Congenital heart disease Development of the heart
The primitive vascular tube is apparent by the third week of foetal life and over the next weeks it folds in on itself, becomes septated and begins to beat (Fig. 48.34). By 12 weeks it has fully developed. Abnormalities may arise from the persistence of normal foetal channels (patent ductus arteriosus, patent foramen ovale), failure of septation [atrial septal defect (ASD), ventricular septal defect, tetralogy of Fallot], stenosis (intracardiac - supravalulvar, valvular, infravalvular; or extracardiac - coarctation of the aorta), atresia or abnormal connections (transposition of the great arteries, total anomalous venous drainage). Echocardiography is now sufficiently sensitive to detect intracardiac lesions in the second trimester.
The incidence of congenital heart disease is about 1 per cent for live births. There is often no obvious aetiology but well-recognised associations include:
Maternal illness:
- systemic lupus,
- diabetes,
- rubella,
- alcohol abuse,
- certain drugs (warfarin, phenytoin);
chromosomal anomalies:
- trisomy 21 (atrial septal defect - primum type, atrioventricular septal and atrioventricular canal defects),
- trisomy 13 and 18,
- Turner's syndrome (coarctation).
If the haemodynamic abnormality is tolerated, elective definitive operation is planned at an appropriate time in childhood but in some cases the infant is very ill and requires surgery in the neonatal period. Close co-operation between the paediatric cardiologist and the cardiothoracic surgeon is essential to define the anatomy of the defect, the degree of compromise and the necessary treatment.
Investigation of a child suspected of having a congenital defect begins with an accurate history from the parents and specific questions about maternal health and drug intake during pregnancy. A detailed family history is important because some defects are familial. Clinical examination may reveal a murmur, evidence of heart failure, failure to thrive and cyanosis. Investigation is much the same as for the adult patient and, with echocardiography available, catheterisation is now avoided whenever possible.
Classification
Congenital heart disease is broadly classified into cyanotic and acyanotic, although the distinction is not often clear cut. Only the more commonly encountered anomalies will be described.
There are three groups of cyanotic congenital heart disease and a representative example from each group will be described in detail.
1. A right-to-left shunt (compare Fallot's tetralogy): desaturated blood enters the systemic circulation before it passes through the lungs.
2. Parallel systemic and pulmonary blood flows (transposition of the great vessels): some mixing must occur or this situation would be incompatible with life.
3. Defects in the connections of the heart where there is mixing of the systemic and pulmonary blood flows [total anomalous pulmonary venous drainage (TAPVD)].
Tetralogy of Fallot
This is a range of conditions in which there is a ventriculoseptal defect with an overriding aorta, pulmonary artery stenosis and right ventricular hypertrophy making up the tetralogy (Fig. 48.35).
It is a relatively common condition accounting for about 10 per cent of all congenital heart defects. The large ventriculoseptal defect results in equal pressures within both ventricles. As a result of the pulmonary stenosis, more blood is discharged into the aorta but this blood is only partially saturated and cyanosis results. The lungs are only partially perfused and the total oxygenation is poor. The right ventricle is the dominant chamber in the circulation. One clinical feature of Fallot's tetralogy is squatting. This increases systemic vascular resistance and consequently blood is diverted into the pulmonary circulation with increased oxygenation. Lethargy and tiredness are common presenting symptoms but cyanosis is the most obvious clinical feature.
There is usually polycythaemia and the chest radiograph reveals a boot-shaped heart with poorly developed lung vasculature. The diagnosis is confirmed by echocardiography and cardiac catheterisation.
Indications for operation. These include severe cyanosis, dyspnoea on exertion and syncopal attacks. The choice of
operation depends on anatomical considerations and the age and general condition of the patient.
There are two approaches to the operative treatment of Fallot's tetralogy (Fig. 48.36). Palliative procedures to divert systemic blood into the pulmonary circulation may be used to improve oxygenation. These include right subclavian to pulmonary artery anastomosis (Blalock-Taussig) or a modification in which an interposition graft is used or an aortiopulmonary artery anastomosis (Potts). Definitive repair may be performed as the first procedure, or some years after a palliative shunt.
Total correction is via a median sternotomy and can include dealing with a previously constructed shunt. The correction is performed using cardiopulmonary bypass and the ventricular septal defect is closed (often with autologous pericardium), the stenotic infundibulum or pulmonary valve is dealt with and the right ventricular outflow tract is widened using a pericardial or a synthetic patch. Repair is often undertaken in the third year and ideally before the child reaches school age.
Transposition of the great vessels
In this condition the aorta arises from the right ventricle and the pulmonary artery from the left ventricle (Fig. 48.37). Oxygenated blood from the lungs is returned to the lungs and desaturated blood is pumped around the systemic circulation. Obviously, if the pulmonary and systemic circulations are separate, the situation is compatible with life. Mixing of blood must occur via an atrial or ventricular septal defect or patent ductus arteriosus. The condition was first described by Morgagni. Palliation was achieved by initially creating an ASD (Blalock) but both Senning and Mustard devised operations to redirect atrial blood into the appropriate ventricle so that oxygenated blood reaches the systemic circulation and deoxygenated blood goes into the pulmonary circulation.
The most obvious presentation is severe cyanosis in the neonatal period, but there is little in the way of respiratory symptoms. Cardiac catheterisation and echocardiography confirm the diagnosis and delineate the anatomy.
Treatment. The initial treatment for this condition is balloon septostomy (Rashkind). A balloon-tipped catheter is advanced from a large vein and manipulated across the atrial septum. The balloon is inflated and forcibly retracted thus producing a large tear in the intra-atrial septum. This allows adequate mixing of the two circulations and provides excellent palliation until a corrective procedure can be performed. Total anatomical correction has become popular and can be carried out even in the neonatal period. This involves disconnecting the pulmonary artery from the left ventricular outflow and the aorta from the right ventricular outflow. The coronary arteries are reimplanted into the aorta which now arises from the left ventricle (as it should). The mortality rate is 10 per cent but the long-term results for those who survive are good.
Total anomalous pulmonary venous drainage
This condition accounts for only 1-2 per cent of congenital heart disease. In this condition the pulmonary venous drainage has become disconnected from the left atrium and drains into the systemic venous circulation at some point (inferior vena cava, superior vena cava, coronary sinus or right atrium). There is mixing of the systemic and pulmonary circulations through a parent foramen ovale.
Diagnosis. There is cyanosis on exertion, often with failure to thrive and feeding difficulties. The chest radiographic appearances depend on the anatomy but may be normal. There is right axis deviation and right ventricular hypertrophy on the ECG. Echocardiography and cardiac angiography are necessary to confirm the diagnosis and establish the location of the anomalous drainage.
Indications for surgery. Prognosis without operation is poor and the exact operative technique depends on the anatomy. The surgical principle is to re-establish the pulmonary venous drainage into the left atrium. Operative mortality is higher in younger patients and in those with complex lesions. The long-term results for survivors of the operation are generally good.
Eisenmenger's syndrome
This occurs following the reversal of a left-to-right shunt. There is a number of conditions resulting in a left-to-right shunt (atrial and ventricular septal defects, patent ductus arteriosus, etc.), but eventually the right ventricle hypertrophies and the pressure in the pulmonary artery increases as a result of the increased flow. Increasing pulmonary hypertension leads to equalisation of pressures either side of the shunt but, at some point, the right-sided pressures will exceed those on the left side and desaturated blood enters the left side of the circulation. Cyanosis and dyspnoea are the most common clinical features. This state of affairs is termed Eisenmenger's syndrome' and is irreversible. Closure of the shunt is contraindicated if pulmonary hypertension is irreversible because the right-to-left shunt now serves to decompress the pulmonary circulation.
Acyanotic congenital heart disease
Persistent ductus arteriosus
This anomaly accounts for 5-10 per cent of congenital heart disease. Following birth, the ductus arteriosus, which facilitates the transfer of oxygenated blood in the foetal circulation from the pulmonary artery to the aorta, begins to close. The trigger for this is poorly understood but the drop in the resistance of the pulmonary circulation as the lungs expand may contribute. The mechanism of ductus closure involves prostaglandins and prostaglandin analogues may be used therapeutically to keep the ductus open in the first few weeks of life. There may be occasions when a patent ductus is necessary for survival as in some forms of congenital heart defects (such as coarctation of the aorta), where the ductus provides the only means of oxygenated blood reaching the systemic circulation. The ductus may be closed during the first few weeks of life by administering indomethacin. In the isolated case of patent ductus, there is a left-to-right shunt of blood resulting in a high pulmonary blood flow. This may lead to respiratory difficulties in the preterm child in addition
to heart failure. If medical treatment to close the ductus is unsuccessful, the lesion may be treated by interventional cardiology (i.e. an umbrella occlusion device inserted percutaneously) or by surgery via a left thoracotomy (Fig. 48.38). Treatment for asymptomatic ductus arteriosus should be considered because of the risk of endocarditis.
Coarctation of the aorta
This accounts for 5 per cent of congenital heart disease. In this condition the arch of the aorta around the area of the ductus arteriosus is narrowed (Figs 48.39 and 48.40). The coarctation puts a pressure load on the left ventricle which can ultimately fail. The upper body is well perfused but the lower body, including the kidneys, is poorly perfused
leading to fluid overload, excess renin secretion and acidosis. There is often radiofemoral delay when examining the pulses. The child often appears well in the first few days of life because the coarctation is bypassed by the ductus arteriosus and oxygenated blood reaches the entire systemic circulation.
As the ductus closes, the child becomes progressively more unwell. Emergency treatment includes the administration of prostaglandin analogues to keep the ductus open and general resuscitation before corrective treatment, which includes balloon dilatation or open operation via a left thoracotomy.
Operative options include resection of the coarctation and end-to-end anastomosis or the use of the left subclavian artery as an onlay flap. In older children, there is upper body hypertension with development of enormous collateral vessels which may cause rib notching and flow murmurs over the scapula. Treatment is advised because of the risk of endocarditis and heart failure, but the preoperative hypertension may not resolve. In the older patient, the subclavian flap operation is not feasible and resection with end-to-end anastomosis, interposition graft or a jump' graft are the surgical options.
Vascular rings
Abnormalities of the great vessels can constrict the structures in the mediastinum, namely the trachea and the oesophagus. Many vascular rings can be explained by the persistence or failure to regress of parts of the aortic arch system during embryonic development. Investigations include a barium swallow, bronchoscopy or angiography. Treatment is indicated for the relief of symptoms and is usually directed at dividing the nondominant vascular component of the ring.
Congenital valvular abnormalities
Among the obstructive lesions are aortic, mitral and pulmonary valve stenoses, as well as supravalvular and infravalvular obstructions.
Pulmonary stenosis. There is an incomplete obstruction in this condition to the flow from the right ventricle. This accounts for about 10 per cent of all congenital heart disease. The obstruction is often at valve level and there may be an associated ASD.
The right ventricle hypertrophies in an effort to overcome the obstruction and pulmonary artery pressures may exceed systemic pressure (Fig. 48.41). The defect is often asymptomatic and a murmur is detected at preschool screening. On chest radiographs the lung fields will be oligaemic and there is often poststenotic dilatation of the pulmonary artery. Treatment is directed at relieving the obstruction and this may be done under direct vision or by balloon dilatation.
Congenital aortic stenosis. This may be valvular, subvalvular or supravalvular but in all cases there is a pressure load on the left ventricle leading to hypertrophy (Fig. 48.42). The most common defect is a bicuspid valve where one of the cusps has not developed; however, this is rarely a problem until adulthood. There may be a lot of calcification by the time initial symptoms present. There may be a regurgitant element to the problem. Echocardiography demonstrates the sire of obstruction.
Indications for operation. Unfortunately the condition is well advanced once symptoms occur and therefore treatment may be indicated to safeguard the patient's future. The operation relieves the obstruction by repairing the cusps, excising obstructing hypertrophic myocardium or replacing the valve. Infravalvular obstruction is dealt with by excising the obstructing membrane and supravalvular obstruction is repaired using a patch graft. There is a high mortality for emergency procedures, but in the elective situation the mortality rate should be less than 5 per cent.
Atrial septal defect
The development of the atrial septum is complex and abnormalities of development lead to three commonly recognised ASDs.
Fossa ovalis defect (syn. ostium secundum ASD)
This is the most common type of ASD and is a defect in the floor of the fossaovalis. Symptoms develop insidiously and may be no more than a tendency to chest infections. Rarely it presents early as a result of a paradoxical embolus from the venous circulation traversing the patent foramen ovale and reaching the systemic circulation. Symptoms appear when pulmonary hypertension develops, usually in the fourth decade, but may appear earlier under conditions of increased cardiac output (i.e. pregnancy).
Should the shunt reverse (i.e. become right to left) because of the pulmonary hypertension, then closure of the ASD is contraindicated. The development of a reversed shunt is termed Eisenmenger's syndrome'.
Atrioventricular septal defect (syn. primum defects)
When abnormalities of this type are confined to the atrial septum they are commonly called ostium primum ASD. Failure of the development of the septum primum is uncommon, but when it occurs it is associated with abnormalities of the mitral valve. A more extreme version may lead to an atrioventricular canal defect. There is a relatively high incidence of this abnormality in those born with trisomy 21 (Down's syndrome).
Sinus venosus
This is a rare defect and is the result of failure of partition of the pulmonary and systemic venous circulations. It is associated with anomalous pulmonary venous drainage (Fig. 48.43).
Treatment of atrial septal defect
Echocardiography will define the anatomy and any other abnormalities including the direction of the shunt. Pressure measurements may be required if pulmonary hypertension is suspected. Treatment is aimed at closing the defect. This may be from simple closure or patch graft in the primum type to an extensive closure and reconstruction of the mitral valve in the secundum type.
Ventricular septal defect (VSD)
This accounts for 15-20 per cent of congenital heart disease and affects 2 in 10 00 live births (Fig. 48.44). There is a high spontaneous closure rate and only 25 per cent persist. There is communication between the ventricles and this may occur in isolation or as part of a more complex set of cardiac abnormalities. Blood ejected from the heart tends to go into the pulmonary circulation where the resistance to flow is lower. If no compensation occurs, severe pulmonary oedema results. The pulmonary circulation may adapt by increasing the resistance to flow but this may lead to irreversible pulmonary oedema if the defect is nor corrected. Small defects may close or cause little systemic disturbance (maladie de Roger).
In the case of larger defects the infant may have frank pulmonary oedema, failure to thrive and recurrent chest infections. In older children, pulmonary hypertension may be the predominant clinical feature with cyanosis present if the left-to-right shunt reverses (Eisenmenger's syndrome).
Echocardiography confirms the diagnosis and can estimate the degree of shunting across the defect. Catheterisation is recommended to quantify the various pressures within the cardiac chambers.
Most VSDs will close spontaneously within the first year of life, but some will lead to death or irreversible pulmonary hypertension if not treated quickly. If the infant is severely symptomatic, the defect should be closed urgently otherwise elective repair is advised between 1 and 3 years of age. Very sick infants can be tided over' by banding the pulmonary artery. This protects the lungs from pulmonary hypertension and diverts the blood into the aorta. Elective surgery can then be carried out at a later stage when the child has grown.