MadSci Network: Medicine |
Thanks for your question. The most common congenital heart defect (one that's present when the child is born) is a communication between chambers that is not normally there. Explaining this will take some setup:
The mammalian heart is usually split into four chambers. Two of them handle pumping of blood to the lungs, and two of them handle pumping of blood to the rest of the body. These two sets of two are split from each other by a wall (called a septum) that separates the two systems. This is important to maintain the blood going to the body separate from the blood going to the lungs, as the former (red) is full of oxygen and the latter (blue) has yet to gain oxygen. If the septum doesn't form correctly (if it has a "defect"), it can allow the blood to mix. If blue blood can get to the red side, the red and blue mix, and the blood going to the body doesn't have as much oxygen as it would normally. Depending on how much blue blood makes it to the red side, this can cause serious problems, as we need our blood to transport oxygen to all the tissues in the body.
The two systems also run at different pressures; this means that the high- pressure side will push blood over to the low-pressure side, and each side has more or less flow of blood than it should if there is a defect in the septum. Because the two systems of blood flow are in series (rather than running in parallel), each side really likes to have just as much flow as the other side. If too much gets pushed into one system because of a defect, it can suffer from and overload of flow and the other side can suffer from insufficient flow. Whether or not the person with the defect can tolerate this depends on the amount of flow diverted, and that depends primarily on the size of the hole and the difference in pressure between sides. So big holes can cause big problems, and little holes can often be well tolerated.
So, in describing these problems above, I referred to serious problems and big problems if the conditions are right when you have a defect in the septum (or "septal defect"). The thick chambers of the heart (each called a ventricle) work at higher pressures, and the difference in pressure between the left and right sides becomes large a few days or a few weeks after birth. The thin chambers (each called an atrium) work at lower pressrues, and the lower pressrues mean there is less of a pressure difference between them. For this reason, a septal defect between each atrium (or an "atrial septal defect" or ASD) usually does not cause big problems unless the hole is really big. A septal defect between the ventricles (a "ventricular septal defect" or VSD), on the other hand, has much greater potential to cause problems.
If the heart cannot pump red blood out to the body, or if it cannot pump enough blood flow to the body, or if it pumps too much blood flow to the lungs, these cause all sorts of problems, and they can be fatal. Sometimes the defect is so severe that the fetus doesn't survive the pregnancy. If the defect isn't severe enough to be fatal and the child tolerates it without some obvious sign (turning purple, for example), they may live much of their life without knowing they have the problem but having serious problems with growth, or lung function, or a variety of other problems. But if the defect isn't severe, people can live their whole lives without knowing they have the defect at all, and have no serious heart problems. Occasionally, someone with a defect like that suffers a stroke because a clot, or gas bubbles, or some other object manages to use the septal defect to cross from the blue blood side to the red blood side, where it is then delivered to the body and lodges in a blood vessel, stopping blood flow to wherever that blood vessel was going. To top it off, many VSDs and some ASDs just close on their own as the child grows.
Holes in the outside wall of the heart (not the septum) usually aren't compatible with survival. Blood needs to stay in the heart for it to work as a pump. Occasionally, a re-sealed hole shows up when people do an ultrasound of a fetus. If the fetus survived it, it can appear as an aneurysm, or a swelling in the wall of the heart. The aneurysms as well as the ASDs and VSDs I wrote about above are often addressed by cardiologists (heart specialists) and cardiac surgeons. Repair of septal defects used to always be open heart surgery, but doctors are learning how to repair the defects in certain patients by placing a patch over the defect using a catheter inserted into the veins or arteries and guided by a video X-ray machine.
All the information above is typical information that any pediatrician learned during their training. I found more information at the American Heart Association, meant for public consumption. The website for a VSD is http://www.americanheart.org/presenter.jhtml?identifier=11066 You can navigate around the site starting there for more information.
Try the links in the MadSci Library for more information on Medicine.