Ventricular Septal Defect

Dateline: 02/08/98

Over the past month, we have discussed the concept of minimally invasive heart surgery, and the use of this novel technique in treating coronary artery disease , heart valve disease and birth defects of the heart. This week, we will go on to something different, the birth defect called Ventricular Septal Defect (VSD).

For more information on minimally invasive surgery, visit the MICAS website. And there's a lot on congenital heart disease at Heart Disease Online.

What is a Ventricular Septal Defect ?

I have discussed atrial septal defects elsewhere. Well, ventricular septal defects - also called VSD - are similar. A VSD is a "hole" in the wall between the two lower chambers of the heart - the ventricles. This hole may be small, medium-sized or large, and may be single or multiple. It may occur in different parts of the wall, and may sometimes be found along with other heart defects.

What does a VSD do ?

The wall between ventricles is meant to separate blood passing through each. This is to prevent mixing of "impure" blood from the veins with "pure" blood going to t e arteries.

When the wall is "broken", mixing occurs. Fortunately, though, only "pure" blood flows from the left ventricle into the right; no flow is seen from the right ventricle across the VSD and so "impure" venous blood does not reach the arteries. This is because pressure in the left ventricle is much higher than the right, and fluids always flow from places of high to lower pressure.

Because of this flow from left to right ventricle across the VSD - also called a LEFT to RIGHT SHUNT - more blood than normal flows into the lungs. Just as in atrial septal defects (ASD), this causes frequent "chest colds" and breathing difficulty in children. When the VSD is large, in a very small child, lung blood flow may be so enormous that the tiny ventricles cannot pump such a volume. This causes HEART FAILURE. Heart failure in a child produces rapid shallow breathing, excessive sweating, inability to feed well, irritability, constant crying, and a failure to grow normally.

Have you felt a kitten purring ? Well, here's something interesting about these children with VSD. When you place your hand over their chest, there is a sensation just like that - called a THRILL. It is produced by the forceful flow of blood across the VSD !

One effect seen in VSD - but not in ASD - is the rapid development of changes in the blood vessels of the lungs. These arteries and veins become thick walled and hard early in life. The reason for this is perhaps because blood from the left ventricle, which is the most powerful chamber of the heart, is pumped under high pressure across the VSD into the lungs. To withstand such force, the tubes carrying blood become thick and strong.

What happens if VSD's are left untreated ?

The changes I have just described keep progressing. Soon the heart fails to keep up with the high blood flow, and heart failure sets in. When the lung blood vessels become very thick, the problem of PULMONARY HYPERTENSION arises. This is a situation where the lung arteries are severely damaged, and at this stage, even surgical repair of the VSD will not be able to cure the disease. When the VSD is located in the upper part of the inter-ventricular wall, close to the aortic valve, it can slowly make the aortic valve "leaky" - a condition called AORTIC REGURGITATION. This usually takes many years. In small VSD's, none of these things are seen often. But there is one complication peculiar to a small VSD - INFECTIVE ENDOCARDITIS. Due to a jet of blood across the VSD, the inner lining of the heart gets damaged. Bacteria can infect this injured layer easily.

VSD along with other defects

VSD may be found alone, as the only defect in a heart that is otherwise normal. Or it may form a part of a "complex" of abnormalities. In this case, it may produce different effects. Some examples of such diseases are TETRALOGY of FALLOT, TRANSPOSITION of the GREAT VESSELS and DOUBLE OUTLET RIGHT VENTRICLE. To avoid confusion, I will describe these conditions separately in other articles.

Should a VSD be repaired ?

There is another special thing about VSD's. Some of them close even without any treatment ! There is yet no way to definitely predict which ones will close. The best chance for closure is in the first six months of life. After this, spontaneous closure becomes rarer. If by the tenth year of life the VSD as not closed by itself, it needs to be repaired.

There is one exception to this rule - the SMALL VSD. There is still much controversy about this defect. While surgeons advise that small VSD's be repaired, cardiologists usually recommend "no treatment". The arguments against repair are the small risk and discomfort involved with surgery, and the absence of any symptoms in patients. The surgeons however claim that

• repair is safe and has very few complications
• all chances of future effects, particularly infective endocarditis, are avoided
• the child and parent are freed of the "psychologic" stigma of heart disease

The decision to repair these small defects would perhaps depend on the hospital, and the philosophies of the parent and the doctor !

When should a VSD be closed ? What are the ways to close a VSD ? Well, these are major topics in themselves, so I'll discuss them next week. Keep in touch again.

For more information on minimally invasive surgery, visit the MICAS website. And there's a lot more on congenital heart disease at Heart Disease Online.