- 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.