TETRALOGY of FALLOT made EASY // Congenital Heart Disease

Hello, I'm Dr. Tala. Welcome to Tala Talks NICU, where we break down medical concepts and make them super easy for you to understand. Today we are going to be discussing Tetralogy of Fallot. So many of you have asked us for this, so we're finally doing it. So as you all know, Tetralogy of Fallot is a congenital heart disease. So I want you to kind of go through this imagining that you were just told there is a mother about to deliver with a Tetralogy of Fallot. What do we need to be thinking about? What do we need to have available? The other thing that I want to talk about right before we start discussing the four features of the Tetralogy of Fallot is something that I really didn't realize until I'd kind of gotten through my training. And that is, is that the Tetralogy of Fallot variation is so massive. So I always kind of thought you've got that diagnosis and the prognosis is going to be very similar. Whereas there are really a huge amount of variability between how bad the presentation of the Tetralogy of Fallot is. And that really depends on the amount of right ventricular outflow tract obstruction there is. So it could be just kind of really mild, the amount of outflow tract obstruction, or it could be so severe, like there's literally like no opening between the right ventricle and the pulmonary artery. And that can really determine how well those babies do in the future and indeed what sort of surgeries they need. So just for you all to realize that saying that somebody has a Tet doesn't immediately put them in one box, that this is the surgery they're going to have and this is the outcome they're going to have. Okay, so before we go over the features that we find in a Tetralogy of Fallot, I want to go over a normal heart. I know you know all of this, but I think it will really bang in the point. So as you all know, I always draw hearts in boxes. So this is our heart. This is the left atrium, left ventricle, right ventricle, right atrium. This is the blood that's flowing back from the body. So the SVC, the IVC, and this is the blood flowing back from the lungs. So this is the pulmonary veins. And out of the left ventricle, we have the aorta. And then out of the right ventricle, we have the pulmonary artery, which as you all know, goes towards the lungs. So what happens in a usual heart? The blood, which is nice and oxygenated, comes back from the lungs because the lungs give it oxygen, comes back through the pulmonary veins, through the left atrium, through the left ventricle, down the aorta. And then the aorta sends it out to the body. The body uses up all the oxygen in the blood. So then when it becomes deoxygenated, it becomes blue. It comes back from the body, the right ventricle, the right atrium, the right ventricle, and then the pulmonary artery sends it back to the lungs again where it can go red. So as you all know, that is a typical, the way that the heart works after a baby is born. Now, there's a slightly complicating aspect of this. And that is, as we've already talked about, that the heart in utero doesn't need to send as much blood to the lungs because the lungs don't do the job of oxygenating the blood in utero. The placenta does. So a lot of this blood that's coming back from the body doesn't need to go to the lungs. In fact, about 80 to 90% of this blood that's coming back from the body needs to be shunted to the left side so that it can go towards the placenta. So in utero, we have two shortcuts. We have the PFO, which is a hole in the wall between the right atrium and the left atrium. And then we have the ductus. So we have a vessel between the pulmonary artery and the aorta. And between these two shortcuts, the PFO and the ductus, the blue blood can cross over into the left side of the heart that can then pump this towards the body. Okay, now let's talk about the four features that make up a Tetralogy of Fallot. So again, Tetralogy, it's got four features. So the first one is the right ventricular outflow tract obstruction. So the right ventricle has an outflow tract. So this is the pulmonary valve outside the ventricle. And then this is the pulmonary artery that eventually leads the blood to the lungs. So the outflow tract is considered kind of the edge of the ventricle and then through the valve and the pulmonary artery. So here you have some level of obstruction. And this is where it gets kind of interesting. So I'm going to put a number one there. So this is kind of where it gets interesting. The amount of obstruction that there is there really determines just how bad the Tetralogy of Fallot is. It could be just mild muscular contraction kind of on the side of the ventricle, or it could be that literally this whole vessel is blocked off and there's like, you know, effectively a pulmonary atresia and there's hardly any blood going through that valve into the pulmonary artery. What we talked about already is that what determines how parts of the body are formed further down is going to be dependent on blood flow in the heart. So if there isn't enough blood going through the right ventricle into the pulmonary artery, then it's also possible that that pulmonary artery is not well made at all. And it could just be really, really skinny and underformed. As you can imagine, that's a huge problem with future repair as well. If not only you have an obstruction there, if you also have like a really skinny pulmonary artery, but that's the first, probably the most important aspect of the Tetralogy of Fallot. The second feature of the Tetralogy of Fallot is a ventricular septal defect. So this is a hole between the right ventricle and the left ventricle. Normally this is perimembranous, but it can also kind of go into the muscle as well. Again, this is really logical because if you think about it, if you have an obstruction of the blood to get to the lungs, you need a way for that blood to get out of the right ventricle. So this VSD allows the blood to go into the left ventricle. So first feature, right ventricular outflow tract obstruction. Second feature, VSD or ventricular septal defect. Then the third feature of a Tetralogy of Fallot, and I feel like this is the one that kind of confuses everybody the most. I know that it confused me a lot in training, is the overriding aorta. That's a really odd term that I feel like is only used in Tetralogy of Fallot. But basically what the overriding aorta means, and again, the aorta is the vessel that takes the blood from the left ventricle into the body. It basically means that this is displaced slightly towards the right. So this is where your aorta now is, right there. So it's displaced slightly towards the right ventricle. So your overriding aorta is here. So why is it considered overriding? It's considered overriding because the way that it's now positioned, it's a lot more likely to get blood coming out from both the right ventricle as well as the left ventricle. So it's not kind of slap bang over here where it's still mostly getting the bright red blood coming out of there. It's now much more likely to be getting the mixed blood from both the right ventricle as well as the left ventricle. So number three is the overriding aorta. And the fourth feature of a Tetralogy of Fallot, and if you all sat down and thought about this for a second, you would figure it out, is the right ventricular hypertrophy. So here the walls of the right ventricle become thickened. Again, super logical. If you've got an outflow tract obstruction, then what is the right ventricle going to try to do? Squeeze harder to get the blood out. And remember, the heart is a muscle. So what happens to muscle when you work hard? It grows. It becomes hypertrophied. So the fourth aspect of a Tetralogy of Fallot is the right ventricular hypertrophy. So again, let's go through the four features. One, right ventricular outflow tract obstruction. Two, VSD. Three, overriding aorta. And four, right ventricular hypertrophy. There are also loads of other features that can be associated with a Tetralogy of Fallot. Remember I said this earlier, that a lot of the heart diseases don't end up falling exactly into those categories that we want them to. And very often they can have associated features. In about 25% of the time, the babies can have a right-sided aortic arch. So it doesn't really show on this diagram, but as you all know, normally the aorta kind of swings round to the left. In about 25% of the time it swings the other way. So it's a right-sided aortic arch. Babies can also have abnormalities with the coronary. So the blood vessels that leave the aorta and then go and perfuse the heart, they can be made abnormally in a Tetralogy of Fallot, which if you think about it, is also pretty logical as well, because the coronaries kind of come off the aorta right at the beginning as well. So if the whole aorta is displaced, it's not crazy to think that there's going to be abnormal coronaries as well. Okay, I am going to kind of stretch this out a little bit more for this next part, because I want you to understand the role of the ductus in this. So again, this is my right ventricular outflow tract obstruction. And this is my pretty skinny pulmonary artery, which are then leading to the lungs. This is my overriding aorta. And I think you can all remember, what is that vessel that goes between the pulmonary artery and the aorta? Yes, the ductus. Yes. So here is the ductus. So now let's talk about the pathophysiology of the actual Tetralogy of Fallot, and why having a heart like this is going to lead us into difficulties. I know everybody looking at it can probably figure it out, but we're all about the step-by-step thing here. So the first thing that I want you to realize is that the VSD, the ventricular septal defect, the hole between the ventricles is pretty large. So that kind of means that the pressures within the right ventricle and the left ventricle are pretty similar. So what is going to determine where the blood goes? Because obviously the blood is going to follow the path of least resistance, least resistance, least pressure. So if the pressure is the same, it's going to be the least resistance. So depending on how big that outflow tract obstruction is, some of that blood will want to shunt through the ventricle and go into the left ventricle, and then you'll end up with this purple blood coming out through the aorta. I have a purple pen. So look at this nice purple blood coming out here. At this point, I just want to point something out. Going back to the hyperoxia test, you realize that even if this blood is 100%, it doesn't really matter just how red this blood is. Because if you're mixing it with blue blood, that's never going to change its color because it still had all its oxygen extracted from it. You're still going to end up with purple blood. So that's why when you put these severe tests under 100%, they're still not going to saturate 75, 80, 90% because you're still getting this purple blood. So what you need to realize at this point is that where the blood shunts depends on how much resistance there is here. So if the resistance is really low, so there's just very mild narrowing through here, then effectively the pressures, especially as the pressure on the systemic side goes up, then you are going to end up with kind of left to right shunting through this VSD. And there are some really mild tests that behave more like a bad VSD. So you don't really get symptoms until a few weeks of life, and then you mostly have symptoms of over-circulation. So those are like the really mild tests. But then as the level of resistance increases on this outflow, you're more likely to have right to left shunting through this VSD. And then like we said before, you're What's weird about this is that very often this level of right ventricular outflow tract obstruction is not fixed. It can be dynamic. So even though you look at an ultrasound one day, and it could look like there's a certain amount of blood going through, sometimes that area, especially the muscles around it maybe, can just spasm and end up with a much narrower area for This is what happens during a TET spell. The baby hasn't been repaired, could be just chugging along, looking reasonably pink, getting enough blood, and then suddenly the baby could get really agitated. This could spasm and the baby starts shunting right to left even more. This is what we call the hypercyanotic spell or a TET spell. So how do these infants present? Like we said before, a lot of this is discovered prenatally. So really kind of the VSD, the overriding aorta, depending on how bad the degree of obstruction is. But these are all signs that aren't as difficult to pick up prenatally. So a lot of times babies are born and we know the diagnosis. Then the way that other babies present, like we keep saying, will depend on the degree of outflow tract obstruction. If there is severe obstruction, and this blood is shunting right to left, then these babies will present with cyanosis. Also in these cases where you do have pretty severe obstruction, but there's still some blood going through this artery, you're probably going to have turbulent blood right here. So there's a good chance that you can hear that blood flowing through and you might be able to hear a murmur. So if you do have cyanosis with a murmur, then in that case, depending on exactly where it is, if you're hearing it in the upper sternal border, which is kind of the area of the right ventricular outflow tract, then you're kind of going in the direction of this being a tetralogy of fallot. Remember though, and this is kind of true of all murmurs, if that's completely obstructed and no blood's going through, you're not going to hear a murmur at all, especially not there, because there's literally no blood going through to create that turbulent flow. If the obstruction is milder and blood is flowing from the left ventricle into the right ventricle through the VSD, then you may hear a murmur. You may hear the extra blood kind of rushing through that pulmonary artery, but you might not hear a murmur at all. Sometimes it takes some time for these babies to present just because they're not cyanotic. These are what we call pink tets. So they've got the anatomy of a baby with tetralogy of fallot, but they are pink. Remember that these are the babies that sometimes, even though they look like they've got just a little bit of obstruction, that sometimes if they do get into agitation or something can trigger it, where they do kind of spasm in that area, and that outflow tract obstruction becomes even more narrow, then suddenly these babies might stop shunting right to left, because now they've got an outflow tract obstruction and they will end up cyanotic. So these are the babies that will have tet spells even though they are pink tets. Right, so how do we diagnose this? As obviously you all know, we diagnose it by an ultrasound, which is also called a echocardiogram. And a lot of times this is done prenatally. It can also be done after birth. What we really want to know, especially in the delivery room and immediately after delivery, is just how bad is that right ventricular outflow tract obstruction? Is it to the point that blood can literally not reach the lungs or is there still enough blood going through that valve that there is still enough blood going to the lungs? That is really what's going to determine what needs to be done immediately after delivery. Really, as you all know, what that determines is whether we need to start prostaglandins or not. Okay, so why would we ever want to start prostaglandins? So remember, the ductus is that vessel that goes between the pulmonary artery and the aorta that antenatally, so when the baby is still in the fetus, it provides a shortcut for the blood to get from the right side of the heart to the left side of the heart because we don't need a lot of blood going to the lungs because the lungs do not oxygenate the blood in utero. After the baby is born, that ductus is still open. It normally takes a couple of days for it to close in a pretty healthy baby. However, we can use the ductus in a lot of these congenital heart disease babies as a way of providing a shortcut to get the blood to go to the lungs or to go to the heart if it's not doing that appropriately. So, in a baby with a Tetralogy of Fallot, if they have such a severe obstruction that literally not enough blood can get into the lungs, we need a way to oxygenate that blood. So, in that case, what's happening when none of that blood is going to the lungs? It's all or most of it is either shunting here or it's shunting at this level, but it's all going to the left side. So, we have this purple blood coming out of the aorta now. How do we get that blood to go back to the lungs by keeping this ductus open? So, we keep the ductus open and then we can get this blood back into the lungs to at least provide some oxygen. If we can't get it into the lungs, this baby will die. So, after the baby is born, if there is a very severe obstruction, then we have to keep that ductus open. How do we keep the ductus open? By starting a prostaglandin drip. Remember, prostaglandin patent to keep the ductus open. I'm going to talk more about the treatment and the management in the next video, but for now, I really want you to understand the anatomy because if you understand the anatomy, then everything else becomes very, very easy. Obviously, we need to know that in the NICU. We need to know basically whether we need to start prostaglandins or not and how stable the baby is before the heart surgeons go in and do heart surgery and start doing repairs or palliative treatments or whatever. They need to know a lot more about the structure of the heart. So, they also obviously need to know if it's a left-sided or right-sided aorta. They want to know exactly where the coronaries are. So, sometimes these babies will also benefit from getting a CT scan or a MRI of the heart so that the cardiac surgeons can figure out exactly what's happening anatomically. And then, we also said this before, you can also get the x-ray and that may help. Again, like I said in the first video, the x-ray is most helpful for me to determine exactly how much blood is going to the lungs. And that can kind of really correlate with just how bad that obstruction is. If you have a really complete right ventricular outflow tract obstruction right there, no blood is going to the lungs. And so, if you get an x-ray, the lungs are going to look completely black. There is not going to look like there's any kind of white streaking from the vessels. Whereas if you get an x-ray and there's good amount of white streaking where the vessels should be, then you can infer that there's probably a decent amount of blood going into the lungs. So again, that's kind of why I like getting an x-ray. Obviously, also to make sure that we don't have lung disease going on as well. Although, as you all know, the kind of classical x-ray finding is the boot-shaped heart. And again, it's because that right side is kind of so prominent because of the right ventricular outflow tract obstruction that we're seeing kind of that boot-shaped heart. Okay, that was part one of Tetralogy of Fallot. I hope that you really understand it now or kind of understand it a lot better. So now you can go on and watch part two, which is kind of like more about the management and what we do when we diagnose a Tetralogy of Fallot. In the meantime, please like this video and subscribe to this channel if you're interested in neonatal content. And thank you so much for being here.