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Hypertrophic cardiomyopathy: Pathophysiology and diagnosis

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Let's talk about the pathogen assist in diagnosis of hypertrophic cardiomyopathy. Now, before we dive into the specifics, let's just briefly review normal cardiac physiology, so I'm going to just draw in a simplified diagram of the heart. Now, as we go through the cardiac cycle, I want to emphasize the two major phases that are known as diastole and systole, and I'm going to describe what's going on in these phases by what's occurring in the ventricles, and by the ventricles, I mean these lower chambers down here, and regarding the ventricles, we'll talk about what's happening with the muscles, and what's happening with blood, and so during diastole, muscles are relaxing, which causes dilation of the chamber, so you can think of D for diastole, and this causes blood to fill the chamber. During systole, the muscles are contracting, and this causes the blood to be ejected from the chambers. So as we're looking at this diagram, I want you to think about this heart as if it's sitting inside someone that you're looking at, so over here, on the left side of the diagram, if it was sitting inside of someone, that would be their right heart, and over here on the right side of the diagram, that is their left heart, so let's start over here in the right atrium, so I'm just going to fill this with some blood here, and this blood is coming from the body, and then over here, in the left atrium, and I'll also fill this with blood, and this blood is now pink because it's been freshly oxygenated as it's coming from the lungs. Alright, so the first stage of this cardiac cycle is diastole, so as these muscles of the ventricle dilate, it draws blood from the atrium into the ventricles, and this causes filling of the ventricles, and you can see now that the atria has emptied all their blood, and the ventricles are now filled, so that's diastole, and now we're going to switch to systole, so you can see that during systole, the muscles are contracting, of the ventricles are contracting, causing the chambers to get smaller, and blood is starting to be ejected out of the ventricles, and what you can also note is that during this phase, I'll go back one step here, during this phase, the atria are also filling with blood. Now, as the muscles of the ventricles finish contracting, and systole ends, we return to diastole, where these muscles relax, so let's see that here, and notice that as they relax, before we start getting filling of the ventricles, not all of the blood from the ventricle was ejected. There's a certain, small amount of residual blood that is left in these ventricles after systole, and the amount of blood that was ejected, so this kind of empty space here, over the amount of blood, the total blood that was in the chamber, is known as the ejection fraction, and a normal ejection fraction is between 50 and 75 percent, and this is important because the ejection fraction can be used as a measure of systolic function of how well the heart is able to contract. So once again, we go back into diastole where the muscles dilate and cause filling of the ventricles, and the cycle just repeats itself. So now that we reviewed normal cardiac physiology, let's talk about the pathogenesis of hypertrophic cardiomyopathy. Do you remember that cardiomyopathy is a disease of the heart muscle by the name, pathy meaning disease, cardio meaning heart, and myo meaning muscle, so disease of the heart muscle, so the first step in the pathogenesis of hypertrophic cardiomyopathy is that you have a problem with the heart muscle, and in hypertrophic cardiomyopathy, this problem is a genetic abnormality of the muscle cell proteins, and what happens is that some of these proteins, these abnormalities in the proteins, don't allow the muscle to contract properly, and so since the heart muscle isn't able to contract as forcefully, it compensates for this decreased contraction ability by hypertrophying, and what hypertrophy means is, the cells get bigger, so let's see this over here on the diagram. What I'm going to do is just make the normal muscles here kind of orange, just to demonstrate that they're diseased, and since this diseased muscle isn't able to contract properly, the muscle cells get bigger, they hypertrophy over time. This is just a compensation for not being able to contract properly, so that kind of looks like this, and something that's very specific to hypertrophic cardiomyopathy is that this hypertrophy of the septum, or this wall between the two ventricles, is asymmetrically enlarged. It's a lot bigger than the hypertrophy of the outer walls, so let's just draw that in, and this hypertrophy of the muscle walls results in two major problems, and the first problem is that now, since these walls are bigger, the chambers have become smaller. You can see that the space in the ventricles is smaller, and this smaller space results in a decreased ability of the heart to fill properly, and if the heart isn't getting enough blood into the chambers, it can't pump enough blood out, so this actually, even though, so this actually results in a decreased outflow, and since it's a problem with filling, which over here we mentioned filling is during diastole, this is known as diastolic heart failure, and this, in a sense, is somewhat similar to restrictive cardiomyopathy, but there's another problem in hypertrophic cardiomyopathy that makes it a very dangerous disease, and this problem is known as an intermittent outflow obstruction. What does this mean? Well, let's go back over to the diagram here to understand this a little bit better. So, you can see that the septum here is hypertrophied, and this hypertrophy causes a narrowing of this outflow track from the left ventricle, so blood is normally coming in, and then going out through the aorta, but when this space is narrowed, you kind of get a blockage here, and it's intermittent because it's dependent on how hard the heart muscle is working, and certain parts of the cardiac cycle, so, for instance, if an individual with hypertrophic cardiomyopathy is working really hard, and their heart rate is really fast, the diastolic period, that filling period, is shorter due to the increased heart rate, and since it's shorter, you have even less filling into the ventricle, and so this space is even smaller than normal, and so you get intermittent blockage, versus when an individual with hypertrophic cardiomyopathy has a normal heart rate, he or she would be able to fill properly, and blood would be able to get out, since that space is a little bit expanded, so that's why you have this intermittent outflow obstruction, and it's the combination of these two problems that result in the signs and symptoms of hypertrophic cardiomyopathy, so now we're talking about the signs and symptoms of cardiomyopathy, let's discuss how hypertrophic cardiomyopathy is diagnosed. So the first step of all diagnosis is to talk about the history and physical, which I'm just going to abbreviate H and P, and what's important about hypertrophic cardiomyopathy is that an individual may actually be asymptomatic. They may have no signs, but if he or she does have signs of hypertrophic cardiomyopathy, some of the things that might be seen are things like dysmia, fainting, which is known as syncopy, or occasionally, the presenting symptom of hypertrophic cardiomyopathy, unfortunately, is sudden death, and since hypertrophic cardiomyopathy is frequently asymptomatic and can have a very serious presenting symptom, it's a condition that is important to be screened for, and screening for hypertrophic cardiomyopathy is performed in all young children, and it's done by listening to the heart with a stethoscope, and a child with hypertrophic cardiomyopathy has a very characteristic heart murmur that's known as a systolic ejection murmur that increases with valsalva, so what does this mean? Well, let's go through it. Systolic ejection murmur. Well, that probably means it's a murmur that happens during systole that's caused by the ejection of blood. Remember that the heart, that systole occurs when the heart is contracting and blood is flowing out of the ventricles, and since you have this obstruction from the septum, you get a turbulent blood flow going out of the left ventricle, and that turbulent blood flow can be heard with a stethoscope, and this is known as a systolic ejection murmur, but how about this heart that increases with valsalva? Well, a valsalva is a maneuver that an individual can perform in which he or she bears down, like they're about to have a bowel movement, and this is important, because what happens when a valsalva is performed, less blood returns to the heart, and this causes this chamber to become smaller, and as I mentioned earlier when we were talking about that intermittent outflow obstruction, when that chamber is smaller, that degree of obstruction increases, so a valsalva worsens the obstruction, increasing the turbulent blood flow, causing the murmur to become louder, so any time a child has a systolic ejection murmur that increases with valsalva, that child needs to be worked up for potential hypertrophic cardiomyopathy because it can have some very serious outcomes, such as sudden death. Well, the next step is to perform some routine tests, and normally when we think of routine tests, one of the things we think about is labs, but there's not really any specific labs to hypertrophic cardiomyopathy, so I'm going to kind of just skip that part of routine tests, and the next one is a chest x-ray, which I'm going to abbreviate CXR, and actually, in hypertrophic cardiomyopathy, a chest x-ray is most likely going to be normal, and the same is going to be true of an electrocardiogram, or an ECG, so really, even though these tests may be performed, anyone who has this positive screening test is going to go straight to their special tests, and the most important special test for hypertrophic cardiomyopathy is an echocardiogram, which is an ultrasound of the heart, and what the echocardiogram is going to show is an increased septum to left ventricular wall thickness ratio, so what that means is, the ratio of the width of the septum compared to the left ventricular wall out here, is going to be increased, and specifically this ratio is going to be greater than one point three to one. Once the echocardiogram is positive, the last step is confirmatory tests, and the first type of confirmatory tests are genetic tests, so I mentioned that hypertrophic cardiomyopathy is caused by genetic abnormalities of the muscle cell proteins, and these abnormalities can be detected in blood tests, and the other type of confirmatory tests is a cardiac muscle biopsy, and this isn't necessary to diagnose hypertrophic cardiomyopathy, but it does have a very characteristic finding, known as myofibral disarray, and so this is something that's seen under the microscope, so if you can imagine that muscle cells are kind of normally lined up linearly, like this. Well, in hypertrophic cardiomyopathy, these muscle fibers are in disarray. They're kind of lined up in all sorts of different directions, and that disarray of the muscle fibers is what causes the original decreased ability of the muscle to contract, so if you can remember that hypertrophic cardiomyopathy is a disease of the heart muscle that's caused by a genetic abnormality of the muscle cell proteins resulting in a myofibral disarray that causes a decreased contraction ability and subsequent heart muscle hypertrophy, causing these characteristic signs and symptoms, and that it is screened by listening to the heart with a stethoscope, and that most important tests in diagnosing hypertrophic cardiomyopathy is an echocardiogram, which will show an increased septum to left ventricular wall thickness ratio.