Annex A > Chapter 3 - Developments in the UK, in the Diagnosis and Treatment of Congenital Heart Abnormalities in Children, 1984-1995 > The specific heart abnormalities and procedures referred to in the Inquiry > Tetralogy of Fallot
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Tetralogy of Fallot
The problem
63 This abnormality is the commonest form of cyanotic congenital heart disease. It occurs in just under 10% of all babies with congenital heart abnormalities. There is a large VSD in the same portion of the ventricular septum as was described for Truncus Arteriosus. The aorta arises dominantly from the left ventricle but overrides the VSD so that there is a tendency for blood to flow into the aorta from both the left and the right ventricle. There is also a narrowing of the outflow from the right ventricle to the pulmonary artery (pulmonary stenosis). The severity of the narrowing varies from one patient to another. Its effect is to increase the resistance to blood flow from the right ventricle to the lungs. The flow of blood to the lungs is reduced and instead, blood then flows along the path of least resistance. In that case it is from the right ventricle, through the VSD and into the aorta. In other words, deoxygenated blood flows from the right ventricle to the body, together with the oxygenated blood from the left ventricle. Consequently, the child shows the features of cyanosis. [10] The greater the severity of the pulmonary stenosis, the more severe is the degree of cyanosis.
64 Those babies who have severe reduction in blood flow to the lungs and more profound cyanosis present early in the newborn period and require early measures to improve pulmonary blood flow. Others, whose pulmonary stenosis is less severe, may not show any symptoms until they are several months old, or not even until they become toddlers. All children with Fallot's Tetralogy are limited in their physical activities and are at risk of complications. The most common of these is the occurrence of `spells' in which the baby suddenly becomes extremely blue and floppy and often loses consciousness for a few minutes. Recovery is usually rapid but on rare occasions an attack can be fatal. Spells are caused by the outflow tract of the right ventricle becoming suddenly narrower as a result of a form of `spasm' of the right ventricular muscle below the pulmonary valve. When the spasm is relieved, the baby recovers from the spell. Another most serious complication is related to bacteria entering the blood stream from an apparently mild infection of the skin or throat. Instead of passing normally to the lungs where the bacteria are trapped and often cause a minor or occasionally more severe lung infection, they pass from the right ventricle, through the VSD to the body and may settle in the brain causing an abscess which can prove fatal. For all of these reasons it is desirable that a child with Fallot's Tetralogy should have a corrective operation as early as it can safely be done.
Diagnosis
65 The diagnosis is usually suspected on the basis of the presenting symptoms and by examination of the patient. It is usually confirmed by echocardiography and on that basis, the initial plan of management can be undertaken. Before proceeding to corrective surgery, additional investigation by cardiac catheterisation has been regarded as mandatory in some centres in order to demonstrate every fine detail of the abnormality. In the mid-1980s the diagnosis could usually be made confidently using echocardiography. The evolution of ultrasound technology during the late 1980s and towards the mid-1990s has enabled cardiologists to be even more confident of some of the finer details of the abnormality. Nevertheless a number of questions that are important to the technical approach of a corrective operation are better answered by proceeding to cardiac catheterisation.
Management
66 Throughout the period covered by the Inquiry's Terms of Reference, i.e. from the mid-1980s to the mid-1990s, the management of the child with Fallot's Tetralogy would have followed a similar pattern in most centres.
67 The newborn baby with severe cyanosis initially requires an increase in the blood flow to the lungs. During fetal life, an artery known as the arterial duct normally connects the aorta and the pulmonary artery. It normally closes within the first two to three days of life but it can be kept open by using a drug, prostaglandin E. By keeping the duct open, blood flows from the aorta through the duct into the pulmonary artery and even if this is the only source of blood flow to the lungs, it is usually sufficient for survival and stability in the short term. However, it is unusual for a baby with Fallot's Tetralogy to become severely cyanosed so soon after birth and it is more usual that the duct will have closed by the time that he is first seen. In such a case it is necessary to undertake an emergency operation known as a `shunt' in which a small tube is used to connect a branch of the aorta to the pulmonary artery. This is the type of operation first described in 1945 by Blalock and Taussig. Shunt operations have improved in both technological and technical terms since the mid-1980s and the mortality has fallen significantly since then.
68 It is more usual for the cardiac team to be faced with a baby whose cyanosis has increased significantly around the age of 2 to 4 months, often associated with cyanotic spells. In those babies it has been usual to begin medical treatment initially with a drug known as a beta-blocker in order to try to reduce spasm of the right ventricular outflow tract. This is a temporary measure and is followed within days or weeks by a shunt operation. In those circumstances the risk of a shunt operation is somewhat lower than when performed in the newborn period.
69 Corrective operations are `open-heart' procedures. Some babies may undergo primary corrective repair if they are large enough and if the abnormality is not too complicated. If they have had a previous shunt operation, it is necessary to close the shunt. The VSD is closed using a patch so that left ventricular blood flows entirely into the aorta. The pulmonary stenosis is relieved, both by cutting open the pulmonary valve, and usually by opening the right ventricular outflow tract and widening it by inserting a gusset. The pulmonary artery branches themselves may be narrowed and often need to be reconstructed. The operation can be relatively routine or quite complicated, depending on how much reconstructive work is necessary. The mortality rate in the UK fell significantly between the mid-1980s and the mid-1990s. There had been many reports from centres of excellence in the United States of low mortality rates in the mid-1980s and in the centres of excellence in the UK similar results were expected.
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Footnotes