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 > The Fontan procedure

The Fontan procedure

83 Thus far, the second half of this chapter has focused on the diagnosis and management of a number of specific abnormalities. This section takes a different perspective, and considers one important procedure, the Fontan procedure, which may be used to help children who present with a range of heart abnormalities.

The problem

84 There is a group of patients who have only one effective ventricle instead of two. The commoner abnormalities in this group are one of the following:

• A single ventricle pumps blood into both great arteries (the aorta and pulmonary artery).
• Two ventricles are present but one is too small to perform its normal function.
• The connections between the atriums and ventricles are unsuitable for an operation that would separate the ventricles into two effective chambers that would then pump blood into the appropriate great arteries.

Figure 10: Tricuspid atresia

&Figure 11: Double inlet ventricle

85 For illustrative purposes, diagrams of two examples are shown above, namely tricuspid atresia and double inlet ventricle.

• In the normal heart the tricuspid valve opens to allow blood to flow from the right atrium to the right ventricle. In tricuspid atresia, the valve fails to develop. Consequently, all the deoxygenated blood that enters the right atrium must flow through the hole that is normally present in the wall between the two atriums in the fetus and newborn baby. Blood flows into the left atrium, then the left ventricle and then into the aorta. In other words, deoxygenated blood flows into the aorta, and causes the baby to be cyanosed (blue). The baby needs a series of medical and surgical procedures in order for it to have adequate blood flow to the lungs and consequently to survive and grow.
• In double inlet ventricle all the blood from both atriums flows into an effectively common ventricle and then out to both great arteries. The overall result is a considerable increased flow of blood to the lungs. The effects on the baby are similar to those described for a VSD (see paras 44-46).
• There are complicated forms of AVSD in which it is technically not possible to separate the two ventricles surgically so that each can function independently. The baby has all the features already described for CAVSD (see para 49) but there is a structural problem in relation to the atrio-ventricular valves such that separation into two valves is not technically possible.
• In hypoplastic [13] left or right ventricle there is a very small ventricle that is incapable of functioning independently in order to pump blood into either the aorta or the pulmonary artery respectively.

Diagnosis

86 In all of the congenital heart abnormalities described earlier, the importance of a careful and complete diagnosis has been repeatedly emphasised. The same principles apply to the diagnosis and assessment of abnormalities in which there is only one effective ventricle. Demands are therefore made on all of the diagnostic skills of the cardiologist. Careful echocardiographic assessment is essential in planning the initial procedure. When necessary, additional cardiac catheterisation is carried out.

Management

87 All of these conditions usually require at least one preliminary operation. The overall aim is that eventually the child will have the type of operation that was first performed in 1968 by Francis Fontan in Bordeaux. He connected the right atrium directly to the pulmonary artery in a patient with tricuspid atresia. Thus instead of the blood being pumped by the right ventricle into the pulmonary artery, it flowed there passively from the right atrium. The operation ensures that the ventricle pumps blood to the aorta and to all of its branches and that the blood returning from the body in the main veins is all diverted to the pulmonary arteries. Blood returning from the lungs flows normally into the left atrium and then into the effectively single ventricle which again pumps the blood to the body.

88 The Fontan operation itself, or one of its modifications, does not usually present major technical difficulties. Its success depends on the careful preliminary preparation of the patient by means of one or more palliative operations. The first surgical procedure is usually undertaken either in the newborn period or in the first few months of life. Depending on the underlying problem, it may be a shunt operation in order to increase the pulmonary blood flow, or it may involve banding of the pulmonary artery in order to decrease the flow. In some cases a more complicated operation may be undertaken in order to re-route blood flow into the aorta and pulmonary arteries; this is known as the `Damus-Kay-Stansel procedure'. Then since the late 1980s, most patients between the ages of 4 months and 1 year have had a further operation in which the superior vena cava (the main vein draining the upper part of the body) is connected directly to the pulmonary artery. It achieves blood flow from the upper part of the body going directly to the lungs and in that sense is essentially halfway towards the Fontan operation.

89 The cardiologist and the surgeon need to plan all stages of the timing and the overall management together, always bearing in mind that the ultimate goal will be the Fontan procedure. Throughout the period of management of the child it is important to recognise the importance of assessing the sizes of the pulmonary arteries and judging whether the resistance to blood flow through the lungs has remained normal. It is uncommon for the Fontan procedure to be undertaken in a child below the age of around 3 years.

90 A few weeks or months before the proposed date of the Fontan operation, detailed investigations are undertaken, including cardiac catheterisation and angiocardiography (see para 20). The suitability of the patient for the operation is determined by the detailed assessment of the function of the effective ventricle and of the structure and function of the pulmonary blood vessels. The chief guiding principle is that the resistance to blood flow through the lungs should not be higher than normal, because if it is, there will be a back-pressure effect in the main veins draining the body, with potentially serious consequences. The pressures and blood flow in the pulmonary arteries are measured and the resistance to flow is calculated. It is also necessary to visualise the pulmonary arteries and their branches and to ensure that there are no areas of narrowing that might cause some increase in the resistance to flow. At the time it might be advisable for the cardiologist to use interventional catheter techniques, i.e. balloon dilatation, [14] in order to enlarge any narrowed areas. It is also important that the function of the ventricle is shown to be adequate and that the presence and severity of any valve leaks within the heart are demonstrated.

91 The Fontan operation or one of its modifications is an open-heart procedure. The technical problems relate largely to the underlying abnormality and the nature of any preliminary operations that may have been performed during earlier years. During the 1980s the `classical' Fontan operation was generally performed. It consists of making a direct connection between the right atrium and the pulmonary artery. Because the pressure in the right atrium is then higher than normal, it becomes distended over the years and blood tends to swirl around in the chamber without moving forward efficiently into the pulmonary artery. Blood flow becomes sluggish and there is a tendency for small clots to form. When the clots advance into the pulmonary arteries, they may block the smaller vessels. This, in turn, increases the resistance to blood flow into the pulmonary arteries with a consequent further increase in the right atrial pressure. The other effect of the right atrial distension is to make the heart vulnerable to rhythm disturbances with consequent deterioration of the function of the heart.

92 During the early 1990s several different strategies or modifications were introduced, some of which were used in combination:

• One was to create a more tube-like connection between the right atrium and the pulmonary artery by channelling the main veins more directly to the connection.
• Another was to make a small hole (about 5 mm in diameter) in the wall between the two atriums. This allowed blood to flow from right to left atrium and tended to reduce the right atrial pressure but had the disadvantage of making the child slightly cyanosed.
• In some centres anticoagulant drugs have been given routinely in all patients in order to reduce the incidence and risk of clots forming in the right atrium and pulmonary arteries.

93 Overall, the results depend largely on the pre-operative factors that were described above. Early post-operative problems after the Fontan procedure are relatively common and do not necessarily depend on the pre-operative findings. They relate to the higher pressure in the main veins draining the body and the back-pressure effect and congestion of many of the organs. The heart itself needs to adjust to a set of unusual circumstances and often requires drug support for several days post-operatively. Careful management of fluid intake and fluid balance is often critical. Despite the most meticulous care it is not uncommon for children to accumulate fluid in the space surrounding the lungs (pleural effusions), and chest drains are often necessary for many days or even for weeks after the operation. The absorption of food from the gut may be inefficient for a period of time and this, too, requires careful attention. Occasionally the kidneys function inefficiently and may require support.

94 All the above post-operative problems usually resolve within a period of a few weeks and the child may lead a full and comfortable life for many years. The main noticeable problem is a lack of stamina compared with other children but participation in short bursts of vigorous activity is usually achieved. In the longer term, especially in association with the `classical' Fontan operation, rhythm disturbances and fluid accumulation become significant problems in many of these patients as they go through late adolescence or early adult life. It is hoped that the longer-term effects of the modified operations and the associated medical treatment will be more favourable.

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Footnotes

[13] The term `hypoplastic' is used to refer to a tissue or organ that is under-developed, usually due to a decrease in the number of cells

[14] Balloon dilatation - a specially designed cardiac catheter is passed into the narrow portion of the pulmonary artery. A balloon, incorporated into the catheter, is inflated under pressure to a pre-determined diameter. The balloon is then deflated and together with the catheter is removed