 So, let's move on to other types of septal defects, AV canal defects. So, as you know, many cases of AV canal can be associated with Down syndrome. Here's a classic case of a complete canal. AV canal defects involve the mitral valve and the trichesis valve, various versions of being a single valve or sort of almost a single valve. Often, there's an atrial septal defect in the primum septum and an in-net ventricular septal defect. You could have normal versus complete canals, incomplete or partial, and then transitional canals. And I'll talk about each of them. But very importantly, before we talk about the details, this is another tomographic ultrasound imaging example. This shows you why when you're scanning the four-chamber view, it's very important not just to scan at one level, but to move back and forth, because it's easy to miss AV canal defects. You could see in which portion, I guess it's this one right here. You could see the AV canal defect. But if you look here, it looks normal. Here it looks normal. It's only in one portion. So the point being that when you're doing a four-chamber view, unless you sweep back and forth a little bit, you may be missing a canal defect. That's an important point. So let's talk about different types of AV canal defects. Complete, transitional, and partial. Complete has a large ventricular septal defect. A partial has no ventricular septal defect. And a transitional has sort of a medium-sized ventricular septal defect that there's a pressure gradient across it. And that has clinical relevance after birth, which I'll talk about. So this is a complete canal right here. You could see one big AV valve, large ventricular septal defect at the in-net septum. And this is a primum atrial septal defect as well. Of course, to look at this, we want to look from different views. But to see the AV valves, this is a nice view to see the AV valves. So when an AV canal is a complete canal with a large ventricular septal defect, what's very important, the next step from our perspective in terms of looking at the heart is whether it's a balanced defect. In other words, as I'm scanning, I'm thinking to myself, is this a defect that down the road after the baby is born, maybe around four to six months of age, the surgeon will be able to septate, close the ventricular septal defect, and have enough tissue to form a tricuspid valve on the RV side, and enough tissue to form a mitral valve on the LV side. And are the ventricles going to be adequately formed? Is it well balanced? If there's not a balanced canal, and if it's an unbalanced canal, then that's the prognosis is much worse, because many of those cases will not be able to undergo two ventricular repair. They go down the single ventricle palliation approach, which has a much more guarded long-term prognosis, multiple surgeries, much more complicated and difficult for the patient and the family. So whether an AV canal, a complete canal is balanced or not is very important. And of course, we also look for valve or regurgitation. The more valve or regurgitation we see early on, like at 20 weeks, the worse the prognosis, and it also goes along often with ventricular dysfunction, more primitive ventricles. Complete canals, of course, when we see those, we need to think about trisomy 21, and many of these patients do undergo aniosyntesis. Now, a partial canal, as I mentioned, is I showed you this side before. It's a lower part of the atrial septum is deficient. So this is the partial canal. They almost always will have a cleft in the mitral valve, which sometimes you could see regurgitation. Sometimes that's difficult to see before birth. The AV valves are at the same level. So this is a partial canal because the in-net ventricular septum is intact. And here's normal in comparison. So these partial canals are different from a complete canal. Complete canal needs surgery within the first four to six months. If we wait on those babies and don't do surgery, they could develop pulmonary vascular disease, much worse prognosis. So whenever you have a fetus with trisomy 21, if you think the heart's normal prenatal, I always recommend doing an echocardiogram after birth to make sure we don't want to miss an AV canal because sometimes they don't present. Then if you wait too late, the prognosis is much worse. In contrast, a partial canal has no ventricular septal defect. These behave like atrial septal defects, like saccunum atrial septal defects, where we don't need to do surgery. We don't need to close them until several years after birth when the neurologic prognosis is much better. We don't want to go on bypass in the first six months if you don't need to. These babies sometimes develop heart failure, but that's unusual. More typically, they're doing just fine. Maybe they need a little lasix and we repair them a few years of age and the prognosis is outstanding. Sometimes the cleft and the mitral valve can be stitched closed at the same time. And again, there is maybe an association with trisomy 21. So a transitional canal, you could see the primum atrial septal defect and you could get a sense of our small ventricular septal defect that's largely closed. We discriminate or distinguish between a complete canal and a transitional because a complete canal requires surgery in the first six months, usually four to six months. Transitional canals, by definition, because the ventricular septal defect is smaller, these babies are not at the same increased risk for pulmonary vascular disease if you wait beyond the year of age. So it's a very different disease, but these babies do require open heart surgery to close. Sometimes the repair can be a little more, even more complicated than a complete canal depending on the anatomy of the mitral and tracheal valves and the anatomy in the ventricular septum here. In all cases, all types of canals, of course we wanted this in old slide, as you get old clips, you wanna look for AV valve regurg, mitral tracheal valve regurg, you wanna get a sense like you could see here, it's not completely well balanced. So sometimes it takes a lot of effort to figure out, is it well enough balanced? Is it balanced or not? Is how well balanced is it? Which are trying to predict whether these babies will be candidates for two ventricular pair with a very good prognosis versus single vitricle pair with a much more guarded prognosis. Here you could see again, a transitional canal. This has a very large prima matrile septal defect and a very small ventricular septal defect. Here's another transitional canal. You could actually see on the left side, you could see the Vavar tissue partially closing the ventricular septum and you could see mitral regurgitation over here. It's from the cleft. So all forms of AV canal defects, you're not looking just at the AV canal. Of course, whenever you have one heart defect, there may be other defects. And particular AV canal defects are often associated with other defects, sometimes with complex forms of heterotaxi, but sometimes just another abnormality. So we always wanna see what are the veins, the pulmonary veins looking like? Is there a common atrium? Is it balanced or not? And then we wanna look at the outflow tracts. Is there tetralogy flow? AV canal, tetralogy AV canal is a very common combination, particularly in the context of trisomy 21. We wanna look, is there double outlet right ventricle? Here's the urtic coming off the RV and the pulmonary is coming off the LV with transposition. The pulmonary is maybe a little small. So it's not just good enough to pick up a diagnosis of AV canal. You also then wanna see if there's anything else going on. That's gonna impact how this baby is gonna do. AV canal defects, if everything else looks perfect, they could have one surgery at four to six months of age that then have a normal cardiovascular prognosis for the most part, with a small percentage of cases having requiring more surgery. Or if it's unbalanced or there's a significant valve or regurgitation or there's outflow track abnormalities, the prognosis can be much worse. So when we counsel patients early on, whether they continue a pregnancy, it's important to know what other abnormalities may be present.