Fetal Echocardiography

Septation Abnormalities

And finally, we'll talk about a class of defects that are the most difficult to visualize.

And these are septation abnormalities.

And as I mentioned, septation is far and away the most complex part of cardiac development.

And we have some photo micrographs showing the process occurring.

Initially, you start off as one chamber and ultimately a septum forms.

And this is what gives us four chambers.

This is what separates pulmonary from systemic flow.

And this is what has allowed mammals to live on land and breathe oxygen from air rather than having to extract it from water.

Now, if we look from inside the ventricle at the septum, what we see is this curved structure and there are usually four places along the septation where defects are going to occur.

And we do very well with these inlet type VSDs and the apical trabecular type VSDs where the heart is the thickest.

And we can see VSDs here.

It's much more difficult to see the outflow type VSDs that occur in either the aortic outflow tract or what's called the supta supra crystal VSD location.

And that's really above the aortic valve on the aortic wall.

And so generally we think of four types of VSDs.

And the key is to use color flow imaging and see that there's abnormal flow from left to right during the cardiac cycle.

And this is what confirms that a VSD is present.

Atrial Septal Defects (ASDs)

Now, there's three types of atrial septal defects, and the most common is the sinus osis defect, basically where the superior vena cava basically enters the atrium and the atrial septum isn't complete.

And there's a connection between right and left atria here kind of at the level of where the superior vena cava meets the right atrium.

The other types of defects are the septum premium and then secundum defects.

And this has to do with where during cardiac development the defect occurs.

Septum premium defects are larger and more significant and more difficult to repair, whereas secundum defects are smaller generally, and even patency of the Freeman Valley as a type of secundum defect.

Endocardial Cushion Defects

And then the most severe kind of defect is the cushion defect.

And this is where the ventricular and atrial septa don't form properly.

And the cru of the heart is missing.

I mentioned this earlier.

And so here's the normal diagram of the heart.

Here's the cru, and you can see the atrial ventricular valves inserting onto the septum appropriately.

Whereas in this one you can see that the crus has not formed and usually you'll end up with one atrial ventricular valve.

There's no insertion onto anything in here.

There's just a big defect in the middle of the heart.

The ventricular septum has formed, the atrial septum hasn't formed.

And this is an image from the literature showing what a large cushion defect looks like.

This is the one that's most commonly associated with down syndrome, and it's one of the more important heart defects to pick up.

And it is very visible on a four chamber view, and that's where we see it.

And this is a large cushion defect.

Now, one thing to be aware of is that you need to see these during the cardiac cycle because in systole it may not be so readily apparent, but as now these are the outflow tracts, aorta, pulmonary artery here.

But as we come back to the four chamber view here, you can just see there's nothing in the middle of this heart.

There's one atrial ventricular valve, and this is a large cushion defect.

Having a cushion defect doesn't mean that you don't have outflow tract abnormalities as well.

But you can see the big defect in the middle here and it's much more apparent on real time imaging than it is on a still image.

And here's just another one.

There's just not a lot in the middle of this heart.

And we can see as we come through the heart here, there's just nothing here.

There's just a big defect.

This is a large cushion defect.

This is low in the trabecular septum in the ventricles.

And then there's usually an atrial septal defect as well.

And this is how we make the diagnosis.

Ventricular Septal Defects (VSDs)

Now, I mentioned that there's four types of VSDs and this is what a VSD would look like.

And these are the ones we pick up fairly readily.

We only have about a 50% sensitivity for all VSDs, and this is because of where they are.

But these low septal defects we tend to pick up.

And what we're really looking for is this little color flow jet going from left to right.

The pressure in the left ventricle postnatally is much higher than it is in the right ventricle at least normally.

And so if there is a defect, there'll be a little jet that occurs during systole from left to right.

And this is really what we're looking for.

So here's the VSD here, and then on color flow imaging, here's the defect here.

Okay, now in utero, pressure is more balanced between the right and left.

And so the flow may not necessarily be from left to right, but once the baby is born and it starts breathing, pulmonary vascular resistance drops significantly, right-sided pressure drops.

And then there's usually flow from left to right postnatally.

And these are the different defects.

These are the ones we see quite readily.

These are the ones that are the most difficult.

They're high up on the aortic outflow tract and they're just very difficult to see.

Mainly because this is a curved structure and sometimes the alignment is difficult to get.

And the real problem is that you can make every one of these look abnormal.

If you're not aware of this various VSDs with the jet, these are in neonates.

This is postnatally after they're born.

And this is very classic of what these look like.

Another VSD here, axial view shown left and right ventricles, and there's a big VSD here.

And then as I mentioned, the outflow tract VSDs sometimes called paramous VSDs or supra crystal VSDs are much harder to detect.

And this is where that occurs.

And you can see a little bit of a flow jet there.

You really, this is a postnatal exam and you can see them much more readily in utero.

It's much more difficult to detect.

This type of VSDs are not lethal anomalies.

They're not ductus dependent lesions generally, as long as the outflow tracts are normal.

If it's big enough, a neonate could go into congestive heart failure from the left to right shunting from the VSD.

But generally, these are not cyanotic type VSDs that are gonna cause hypoxia in a neonate, and this is a high one, these are outlet VSDs or supra crystal type VSDs.

And you can see the little flow jet occurring almost at the level of the aorta.

Okay, you're still in the left ventricular outflow tract at this level.

And the jet actually does go back into the right ventricle here.

And that's why by definition this is still a VSD.

Tetralogy of Fallot

Now, tetrology of fallo is generally characterized as hypoplasia of the pulmonary artery.

And if we look at this three vessel view, we've discussed this view here.

Here's the pulmonary artery.

It's originating to the left and anterior to the aorta.

So the orientation is normal.

This is a little bit of right atrium.

I mentioned sometimes you don't see the SVC particularly that the shot is more angled through the atrium.

And that's what we're seeing here.

But you can see that the pulmonary artery is much smaller than the aorta, and that's really the diagnosis.

Now these have a VSD as well, and that's a little more subtle.

And this is an outflow tract type VSD, and you can see the septum is not in continuity with the anterior aortic wall.

And the aorta has moved rightward slightly so that it now overlies the septum.

And we kind of approximate how much of the aorta is over the septum.

So I would call this a 50% overriding aorta over a VSD.

And this is very characteristic of tetra of fallot.

On the schematic, you can see the septum is normal and the pulmonary artery is normal, whereas in a tetrology, the pulmonary artery is smaller than the aorta.

And there's a VSD as well.

And that's really how you diagnose this abnormality.

If you get severe enough and this pulmonary outflow tract is very small, you'll get reversal of flow in the aorta in the ductus arteriosis to maintain flow to the aorta here.

And then it can become a ductus dependent lesion.

And these are cyanotic defects.

Because the pulmonary artery is small, there's not a lot of blood going to the lungs.

And so when the baby is born, it isn't oxidating blood as appropriately as it should.

And this leads to cyanosis and fetal hypoxia.

Okay, we talked about concordance between atria and ventricles, and then concordance between the outflow tracks and the ventricles as well.

And here this is almost like a three vessel view with ductus pulmonary artery to the left and anterior to the aorta, and then superior vena cava there.

And again, another tetrology of fallo, and these can be difficult to see.

What you're really looking for is that the pulmonary artery is small.

So here's the aorta, here's the aorta there, and there's a defect right there, right there in the outflow tract right there.

It's difficult to see, but I think you can see it, right?

I'll try one more time here.

There it is, right there.

And so that's the VSD part.

Now in utero, here's the aorta and the pulmonary artery.

And at this point in time, the pulmonary artery isn't that small, and this is why we miss ology of fall sometimes it's not necessarily that visible in utero.

Another view, this is a four chamber view, and as we look up, you can see that, you know, it's going very fast.

There's a defect actually in the aortic outflow tract here, but it's very subtle and that's why these could be missed sometimes.

Here's another view.

This is more of a sagittal view.

So we're starting off with right atrium.

Here's the left ventricular outflow tract, and right there there's a defect.

It's very subtle.

But that's the VSD part of a tetrology of fallot.

Okay, one more video loop here.

And we can see as this plays the four chamber view, you can see there's a big defect here.

And this is high.

This could almost be an endocardial cushion defect.

It's not uncommon at all for the VSD to actually be larger than just the VSD and be a cushion defect and have tetralogy, a fellow.