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Current time:0:00Total duration:11:09

Video transcript

for tetralogy a fellow don't worry about what fellow means that's just the name of the guy this French physician who named this disease so we want to focus on the first word here which is tetralogy and going back to Latin here tetra tetralogy the word is telling us that there are four defects that we care about that make up this particular heart disease remember that this is congenital so people are born with these four defects in the heart but first let's quickly review what a normal heart does so blood from the body that returns to the heart initially is going to be blue because it's low and oxygen the muscles have used up the oxygen so it returns to the heart into the right atrium the receiving chamber from there goes to the right ventricle which pumps it into this blood vessel which is the pulmonary artery remember that any vessel that receives blood going out of the heart is an artery so even though it's an artery it's still blue - donated blood from the lungs red oxygenated blood returns here via the pulmonary veins into the left atrium and there goes to the left ventricle and goes out this big red structure the aorta to the body so neutrality the first effect that we worry about some would argue it's the defect that governs how this heart functions is called pulmonary stenosis so pulmonary you know has to do with the lungs in this case is referring to the valve that leads blood to the lungs so the pulmonary valve is right here cenotes is a structure and narrowing so this pulmonary valve here is thickened see as the right ventricle is pumping blood into it it is harder to pass through it because it's literally just thick and restricting so the degree of pulmonary stenosis determines how hard is it to pump blood into the pulmonary arteries and determines how severe this heart is functionally damaged now our second defect is a direct result of this and also depends on the degree of stenosis and that is right ventricular hypertrophy so imagine trying to pump blood against a narrow open day in and day out hypertrophy is when the muscle is over exercised and overused and it literally becomes bigger so the right ventricle this chamber right here becomes thicker just on the extra workload that it has for pumping against this narrow valve so a lot of times this hypertrophy is enough to alter the shape of this right ventricle here so do you see in the way I've drawn it before has a nice slope so if our normal heart follows a curvature kind of like this in technology the shape can actually look more like this it comes down here right angle and that's why some people actually say on x-ray we're just looking at the growth shape of the heart can look like a boot so the boot sign is something that we associate with tetralogy because of the severe right ventricle hypertrophy that can happen all right let's move on to the third one so usually if there is a hole between the right and left ventricle the bottom chambers we draw this whole red here it can actually be anywhere along this septum and we call it a VSD which stands for ventricular that tells you where it is it's between the ventricles septal which is the wall the septum between them defect have a hole okay I'm going to draw this right here so now in the machinery of the heart we have a connection between the left and right and now for the last defect we have an overriding aorta what is the overriding so the aorta is usually plugged into the left ventricle but overriding means that it actually receives blood from both the left and right now and from the place I've drawn the VSD right under the aorta I could almost just leave it like this but just to drive the point home I want to redraw this part that the aorta comes over to the right and it's now this kind of central structure now from here now it can receive blood both from the right and the left so now let's think about if I'm drop of blood where I want to go in this new heart with these four defects so from the right atrium go to the right ventricle that's normal so from here I have a choice right I can either go up this pulmonary artery's through this very narrow opening in the valve that's going difficult or I can easily go into this a Horta with a valve that's more welcoming that's less restricted see I draw these two arrows with different calibers as I'm leading you to the answer which is that I want to go this way into the aorta also in general blood in the right ventricle is going to be push toward the left because look at how big the right ventricle is now it's this huge powerful muscle and it serves as the motor that drives this right to left shut and there and you have the answer for why this is cyanotic disease because blue blood is being forced to the left because a it's hard to go through the pulmonary artery we're supposed to go and be the right ventricle is so powerful it's going to push it across the VSD remember blood follows the easiest path so the left ventricle is still pumping and the blood is basically going to go into the aorta so now in the aorta going out to the body we have red blood and we have blue blood so what actually goes out to oxygenate our body is this purplish mixture purple some blue some red and at any given moment how blue it is or how red depends on the tug-of-war between all these factors how restricted is this pulmonary artery how much resistance is coming from the lungs remember the pulmonary arteries are plugged into the lungs how hard the right ventricle is pumping blood across the VSD so these are all factors that determine how much our purplish mixture is red vs. blue sometimes kids who have tetralogy can have a sudden Tet spell which is when they get acutely worse and they can't breathe that's because their pulmonary artery pressure a resistance when the lungs has suddenly increased all that does is create more back pressure in the pulmonary artery it's already hard to get blood in here and the Tet spell makes it even worse so a Texas patients more blue blood into the aorta this mixture becomes even bluer this is a life-threatening emergency in tetralogy and lastly I want to talk about the fact that before people even knew what tetralogy was or what the heart actually looked like we noticed that kids who have it or this type of kid would suddenly squat onto the ground especially when they've been playing or running around they'll suddenly feel a lot worse they'll squat and they'll feel better so here we have a kid I was a kid because for the most part this is still a pediatric disease we correct it in the patients when there are kids so they're running around let's say they're four years old and suddenly they'll stop and they'll squat on to the ground how do you draw a squatting stick figure does that make sense that looks more like they're sitting like and try again so they're squatting there we go and as they get into this position for a few seconds they feel better too let's think through this step by step okay two things happen when somebody with tetralogy or I guess anybody is running around the first one is at the o2 or oxygen saturation in their veins drops because their muscles are working hard and they're extracting more oxygen from it so the blood going back to the heart here and here have a lower oxygen content and secondly what happens is that their vessels in their legs or whatever muscles they're using a lot they vasodilator so the body can get more blood they're literally the vessels in their blood the diameter goes from this to this it just gets bigger so let's look at this one at a time so if the o2 in the veins drop what happens so the blood returning to the heart is essentially bluer so the blood returning to the heart has a lower oxygen concentration and some of it goes right back out to the aorta then running around has made our blood bluer in the aorta all this does is make our cyanosis worse that's going to make our patient more blue in the face and they don't feel good for vasodilation what happens is the structure or the caliber of the vessels determines how much resistance is pushing back on our aorta so the vasodilation really lowers the resistance in the aorta so in the competition between the right and left between the blue and the red again this makes us bluer making this red straw sure have lower resistance means more of the blue blood will get into it so again we're bluer and more cyanotic so now this child is really not feeling well and look when they squat both of these things are reversed first of all they've stopped running around so the oxygen content in their veins can go up so here they've got slightly higher oxygen content in their veins just by stopping and trying to take deeper breath and secondly they're literally taking the vessels in their legs and squeezing them which increases their systemic resistance this is the resistance of all the arteries in the body systemic resistance since they're all connected to the aorta this increases the resistance that the aorta is pumping against so ask these two colors of blood rush at this general area when the resistance in the aorta increases it literally just forces more blood into the pulmonary artery so the competition is where where is it harder to go and when this child has squatted it is harder to go into the aorta at this point because it's like they've taken the end of a hose and they squeeze it down so this just force it's more blood into the pulmonary artery it's still restricted but it's not the difference between the two has lessened so when blood goes into the pulmonary artery this child will feel like it's easier to take some good breaths and this will also increase the return of oxygenated blood into the left side of the heart so the whole effect is that we reverse the shunt a little bit we get more blood out to the lungs the pulmonary artery and we just increase the overall Austrian content in our mixture a little bit so when we think of tetralogy the things that most determine how bad or how severe a person's symptoms are one the pulmonary stenosis how severe is it and to where is the VSD so I would think of tetralogy overall as a constant fight a tug-of-war for the heart to pump blood into either the pulmonary artery or the aorta and the state of the mixture between the red and blue blood determines this person's symptoms at any given moment