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What is myocarditis and pericarditis?

Created by Raja Narayan.

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Video transcript

- In the next couple of videos, we're going to talk about two disorders that are often discussed together. One is called myocarditis, myocarditis, and the other one is called pericarditis, and they refer to two different diseases that are inflammatory reactions of certain parts of the heart, and I think you may have guessed that just because both of them use this part, card, meaning cardiac, and perhaps you also recognize that anything that ends in itis, itis like that, means that that's an inflammation or an inflammatory process of whatever it's coming after, like cellulitis is inflammation of the skin. Optic neuritis is inflammation of the optic nerve. So, myocarditis is inflammation of the myocardium, which is the muscle of the heart, and pericarditis is inflammation of the pericardium, which is the outer layer of the heart. So, I've started throwing some fancy terms at you. So, let me define them. So, when we talk about the myocardium and the pericardium, where do they sit in our structural cardiac anatomy? So, let's start from the very core, and I'll draw a simplified heart. Of course, you know that the heart isn't really shaped like this, but there are three layers to the heart. I've drawn one right here, and then there's another layer on the outside like this, so let me just draw this layer out here, and I'll color this layer there, and then we can start to label things. This inner layer right here, and that also involves everything that's on the inside, is the part of the heart that makes contact with blood as it's pumped through to the rest of the body. This is called the endocardium, the endocardium, and we're not going to talk about endocarditis in this video but that's definitely a significant disorder to think about. So, that's the endocardium. The next layer, this meaty red layer that's on the outside, is the muscle of the heart. This is the myocardium, so that's the myocardium, so let me label that there and this is the part that's affected in myocarditis as we're going to discuss, and then this outermost layer that's all the way around here, it's sometimes called the epicardium, so the epicardium, but no one really calls it that. The term most people refer to it as is the pericardium. So, it's the pericardium and in fact, that does refer back to what we were initially setting out to discuss. Pericarditis is an inflammation of this layer, but the pericardium isn't just one layer. This layer that I've drawn here that goes like this and wraps around here will come back and reflect up that way. So, let me draw it going all the way around. It comes down here, flips back this way, and then it comes and meets back up there, and notice that this lining was coming in right here. It flips here, and then starts going that way. So, in a sense, it's a continuous lining, but it forms these two layers, and I'll color this portion inside here. This is going to be its own little cavity or this space here, and we refer to this as the pericardial space. This is the pericardial space. All right. So, I've set up these two layers right here of the epicardium or the pericardium, and, in fact, the layer that's here that touches the myocardium and the inside of this outer layer here, has a special name. It's called the serous, the serous pericardium, and some anatomists will make distinctions. This is the visceral layer of the serous pericardium, and this is the parietal layer of the serous pericardium. I'm not going to write those down because I think that's too much detail for what we want to talk about. Just know that there are two layers to the pericardium here, and there's pericardial space, and then finally on the outside, this outer layer of the parietal layer of the serious pericardium has a lot of fibrous tissue, or fibrous tissue on it, and so I'm just going to go around and just draw that, and all that means is this outer layer is kind of rough, and so, remember, the inside part of this lining is called the serous pericardium. This outer layer that's a little more rough is called the fibrous. It's the fibrous pericardium, okay, and the fibrous pericardium is what you would see if you were to dissect out the heart in a cadaver lab or when you're doing surgery. So, now that we know all of our different layers for our structural heart anatomy, I can tell you that the myocardium, as we discussed, is the heart muscle, and so any disease of the heart muscle will then undermine the ability of the heart to pump blood to the rest of the body, and so myocarditis is an inflammation of the heart muscle, which can then lead the heart to dilate or this wall can become thicker or the chambers can become enlarged, making it difficult to actually pump blood out. On the other hand, the pericardium, the serous pericardium, which is the main thing we talk about here, is the outer lining. It's the outer lining of the heart, and if there's an infection or some other inflammatory process of the pericardium, that would make it even more stiff, and so what that means is that when the heart tries to fill with blood that it receives that's deoxygenated or doesn't have any oxygen and it wants to send it to the lungs to get oxygenated or send it to the rest of the body, it's not able to pump a lot of blood out because it can't collect it in the first place. So, if the pericardium becomes inflamed, it doesn't allow blood to return to the heart, and functionally, that's the same problem here. If you don't get enough blood back to the heart, you can't pump it outside to the rest of the body. All right, so I think we have an idea of why it's so troublesome to have myocarditis or pericarditis and we've talked about the card part of where they exist in our anatomy, but let's talk more about the itis. Let's talk about inflammation and what does that mean.