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What is coronary artery disease?

Created by Vishal Punwani.

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Video transcript

- So you got your heart, right, and so your heart is sitting in your chest and it's this muscular pump that will pump blood throughout your body. So it needs to pump blood to all the places in your body. And it actually does a lot of work. It pumps about 100,000 times a day. I'm not making that number up. It actually pumps, if you take the average heart rate which is about 72 beats a minute and then you multiply that through for a day, that ends up being about 103,000 beats per day, right. So it's this really hard working muscle, this really hard working organ. And what do hard working muscles need? Well, just think about the last time you went on a run, or climbed a fence, or did a back flip, or whatever it is that you do to get your muscles working. They need a lot of oxygen, right? What did you feel after you did all this exercise? I mean you were probably gasping for air, you were panting, at least you were breathing heavier, right? And the reason for that is because your muscles, you've used them, you've exhausted them a bit, and now you have to pay back oxygen, right. You have to give them oxygen. Your heart is really no different. You might be thinking, well the heart is getting access to all of the blood that it pumps out, right, so doesn't it just get, like, basically an unlimited supply of oxygen from that? From that blood? Well, it doesn't actually. So let me actually draw this for you in cross section. So we're going to take a section through here and we'll blow it up right here, and you can kind of see right here that the walls are pretty thick. And so the oxygen in the blood flowing inside the heart, it can't actually reach all the way across the thick heart muscle wall. It might be able to get to a little bit of the inner section of the wall, but it can't diffuse across the whole heart muscle wall because it's just too thick. So we have a solution for that, actually, and this solution is the coronary arteries. And the coronary arteries run on the outside of the heart. So here's a heart, you can see this person's right coronary artery and you can see this person's left coronary artery, right? Actually this is actually the left anterior descending artery, which is a branch of the left coronary artery. So, again, these coronary arteries are the solution right? Where they bring copious amounts of blood to the heart muscle and they feed it enough blood to do all the work that the heart needs to do. But sometimes they can get diseased, and so coronary artery disease is one of the problems that can go wrong with the coronary vessels. So you may have heard the term "clogged arteries" to describe coronary artery disease. And why they're called clogged arteries is because there's this build up of fatty substances that's almost like plumbing being clogged. So let's actually draw this out. So here is, here's a close up of the coronary vessel right, so we have one wall there and the other wall here. So here's your blood, and here's some components of your blood. So you've got your red blood cells, and here's some cholesterol, and here's some white blood cells, and when the cholesterol is sort of flowing through your blood, and it comes across a bit of damaged blood vessel wall, the cholesterol thinks "Hey that looks like a pretty cool spot to hang out." And so the cholesterol actually will start to deposit inside the walls, inside the damaged walls of your blood vessels. And the white blood cells don't really like this, so the white blood cells try to follow in after the cholesterol to get rid of them. To get them out of the wall. And that kicks off this big inflammatory process called Atherosclerosis. And that just means hardening of the blood vessel, because this whole process over time makes that blood vessel wall become hard and stiff. And unfortunately, during the process, a lot of the white blood cells die. So the cholesterol can just keep depositing in there, and the cholesterol and the white blood cells create this fatty bulge called a plaque, and over time the plaque will start to bulge into the vessel. Why is that a problem? Well, I mean, blood needs to get through right? If you've got this big bulge in the way how is blood going to get through? So for the first little while, I mean, blood can through and you won't have any problems. But over time, and I mean this plaque takes decades for it to build up to clinically significant level. And that means when you start to get symptoms. So over time it'll just continue to grow, and then you'll start running into some problems. So, again, just to be perfectly clear, coronary artery disease is when you start to get buildup of this plaque, this fatty substance within the arteries of your heart. Let me just make some room here. And why it's bad, why coronary artery disease is bad, is because downstream, later in your life, it can lead to some other heart diseases. So we'll just briefly describe the main ones. And we'll start with one you may have heard about before. We'll start with stable angina. So let's look at this bit of muscle down here that the artery's sending blood to. And let's put our plaque here, let's say our plaque is here upstream. When you're at rest, when your heart's not doing too much work, enough blood can get past that plaque and get down and feed that muscle. So that muscle's, you know, happy. It's getting enough oxygen from the blood that's getting to it and it's not feeling any adverse affects. It's totally happy, all right? But what happens when you start to, you know, maybe you're going to miss your bus, you need to run for your bus, or you really want to impress that girl so you start taking dance classes. When you ask your heart to do more work, you know your heart rate's going to go up your heart's going to beat a bit faster. Then all of a sudden not enough blood is going to be able to get past that plaque and feed that muscle, right? And so that piece of muscle becomes hypoxic. When that muscle down there gets hypoxic when it doesn't have enough oxygen to carry out its function, you start to actually get a symptom called angina pectoris. What angina pectoris refers to, let's actually just look at the two words. So you've got angina, right, and angina is from the Greek word "to strangle" right. I know it sounds weird, but people describe the feeling of angina as sort of a tight, strangling, feeling in their chest. Pectoris refers to "chest." So angina pectoris is this tight strangling feeling in your chest that is brought on when your heart muscle doesn't have enough oxygen. This is reproducable, this is reproducable. So if you sort of lower your activity level, if you stop that amazing dance move I'm sure you're doing, or if you stop running for the bus, and you sort of take a breather, then your heart your essentially asking your heart to do less work. Right? And when your heart is doing less work it needs less oxygen. And so all of a sudden that blood that is getting past that plaque is enough to supply that downstream bit of muscle again, right? So the symptom of angina goes away. The chest pain goes away because your heart muscle's getting all of the oxygen that it needs again, okay? So the reason that it's called stable angina, remember this overarching condition is called stable angina, and the reason it's called stable angina is because you can bring on, you can predictably bring on the chest pain when you ask your heart muscle to do too much work. Exercise or exertion is gonna cause it, and rest is gonna relieve it. Now, things can get a little bit worse than that. And when they get worse than that, they can result in a suite of, not sweet as in sweet "I want that" 'cause you definitely don't want this, but it refers to a set of conditions, diseases, you can get called acute coronary syndrome. And acute coronary syndromes they can be further sub divided into something called unstable angina. Let's make some more room. So you can imagine already, because you know what stable angina is, you can kind of imagine what unstable angina is. You've got unstable angina, and then you have your heart attacks. So unstable angina, just to be clear again, stable angina, not a heart attack. Unstable angina, not a heart attack. Heart attack, is a heart attack. Go figure. So let's look at unstable angina first before we look at heart attacks. Unstable angina is, remember that plaque we talked about, let's go back to our nice little blood vessel here, well it's not nice any more, it's got a huge honking fatty plaque in it. But that's all right. So here's our blood vessel, right, here's our plaque. Now sometimes, because of whether it's hypertension putting sheer stress on this plaque, or whether it's spontaneous, this can happen spontaneously, you know there'a couple other reasons but those are probably the two major reasons, the plaque can rupture, right. And when I say rupture, I mean that this covering of the plaque on the inside of the blood vessel can kind of burst, right, and when it bursts it exposes all the plaque material all that fatty gross sort of necrotic, necrotic means dead cells by the way because the cells in here have some of them are dead at this point, it exposes them to the blood, right. And plaque material is really thrombogenic. What does thromogenic mean? Thrombogenic means it causes blood clots to form on it. And let me just re-draw this, it's a little messy. So when the blood sees that plaque material it's going to go crazy. You've got your platelets in your blood, and you have your clotting factors in your blood, and they're all going to grab onto that ruptured plaque material. You're going to start to form a clot, a blood clot, on this ruptured plaque. And from here, one of two things can happen. Either this ruptured plaque can start to sort of flap back and forth, because it's ruptured on this end, but it might still be attached on that end. So what does this mean? That means that you're gonna get, sometimes, your blood vessel's gonna be completely occluded, it's gonna be completely blocked off, and sometimes you're not gonna have an occluded blood vessel because the plaque will be kind of stuck against the wall again. It's sort of flapping around there in your blood vessel as blood goes by, okay. And so remember what we said earlier if we deprive downstream parts of the heart of blood, you start to get that hypoxia happening and you start to get that chest pain, that angina, happening. But remember, now we have this plaque flapping around. So at any point you could just loose blood supply to a downstream part of your heart temporarily. And so in this condition, unstable angina, you can get chest pain at rest. You don't actually have to exert yourself for chest pain to come on, right. And that's because it's just flapping around there. It can happen at any point. So that's why we call it unstable angina, because it's not predictable and it can really just happen any time. So the last thing now we need to talk about, that's part of acute coronary syndrome that's caused by coronary artery disease, is heart attack . Right? And so remember we said that this ruptured plaque is now exposed to the blood, and remember the clotting factors have all started to clot onto it well blood cells can join in, right, join the party, and one of two things can happen. Either the clot, also called a Thrombus by the way, a clot is also caused a Thrombus, can get so big that it completely blocks off that blood vessel. And that's also called Thrombosis. To completely block off a blood vessel by a clot is called Thrombosis. Or it can break off, so this clot, this Thrombus can break off, also called embolization. So when a bit of a Thrombus breaks off it's called embolization. So it can embolize and float downstream and block off a smaller blood vessel. So this is it floating downstream and blocking off a smaller blood vessel, right? So when either of those two things happen, that's when you end up with something called a heart attack. Right? Because now, that's not going to resolve on it's own. You've completely cut off oxygen to a part of the heart. And so the heart muscle that that artery is supplying will die. Because now it doesn't have it's supply of oxygen. And, you know, if you actually get to a hospital and you get either medication or some type of surgical intervention before about 20 minutes, then you can save that bit of heart. If that blockage, so either via complete Thrombus so blockage of the artery, or embolization and blockage of a downstream artery, if that lasts for more than about 20 minutes, then that heart muscle, that bit of heart muscle will permanently die. And that's what a heart attack is. Now one more thing I want to clarify. Heart attack is not the same thing as heart failure. Heart failure is when your heart can't pump enough blood to meet the needs of your body. That's heart failure. Right? So heart attack is different. A heart attack is when a piece of your heart muscle actually dies because it itself isn't receiving enough oxygen. Okay? That's the difference between heart failure and heart attack. Although they can actually cause each other to happen.