What is a Ventricular Septal Defect (VSD)?
S. Sivasubramanian, M.D. , Madras, India
VSDs - are 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. The defect may occur in different parts of the muscular wall between the lower heart chambers, and may sometimes be found along with other heart defects.
What does a VSD do?
The muscular wall between the lower heart chambers is meant to separate blood passing through each (i.e. "ventricle"). This separtion prevents unhealthy mixing of blue blood from the veins with red, oxygen-rich blood going to the arteries. When the muscular wall (i.e. septum) is incomplete or "broken", mixing occurs. In most situations, this leads to red blood passing across the defect and mixing with the blue blood on the right side of the heart. This is called a left-to-right-shunt and leads to abnormally high blood flow 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 congestive heart failure. Heart failure in a child produces fast shallow breathing, excessive sweating, inability to feed well, irritability, constant crying, and a failure to grow at a normal pace.
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 tiny branches of the pulmonary artery become thickened and obstructive. This condition is known as Pulmonary Hypertension or Pulmonary Vascular Obstructive Disease (PVOD). The consequences of leaving a large VSD open is the eventual development of PVOD which may render the patient inoperable at some point in life.
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 reverse the changes.
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 called 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.
VSDs associated with other defects
VSDs 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 spontaneous closure is in the first six months of life. After this, spontaneous closure becomes less likely . If by the tenth year of life the VSD has 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:
1. Repair is safe and has very few complications.
2. All chances of future effects, particularly endocarditis are eliminated, and
3. 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 repaired?
This is yet another area where decision making is very complex. Factors to be considered are the age of the patient, size and location of the VSD, severity of lung vessel blood pressure and the degree of symptoms
In very small babies with severe heart failure, usually with large VSD, IMMEDIATE repair is recommended. If there is no heart failure, repair is postponed until 6 months of age. The reason for this is that a certain number of VSD's will close naturally by this time. Beyond six months, the decision to close a VSD is based on measurement of the Pulmonary Vascular Resistance - that is, the degree of damage to lung blood vessels. If the damage is less, closure is strongly recommended. If the damage is severe, repair of the VSD may actually be more HARMFUL than not doing anything at all! These patients have crossed the boundary of "operability".
With medium-sized VSD's, a longer waiting period is possible. If even after five to ten years the VSD has not closed, repair is justified. A special group is the VSD's that are just below the aortic valve. Because of the risk of the valve becoming "leaky" in these patients, earlier repair - before five years of age - is better.
What are the ways to close VSD's?
As always, surgical closure by an open heart operation is the "tried and tested" approach for VSD. The surgeon may close the VSD by opening the right atrium or right ventricle, or maybe the pulmonary artery or aorta. Rarely, when multiple VSD's are present - the so-called SWISS CHEESE VENTRICULAR SEPTUM - an access through the left ventricle is preferred. In a small VSD, simple stitching of the hole with thread made of polypropylene or similar material is enough. When the defect is large, a synthetic "patch" made of a fabric like Dacron® or Gore-tex is used. Interestingly, some surgeons have also used a kind of "glue" to simply plug any holes in the wall in some cases.
The 1990s is the era of "minimal access surgery". In keeping with this trend, the interventional cardiologists have developed a way to close VSDs using catheters. Through a narrow plastic tube - called a catheter - a special device is guided into the heart through one of the major arteries. An umbrella-like device is passed across the VSD and opened. The umbrella effectively blocks the VSD and stops the flow of blood across the defect. Though elegant, this method is still under evaluation. If found equally effective, this may replace surgery for closure of small VSD's.
Is VSD repair absolutely safe?
Not ABSOLUTELY, but yes, it is reasonably safe. The risk of death due to operation is very low, and in most hospitals will be below 2%, except in very sick patients with a large VSD and other defects, when it is a little higher. Most complications are not serious. There may be excessive bleeding requiring a blood transfusion. Infection may occur but can usually be treated successfully with antibiotics. There is however one problem that used to be seen often in the early years of cardiac surgery, but which still may happen. This is a deficit in conduction of the electrical signals between the upper and lower chambers called HEART BLOCK.
What is heart block?
As we have seen earlier, the weak electrical current inside the heart follow a definite path. This pathwy is composed of a small bundle of CONDUCTION TISSUE - special heart muscle cells designed to "conduct" or carry electrical current. The conduction tissue of the heart passes very close to the margins of some VSD's. When stitches to repair the VSD are applied, they may injure this conduction tissue. As a result, electric impulses will not be carried normally, and will get "blocked". This is called heart block. In some cases, it will recover naturally within a week or two. However in some it does not, and the patient is treated with a permanent pacemaker - a device that delivers an electric current and sets the "pace" of the heart!
How does the "VSD-repaired" patient do in the long run?
Fortunately, very well. Most children with VSDs lead normal lifestyles. Very few restrictions apply. For instance, if they have had surgery through an incision through the breast-bone, they are limited from playing rough contact sports for a while. If a synthetic "patch" was used to close the VSD, some medicines may need to be taken for the first few weeks after operation to prevent blood clotting on the patch. Even later on, before some minor operations or medical tests - like before having a tooth removed - antibiotic prophylaxis to prevent endocarditis may need to be taken for a day or two to decrease the risk of infection on the patch. During any illness in the future, don't forget to mention to the doctor that a patient has had operation for a VSD! Other than this, VSD-repaired patients have an almost normal life.
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