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Studying for a test? Prepare with these 15 lessons on Circulatory system diseases.
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Lecturer: I wanna talk about a condition that is called atrial septal defect and, you know, that might sound a bit complicated but it really isn't. Let's break it down one step at a time. A atrial, of course, we're dealing there with the right and left atria so that's the first word. Septal. A septum is a wall and we have a wall right here in between the left and right atria so that makes sense too. And if we have a defect, we have some type of a structural abnormality and with atrial septal defects what we are usually dealing with is a whole in the wall. So we have a hole, which is a defect, in the wall, which is the septum, and it's gonna be between the left and right atria. So it all makes sense. So ever here we have our right atrium, over here with have our left atrium and, of course, we have our right ventricle and left ventricle. We're not gonna focus on those in this video but I just want to mention that really quick. Alright, so. If we have a hole in the wall between the left and the right atria, what's gonna happen? Well, this left side of the heart is doing a lot of work. It's sending blood all throughout the body, literally all throughout the body, it's going, you know, in this direction, it's going to the head, it's going to the upper extremities and then it's also going down to the lower extremities. It's going everywhere so this side is gonna be significantly stronger than this side. Significantly higher pressure on the left than we have on the right. Because the right, where are we going? Well, it's taking this deoxygenated blood and it's going to our lungs. The lungs are right here, let me draw in a lung right here really quick. So this is my lung. It's not far. It's not a huge distance it has to travel. So we have lower pressure on the right side. So as a result, of that, what we're gonna end up in an individual with an atrial septal defect is we're gonna have blood kinda squeezing in through that opening, and going from the left atrium to the right atrium. And of course, if you have some blood squeezing there, it's gonna continue on the path that it normally travels and it's gonna go back to your lungs. Now, in terms of the positioning, most times we have the atrial septal defect kind of right here in the middle. And that has to do with the fact that when you look at the heart, when it's developing in the embryo, this wall isn't there in the beginning. But when it comes there is an opening that allows for blood when it comes back from the placenta because it's getting oxygen from the mother, that's gonna bypass the lungs because the lungs aren't functioning as yet in that developing embryo. So it's gonna bypass the lungs and one of the ways it does that is by going through this opening. So if that opening fails to close, it's suppose to close, we want it to close, and that closes soon after birth. But if it fails to close, we can get an atrial septal defect and this positioning is called "ostium secundum." Alright, so that's the position, that's the place where we usually have it. Right there in the middle of the wall and that is considered ostium secundum. But it can also be lower down. So if we were to have a hole down here. Let's make sure I have that selected. So if we have a hole down here, to the point that maybe it even involves this valve between the atrium and the ventricle, well what that is considered to be is. Let's draw that over here. Let me do it in a different color just to be fancy. That is gonna be "ostium primum." Alright, so that's lower down. That's not generally seen but it is seen in individuals with, in some individuals, with Down's syndrome. This is gonna be the most common congenital heart defect, and congenital, it just means that individual is born with it. But that's gonna be the most common congenital heart defect in people, in babies with Down's syndrome. So what are the signs? Well, it's usually. Ok let's just put over here "signs." It's usually asymptomatic. So number one, let's just put "asymptomatic." And the reason for that is, ok, you have a hole in the heart. It sounds like a huge deal but it's not necessarily a huge deal because that's just get a little more of the oxygenated blood going back to the lungs. But the oxygen levels are still relatively fine. They're adequate for normal function so we don't generally have problems. But another thing that we can see in individuals with atrial septal defect is what's called a "paradoxical embolus." Paradoxical embolus. And what that is, let's say... Just draw this simply. This is somewhere in the body and let's say, here we have, since I'm drawing a blood vessel I'm gonna draw the blood vessel in red. So here we have a blood vessel. Doesn't matter what blood vessel it is. And this blood vessel is in the legs. And in that blood vessel, for some reason, we get a clot, there's some kind of damage that causes a clot to form. As the blood is rushing through there, a piece of that clot might break off. And that clot can travel back to the heart, going through the right atrium and right ventricle and normally what can happen is that clot gets stuck in the lungs, and there we have a pulmonary embolism. But in individuals with an atrial septal defect, that can potentially give that clot or that embolis a different direction, a different route to travel. Now, that's usually not gonna happen because of course, higher pressure over here in the left pushing towards the right, so the stuff isn't necessarily going from the right atrium to the right ventricle. But let's say that individual is straining to do something and they're baring down or let's say even that individual goes to the restroom and, you know, they go to take a poop. And when they go to take a poop, of course, they're applying a lot of pressure and that applies pressure on this side and if that increases above the left side, that can cause that clot to travel into the left side. And then via that left side, it can go via these major vessels and possible even go to... This is a terrible attempt at a brain. And imagine if it's going to a blood vessel that's going to the brain. What can that cause? Well, that can actually cause a stroke. So it's not usually a problem, but you can see how it can potentially be a problem if there's a clot that then travels to the left atrium and then goes to the rest of the body. Possibly even going to the brain and causing a stroke. Now, how these atrial septal defects are normally noticed, at least at first, they're noticed because when the baby is born, I remember when my son was born, one of the first things they did is the nurse took a stethoscope and she listened to the sound of the heart. And when she listened to the sound of the heart fortunately, it sounded fine. But one of the ways that you can detect this is when you listen to the sound, you hear something like, what you're suppose to hear. Lub, dub. So let's say this represents those two sounds, lub dub. Now this first sound is gonna represent the closing of the valves between the atria and the ventricle. So this valve right here between the left atrium and left ventricle. And then this valve over here between the right atrium and the right ventricle. That's the "lub" sound. That this first sound that you hear. The "dub," the "lub dub." This second sound is gonna be because of the closure of two other valves. The two other valves would be this pulmonary valve here, going into the pulmonary vessels. And this aortic valve which leads, which the blood goes through to lead into the aorta. So this "dub" is the closure of these two valves. Now, with an atrial septal defect, what you have, because blood is gonna be shunting from the left to the right, we're gonna get an increase in the amount of blood that's going to the right side, and because we get that increase, we're gonna get an increase in the blood that's going to the pulmonary circulation and as a result of that, we're going to get this valve closing just a little later than this valve. So what's gonna end up happening as a result if we look at this second sound. It's gonna look a little different. Now this isn't gonna be 100% accurate but it's gonna illustrate the point. It's gonna look a little different in that we are gonna split this second sound. So it's no longer a "lub dub" it's a "lub durub, lub durub" because the pulmonary valve is closing just a little later than the aortic valve, resulting in this split sound. So that's pretty much what you get with a atrial septal defect. It is usually ostium secundum. It can be ostium primum, especially in individuals with Down's syndromes, usually asymptomatic, sometimes resulting in a paradoxical embolis, which can potentially lead to a stroke. And when you listen to the sounds of the heart with a stethoscope, you get this split S two.