Heart to Heart

SHANGHAI

"ASD" - AtrialSeptal Defects

The following is a brief explanation of this condition:

The two upper chambers of the heart are called the right and left atrium. A “wall”, called the atrial septum, separates them. Sometimes, this “wall” is not complete - there is a hole in it. This hole is called an Atrial Septal Defect - or ASD, in short.

ASDs may be large or small, single or multiple. The heart may be otherwise normal, or there may be other defects too.

What happens when there is an ASD?

In the normal heart, blood flowing in the right-sided chambers (atrium and ventricle) is completely separated from the left sided chambers by the atrial septum. When there is a hole in this “wall”, blood from the left atrium flows through the hole into the right side.

You might well ask, "Why only from left to right?”. That's because the pressure of blood in the left atrium is higher than in the right and, as we know, any fluid (including blood) will flow from a place of high pressure to one of a lower pressure.

So what is the effect of this?

The right ventricle (lower chamber) now receives blood from two places. The normal amount of "impure" blood coming from the veins through the right atrium reaches it. In addition, some extra blood comes through the hole in the atrial septum into the right ventricle. So, the ventricle now has to work harder to pump this increased volume of blood into the lungs. As a result, the lungs also receive a larger blood flow than normal.

Too much of a good thing is not good! When the lungs get more than the usual amount of blood they become “flooded” and stiff. Breathing becomes difficult. When there is a lot of blood in the lungs, it does not flow quickly and this increases the risk of chest infections. Children with ASDs often catch a “chest cold” - maybe even several times a month.

As many years go by, the right ventricle may become weak due to the constant hard work. Then it will “fail” to pump out the blood entering it - a condition called heart failure. Fortunately, in most ASDs, these changes take many years to develop. Many children and young adults with an ASD are not even aware of it until they are 30 or even 40 years old!