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Current time:0:00Total duration:9:50

Restrictive cardiomyopathy: Pathophysiology and diagnosis

Video transcript

- [Voiceover] Let's talk about the pathogenesis, and diagnosis of restrictive cardiomyopathy. But before I get too far into this, I want to just briefly review some normal cardiac or heart physiology. So I'm going to just draw in here, a simplified diagram of the heart. Now the heart can kind of be thought of as a series of two pumps that are separated by the lungs in the body. And when you're looking at this heart, I want you to think of it as if you're looking at it inside of someone else who you're facing. And so, the sides are going to be a little bit mirror imaged as if you're facing someone, so over here on the left side of the image, is what is called the right heart. And the right heart takes blood from the body, and it enters this right atrium here. And then it sends blood through the right ventricle to the lungs. And over here would be the left side of the body. Blood comes in from the lungs after it's oxygenated, so I'll draw it in as red blood, into the left atrium here, and then it's taken into the left atrium and sent out to the body, and then that blood is used by the body, and then eventually returns back to this right atrium. All right now, so as we're going through this cardiac cycle, I want to emphasize what's going on in the ventricles, and by the ventricles I mean these chambers down here at the bottom of the heart. And there's two major phases, and these phases are known as diastole and systole. During these two phases, we'll emphasize what's happening in the muscles of the ventricle, and what's happening with the blood in the ventricles. And, during diastole, the muscle is dilating, or relaxing so write that in here, and you can remember D for diastole. And during this time blood is filling the ventricles. And during systole, the muscles are contracting. And this causes blood to eject from the ventricles. And during diastole, these muscles lining the ventricle, the muscles of the heart, they relax, and this causes the ventricles to dialate, so let's see that happen, and you can see that as that muscle dilates, it draws blood in from the atria, and then now we'll move to the second phase of the cardiac cycle, which is systole, where the muscles of the ventricle begin to contract, and on the right heart, this blood is going to the lung, and from the left heart, this blood is going out of the aorta, back to the body, and then after systole, you go right back to diastole, where the muscles relax, and notice here that when the muscles relax before blood enters the ventricles from the atria, not all of the blood was ejected from the ventricles. Only about 3/4s or so was, and the proportion of blood that was ejected versus the amount that's remaining in the ventricle is known as the ejection fraction, and the normal ejection fraction is between about 50 and 75 percent. All right, so now let's talk about the pathogenesis of restrictive cardiomyopathy. And remember that if you break down the word cardiomyopathy into cardio, myo, and pathy, you can remember that it is a disease, a pathy, of the heart, cardio, muscle, myo, so cardiomyopathy is a disease of the heart muscle. So the first step in the pathogenesis of restrictive cardiomyopathy is a problem with the heart muscle, and in restrictive cardiomyopathy, there's kind of two processes that could be going on. The first one is that you could have fibrosis, or scarring of this heart muscle, so let's draw that in here so we can... And this fibrosis can be caused by things like radiation from cancer treatment, or it can be idiopathic, meaning that we don't really know exactly what causes this. And the other form of problem with the heart muscle in restrictive cardiomyopathy is something known as infiltration, and with infiltration, there's different particles that actually get deposited into the heart muscle, and this can be caused by things like amyloidosis, in which proteins are deposited in the heart muscle, or sarcoidosis, in which there are granulomas in the heart muscle, this can be caused by inborn areas of metabolism, which I'm just going to just abbreviate IEM, and this is a set of genetic diseases in which certain metabolites are deposited here in the heart muscle. And then the last one I want to mention is something called hemochromatosis, which is also a genetic disease in which iron is deposited in the muscle fibers. And whether it's fibrosis or infiltration, the physiology is very similar. This heart muscle isn't able to relax, so remember before, we had this relaxation of the heart? Well, in restrictive cardiomyopathy, that isn't able to happen, the muscle just stays the same size, and so the heart isn't able to fill properly, because it's that relaxation of the heart during diastole, that dilation that causes filling. So let's just write that in here. And when the heart isn't able to fill properly, even if it contracts, and has a normal ejection fraction, you're still going to have a decreased volume of blood exiting the heart, and since this problem is during the filling stage or the diastolic phase of the cardiac cycle, this is known as a diastolic heart failure. So this decreased filling prevents a normal amount of blood from being ejected out of the heart, and so you get a decreased outflow, resulting in the signs and symptoms of heart failure. So now we're talking about the signs and symptoms of heart failure, of restrictive cardiomyopathy. How is it diagnosed? Well, the first step is to consider the history and physical exam, which I'm going to just abbreviate H and P. And this is going to be consistent with heart failure. Things like shortness of breath, they may have weakness and fatigue, and then since the heart is not able to pump blood forward, the blood gets backed up into the body, and you get swelling of the legs or the abdomen known as edema or ascites, and the next step is to do some routine tests. And normally in routine tests, we think about labs, but there aren't any labs that are specific to restrictive cardiomyopathy, so although a provider may perform labs in the workup of cardiomyopathy, there's none that are really specific to this disease. The next one is a chest x-ray. And a chest x-ray is going to show pulmonary congestion, which is a sign that fluid is getting backed up into the lungs, but it's going to show a normal heart size. And the reason this is important is because pulmonary congestion is common in other types of heart failure like ischemic heart failure, or dilated cardiomyopathy, but in those conditions, the heart is going to be enlarged. So it is important that you're going to have a normal heart size in restrictive cardiomyopathy. And then, a provider may also get an electrocardiogram, or an ECG, and this is going to show low voltage QRS complexes. And now, after some of these routine tests have been done, we'll go on to some more special tests. And the most important of these is the echocardiogram. Which is an ultrasound of the heart. And in an echocardiogram, what you're going to see is increased ventricular thickness, which you can kind of appreciate here in this diagram of restrictive cardiomyopathy. And then you might also see, although not always, is bi-atrial enlargement, and I didn't draw this in in this diagram, but what this means is as the heart chambers are not able to dilate and expand, and fill with blood, the atrium here and here, blood gets backed up in them, and they start to expand to accommodate that backup of blood so sometimes, these atria will be enlarged and so you can see that on an echocardiogram. But another important finding that is consistent with restrictive cardiomyopathy versus other causes of heart failure, on the echocardiogram, you'll see a normal ejection fraction. Now, at this point, all of these findings here on these tests can look similar to other conditions like pericarditis, which is an inflammation of the heart muscle, so there's a couple of other tests that can be performed, to confirm that someone has restrictive cardiomyopathy. And these are things like an angiogram, or a cardiac MRI, and these can rule out pericarditis. Or, a cardiac biopsy can be performed. And a biopsy doesn't need to be performed to diagnose restrictive cardiomyopathy, but sometimes they're performed, and they can give specific evidence to the actual cause of the restrictive cardiomyopathy whether it's amyloidosis, sarcoidosis, or radiation and so this biopsy will vary by the different causes, underlying causes of the restrictive cardiomyopathy. So, to briefly recap this, remember cardiomyopathy is a disease of the heart muscle, and in restrictive cardiomyopathy, this problem with the heart muscle has to do with fibrosis or infiltration that causes the muscle to be unable to dilate, and therefore fill properly with blood, so this causes a diastolic heart failure, and to diagnose it, the main test is going to be an echocardiogram, which will show increased ventricular thickness, with a normal ejection fraction, and sometimes a cardiac MRI or angiogram needs to be performed to rule out pericarditis.