Transposition of great arteries

- Transposition is finally a defect where the name actually describes what it is. Transposition is a switching, one-for-one switch, A for B, and B going where A is supposed to go. Transposition of the Great Arteries. So the two great arteries that come out of the heart are the pulmonary artery, which leads to the lungs, and the aorta-- oops, it's not artery, it's arteries. The other one is the aorta that leads to all the arteries in the body. Transposition of the Great Arteries. So, literally it means, the aorta being where the pulmonary artery is supposed to be, and the pulmonary artery being where the aorta is. Really quick, you're a drop of blood, you come into the heart into the right atrium, going to the right ventricle, supposed to get pumped out through this blue vessel, the pulmonary artery, into the lungs, and then you come back as oxygenated blood into the left atrium, going to the left ventricle, gets pumped out through this red aorta to the body. So in transposition-- I'm going to erase this whole part, this is all messed up. Remember these two are plugged into the opposite place where they're supposed to be. Okay, let's erase that. As I'm erasing, take a minute and think about how our loop changes. So now a drop of blood, where is it going? So staying with the blue, the pulmonary artery leading to the lungs now plugs over here, into the left ventricle. Erase a little bit more there, so we can get-- our aorta is now plugged into the right side. It's receiving deoxygenated blood from the body. Boy, that doesn't look very pretty, but I just wanted you to get the idea of the switch. So now you're blue blood coming in here. You go into the right ventricle, and it's going out this red vessel. This is going to be filled with blue blood, and then if you're red blood coming back into the heart this way, through the pulmonary veins, remember the vessels that return blood to the heart have not switched, so red blood still comes back into the left atrium, goes to the left ventricle, and then is going out back to the lungs again, through the pulmonary artery. Now you see that the color inside the vessel does not match the color of the vessel that I've drawn. So if you just follow this path that I describe right here, you should realize that we actually don't have a circuit like we usually do. We actually have two completely closed-off circuits. So we have the body going to the right side, and going right back to the body. We have the blue cycle, the body going to the heart, right atrium, right ventricle, and here back into the aorta, right into the body. We don't go through the lungs in this cycle, so the blood never gets oxygenated, just stays blue. And on the right side we have blood coming from the lungs, red blood, left atrium, left ventricle, back out through the pulmonary arteries back to the lungs, where it picks up more oxygen. So we have a red cycle and a blue cycle, and there's no mixture. Now you're gonna say, "Wait a minute, "you can't live like that, right? "You will die very quickly because you "never pick up any oxygen. "You've just got two cycles running parallel to each other, "never mixing." Which is why, for this patient of this trial to survive, there has to be a communication between the two systems. And that's why usually transposition comes with a VSD, I would almost say, always, ventricular septal defect. So, Ventricular Septal Defect, which is a part of a lot of different cardiac defects. And sometimes it can just be on it's own, and close up as the baby grows older, but in this case the VSD is life-sustaining. It gives these two cycles a place to mix. So at least we get some oxygen into the body. Also, don't forget that newborns have a ductus arteriosus here, between the aorta and the pulmonary artery. So, ductus arteriosus. In this case, it's also providing a way for the two loops to have some communication. This way, of course, we're still cyanotic because, even at its best, we only have a mixture of the two kinds of blood going out into the aorta. So our goal here is that there's enough mixing that at least the blood we're sending out to the body is purple, with some oxygen in it. This child is gonna be blue, and in fact they probably can't survive in the first six months without some type of surgery. But thankfully now, we have standard surgical procedures to plug everything back, and connect the two loops to make one big circuit. So when you see transposition of the great arteries, think of the fact that the two great arteries leading out of the heart are switched. We've got two independent cycles that are parallel, and that for this child to be alive, we need some kind of communication between them.