Causes of pericarditis

- [Voiceover] So, let's shift over to pericarditis now, and let's start with infectious causes there. It used to be that the Coxsackie virus also was the most common cause of pericarditis, but recent studies have suggested that the number one cause of pericarditis, and this is again for the first world, so in developed countries, first world, may be from viruses, so I'll write viruses. So, viruses such as what's called cytomegalovirus. There's also herpes simplex virus, which is the herpes virus you hear about a lot, and there's also the human immunodeficiency virus or HIV, which you may have heard of as well. In the third world, however, we make a distinction for pericarditis. There's a different most common cause out there, in the third world countries, so the third world. Pericarditis, especially if it's advanced, is from a type of bacterium that you may have heard of before. It's called mycobacterium tuberculae or TB. TB is the most common cause of pericarditis in the third world, and I'll write down here as a side note, this is especially true, so especially true for constrictive, constrictive pericarditis. And we'll talk more about what constrictive pericarditis means, but I think I've already touched on it. It's so much inflammation of the pericardium that the heart isn't able to fill with an adequate amount of blood to pump to the rest of your body. So, TB is especially the cause of constrictive pericarditis. So, let's skip on down here, and let's talk about some non-infectious causes of inflammation of the pericardium, and I think one of the most interesting ones is what's referred to as a post-myocardial, post-myocardial infarction pericarditis, post-myocardial infarction pericarditis. And maybe I'm throwing a lot at you by saying that here, but just suffice it to say a myocardial infarction is the exact same thing as a heart attack, heart attack. Myocardial you might recognize as myocardium, and infarction means a loss of blood flow leading to tissue death. So, a myocardial infarction, or it might be called an MI, you may have heard that term, but this is also referred to as Dressler's syndrome, Dressler's syndrome, and Dressler's syndrome happens between something like two to three weeks. So, I'll write two to three weeks to one month. I'll use or take advantage of the terminology we just introduced earlier, one month post-MI, or after a heart attack, where you have markers in the myocardium that are altered because of the ischemia or the loss of blood flow released into the blood stream that causes the immune system to create antibodies to it. And these antibodies, for some reason, will also attack the pericardium as well, resulting in post-myocardial infarction pericarditis. All right, let's move on. Another important cause of pericarditis could be radiation exposure, and this isn't just one chest x-ray. This is having multiple CAT scans of your chest over and over again over decades could cause radiation-induced pericarditis, and the mechanism for this is what's called reactive fibrosis. Reactive fibrosis is what results in pericarditis here. Another important cause is cancer. Not cancer of the pericardium, but cancer elsewhere. Maybe you've got lung cancer, or you've got breast cancer, and what happens is these cancers that are occurring elsewhere, they spread to seed. So, seeding meaning they start invading or populating. So, they seed the pericardial space. They seed the pericardial space, and they cause reactive inflammatory changes because they are present there. Another important cause of pericarditis is just plain old trauma. Maybe you're in a motor vehicle collision, and it's a deceleration collision, where your car is stopped really abruptly because you've run into a wall, and then you fly forward, and your chest hits the steering wheel so hard that the steering wheel is deformed. So, what that does then is, you end up getting what's called a contusion. Contusion, which is just a fancy word for a bruise. So, a contusion from compression of the sternum. So, compression of the sternum, which is a bone in your chest, and I'll show you a picture of it in a second. So, the sternum, which is also known as your breastbone, on the pericardium. So, it's the sternum on the pericardium, and it compresses it and causes damage to the pericardium, and when the immune system tries to heal the pericardium, it ends up becoming inflamed temporarily, which causes pericarditis. So, I've got this nice animation here, and oh, this is so cool. This is an animated sagittal cardiac MRI. So, MRI meaning this is a magnetic resonance image, and this is just a special way of taking a look at what's happening in the chest. Sagittal meaning we've cut this person in half, like if you karate chopped them right through the head and down through the legs. What we're seeing here is the right side of the heart, and this is the right ventricle pumping blood through the pulmonary artery and out towards the lungs, and this part that ends abruptly, this is the aorta. This is the arch of the aorta that goes into the thoracic aorta, if you know those points of anatomy. If you don't, that's okay. But the aorta here is supposed to connect to the left ventricle, but we don't really see how it connects. It ends abruptly up here, because we've karate chopped between the right and the left ventricle. And so, that's why we're only seeing this here. And the heart, of course, is just beating away blood into the aorta very beautifully. The point of this image I want to show you here is this bone that sits here. This is the sternum. This is the sternum that's right here, and this is the top part. You have the sternal notch that's around here, and when you have a car accident, and the steering wheel compresses against the sternum here, this will then be shifted backwards, and it'll hit against the pericardium. It'll hit against the pericardium and then compress the heart. And, in fact, in CPR or cardiopulmonary resuscitation, when you compress on the chest, you do chest compressions to artificially pump blood out of the heart, into the aorta, and up into your brain to oxygenate tissue while a person is not beating their own heart, you also do the same thing, where you have the sternum press up against the pericardium. That's another cause, potentially, of pericarditis as well. So, this is a great image that we can see all of this happening here, as normally it should with the heart pumping, but realize the sternum sits right here and could compress against the heart in a traumatic way in an accident. So, let's be gone with this image. Go away. And let's keep talking right here. So, the last sort of subgroup of causes I want to talk about that are non-infectious are metabolic causes of pericarditis, metabolic causes, and there are two main ones I want to talk about here. One is called hypothyroidism. You may have heard about the thyroid. The thyroid is an organ that sits in your neck. Hypothyroidism is when this organ is not releasing much thyroid hormone. And thyroid hormone is responsible for increasing your metabolic rate, increasing blood pressure, and a lot of other things in your body. When you have hypothyroidism, you don't have enough of the thyroid hormone. So, you can get arrhythmias. Your skin can become course, because you have a slow metabolic rate. These people tend to gain weight as well. So, hypothyroidism, for some reason, will also cause pericarditis that is best treated by replacing this missing thyroid hormone. Another important metabolic cause of pericarditis is what's called uremia. Uremia is just the build up, so I'll write in parentheses here build up of nitrogenous waste. I'll just write N for nitrogenous, nitrogenous waste, and it's the same type of waste your kidneys should be getting rid of. It's urea, if you've heard of that type of waste product. It's a nitrogenous waste product, but in folks that are on dialysis with end-stage renal disease or chronic kidney disease, their kidneys don't work. And so, they rely on dialysis to get rid of these waste products. If they skip a dialysis session, then maybe these nitrogenous waste products can build up and irritate the pericardium, leading to what's called a uremic, uremic pericarditis, which is something that's treated with dialysis. You get rid of the nitrogenous waste, you get rid of the uremia, you get rid of the pericarditis. So, in the next couple of videos, we're going to start talking about how we can treat or diagnose myocarditis and pericarditis. For infectious causes, unless it's a viral pericarditis, you'd probably use an antibiotic for a bacterial or a fungal or a protozoan cause of your myocarditis or pericarditis. For a non-infectious cause, you would treat the cause. If it's something that you're missing, like thyroid hormone, you would replace thyroid hormone. Some things you can't treat. You can't make trauma not happen, but it's important to understand what the cause of their disease was, to help guide the way you would treat it.