The interventricular septum contains membraneous and muscular components. The membranous portion is a relatively small fibrous area which extends from the inferior limit of the interatrial septum to the superior extent of the muscular interventricular septum. The mitral and the tricuspid valves are attached to the septum. The plane of mitral valve attachment is at a higher level than the plane of the tricuspid valve (Fig. 1) 1694. Thus, a small portion of the membranous septum lies below the muscular portion of the interatrial septum to the left of the tricuspid annulus, and this separates the right atrium from the left ventricle. Absence of this portion of the septum results in an intracardiac shunt from the left ventricle to the right atrium (Gerbode defect). The muscular part of the interventricular septum is composed of the inlet (behind the septal leaflet of the tricuspid valve), and the trabecular and outlet portions (Fig. 2) 1695. The outlet septum, also called the infundibular septum, represents septation of the bulbus cordis into right and left ventricular outflow tracts. As a result of the difference in configuration of the two ventricles, the various components of the interventricular septum normally subtain considerable angles to each other. The inlet septum is nearly at right angles to the outlet septum and is at about 45° to the trabecular septum.

The normal alignment of the interventricular septum is often disturbed by the developmental anomalies which result in various congenital cardiac malformations. Malalignment anomalies can be divided into three categories:

This results in a perimembranous inlet ventricular septal defect, sometimes associated with straddling of the tricuspid valve (i.e. the tension apparatus of the valve is attached to both sides of the septum or to the septal crest) and/or over-riding, where the valve annulus is related to both ventricular chambers.

Anterosuperior deviation of the outlet septum in relation to the rest of the septum results in a typical subarterial ventricular septal defect. This is commonly encountered in tetralogy of Fallot, double outlet right ventricle, and transposition of the great arteries. Tetralogy of Fallot, the most common cyanotic heart defect, is described in detail below.

Such an anomaly is encountered in univentricular atrioventricular connection. Double inlet left ventricle is the most common example: the main ventricular chamber is of left ventricular morphology and the rudimentary ventricular chamber has right ventricular morphology. This is discussed briefly below.

Tetralogy of Fallot is characterized by a large ventricular septal defect (usually of similar size to the aortic valve annulus), right ventricular outflow tract obstruction, due to the presence of abnormal muscle bundles which act like calipers varying the calibre of the outflow tract, a dextraposed and over-riding aorta, and right ventricular hypertrophy (see Fig. 6 1700). The hallmark of this anomaly is the anterosuperior deviation of the infundibular septum which causes the infundibular septum and its parietal extension to lie in a sagittal rather than the usual coronal plane (Fig. 2) 1695. The resultant malalignment between the infundibular septum and the trabecular septum produces a characteristic type of infundibular pulmonary stenosis and a ventricular septal defect. Although this malalignment is primarily responsible for the right ventricular outflow tract obstruction, other mechanisms such as anomalous right ventricular muscle bundles and accessory tissues derived from either the membranous ventricular septum or from the septal leaflet of the tricuspid valve may also contribute. Developmentally, tetralogy of Fallot results from the maldevelopment and unequal partitioning of the distal bulbus cordis. Lack of normal rotation of the distal bulbus creates a situation where the aortic segment is not completely transferred towards the left ventricle and comes to overlie the right ventricular outflow tract (Fig. 3) 1696. The condition can therefore be considered as part of a spectrum of congenital cardiac malformations characterized by transfer of the aorta from a position above the left ventricle, over-riding a ventricular septal defect, towards a position directly above the anatomic right ventricle.

A variety of patterns of infundibular stenosis can be recognized, ranging from a well-formed infundibular chamber with a low-lying infundibular stenosis to absence of the infundibular septum, resulting in a subpulmonary ventricular septal defect. Pulmonary flow may also be obstructed by pulmonary valve stenosis (60–70 per cent of patients), a small pulmonary valve annulus, supravalvular narrowing, stenosis of the pulmonary artery bifurcation, localized stenosis or atresia of either pulmonary artery (usually the left), or incomplete distribution or hypoplasia of branch pulmonary arteries within the lung. The infinitely variable spectrum of obstruction which results must be assessed thoroughly preoperatively. Corrective surgery should relieve all possible sites of obstruction.

The classical clinical presentation of tetralogy of Fallot is with cyanosis due to right to left intracardiac shunting of blood across the large ventricular septal defect into the over-riding aorta. The severity and the timing of onset of cyanosis varies with the degree of obstruction to the pulmonary blood flow. Infants with severe infundibular and valvar stenosis, or with valvar stenosis and diffuse right ventricular outflow tract hypoplasia are often deeply cyanosed from birth. They rarely suffer from cyanotic spells but the cyanosis increases gradually. By contrast, infants with dominant infundibular stenosis have a delayed onset of cyanosis: ‘cyanotic spells’ due to infundibular spasm may not occur until the second year of life. Such spells become less frequent with age, presumably because the infundibular stenosis becomes ‘fixed’ due to the secondary development of endocardial fibrosis. As the child begins to walk, cyanosis is almost always accompanied by dyspnoea and squatting is often adopted, which may be nature's attempt to improve pulmonary flow by increasing systemic arterial resistance. A few children and adults with tetralogy are acyanotic at rest and only mildly cyanotic on exercise because the pulmonary valve is normal and infundibular stenosis is mild.

Unusual clinical presentations are occasionally encountered. Patients in whom the intracardiac shunt is predominantly from left to right may remain acyanotic for many years, presenting within the first and second decades of life as the infundibular stenosis slowly increases in severity. At the other extreme, infants born with pulmonary valve atresia develop increasing cyanosis within the first few days of life. In a small subset of patients who may require surgical relief in infancy, presentation is initially that of a large ventricular septal defect, resulting in pulmonary plethora and congestive cardiac failure at 2 to 3 months of age. Cyanosis at rest develops gradually at about 6 months of age.

Cerebrovascular accident as a result of cerebral thrombosis may occur at any age in patients with severe cyanosis and polycythaemia. This problem is compounded by relative anaemia due to iron deficiency because of increased blood viscosity. Dehydration may be a precipitating factor. Hemiplegia may also follow paradoxical embolism or a cerebral abscess. In older patients, rupture of bronchial collateral vessels may lead to massive haemoptysis. Without surgical intervention, cyanosis and polycythaemia increase. This is due in part to the ‘fixed’ orifice pulmonary valve, which becomes relatively more stenotic as the child grows, but also because of a tendency to develop thrombosis of the pulmonary arteries with progressive reduction in pulmonary blood flow. The few patients who survive into the fourth or fifth decades of life die from chronic congestive heart failure due to secondary cardiomyopathy resulting from right ventricular pressure overload and chronic hypoxia in association with polycythaemia.

Cyanosis and clubbing are often obvious in a child with tetralogy of Fallot. The jugular venous pressure is normal and the radial pulse may be of low volume. A moderate intensity midsystolic pulmonary ejection murmur is audible, and maximal in the second and third intercostal spaces. This becomes less prominent when stenosis is very severe, and may disappear completely during a cyanotic spell as a result of infundibular shut-down. A continuous murmur from a previously created systemic to pulmonary artery shunt may be audible over the precordium.

Older infants and children usually have an elevated red blood cell count and haemoglobin level, the degree of which correlates with the degree of arterial desaturation and thus with the severity of outflow tract stenosis. The haemoglobin level may be falsely low if iron deficiency is present, in which case the haematocrit is a more accurate reflection of the severity than the haemoglobin.

Chest radiographs in affected children may show a typical ‘boot-shaped heart’ with oligaemic lung fields, and demonstrate the position of the aortic arch, which is right sided in approximately 25 per cent of cases. Patients in the second or third decades of life may show progressive kyphoscoliosis.

The electrocardiogram reveals right ventricular hypertrophy and absence of Q-waves with low voltage R-waves in the left precordial leads. In the right chest leads the R-wave is dominant in infants, usually with an associated upright T wave.

The echocardiogram clearly demonstrates the ventricular septal defect, aortic over-ride, and narrowing of the right ventricular outflow tract. However, definitive preoperative evaluation is still dependent upon cardiac catheterization and high-quality angiocardiography.

The aim of the study is to demonstrate all morphological features of the malformation, to delineate coronary arterial anatomy, diagnose any major associated intracardiac anomalies, confirm the position of the aortic arch, and to identify major aortopulmonary collateral arteries, if present. Figure 4 1697,1698 shows some of the characteristic features of tetralogy of Fallot as seen on cineangiogram.

Cardiac catheterization discloses identical peak systolic pressures in the two ventricles and ascending aorta, and subnormal pulmonary artery pressure. Separate systolic pressure gradients may be demonstrated at infundibular and valvular levels. However, it may be impossible to enter the pulmonary artery with the catheter, due to severe right ventricular outflow or valvular stenosis. Persistent probing with the catheter carries a risk of precipitating ‘spells’ in patients with no previous aortopulmonary shunt. Angiocardiography should be performed in several views. Oblique and angled views allow the severity and morphology of right ventricular outflow tract obstruction to be assessed. The configuration of the right ventricular sinus and infundibulum, morphology of the pulmonary valve, the diameter of the pulmonary annulus, main pulmonary artery, bifurcation of the pulmonary trunk, origin of left pulmonary artery, and the size and morphology of branch pulmonary arteries are noted. The subaortic ventricular septal defect is identified and the degree of over-ride of the dextraposed aorta is assessed. Particular attention is directed towards the identification of any additional ventricular septal defects which, if present, are usually situated in the trabecular muscular septum. The size and function of the left ventricle are assessed by injecting contrast medium into the left ventricle. The origin and course of major coronary arteries are noted with a view to identifying anomalous origin of the left anterior descending coronary artery from the right coronary artery. This anomaly is found in 2 to 5 per cent of patients with tetralogy of Fallot and is important from the surgical viewpoint as it crosses the infundibulum to seek its position in the anterior interventricular sulcus. Thus, this important artery may cross the desired site of right ventriculotomy if outflow tract patching is required. If a systemic to pulmonary artery shunt has been created previously, its site and patency are noted by selective injections.

Most infants with tetralogy of Fallot have a patent foramen ovale. Associated cardiac anomalies such as atrial septal defect, persistence of a left superior vena cava, aberrant origin of right subclavian artery, persistence of the ductus arteriosus, complete atrioventricular canal (often associated with Down's syndrome), and multiple ventricular septal defects, though rare, are also diagnosed, if present.

The diagnosis of tetralogy of Fallot is an indication for operation in view of its poor prognosis without surgery and the very good early and late results following total correction. However, the morphological and clinical variations are so numerous that it is important to assess each patient individually with regard to the timing and the type of surgery to be undertaken. Patients with uncomplicated anatomy with pulmonary valve stenosis, but with adequately developed left and right and intrapulmonary arteries, should undergo total intracardiac correction, as a primary procedure or following an initial palliative systemic pulmonary shunt. Although this should ideally be performed before the age of 3 to 4 years, older age is not a contraindication to operation. Some centres advocate primary total correction in infancy, and produce excellent results. However, the ultimate decision on whether to perform one-stage or two-stage correction depends upon the characteristics of the right ventricular outflow tract obstruction, the experience of the surgeon and his team, and the available postoperative care. Regular audit and analysis of surgical results is helpful in making these decisions.

Infants and children with severe cyanosis and hypoxic spells are treated with propranolol (2–4 mg/kg.day) while awaiting surgery. This minimizes or abolishes infundibular muscular spasm in many cases.

The objectives of palliative surgery are to increase pulmonary blood flow and to allow hypoplastic pulmonary arteries to grow in calibre with age.

‘Shunts’ may be created either centrally between the ascending aorta and the main pulmonary artery (Davidson or Waterston anastomosis) (Fig. 5(c)) 1699 or peripherally between the subclavian artery and right or left pulmonary artery by direct anastomosis (classical Blalock-Taussig shunt) (Fig. 5(a)) 1699 or using a tube of polytetrafluoroethylene (modified Blalock-Taussig shunt) (Fig. 5(b)) 1699.

The Blalock-Taussig or modified Blalock-Taussig shunt continues to be the shunt of choice, even in infancy, and can be performed on the side opposite to the aortic arch so that the subclavian artery is used, originating from the innominate artery. This minimizes the risk of kinking of the subclavian artery at its origin. The Waterston anastomosis provides satisfactory symptom relief in small infants. However, it has lost favour because of the relatively high incidence of distortion of the right pulmonary artery and the risk of creating too large a shunt, resulting in cardiac failure, and later, pulmonary vascular hypertension. Pott's shunt (between the descending aorta and the left pulmonary artery) has been almost completely abandoned for the same reasons and because of the difficulties encountered closing the anastomosis at the time of total repair. Since the Blalock-Taussig shunt is the most common type of shunt performed in infancy, it will be described in detail.

Thoracotomy is performed on the appropriate side and the lung is retracted posteriorly. The main pulmonary artery is identified, and an adequate length is dissected, taking care not to injure the phrenic nerve. Two snares of heavy silk are passed round the upper and lower lobe pulmonary arteries, which, when tightened, prevent retrograde bleeding from the arteriotomy. The mediastinal pleura is incised from the pulmonary artery up to and along the subclavian artery. A groove is then created by blunt dissection between the trachea and the superior vena cava, safeguarding the vagus nerve and its recurrent laryngeal branch on the right. The dissection is continued to the subclavian artery. The most accessible portion of the vessel is dissected and a tape passed around it. The subclavian artery is then tied distally close to the first rib, and divided just proximal to the ligature, the proximal end being controlled in a vascular clamp. On the right side, the artery is then drawn through the loop of the recurrent laryngeal nerve using a right-angled forceps passed beneath the vagus and the recurrent nerve. The subclavian artery is turned down, its distal end trimmed and cleaned. Extra length can be obtained by adequate mobilization of the innominate and carotid arteries and, if necessary, by dividing the inferior pulmonary ligament.

Proximal and distal control of the pulmonary artery is achieved and the artery is opened transversely on its superior border. End-to-side anastomosis of the subclavian artery to the pulmonary artery is performed using 6/0 or 7/0 Prolene. In small infants, heparin (1 mg/kg) is often administered before the subclavian artery is divided. Once the anastomosis is completed, the snares are released and swabs are used to apply gentle pressure to the suture line for a few minutes. In small infants, it is important to maintain a systolic blood pressure of over 70 to 80 mmHg, if necessary by using inotropic support. Hypotension in the early postoperative period predisposes to clotting of the anastomosis. In case of excessive oozing, heparin is reversed with protamine sulphate.

If a modified Blalock-Taussig shunt is planned, then an appropriate length of PTFE tubing (5 or 6 mm in diameter) is trimmed at both ends and is anastomosed to the lateral aspect of the subclavian artery and to the superior surface of pulmonary artery using 6/0 or 7/0 Prolene. Once haemostasis is secured, the chest is closed, leaving a chest drain in situ. Various types of shunt procedure are shown diagrammatically in Fig. 5 1699.

Limited resection of muscle bundles obstructing the right ventricular outflow tract may be performed on cardiopulmonary bypass. Pulmonary valvotomy is also performed, but closure of the ventricular septal defect is undertaken at a later date, when the ‘run off’ through the lungs has developed sufficiently to allow the right ventricle to work at an acceptably low pressure following patch closure of the defect.

Resection of infundibular muscle bundles can also be undertaken with insertion of a valveless conduit of pericardium or synthetic material from the right ventricular outflow tract to the pulmonary artery.

The principles of total correction are patch closure of the ventricular septal shunt and the relief of all sites of obstruction to pulmonary blood flow. This includes resection of infundibular muscular stenosis, relief of pulmonary valvar obstruction, repair of main or branch pulmonary artery stenosis (which may be present either as a manifestation of the anomaly or as a result of a previously constructed shunt), and enlargement of the right ventricular outflow tract and hypoplastic pulmonary valve annulus. This is achieved by the use of a monocusp aortic homograft or by a free transannular patch of Dacron cloth or pericardium. In addition, previously constructed systemic to pulmonary artery shunts are ligated. It is therefore imperative that the surgeon enters the operating theatre with a clear concept of the cardiac morphology as displayed by the cineangiocardiogram and echocardiogram.

The chest is opened through a medium sternotomy. Preparations are made to establish cardiopulmonary bypass. If systemic-pulmonary artery shunts are present, they are dissected and ligatures are passed around them. Intravenous heparin (3 mg/kg) is given. Appropriately cannulae are inserted in the aorta and in the right atrium for bypass. Cardiopulmonary bypass is established and the systemic-pulmonary artery shunts are occluded without delay. The patient is cooled to 25 to 28°C: infants weighing less than 10 kg may be placed under deep hypothermia (18°C) and total circulatory arrest. The aorta is cross-clamped and the myocardium is protected by infusing an initial dose of 20 ml/kg of cold crystalloid or blood cardioplegia. Repeat doses of half the volume of the initial dose of cardioplegic solution may be given every 30 min.

If preoperative assessment suggests the necessity of a transannular patch, a vertical right ventriculotomy is performed; this is controlled by two stay sutures on the outflow tract and later extended across the annulus on to the pulmonary artery. If there is associated valvular stenosis but the pulmonary artery annulus is of adequate size, a transverse ventriculotomy and a separate pulmonary arteriotomy are used. The direction and extent of the right ventriculotomy may be dictated by the distribution of the coronary arteries. Some surgeons advocate the right atrial approach for the closure of the ventricular septal defect and infundibular muscle resection, and sometimes even for the relief of valvular pulmonic stenosis.

After performing the right ventriculotomy, the obstructing muscle bundles are divided. The identification of muscle bundles through the right ventriculotomy is depicted in Fig. 6 1700. Initially, the parietal extension of the infundibular septum is dissected away from the right ventricular free wall and from the ventriculo-infundibular fold and divided transversely, safeguarding the right coronary cusp of the aortic valve. This precaution increases the diameter of the infundibulum at its rightward end and is also a key to the complete access to and closure of the ventricular septal defect. Any obstructing muscle bundles to the left of the outflow tract (septoparietal bundles) are excised completely. Low-lying obstruction is relieved by dividing the obstructing trabeculations above the moderator band, which is usually preserved intact. Throughout the procedure, great care must be taken to protect the tension apparatus of the tricuspid valve. The ventricular septal defect is closed, using an appropriate sized circular patch of two-way stretch woven Dacron with pledgetted Ethibond or Prolene sutures, taking care to avoid placing stitches in the region of the conduction bundle, the distribution of which is shown in Fig. 7 1701. Stay sutures are passed through the septal and anterior leaflets of the tricuspid valve, as it is often necessary to attach the patch to the base of the anterior leaflet when this is related closely to the lower border of the defect.

If pulmonary valvotomy is necessary, a pulmonary arteriotomy is performed, taking care not to injure the pulmonary valve and commissures. Commissural fusion is divided after mobilizing cusp tissue from the vessel wall: in order to relieve the stenosis adequately it is often necessary to excise the thickened cusp edges. This will normally result in some pulmonary valve incompetence.

The decision of whether to enlarge the pulmonary valve annulus is based on a critical assessment of its size. Preoperative measurements of the combined cineangiographic diameter of the right and left branch pulmonary arteries are compared with the diameter of the descending thoracic aorta at the diaphragm. At the time of operation, the absolute size of the main pulmonary artery and its relationship with the size of the aortic root is assessed. The true diameter of the pulmonary annulus can be estimated using Hegar dilators. The observed values are compared with standard values for the age and weight of the child and, using a predefined formula, the post-repair ratio of peak systolic pressure in the right ventricle to that in the left ventricle (P&subR;&subV;&subsol;&subL;&subV;) is estimated. A ratio of less than 0.8 is acceptable, but 0.5 to 0.7 is desirable.

If the above observations suggest that the valve annulus requires enlargement, the transannular patch can take the form of a monocusp aortic homograft or a piece of pericardium or Dacron or PTFE. A patch of appropriate size is prepared and sewn in with continuous Prolene sutures. Since the purpose of the monocusp aortic homograft is to maintain reasonable pulmonary valve function, it is important that the bases of the native pulmonary valve cusps are in exact alignment with the base of the monocusp homograft (Figs 8,9) 1702,1703. Alternatively, an entire homograft valve may be inserted (Fig. 10(a–d)) 1704.

If it is only necessary to widen the right ventricular outflow tract proximal to the valve, the right ventriculotomy is closed by the inclusion of a patch of preclotted woven dacron or pericardium. The pulmonary arteriotomy is closed by direct suture or with an autologous or xenograft pericardium patch. If an atrial septal defect is present, it is closed via a separate right atriotomy, or through the tricuspid valve. Closure of the ventriculotomy and the pulmonary arteriotomy can be performed following the release of the aortic cross-clamp, thereby reducing the time of myocardial ischaemia. The patient is rewarmed and, following evacuation of air, especially from the left side of the heart, cardiopulmonary bypass is discontinued. Heparin is reversed with protamine sulphate. Following confirmation of haemostasis, the chest is closed leaving pericardial and mediastinal drains in situ. It is advisable to insert ventricular pacing wires, in case these are required during the postoperative period. If sequential pacing is contemplated, two further electrodes are attached to the right atrium close to the sinoatrial node.

Pulmonary atresia implies pulmonary valve atresia with or without absence of the main pulmonary artery; there may thus be a gap from the right ventricle to the confluence of the branch pulmonary arteries. Closure of the ventricular septal defect and insertion of a suitable bridge in the form of an antibiotic-sterilized or cryopreserved aortic or pulmonary valved homograft conduit, or a valve-bearing Dacron tube graft, will only be successful if the pulmonary arteries are of adequate calibre to allow the right ventricle to work at an acceptably low pressure. When the native pulmonary arteries are hypoplastic or are absent, pulmonary blood flow is supplied by major aortopulmonary collateral arteries, which usually originate from the descending thoracic aorta.

Repair of tetralogy of Fallot with anomalous origin of the left anterior descending coronary artery from right coronary artery

It is important that this anomaly is recognized preoperatively by cineangiography. The left anterior descending coronary artery may be buried in the myocardium or fat, especially if pericardial adhesions from a previous sternotomy have obliterated the pericardial space. The passage of this artery across the right ventricular outflow tract poses a special danger if a vertical incision into the right ventricular outflow tract is required. The available options are: (1) transverse ventriculotomy and repair using a homograft conduit from the right ventricle to the pulmonary artery, thus bypassing the critical area, or (2) dissection of the left anterior descending coronary artery from its bed in the right ventricular wall throughout most of its length from its origin to within a few millimetres of the interventricular groove. The ventriculotomy is then made beneath the artery and across the annulus if necessary. If this option is selected, great care must be taken not to damage any coronary artery or branches.

Following shunt operations, babies are nursed in a special unit whose nursing staff are familiar with the management of neonates. A rare, but often lethal complication following a shunt is haemorrhagic pulmonary oedema, which can produce hypoxia and rapid clinical deterioration. The chest radiograph is diagnostic, showing severe vascular congestion of the ipsilateral lung. This is due to the direct effect of the sudden increase in pulmonary blood flow and may be an indication for immediate reoperation. The anastomosis is narrowed appropriately. Low dose heparin may be continued in the early postoperative period and is replaced later by low dose aspirin to maintain the shunt patency. Less marked overperfusion of the lungs is usually controlled with diuretic therapy, which may be required for several weeks. Following reconstructional surgery, patients may require cardiorespiratory support, including sedation and ventilation and infusion of an inotropic agent such as dopamine. Complete heart block, which is rare and usually temporary, is managed by ventricular pacing.

Patients with tetralogy of Fallot show a particular tendency to accumulate interstitial, pleural, and peritoneal fluid early in the postoperative period. This may be due to chronic cyanosis, which affects the permeability of capillary membranes, making these patients particularly sensitive to the damaging effect of cardiopulmonary bypass. Haemocentration should therefore be avoided in the early postoperative period; this requires frequent monitoring of the haematocrit level. Fluid retention is particularly common in the early period, and diuretic therapy is often necessary, keeping the central venous pressure as low as possible while maintaining cardiac output.

The creation of classical and modified Blalock-Taussig shunts in children with uncomplicated tetralogy of Fallot carries a low operative mortality rate (0.1–2.5 per cent). However, when performed in very young infants with pulmonary atresia the mortality rate can be as high as 10 to 15 per cent. The Waterston shunt has a higher complication rate than the Blalock-Taussig shunt. While palliative transannular patching with cardiopulmonary bypass has a low hospital mortality in children and young adults, it can be in the region of 10 to 20 per cent in infants.

Since tetralogy of Fallot is morphologically and clinically a highly variable entity, it is difficult to make generalizations about surgical results. However, it is certain that the in-hospital mortality after repair of uncomplicated tetralogy of Fallot has steadily declined over the last three decades. Under proper conditions, the mortality rate in this group of patients, whether the repair is carried out primarily or as a two-stage procedure, is approximately 4 to 8 per cent. The risk is higher in patients with coexisting pulmonary arterial problems, associated cardiac anomalies, or in those with high haematocrit or a small left ventricle. The long-term results following total repair, both in terms of late survival and quality of life, are excellent. However, the operation cannot be considered curative in all patients, since the survival curve beyond 10 years is slightly but significantly less than that of a matched general population.

The terminology used to describe univentricular heart has varied in the literature. In the past, reference has been made to a single ventricle, common ventricle, double inlet left ventricle, primitive ventricle, and corbiatriatum triloculare. This are synonymous with univentricular atrioventricular connection. Although this congenital abnormality has been known to cardiac pathologists for a number of years, it is only in the past 15 years that significant advances in its surgical management have been reported.

Univentricular hearts can be subclassified,, according to the morphology of the main ventricular chamber. This may exhibit left ventricular morphology (the most common variety), right ventricular morphology, or an indeterminate trabecular pattern. From the surgical standpoint, it is important to distinguish between patients with and without an outlet chamber. This gives origin to one or both of the great arteries. The ventricular septal defect (bulboventricular foramen) connecting the main chamber to the outlet chamber may be restrictive in size. In the univentricular heart of left ventricular morphology, the atria connect with the posterior ventricle, and the outlet chamber (minor ventricle) is always positioned anterosuperiorly either to the left or to the right of the main ventricular chamber, or very occasionally centrally. The reverse is true for the univentricular heart of right ventricular morphology. Different morphological types of univentricular heart are shown in Fig. 11 1705. Other features of surgical importance are the type of atrioventricular connection (double inlet, or absent right or left atrioventricular connection), mode of atrioventricular connection (two valves, common valve, or a single valve), type of ventriculoarterial connection (concordant, discordant, double outlet, single outlet), presence or absence of subpulmonary or pulmonary stenosis, and any associated malformations: these occur in approximately one-third of patients.

The clinical features vary with the morphology of the pulmonary valve and subpulmonary region. Patients without pulmonary stenosis (approximately one-third) have a presentation similar to that of a large ventricular septal defect except that, since the main chamber acts as a common mixing chamber, mild cyanosis may be present. A mild to moderate pulmonary stenosis may cause no symptoms in the early years of life, although cyanosis and a systolic murmur usually ensues in childhood. Severe pulmonary stenosis of pulmonary atresia usually presents with severe cyanosis in the neonatal period; this may be mistaken for tetralogy of Fallot.

The electrocardiogram and chest radiograph raise the suspicion of univentricular heart, which is confirmed by echocardiography. Cineangiography is carried out if surgical treatment is under consideration.

The natural history of the condition is almost as varied as its morphology. It is usually a lethal cardiac abnormality, and results in a greatly reduced life expectancy. The most common causes of death are dysrhythmias, congestive cardiac failure, pneumonia, and sudden death.

In view of the poor natural history of the condition, complete repair of univentricular is desirable if the surgical risks are not too great. The type of surgery and the approximate timing are highlighted in Fig. 12 1706. Since repair in the form of septation or the Fontan procedure of right atrial to pulmonary artery connection is best accomplished in older patients, children less than 5 years of age are usually subjected to palliative procedures as indicated. Patients with high pulmonary blood flow and cardiomegaly resulting in cardiac failure are managed initially by pulmonary artery banding. Those presenting with severe cyanosis are offered a systemic-pulmonary artery shunt, which is often combined with atrial septectomy if the atrial septal defect is restrictive or if one of the atrioventricular valves is stenotic or atretic.

This is performed through an anterolateral thoracotomy on the same side as the pulmonary artery. The pericardium is opened anteriorly and the dilated pulmonary artery is separated from the aorta with great care. Minimal dissection is performed to diminish the risk of band migration. A 3 to 4 mm wide Teflon tape is passed round the main pulmonary artery using a right-angled instrument passed around and behind the aorta to grasp one end of the tape, which is pulled between the great vessels. The other end is retrieved by forceps and is passed through the transverse sinus. Alternatively, the Teflon tape can be passed directly around the main pulmonary artery. With the tape in place, a trial banding is performed using a vascular clamp as a snare on the tape. At the desired tension, the pulmonary artery is banded by joining the two opposing surfaces of the tape with one or two mattress sutures of Ethibond or Prolene. The excess band is trimmed away. Heart rate, oxygen saturation, and systemic arterial pressure are noted throughout the procedure. If bradycardia develops due to a significant reduction in oxygen saturation, the band is loosened a little; if the band is too slack, as judged by the pressure difference across the band (distal pulmonary artery pressure should be between 60 and 50 per cent of the systemic pressure), the band is tightened. One or two stitches are placed between the pulmonary artery adventitia and the band to prevent it migrating towards the bifurcation of the pulmonary artery, as this may cause severe obstruction at the origin of the right main pulmonary artery. The pericardium and the chest are closed, leaving a drain in situ. A postoperative cine film of a child with pulmonary artery band in place is shown in Fig. 13 1707.

Following an appropriate palliative procedure, indications for repair by septation or by modified Fontan procedure include significant or increasing symptoms, progressive cardiac enlargement, and a rising haematocrit and haemoglobin level. In view of the increased operative risks incurred when a valved extracardiac conduit is added to septation to bypass severe subpulmonary stenosis, or when concomitant atrioventricular valve replacement is necessary, septation is usually not offered to these categories of patients. The modified Fontan procedure is preferred for patients with low pulmonary arterial pressure and resistance, since this creates a wide direct anastomosis between the right atrium and the pulmonary arteries.

In view of the potential for cardiac transplantation in the future, all operative procedures are planned to avoid development of pulmonary vascular disease and distortion of the pulmonary arteries. The technical aspects of septation or modifications of the Fontan procedure are beyond the scope of this chapter. However, Figs. 14 to 16 1708,1709,1710 give an overview of different procedures. Some spectacular surgical successes have been reported from a few centres when septation has been performed in hearts of left ventricular morphology with a left-sided outlet chamber, giving rise to an unobstructed aorta.

Hospital mortality rates following septation are still high. However, since the technical details and indications for septation continue to evolve, this current high mortality may not pertain in the future. The mortality rate associated with modified Fontan procedures varies between 10 and 20 per cent, and is largely dependent upon careful patient selection. The medium-term results of both septation and modified Fontan procedures are considered encouraging in many patients.

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