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Video transcript

- [Voiceover] So what you're looking at here is an ultrasound, or what they call an "echo," of the heart, and you can see the four different chambers and you'll see I've labeled the left ventricle and the left atrium, and what you'll notice is that the arrow is pointing to the valve in between the left ventricle and left atrium, which is the mitral valve, and that valve is actually not opening. When that valve is really tight or doesn't open, that is what's called mitral stenosis. So like I said, mitral stenosis is when you basically have a tight mitral valve. Now what I'm going to do is I'm going to draw a little set of lungs here, and kind of briefly take you through how blood flows from the right heart through the lungs, and then from the lungs, and now I'm drawing back to the left heart, and so those arrows are going to the pulmonary veins, which go into the left atrium, which I'm marking off here, LA, and then the left ventricle, LV. And that, that I'm circling right now, is the mitral valve. The progression of blood is left atrium to left ventricle, out the aorta, and to the rest of the body. And of course that blood into the left atrium, like we just said, was from the lungs. Now if the blood can't get from the left atrium to the left ventricle, it is going to back up in the left atrium and the lungs, everything that was before it. Let's talk about some of the causes of mitral stenosis. What causes this valve to be tight? Well, you can have what's called rheumatic fever, or more specifically, rheumatic heart disease when it affects the heart. So another cause can actually be what's called endocarditis, and that's really an inflammation or an infection of the actual valve. These are are some of the major causes of mitral stenosis. There are obviously others, but I want to keep you focused on the major ones. So what causes rheumatic fever? It's actually a pretty specific bacteria, and it's part of a group called "group A streptococcus." We can actually abbreviate that "GAS," Group A Streptococcus, and what we're really talking about here is a specific bacteria called streptococcus pyogenes. This bacteria is actually what just causes strep throat. So what'll happen is someone gets a strep pyogenes infection, or a pharyngitis, meaning a throat infection, and two to three weeks later, if it's not treated correctly, the person can actually present with some pain in their joints, or arthralgias, heart problems, like a new heart murmur, some skin problems, and a bunch of other symptoms, but for the most part, the joints, the skin, and for our sake, the heart problems are what we really want to focus on. Now the mechanism behind why this infection by this bacteria actually causes heart problems is called "molecular mimicry," and what happens is here, if you see I draw this antigen, this green antigen, as a triangle, and then this red antibody, and so the antigen is really going to be part of the bacteria that our body's immune system is going to respond to with an antibody, but what happens is some of the antigens that this particular type of bug, strep pyogenes, puts out are actually very similar to some of the normal antigens or components of the tissue of the heart valves. So what can happen is when you actually form an antibody response to the particular infection, those antibodies can actually go ahead and attack the heart. The reason why you get all the other symptoms are because those antigens are also found in those parts of the body, so the joints, the skin, and other things. Now the early lesion of rheumatic heart disease is mitral regurgitation, but the late lesion, meaning when you've had repeated bouts of this rheumatic heart disease, or of this infection with strep pyogenes, you actually get mitral stenosis, which is what we're talking about now. Mitral stenosis is characteristic for rheumatic heart disease. So really what I'm trying to say is that a strep pyogenes infection itself, the bacteria itself does not cause the heart problems, it's actually our body's immune system responding to that infection that causes the heart problems. So let's talk about endocarditis now, which we said is an inflammation or infection of the heart valves. Now, I'm going to write "infective" here because there are other rare, more rare, types of endocarditis, but for the most part, this is usually infective endocarditis, when it has something to do with an infection, either by a bacteria or a fungus or a virus. So there are kind of different ways that this can happen. You can get an infection of a completely normal valve and the way that this happens is you actually have a bacteria that's really bad, and so it's bad enough that it can infect a normal valve. This is something like staph aureus. Now, you can also have an infection of a previously damaged valve, so if someone already had some damage to their valves, a bacteria that's not as bad may be able to actually cause this problem. This is often seen with normal flora in the mouth, or bacteria that normally colonize in the mouth, such as strep viridans, and that's actually a class of bacteria, but these bacteria are just in the mouth, and so this is actually why some people can get infections of their valves after having work done at the dentist, because they actually become bacteremic, or have these bacteria in their blood after their teeth and mouth have been manipulated. The last type is when someone has a prosthesis, or a prosthetic valve, has had a valve replacement in the past, and these are characteristically caused by staph epidermidis, or staph epi. These like to form little layers on prosthetic valves that allow them to survive and cause problems, or endocarditis. In addition, the worst bacteria usually cause what we call "acute bacterial endocarditis." The less virulent bacteria usually cause what we call "sub-acute bacterial endocarditis," and you should just remember that this infective endocarditis can be caused by bacteria, viruses, and a little bit more rare, but can happen, fungi. Now let's talk about the signs and symptoms associated with mitral stenosis. Now granted, these may be based on the mechanism, or how it was caused, so if you have something like endocarditis as a result of an infection, the person may have typical signs of an infection, like fever, chills, and elevated white blood cell count, stuff like that, but for signs and symptoms of mitral stenosis, specifically we're going to talk about signs and symptoms relating to the heart and cardiac physiology. If we go back to our drawing of the lungs, which then return oxygenated blood to the left atrium, which then goes through the mitral valve to the left ventricle, and then to the body through the aorta, we can see that if blood backs up, you don't have as much output of blood to the body, so you can get fatigued, you can be short of breath because blood is backing up into the lungs, you can have exercise intolerance because you can't get enough blood to the body to profuse or to adequately oxygenate your tissues, give you enough oxygen, or you can have a cough, again, because you're backing up blood into the lungs. Some signs that you may be able to see on echo, or with your physical exam, or maybe on an EKG, would be signs of left atrial enlargement, because if blood is backing up into the left atrium. You can have pulmonary congestion, or edema. And then you would also have a characteristic auscultatory finding, or finding that you hear when you listen with a stethoscope, and that would be a diastolic rumble. Now, there's also another characteristic finding that occurs just before that diastolic rumble. Do you happen to remember what it is? It's an opening snap, and if you forget any of these symptoms, just remember that if you stop bloodflow from the left atrium to the left ventricle, it backs up into the lungs, and then you can kind of regenerate what kind of symptoms and signs that someone may present with when they have mitral stenosis.