[ASD] [VSD] [PDA] [Coarctation] [Tetralogy of Fallot] [Pulmonary Atresia] [Tricuspid Atresia] [HLHS] [Transposition] [DORV] [TAPVC] [AV Canal] [Pulmonary Stenosis] [Truncus Arteriosus] [Ebstein's Anomaly] [Coronary Anomalies] [Single Ventricle]
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I hope you still remember about the great arteries of the body, and which chambers of the heart they arise from. If not, please take a peep at my article on "What is the Heart ?" before going further. It may make the rest of this section easier to understand.
The two "great" arteries of the body are the AORTA and the PULMONARY ARTERY. The aorta comes out of the left ventricle, and carries pure blood to the rest of the body. The pulmonary artery arises from the right ventricle and carries impure blood from the veins into the lungs for oxygenation.
Transposition of the Great Arteries - TGA, for short - as the name implies, means the two arteries are "transposed". That is, the aorta arises from the RIGHT ventricle, and the pulmonary artery from the LEFT ventricle !
You have read all about the circulation of blood in the body. So it must be clear to you that a situation like TGA will not permit normal circulation and oxygen supply.
When "impure" venous blood returns to the right ventricle, instead of going to the lungs normally, it passes into the transposed AORTA. This impure blood then is distributed to the rest of the body. So every organ of the body will receive blood with less oxygen and plenty of waste materials. The patient looks "blue" - CYANOSIS - and so TGA is another example of congenital cyanotic heart disease, like Tetralogy of Fallot and Pulmonary Atresia. During successive cycles of blood flow, the condition becomes worse.
On the contrary, when "purified" blood with oxygen returns to the left ventricle from the lungs, instead of being pumped into the aorta, it passes into the transposed PULMONARY ARTERY. This "pure" blood makes another trip to the lungs ! As it is already loaded with oxygen, this trip is useless.
If the two sides of the circulation were completely separate, life would not be possible beyond a few minutes. But once again Nature plays its wonderful role, as the surgeon's helper. By creating an additional defect, the child is kept alive for a few hours or days, so that medical care can be given, and the condition repaired.
The basic problem of transposed arteries cannot be corrected without operation. However, if the two sides of the circulation could be made to "MIX" with each other, there would be atleast partial improvement. The child could live a little longer; long enough for surgery to be performed !
How then can this mixing be brought about ? In many cases of TGA, there is an associated hole or defect in the wall between the atrium or ventricle - called Atrial Septal Defect (ASD) or Ventricular Septal Defect (VSD). Across these defects, blood mixes. But even when these defects are absent, there is still another chance.
This other site of mixing is the PATENT DUCTUS ARTERIOSUS (PDA). If you remember, PDA is a tube connecting the aorta and pulmonary artery. It normally closes within minutes or hours after birth. But it can be kept open artificially by using a drug called PROSTAGLANDIN. Prostaglandin is a "miracle" drug, that has been a boon for children with complex birth defects of the heart. It is also the mainstay in treatment of TGA patients. Prostaglandin infusion is started as soon as the diagnosis of TGA is made, and continued until surgery is possible, usually within a few hours or days.
By now it must be clear to you that TGA is not a condition that is compatible with survival. Unless treated, over 90% of patients will not live to see their first birthday.
There are a few exceptional circumstances.
First is the child with TGA and a large VSD. "Mixing" of blood from both sides of the heart takes place across the VSD. So there is enough oxygen supplied to the different organs to permit adequate, though not normal, function. These children will develop symptoms at a later age. Although there is some oxygen supply, it is not enough for active play or work. The child with TGA and VSD will easily tire during any prolonged activity. Giddiness and fainting spells may occur. In addition the problems of a VSD are there. These include frequent chest infections, breathlessness and in long standing cases, development of high pressure and wall thickening in the blood vessels of the lung - PULMONARY HYPERTENSION.
And then there is the extremely fortunate combination of TGA with VSD along with narrowing of the pulmonary valve - PULMONARY STENOSIS. These patients have all the benefits of a TGA with VSD child, with one added advantage. The pulmonary valve, which guards blood flow into the lungs, is narrow. This prevents too much blood entering the lungs, and avoids chest infection, breathlessness, and most important, the later development of pulmonary hypertension. These patients sometimes survive into their 20's and 30's without treatment !
The answer in most cases is "AT BIRTH" ! There are many reasons for this. Most cases of TGA will not survive without immediate prostaglandin therapy. The results of operation are best when performed early. And suitability for different types of operation vary as the child becomes older.
What are the treatment options ?
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