Coronary artery disease
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Healing after a heart attack (myocardial infarction)
- Let's look at how your heart will typically heal up after a myocardial infarct, after a heart attack. So to do this we're going to zoom in on this bit of heart muscle here, part of the left ventricle. So I'll draw in these cardiomyocytes, these heart muscle cells here. And these are the striations that they have because of their contractile proteins, and here are their nuclei. So we'll start off with this non-infarcted heart here, with nice intact muscle. So remember, a clot is going to develop upstream in the coronary artery that serves this area, right? And that clot will stick around for over 20 minutes, to cause irreversible damage in this heart muscle, right? Depriving this area of oxygen. And so, without oxygen the environment here becomes not very hospitable, and all of this area starts to die off after about four hours. So up until about four hours, these cells are just struggling. They're using up all of their energy stores, and they're really trying their hardest to survive. So after about four hours, their membranes start to become leaky, and enzymes start denaturing or breaking down the structural proteins of these cardiomyocytes, and other proteins inside the heart muscle cell begin to unravel and die off as well. But as you can see in this little picture here, the relative architecture of these dead cardiomyocytes is basically preserved for a few days after they die. So this process of the cardiomyocytes dying but still having their architecture preserved is called coagulative necrosis, necrosis referring to the death of your cells and coagulative referring to this sort of jelly-like substance that the denatured proteins form after they break down. So in this drawing I'm showing that protein is leaking out of your cardiomyocyte, but, of course, a lot of them stay in there as well. And so, they start to become a part of coagulative necrosis. As they denature, they form this sort of jelly-like substance. And you might also get some bleeding into this area from tiny little blood vessels that surround the infarcted area that have become damaged. And so, after about 12 hours, 12 to 24 hours actually, these special white blood cells called neutrophils begin to enter the area of infarction. One of the things they love to do is to clean things up. So they'll realize that there's dead muscle everywhere that needs cleaning up, and they'll start to. A, they'll start to clean up, and B, they'll start to call for help, call in other neutrophils to come in and help them. So I say clean up, but what exactly do I mean? Well, here are our neutrophils. They sort of come in, and they break down the dead cardiomyocytes even more. They sort of release these enzymes into the cardiomyocytes and into the area and cause the heart muscle cells to break down even more. So what does that mean? It means that their nuclei will start to degenerate, and their striations will also start to degenerate, and everything sort of just begins to fragment and come apart. So now a little bit later, between about one to three days, the cavalry arrives. There's lots of neutrophils around now. So you've got your cardiomyocytes still degenerating. Their nuclei are going away. Their striations are disappearing, and your neutrophils are just everywhere. They're just taking apart or lysing the dead cardiomyocytes. So now, between four and seven days, the neutrophils start to die off, because they're really just overworking themselves, trying to clear everything up. So, luckily, new reinforcements arrive, the macrophages. And macrophages are another type of white blood cell of the immune system, and they're really good at cleaning up debris and cleaning up dead tissue. So here they begin to remove all the necrotic debris, including the dead neutrophils, our hardworking fallen friends here. So they begin to phagocytose all the debris. They ingest it all, and they break it down. That's what phagocytosis is. So all this area here, all this necrotic area is being phagocytosed. And our focus here is to just look at the healing of an infarct, not really the complications, but I should quickly mention that this time, between four and seven days, is probably the most dangerous period for a rupture of your myocardium, of your heart muscle, because of all the work the macrophages are doing here to sort of clear out and really, therefore, thin out the infarcted area. So what happens next? Well, between seven to 10 days, the necrotic area is still being cleared up by our trusty macrophages, but at this point something really interesting starts to happen. You start to get this ingrowth of these really thin blood vessels into the area, and that's great because it provides all these working cells the oxygen that they need to get your heart repaired. So now that there's an oxygen source in place, we can start to think about laying down a sort of scaffold for rebuilding this wall again. So, we actually do get that. We get these cells called fibroblasts laying down these thin, sort of spindly strands of structural protein, called type III collagen. So all of this, these new little blood vessels and this new collagen is collectively called granulation tissue. And actually, healing by granulation tissue is the same sort of thing that happens after most injuries. So even if you get a skinned knee, right? Let's say you're, oh I don't know, let's say you're rollerblading and you get attacked by bats and fall and scrape up your knees. That actually happened to me a few years ago. It was terrible. Your scrapes, your wounds will actually heal up by the same granulation tissue-mediated process. So it's a tried and true sort of healing technique used by our bodies. What's next? Well, after about a month, month-and-a-half, the type III collagen and the granulation tissue will be completely replaced by a way stronger type of collagen, called type I collagen, and that's actually what we know as scar tissue. So if you have a scar anywhere, you know what scar tissue is. It's the same thing here in the heart. So there's two little points about this scar tissue. So the first thing is that it's not as strong as normal heart muscle, but it is pretty strong. So the hope is that it won't tear or allow any blood to leak out of the heart. The second thing is that it's noncontractile, and I think by now we can all appreciate that if you want your heart to be able to do one thing, it's contract properly. So having scar formation in your heart muscle would predispose you to weaker contractions and possibly heart failure down the line, because remember, heart failure is essentially a reflection of your heart's inability to sort of pump out enough blood to meet the metabolic needs of your body tissues, right? So you can imagine that if you have scar tissue in your heart, and your heart isn't really that contractile, then that means that your heart won't be able to sort of muster up the contractions to pump enough blood out, and that's essentially heart failure. So that's a bit about the physical healing after a myocardial infarct, but that's really only half the story. We kind of have to talk about mental healing too, because there are some really big psychological effects of having had a heart attack that need managing and coping with. For example, for some people it might be a bit of a shock to the system when they go from taking maybe no medications on a daily basis to this new cocktail of maybe four or five medications daily. Also, we know that some people are at risk of depression after a heart attack. So that needs looking after as well. And finally, it's important to remember that when a person has a heart attack, it doesn't just affect that person. It likely would also affect their loved ones, their family and their friends on a psychological level as well, and dealing with that is part of the healing process as well.