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 want to 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 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 QRS complex. Remember, that's the ventricles depolarizing, followed by this T wave, and that T wave is the ventricles repolarizing. 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, and arrhythmia, well, that refers to the rhythm. It doesn't have a rhythm or doesn't have the right rhythm, at least. So, we're going to 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 want to first define what a normal heart rate is. And so we're going to say here in a normal ECG, the resting heart rate is expected to be between 60 and 100 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 going to be if it's too slow, and one's going to 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 going to say that that is a resting heart rate that is going to 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 QRS complex. We can see the T wave. That all looks normal. We can see it here. But then as it repeats, it's just kinda 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 going to 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 a 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 puts them into an abnormal range, but it's not unhealthy. They just have this abnormal cardiovascular fitness. Alright. Now in the other direction, we have tachycardia. Tachycardia is going to be if that resting heart rate is too fast. Now that's going to be a resting heart rate of 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 QRS complex, and the normal T wave. But that pattern, well, 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. Alright.

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 coordinated 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 kinda 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, AFib.

Alright. 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 polarizations 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 coordinated 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. You put that big, hold electric shock through. Now that electric shock coordinates the heart. It causes all of the heart cells to depolarize at one time, and then, hopefully, they repolarize simultaneously, and the SA node or the AV node can take back over and coordinate heart function again. Alright.

As we move on, I want to note 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 going to 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 going to 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 QRS 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. QRS 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 afterward. 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 depolarized, something in there is stalling out. So maybe something with the AV node may be to blame. Okay.

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 vocabulary words that we said here, the bradycardia, the tachycardia, and the fibrillation. And I would also just practice seeing, well if