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Tricuspid atresia

Created by Amy Fan.

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  • spunky sam blue style avatar for user Amanda
    1.) How do electrical impulses change in this scenario? How do the impulses from the atria reach the Bundle of His if so much of the septum is missing? Do these special pacemaker cells still manage to send the impulse down the normal pathway (SA-Bachmann's Bundle-AV-Bundle of His-Left & Right bundle branches-Purkinje Fibers) or does the heart have a ventricular rate?

    2.) Also, does the right ventricle contract despite being empty?
    (6 votes)
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    • hopper cool style avatar for user SofiyaMarkova
      1. the atrioventricular node is in the normal position it is just short but works the same, it does not get impacted by the ventral septal defect (if a heart had the defect in a way that the node was missing it would not beat and the child would be dead so could not be diagnosed with tricuspid atresia)
      2. the right ventricle does contract “the A-V bundle was situated in the left ventricle aspect of the subendocardium and passed posteriorly to the ventricular septal defect”. And “tricuspid atresia with or without transportation is not a form of single ventricle” meaning the right ventricle still work and has the Purkinje Fibers in it, it just doesn’t actually serve its purpose though contracts.

      Source exactly answers the question: https://www.ahajournals.org/doi/pdf/10.1161/01.CIR.56.3.423
      (1 vote)
  • spunky sam blue style avatar for user Amanda
    If the body is being supplied a lower amount of oxygen due to the mixing of blood, does this cause the left ventricle to hypertrophy and work harder to try and compensate for the lower oxygen concentration?
    (4 votes)
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  • blobby green style avatar for user txmedic8907
    Is the ASD mentioned that is necessary for survival the same thing as a patent foramen ovale?
    (1 vote)
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Video transcript

- So, atresia means something is not developed, or underdeveloped, so when we talk about tricuspid atresia, we're referring to the fact that the tricuspid valve does not develop, that it's not there. So usually, if we have our normal heart here, the oxygenated, blue blood comes from the body like that, goes in to, from the right atrium, to the right ventricle through the tricuspid valve. So remember, it's on the right side and has three leaflets, that's why it's tricuspid. So blood goes through here, and from the right ventricle it gets pumped to the pulmonary artery, which goes to the lungs. So in tricuspid atresia-- I'm gonna erase this whole thing here, because the tricuspid valve actually does not develop. Instead of an opening there, and a valve to prevent backflow, we just have solid tissue here. It's literally just blocked off. Before we worry about what happens to the blood here, let's look at the right ventricle. Since this is something that happens when the baby's still in the uterus, the first thing that happens is our right ventricle also does not develop. It's kinda like, "You don't use it, you lose it." So since it doesn't get to pump blood-- there's nothing in here-- the muscle doesn't develop and our right ventricle is just a tiny little sac. It's not functional, and therefore, there's no blood going to the lungs either. I'm just gonna block off this whole area, it doesn't work. All right, now we got a big problem, because there's no blood going to the lungs, and that is why-- First, lemme draw. I always forget to draw the atrial septum here 'cause it's... Like that, this is the atrial septum, separates the left and the right atrium. Therefore, in tricuspid atresia, we need a few septal defects for this child to survive. So we have an atrial septal defect, or where you just call it ASD. This way, when the blue blood comes in to the right atrium, since it can't go this way in to the ventricle, it has somewhere to go and, in fact, it flows through this ASD, in to the left atrium. And the left atrium also receives oxygenated blood coming back from the lungs. And you might say, "Wait a minute, "you just said there's no blood flow to the lungs." Well, there is, and we'll see in a second, but for right now, remember that blue blood coming from the right side through the ASD in to the left atrium, red blood coming from the lungs here, and then we have a mixture of purple blood in the left atrium. So the valve here on the left side is fine, this is the mitral valve, or the bicuspid. It has two leaflets. So this purple blood flows through here in to the left ventricle, and from there it can go in to the aorta. So we have purple blood going in to the aorta to the body. It's not good red blood, but at least we get some out there, get some oxygen out there. And now we have to come back to "How did the blood get "to the lungs in the first place?" And that's where we have our second septal defect. This is our ventricular, ventricular septal defect, or VSD. And of course, this one happens between the left and right ventricle. So this mixture of purple blood, aside from going to the aorta, it also comes through here and in to our pulmonary artery. Since the right ventricle is out of commission, the left ventricle does the job for the right side, and pushes blood, purple blood, in to here as well. And from there it goes to the lungs. Gonna use green for the branches of lungs. From there, it picks up oxygen and comes back here to the left atrium. So this is how our cycle works. By taking this right ventricle out of the game, we have a hole here to allow the left ventricle to push some blood to the lungs, and we have a hole above here in the ASD area so that blood can get to the left side of the heart to begin with. At any time you see purple blood going in to the aorta, this child will be cyanotic, 'cause that just means the oxygen content of blood we're giving to the body is not very high. And the lungs don't care if it receives purple blood, because all it does is give it more oxygen. So we actually have a higher oxygen content in the blood going to the lungs, but what makes it cyanotic is the fact that purple blood instead of red blood is going out to the body through the aorta. So there you have it, tricuspid atresia. No tricuspid valve, meaning no right ventricle.