What is an Atrial Septal Defect ?
The two upper chambers of the heart are called the right and left atrium. They are separated by a “wall”, called the ATRIAL SEPTUM. Sometimes, this “wall” is not complete. There is a hole in it.
This hole is called an Atrial Septal Defect – or ASD, in short. ASD’s 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 you know, any fluid, including blood, will flow from a place with high pressure to one with 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. And 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 ASD’s 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 ASD’s, 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 !
Does this mean an ASD is harmless ?
Well, not quite. As I said before, frequent chest colds occur. If very severe, these may prevent normal growth and development of a child.
Also, the lungs receive a large blood volume, and this is harmful after some years. The blood vessels in the lung become hard and thick, and pressure inside them increases. This condition is called Pulmonary Hypertension – “pulmonary” for lung, “hyper” for high, “tension” for blood-pressure – which is a very serious complication.
After several years, the ventricle may “fail” – Heart Failure.
Another serious complication is arrhythmia – which means an irregularity in the rhythm of the heart. Since it handles a large volume of blood, the right atrium enlarges. This causes a disturbance in the heart’s electrical activity, causing it to beat faster – a disease called Atrial Fibrillation.
All of these problems are common in Large ASD’s.
But what about the little ones – are they safe ?
They are less dangerous than the large ones. But there is one other problem which may occur in both large and small ASD’s – Paradoxical Embolism.
What is paradoxical embolism ? Blood flow in the veins is normally slow and sluggish, and some small clots may form. Clots are small pieces of hardened blood. In a normal person, these clots may pass from the veins, through the heart and into the lungs. Here, they are “filtered” and prevented from entering the arteries along with the purified blood.
When there is an Atrial Septal Defect, however, the clot, on entering the right atrium, may pass across the ASD into the left atrium. Along with the “pure” blood, it can then pass into the arteries, and from here to the brain. In the brain, it may block a blood vessel, preventing blood flow to a part of the brain. This causes a stroke.
A stroke is an injury to the brain. It may cause weakness or paralysis of an arm or leg, or inability to speak or unconsciousness. It can become a very serious problem, sometimes. It’s because of this risk of stroke that doctors advise that even small ASD’s be closed, by surgery or other methods.
ASD’s With Other Defects
Some types of ASD have other co-existing defects of the heart. The tubes that carry “pure” blood from the lungs back to the heart – the pulmonary veins – normally connect with the LEFT atrium.
In one variety of ASD, these pulmonary veins may connect with the RIGHT atrium – a condition called anomalous drainage of pulmonary veins (PAPVC, in short). In other types of ASD, the mitral valve may be abnormal. The wall between the lower chambers of the heart (ventricles) may also have a “hole” – a condition called Ventricular Septal Defect.
Indeed, any other birth defect of the heart may co-exist with an ASD.
Should an ASD be closed ?
Most doctors would say YES. Recently, a very few cardiologists are questioning the need for ASD closure in some patients, but it is a very uncertain issue. The best way I can put it is, if I had an ASD, I would elect to have it repaired.
When should an ASD be closed ?
Since most children with ASD’s are totally without symptoms, it is usual for an ASD to be detected only when the child is examined at school on a routine check-up, or while tests are being done for some other illness. Sometimes, it is detected only in young adulthood.
Although there is no urgency, the closure should be done as soon as possible to avoid even the small risk of heart failure or paradoxic embolism. Preferably, operation is avoided in very small children. On the other hand, in some cases, ASD’s cause problems very early in life.
One such is the Ostium Primum type ASD, which usually has other defects – like mitral valve clefts – associated with it. These children may develop heart failure very early in life, and need surgery sometimes even within the first year of life.
How can ASD’s be treated ?
Closure of ASD without any treatment is a “medical curiosity”. Most need to be closed by doctors.
Traditionally, closure by operation has been the method that has stood the test of time. By an open heart operation, the hole in the atrial septum is stitched using a special thread made of a polymer material called Prolene or polypropylene.
When the ASD is very large, it may have to be closed with a “patch” of material placed over it and stitched in place. This “patch” may be the patient’s own tissue – the covering of the heart called pericardium is commonly used – or a synthetic material like silk cloth or dacron.
When other defects occur in addition, the operation is a little more complex. When the pulmonary veins are opening into the right atrium, they must be re-directed back to the left atrium. When the mitral valve is abnormal, it must be repaired, or in very rare instances, replaced with an artificial valve.
And there are some newer methods developed recently to close ASDs.
Newer Methods of ASD Closure
Recently, some alternatives to surgery have emerged. These are experimental”, in the sense that their effectiveness in the long run has not been proved. The advantages with these new procedures is that they are less painful, make hospital stay shorter, and avoid a scar of a surgical incision.
One of these is trans-catheter closure. A catheter is a special thin tube passed into the blood vessels through a small “needle-stick” in the groin or forearm. Through this catheter, a special device similar to an umbrella – called a “clamshell device” – is passed into the heart. The “umbrella” device is pushed across the ASD and opened. The hole is now blocked by the umbrella, which is
then fixed in place.
Another method makes use of the idea of Minimally Invasive Heart Surgery.
Through 3 or 4 small “puncture” holes in the chest, specially designed instruments are passed into the chest and used to repair the ASD.
What are the complications after surgery ?
Surgery for ASD is among the safest operations in cardiac surgery today. There should be NO mortality – but then things aren’t always perfect. In most hospitals, however, the mortality risk after an ASD repair is less than one percent.
Major complications are also uncommon. Rarely, bleeding may be excessive, and blood transfusions are needed. Hospital stay varies in different countries, and in India is around five to seven days.
What about the future ?
An ASD repair is probably one of the few heart operations where we are able to restore a “normal” heart. Most patients lead a perfectly normal life. Usually no medication is required after surgery. Patients can perform almost any physical activity without ill effects.
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