The last thing you'd ever want to hear when on a nice cruise is that there's a big hole on the side of the ship with water leaking in. That's never good news.
And even something a bit less dangerous, like a hole in the roof of your house, isn't very pleasant, because all sorts of cold air and water can enter the house for no good reason or purpose.
As you can only imagine, if I told you that some people have a hole in their heart where there shouldn't be one, then the consequences of such a void are probably not good. Therefore, we'll be taking a look at what these holes are and what they can cause.
Cardiac Anatomy Overview
But before we get to this, we need to have a quick rundown of our cardiac anatomy just in case you've forgotten some of it. We can make this really simple and interactive. Take out a piece of paper and draw a square on it with a pencil. Then, divide the big square into four equally sized squares.
Label the top-left square the right atrium, the top-right square the left atrium, the bottom-left square the right ventricle, and the bottom-right square the left ventricle.
This type of mirror image mimics our way of looking at the four chambers of the heart, the two atria and two ventricles, which pump blood to the lungs and out into the body.
Remember, that deoxygenated venous blood enters the right atrium, goes into the right ventricle, then into the lungs via the pulmonary artery. In the lungs, the blood becomes oxygenated, enters the left atrium via the pulmonary veins, goes into the left ventricle, and then from there out into the aorta and into general circulation.
This means on the right side of our heart, the blood is oxygen poor, and on the left side of our heart, the blood is oxygen rich. It's like a yin and yang circle where the left side of the image (which is the right side of our heart) is black and dark and not conducive to life since it's deoxygenated, while the right side of the image (which is the left side of the heart) is white and full of life-giving oxygen.
Atrial Septal Defect
Normally, the left side of the heart has a higher pressure and is stronger than the right side of the heart. This is an important point to remember for this entire lesson.
In some cases, people are born with a congenital heart defect known as an atrial septal defect (ASD). This is a heart defect present at birth that results in a hole in the wall dividing the left and right atria. One particular form of ASD, when a fetal structure, known as a foramen ovale, doesn't close after birth, is known as a patent foramen ovale.
Anyways, take a look at the four squares you drew in before. Look at where the right and left atria are. Notice how there's a solid line diving the two. That's the tissue wall that separates the atria of the heart. More technically, it's called the interatrial septum. Now, erase a little part of that line to create a hole between the two atria. That's the atrial septal defect.
This defect, if it's small enough, may cause no significant problems. But in other cases, serious issues can occur.
Because I said the left side of the heart carries oxygenated blood at a higher pressure than the right side of the heart carries blood, then it should be obvious that the hole in the atrial septum allows for oxygenated blood to be pumped into the right side of the heart as a result of this pressure difference. This is known as a left-to-right cardiac shunt and is basically an improper back leak of blood into the wrong chamber as a result of the atrial septal defect.
You must realize, based on our cardiac anatomy, that although the right atrium will now have oxygenated blood mixed with normally present deoxygenated blood, the right ventricle will contain this mixture as well. That's because blood normally flows from the right atrium and into the right ventricle anyways.
Now, let's go back to our image of yin and yang to help remember this. Notice how the left side of the circle is black (deoxygenated) but also has a small white circle. That small white circle, in our case, represents oxygenated blood entering the right side of the heart through the atrial septal defect.
We can use the ying and yang symbol to picture how the heart functions
This isn't the only thing that occurs as a result of this shunt. Since the right side of the heart is now receiving more blood than it should, the atrial septal defect leads to right-sided volume overload, leading to right ventricular enlargement and possibly right heart failure and death if the septal defect is not surgically repaired.
Ventricular Septal Defect
In any case, the ventricles are not immune to a similar defect. In fact, a ventricular septal defect (VSD), a congenital anomaly where a hole exists in the interventricular septum, can occur as well. Again, go back to that drawing you made and now erase a little bit of the solid line dividing the two ventricles. That's our VSD.
In this case, oxygenated blood will enter the right ventricle from the left one. But unless another anomaly is present in the heart, oxygenated blood will not increase in the right atrium since blood shouldn't be flowing there from the right ventricle in any case. That's an important difference between an ASD and VSD.
Because the volume of blood in the right side of the heart increases in a VSD as well, the amount of blood flow to the pulmonary artery increases, resulting in pulmonary hypertension. In severe cases of pulmonary hypertension, the pressure in the right side of the heart may actually increase so much (due to increased resistance to outflow) that a reverse right to left shunt will occur. This is termed Eisenmenger syndrome.
Just imagine swimming against a very strong current. It's really hard work. The strong current is like our pulmonary hypertension that causes changes in the pulmonary vessels that leads to increased resistance to outflow from the right ventricle. Just like it's hard for you to swim against a strong current, it's hard for your right ventricle to pump against increased resistance to outflow. Therefore, you switch direction and swim with the current to make it easier on yourself just like the flow of the blood through the defect switches to the direction of least resistance to outflow. In Eisenmenger syndrome, this causes a switch to a right-to-left shunt.
And as a final point regarding congenital septal defects, there's also a congenital anomaly common in children with Down syndrome that results in a combination of an ASD and VSD, along with a deformity in the mitral and tricuspid heart valves, and this is known as an atrioventricular septal defect.
Diagnosis and Treatment
People with septal defects can be diagnosed through a combination of listening to the heart (where murmurs may be heard) and an echocardiogram that helps visualize the heart defects.
Treatment can range from monitoring to see if the defect will close on its own as the child grows, catheterization resulting in the plugging of the hole, or open heart surgery.
This lesson first discussed something known as an atrial septal defect (ASD). This is a heart defect present at birth that results in a hole in the wall dividing the left and right atria.
The tissue wall that separates the atria of the heart is more technically called the interatrial septum.
A ventricular septal defect (VSD), a congenital anomaly where a hole exists in the interventricular septum can occur as well, as can an atrioventricular septal defect. This is a congenital anomaly common in children with Down syndrome that results in a combination of an ASD and VSD, along with a deformity in the mitral and tricuspid heart valves.
What you should've gathered from this lesson pathophysiologically is that a hole in the septum causes a back flow of blood from the left side of the heart to the right side, resulting in volume overload of the right side of the heart, which then causes right-sided heart enlargement, pulmonary hypertension, reversal of the initial left-to-right shunt into a right-to-left shunt, and eventual heart failure.
After completing this lesson you should be able to:
- Describe the anatomy of the heart
- Compare and contrast an atrial septal defect and an atrioventricular septal defect
- Explain how to diagnose and treat both types of septal defects