has to pass through the A V node and the A V bundle. So, because this ventricle isn't contracting regularly, it tells me that that action potential must be stalling out somewhere in here. Now, the technical term that we're looking at this is a heart blocking, it's actually quite serious. All right, as we look at our second one, I can label things again. Well, I'm gonna look for my P wave QR S complex and T wave and look P wave QR S and mit wave that looks normal. And as I look down, that normal pattern just repeats over and over again. So, does that look normal or pathological to you? Well, this just looks like our normal ECG, I'm gonna give it an end. Therefore, what's the failing part of the conduction system? Nothing's failing. So I don't really need to write anything in that box. All right. Our final one here. Let's see what we can label in this ecg down here at the bottom. As I look there, I don't think I can name a P wave. I do see QR S complexes, these QR S complexes, these massive depolarizations here that represent the depolarization of the ventricles. Those seem to be happening, right? I see a lot of those QR S complexes, but I can't see the P waves and I can't see the T waves. So knowing that normal or pathological, now this looks pathological to me. So because I see that QR S complex that tells me that the ventricles are contracting. But in between, when I would expect to see that normal P wave, I just get this sort of fluttering this random depolarization and repolarization. Now, I know that's not from the ventricles because the ventricles are giving me that QR S complex. So what must be happening here? This is atrial fibrillation. Now, you could see in sort of more simple terms, you could say there's something wrong with the atria. The atria are not passing that actual potential correctly. But what we're seeing here is this sort of random unorganized depolarization on the cells in the atria that we call fibrillation. Ok. Now again, you do not need to be an expert at reading these ecgs and identifying pathologies. But hopefully you see here that by knowing what you're supposed to see, it's actually not that hard to figure out what is a pathological and what might actually be going wrong in the heart when you see it. All right with that, we got more practice to follow. Give it a try.
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Problem
Problem
Fibrillation can happen in either the atrial or the ventricles. When fibrillation happens in the ventricle it is usually immediately be life threatening. Which ECG below do you think shows ventricular fibrillation?
A
B
C
D
8
Problem
Problem
A varsity athlete went for their physical, which included an ECG. The doctors noticed that the student’s heart rate was unusually low, but they told the student not to worry. What term would the doctors include in their chart to describe the student’s heart?
A
Fibrillation.
B
Bradycardia.
C
Heart Block.
D
Tachycardia.
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