What Causes A Hole In The Heart?

My brother-in-law has just discovered he has a hole in his heart. Is this something that can be fixed, and what causes this?

A “hole in the heart” refers to a defect — a literal hole — in one of the septa separating the two pairs of cardiac chambers from each other. This does not refer to a hole in the outside of the heart which would allow blood to escape into the space surrounding the heart and would be rapidly fatal.

To better understand the concept of septal defects, draw four circles on a piece of paper, two small ones above, two larger ones below, and each touching the circle next to it, and the circle above or below it. The two smaller upper circles are called the atria, the upper two chambers of the heart. The spot were they touch is the interatrial septum, that is the septum between the two atria. The two larger, lower circles are called the ventricles, and the spot where they touch is therefore the interventricular septum.

The spot where each upper circle or atrium touches the larger circle or ventricle below it represents a valve between the upper chamber and lower chamber of the heart. On the left as you look at your drawing is the tricuspid valve, which is actually on the right side as the heart is positioned in the body. On the right of your drawing, but on the left side of the heart between the left atrium and the left ventricle is the mitral valve. Not represented on your drawing are the aortic valve, separating the left ventricle from the aorta, the main artery going to the body, and the pulmonic valve, separating the right ventricle from the pulmonary artery, which carries blood to the lungs. Also not represented are the large veins bringing blood to the heart, the vena cava from the body into the right atrium, and the pulmonary veins, from the lungs into the left atrium.

The normal flow of blood through the heart, therefore, goes like this: from the body via the vena cava into the right atrium; pumped by contraction of the atrium into the right ventricle; pumped by contraction out the pulmonary arteries to the lungs, where the blood picks up oxygen; back through the pulmonary veins into the left atrium, pumped into the left ventricle; pumped out the aorta into the body. The valves I described serve to prevent backflow of blood when the heart is not actually contracting.

The septum between the two atria is a thin membrane. During fetal life there is normally a hole in it, since a fetus does not need to separate the blood streams to and from the lungs. It gets all its oxygen from its mother through the placenta. This hole, called the foramen ovale, normally closes at birth as does the other connection between major arteries near the heart, the ductus arteriosus, which connects the aorta to the pulmonary artery during fetal life. The foramen ovale can remain open after birth, allowing a persistent hole to exist between the two atria, but actually the more common atrial septal defects occur elsewhere in the membrane.

The septum between the two ventricles is mostly muscular and fairly thick, since the pressures in the ventricles are much higher than in the atria, and the septum is correspondingly stronger. There is no hole in this septum during normal fetal life. Nonetheless a hole here, a ventricular septal defect, is a fairly common congenital anomaly. No on knows how these septal defects arise, except to say that they are all present at birth. They probably represent some small failure in the complicated fetal development of the mammalian heart.

Ventricular septal defects always produce a pretty distinctive murmur, and are therefore usually discovered during a childhood examination. (Most heart murmurs, both in children and adults, are not due to any serious heart defect.) A ventricular septal defect of any size should usually be repaired during childhood, since the pressure changes it produces, that is high pressure blood from the left ventricle crossing into the normally low pressure right ventricle, can damage the lungs permanently. Since I assume that your brother-in-law is an adult, I doubt if he has a ventricular septal defect, unless he avoided the medical system entirely during his childhood.

Another kind of heart problem, Atrial septal defects are often not discovered until adulthood, often not until the person is in their 40s or 50s. This is because the pressure in both atria is normally low, and the flow of blood across the defect, which would ordinarily be from the left atrium to the right for many years, doesn’t generate enough noise to be heard as a murmur. This type of defect also may not cause any symptoms, since the amount of blood being pumped out to the body is normal, and its oxygen content is normal. (Blue babies, who most commonly have a congenital heart defect called Tetralogy of Fallot, are blue because the blood normally mixed with oxygen from the lungs, which is quite red and normally goes out to the body directly, is mixed with blood from the body which is much darker since it has little oxygen. This mixture causes the child to appear blue.)

Whether your brother-in-law will require surgery to close his atrial septal defect can only be determined by further tests including perhaps a cardiac catheterization. The decision will depend on the size of the defect, its location, whether any nearby structures are also damaged, the amount of flow across the defect, and the pressures in both atria and the pulmonary arteries. The most serious problem that can come from this is a fixed increase in the pulmonary artery pressure, which is caused by the increased flow across the defect which leads to increased flow to the lungs. A defect leading to substantially increased flow should be closed before the pulmonary artery pressure rises. This is best done in childhood if the defect is discovered then, but may still be helpful in avoiding the pulmonary hypertension if done in adulthood.

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