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Congenital Heart Disease

Tricuspid Atresia: Current Concepts in Diagnosis and Treatment Robert M. Sade, MD, * and Derek A. Fyfe, MD, PhDt

HISTORICAL NOTE Tricuspid atresia was probably the cardiac malformation that was vaguely described in a case report in the London Medical Review in 1812, but the first clear description of an anomaly consistent with what we now call tricuspid atresia was that of Kreysig in 1817. 56 The word atresia was first used in 1861. 61 In 1906 Kuhne observed that patients with tricuspid atresia may have either normally related or transposed great arteries. 37

CLINICAL FEATURES The incidence of tricuspid atresia is approximately 1 per cent in clinical series of children with congenital heart disease, and is approximately 3 per cent in autopsy series. 35 Boys and girls are affected almost equally. About half the patients are diagnosed on the first day of life because of the discovery of cyanosis or a heart murmur, and 85 per cent of all patients are diagnosed within the first 2 months of life. Among all patients with tricuspid atresia, cyanosis is the most constant clinical finding and clubbing is usually seen in cyanotic patients who are older than 2 years. Hypoxic spells may be seen in half the patients, and squatting occurs rarely.4 Congestive heart failure is seen at some time in 12 per cent of patients, and is most often seen during infancy. Severe congestive

From the Medical University of South Carolina, Charleston, South Carolina

* Professor of Surgery, and Chief of Pediatric Cardiac Surgery t Assistant Professor of Pediatric Cardiology, and Director of Pediatric Echocardiography Laboratory Pediatric Clinics of North America-Vol. 37, No.1, February 1990

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TRICUSPID ATRESIA: CURRENT CONCEPTS

heart failure is associated with a high mortality rate, with or without surgery. Right heart failure may be a consequence ofleft heart fi-dlure, or may be due to obstruction to right heart emptying by a small atrial septal defect. It is manifested by systemic venous congestion, hepatosplenomegaly, liver and jugular pulsation, and peripheral edema. Cerebral vascular accidents, brain abscess, and infective endocarditis may be seen, but each is relatively uncommon (less than 5 per cent of cases).

NATURAL HISTORY Early death is the outcome for most patients without surgical intervention. Markedly increased or markedly decreased pulmonary blood flow usually is associated with death before the age of3 months, and 50 per cent of all patients die within the first 6 months oflife. Only one-third of patients survive their first birthday, and no more than 10 per cent are alive by the age of 10 years. 35 The longest survivors are those who have balanced pulmonary blood flow (mildly cyanotic without excessive pulmonary flow) and no associated heart malformations. The oldest patient to survive without surgery was still alive in 1987 at the age of 57 years. 5 ! With advancing age of patient, anatomic and physiologic changes may take place. Cyanosis may increase over time for two reasons: the ventricular septal defect may become progressively smaller, and pulmonary vascular obstructive disease may develop in patients with unrestricted pulmonary blood flow, leading in both cases to decreasing pulmonary blood flow and progressive cyanosis. 54 Left ventricular function may decline with increasing age regardless of whether a shunt operation has been done. 38 Life insurance practices in the United States reflect the bleak prognosis of tricuspid atresia. 52 Patients with many types of congenital heart disease are considered by most insurance companies to be insurable at standard or increased rates, but patients with the diagnosis of tricuspid atresia are considered completely uninsurable by 89 per cent of insurance companies, regardless of whether an operation has been done. 53

ANATOMY, CLASSIFICATION, AND PATHOPHYSIOLOGY All types of tricuspid atresia have in common the absence of any direct communication between the right atrium and right ventricle. The atresia of the right atrioventricular connection most commonly takes the form of a dimple of the floor of the right atrium directly over the ventricles. 57 Other less common forms of atretic atrioventricular connection include a normally formed right atrium and right ventricle separated by an imperforate membrane in the tricuspid orifice,1O atresia of the displaced valve in Ebstein's malformation,54 and total

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atrioventricular canal with no connection between valve and right ventricle. In addition to an absence of the right atrioventricular orifice, all patients have an atrial septal communication through which all the systemic venous return flows, and a ventricular septal defect between a large left ventricle and hypoplastic right ventricle. The most generally used classification of tricuspid atresia is that of Edwards and Burchelp8 in modified form (Fig. 1). Their classification focuses on associated malformations: the relation of the great arteries (types I, II, and III), and the degree of reduction of pulmonary blood flow (types a, b, and c). In the most common type of tricuspid atresia (type Ib), the tricuspid valve is represented by a dimple in the muscular floor of the right atrium, the ventricular septal defect is small, the right ventricle hypoplastic, and the great arteries normally related. Systemic venous return cannot reach the ventricles directly, so it crosses an atrial septal communication from the right to the left atrium. In the left atrium, blood mixes with the pulmonary venous return and transverses the mitral valve, entering the left ventricular cavity. Blood is pumped by the left ventricle into the aorta; some blood reaches the pulmonary arteries by traversing the outlet foramen (ventricular septal defect) into the hypoplastic right ventricle which leads to the pulmonary artery. In a few cases, additional pulmonary blood flow may come from a patent ductus arteriosus. Most cases of tricuspid atresia have restricted pulmonary blood flow due to a small outlet foramen or subvalvar or valvar pulmonary stenosis. Thus, the pulmonary venous return is reduced, so these patients are moderately to severely hypoxic and are clinically cyanotic. The left ventricle pumps both the pulmonary and systemic venous return, and easily tolerates the relatively small volume load imposed by the reduced pulmonary blood flow; congestive heart failure is seldom seen in these patients. Patients without anatomic pulmonary obstruction usually have excessive pulmonary blood flow with pulmonary artery hypertension. 15 The large amount of pulmonary venous return causes a relatively highly oxygenated admixture of blood in the left atrium, so these patients usually are not cyanotic. The left ventricle, however, is overloaded by the large pulmonary blood flow, often leading to congestive heart failure. This clinical situation is seen most often in patients who have transposed great arteries. Congestive heart failure may be severe, and if unresponsive to anticongestive medication, surgery may be needed to deal with the congestive heart failure and prevent pulmonary artery hypertension. A few patients with normally related great arteries and a large ventricular septal defect may have mild or moderate congestive heart failure due to increased blood flow which responds well to anticongestive medications. The outlet foramen, however, frequently becomes smaller over time, leading to progressively increasing pulmonary outflow obstruction, decreasing congestive heart failure, increasing cyanosis, and eventually the need for a surgical shunt. 26

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TRICUSPID ATRESIA: CURRENT CONCEPTS TRICUSPID ATRESIA WITH NORMALLY RELATED GREAT ARTERIES

la Pulmonary atresia

Ib Pulmonary hypoplasia. Small ventricular septal defect

Ic No pulmonary hypoplasia. Large ventricular septal defect

TRICUSPID ATRESIA WITH L-TRANSPOSITION

lib Pulmonary atresia

lib Pulmonary stenosis

IIc Large pulmonary artery

TRICUSPID ATRESIA WITH L-TRANSPOSITION

III Subpulmonary or subaortic stenosis

Figure 1. Classification by associated lesions. Type I, normally related great arteries; II, D-transposed great arteries: a, pulmonary atresia; b, subpulmonary or pulmonary valvular stenosis (reduced pulmonary blood flow); c, no pulmonary stenosis (normal or increased pulmonary blood flow); and III, L-transposed great arteries. (Adapted from Edwards JE, Burchell HB: Congenital tricuspid atresia: A classification. Med Clin North Am 33:1177,1949.)

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LABORATORY STUDIES OF PHYSIOLOGY AND ANATOMY Electrocardiography The typical electrocardiogram of tricuspid atresia (Fig. 2) demonstrates left ventricular hypertrophy and left axis deviation. Right axis deviation may be seen in a few patients with associated transposition of the great arteries with increased pulmonary blood flow. The P wave is usually large, indicating right and sometimes left atrial hypertrophy. Radiography The chest radiograph is not helpful in distinguishing tricuspid atresia from other malformations. Cardiomegaly is uncommon, being seen in the few patients who have increased pulmonary blood flow. The cardiac silhouette may be similar to that of tetralogy of Fallot (coeur-en-sabot), or of transposition of the great arteries (the so-called egg-shaped heart). Right aortic arch is much less common (8 per cent) than it is in tetralogy. The lung fields may have decreased pulmonary vascular markings in cyanotic patients but pulmonary plethora may be seen in patients with large pulmonary blood flow.

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Figure 2. The electrocardiogram typically demonstrates left axis deviation and left ventricular enlargement; a large notched P-wave may be present, indicating atrial enlargement (P-tricuspidale).

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Echocardiography

Echocardiography is now the primary modality for the initial diagnosis and classification of tricuspid atresia. 5o M-mode and twodimensional echocardiography can define the size and location of cardiac chambers, great arteries, valves, and flow pathways, as well as the atrial and ventricular septal anatomy (Fig. 3). Associated malformations can also be documented, including subaortic stenosis, coarctation of the aorta, left superior vena cava, and juxtaposition of the atrial appendages. Blood flow characteristics can be quantitated by pulsed and con-

Figure 3. Echocardiogram of heart with tricuspid atresia: A, Subcostal four chamber view demonstrates the atrial septal defect and absence of the tricuspid valve. (Key: ASD = atrial septal defect; ATV = atretic tricuspid valve; LA = left atrium; MV = mitral valve; RA = right atrium.) B, The long axial view shows severe subpulmonary and pulmonary valvular stenosis with thickening of the pulmonary valve. The aorta is anterior in this patient with associated transposition of the great arteries. (Key: Ao = aorta; PA = pulmonary artery; PV = pulmonary valve.) C, The long axial view in this patient with associated transposition of the great arteries case shows associated severe subaortic stenosis. (Key: AoV = aortic valve; LA = left atrium; subAS = subaortic stenosis.)

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tinuous wave and color flow Doppler echocardiography. Doppler techniques can measure pressure gradients across stenotic orifices accurately.l2 This may be particularly useful before a reparative operation, in permitting estimation of the pulmonary artery pressure even when the pulmonary artery cannot be entered at cardiac catheterization. The Doppler-measured pressure gradient may be subtracted from the ventricular systolic pressure, yielding a peak systolic pulmonary artery pressure. 24 Interatrial pressure gradients can be measured25 and may be useful in evaluating the need for atrial septostomy or septectomy. Although echocardiography can demonstrate the central pulmonary arteries well, a limitation of the technique is its difficulty in defining completely the peripheral pulmonary vessels, particularly with respect to peripheral stenoses. Color flow Doppler imaging is useful in documenting the anatomy of flow pathways through ventricular septal defects and ventricular outflow tracts, and is especially valuable in providing a semiquantitative evaluation of valvular regurgitation. Magnetic Resonance Imaging and Radionuclide Scanning Magnetic resonance imaging (MRI) may provide anatomic information similar to echocardiography, but seems less useful in evaluating physiology. MRI has been used to clarify visceroatrial situs, ventricular loof' relations of the great arteries, and the size of cardiac chambers.l It may be helpful in distinguishing rare forms of tricuspid atresia like imperforate valve or Ebstein's anomaly from the more typical absent valve. l9 Radionuclide studies have been used in evaluating postoperative patients. They may detect residualleft-to-right shunts, atriopulmonary obstruction and stasis, and pulmonary arteriovenous fistulas, and may evaluate left ventricular functions. 5 Cardiac Catheterization In infants, catheterization is used to perfonn balloon septostomy in the occasional patient with inadequate interatrial communication. In patients with pulmonary artery hypoplasia, the size and relation of the pulmonary vessels and brachiocephalic arteries may be defined before a shunt operation. In later childhood, catheterization is necessary to define anatomic and physiologic features prior to corrective operation. Distortion of pulmonary artery morphology due to palliative shunts may be best defined by angiocardiography (Fig. 4). The pulmonary artery may be difficult to enter at catheterization, but as noted above, the pulmonary artery pressure may be accurately estimated by measurement of ventricular pressure with simultaneous Doppler echocardiographic measurement of trans pulmonary pressure gradient. Angiocardiography may allow inferences about pulmonary flow and resistance when they cannot be measured directly. Other risk factors for subsequent corrective operation may be clarified. Arteriovenous fistulae subsequent to an earlier cavopulmonary anastomosis may be shown, as can left ventricular outflow obstruction. Left ventricular end

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Figure 4. Pulmonary angiogram, left anterior oblique projection. Important stenosis of the left pulmonary artery (arrow) is present immediately distal to the pulmonary artery anastomosis of the PTFE tube in a patient with modified B1alockTaussig shunt. This stenosis later was successfully reconstructed with a patch several months before a successful Fontan operation.

diastolic pressure and the presence or degree of mitral regurgitation may be defined. The size of the pulmonary outflow tract may also be demonstrated (Fig. 5), as can the size and location of the atrial septal communication. Pressure and oxygen saturation data are characteristic: there is a prominent A-wave in the right atrium and a right-to-Ieft shunt across the atrial septum. Because complete admixture of the pulmonary and systemic venous returns occurs in the left atrium, nearly identical oxygen saturations are found in the left ventricle, right ventricle, and great arteries. An obstructive atrial septal defect may be demonstrated by a large pressure gradient across the atrial septum (gradient greater than 3 torr).

Figure 5. Left ventricular angiogram, left anterior oblique projection. The three potential levels of pulmonary stenosis are demonstrated here: small outlet foramen (ventricular septal defect, arrow); infundibular stenosis (open arrow); pulmonary valvular stenosis (arrowhead).

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PALLIATIVE SURGERY An operation is available to separate the two circulations, the Fontan procedure. Because of the requirement for low pulmonary vascular resistance, the Fontan procedure cannot be done in early infancy; palliative operations may be needed for patients with insufficient pulmonary blood flow, excessive pulmonary blood flow, or inadequate interatrial communication. Reduced Pulmonary Blood Flow Most patients with tricuspid atresia have inadequate pulmonary blood flow. Palliation can be provided by increasing the pulmonary blood flow, which can be accomplished in several ways. Newborns with severe cyanosis can be resuscitated and temporarily palliated by continuous infusion of prostaglandin El (0.05 to 0.1 p,g per kg per min) to maintain patency of the ductus arteriosus. 49 When the patient has stabilized hemodynamically, a surgical shunt can be carried out electively. The operation most widely used to increase pulmonary blood flow is the Blalock-Taussig shunt, either in its classic form 4 (subclavian artery divided and anastomosed end-to-side to the ipsilateral pulmonary artery), or in a modified form 45 (polytetrafluoroethylene [PTFE] graft between a subclavian artery and a pulmonary artery). The mortality risk of this procedure in patients with tricuspid atresia should be less than 10 per cent. Palliation is very good, usually resulting in arterial oxygen saturation of approximately 85 per cent. The advantage of the Blalock-Taussig over other kinds of shunts is that pulmonary blood flow is limited by the diameter of the subclavian artery, so congestive heart failure due to excessive flow is rare. Decreased growth of the ipsilateral arm occurs,l1 but is rarely severe and tissue loss due to ischemia of the arm is rare 27 (less than 1 per cent of cases). Unfortunately, adverse anatomic and physiologic consequences of any shunt may increase the risk of a future Fontan operation. These effects include stenosis of the pulmonary artery at the shunt site, increased pulmonary vascular resistance due to increased pulmonary blood flow or thrombosis of pulmonary vessels, and high left ventricular end diastolic volume and pressure. All of these problems are more likely to occur after a direct aorta to pulmonary artery anastomosis because of difficulty in achieving accurate shunt size, l additional reasons for the preference of the Blalock-Taussig shunt. The cavopulmonary anastomosis (Glenn shunt) may also be used to palliate tricuspid atresia. In this procedure, the superior vena cava is separated from the right atrium by ligation or division and is connected to the divided distal end of the right pulmonary artery29 (classic shunt) or to the side of the right pulmonary artery31 (modified shunt). This anastomosis leads to an obligatory flow of the superior vena caval return through the pulmonary capillary bed. Because pulmonary vascular resistance is normally very low, the superior vena caval pressure rises only a few torr after the shunt. The major advantage of cavo-

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pulmonary anastomosis is that there is no volume load on the ventricles, so left ventricular function is well preserved; pulmonary hypertension occurs rarely. Problems that may be associated with this anastomosis are superior vena cava syndrome immediately postoperatively, and late clinical deterioration with increasing cyanosis. The latter may be related to ventilation-perfusion imbalances induced by the shunt,43 development of pulmonary arteriovenous fistulae, 7 development of collaterals from superior vena cava to inferior vena cava which decreases pulmonary blood flow,39 and increasing pulmonary vascular resistance due to the high viscosity associated with polycythemia. 43 Mortality after this operation is higher in young patients, so it should not be done in young infants. Although there are no good data to support the conjecture, it now seems likely that a patient who can tolerate a cavopulmonary anastomosis can probably tolerate a Fontan operation. For the reasons cited above, a cavopulmonary shunt is not often used in the treatment of tricuspid atresia. Restrictive Atrial Septum All the systemic venous return must cross the atrial-septal communication. If this communication is small, signs of right heart failure appear that include peripheral edema, distended and pulsatile neck veins, and hepatomegaly. In addition to these clinical findings, laboratory findings may include very large P waves on electrocardiogram, and markedly enlarged right atrium on chest radiographs. The echocardiogram is definitive in demonstrating the small diameter of the atrial septal defect, and in estimating the interatrial pressure gradient by DOfpler detection. 25 If right heart failure is severe, balloon septostomy5 at cardiac catheterization may be effective in children under 1 month of age, and blade septostomy may be used in older children. 50 Surgical creation of an atrial septal defect3 may be done if catheterization measures fail. A mildly obstructive atrial septal communication without signs of important right heart failure may not require enlargement. Unrestricted Pulmonary Blood Flow Unrestricted pulmonary blood flow is seen in less than 20 per cent of cases of tricuspid atresia. The small number of these patients who have congestive heart failure can usually be treated successfully by medical means. A few patients, however, may require surgical treatment because of severe congestive heart failure. Banding of the pulmonary artery has been the procedure of choice for many years. 46 Banding leads to decreased pulmonary blood flow, decreased volume overload of the left ventricle, and improvement of congestive heart failure. Pulmonary artery banding, however, may be associated with anatomic and physiologic changes that increase the risk of a future Fontan operation. Banding may not completely protect against the development of pulmonary vascular obstructive disease and increased pulmonary vascular resistance. 34 Stenosis of branch pulmonary arteries

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often occurs which is a significant risk factor. Subaortic muscle, like the outlet foramen in patients with transposed great arteries, may become increasingly obstructive after banding. This subaortic obstruction, which may be subtle and difficult to detect by either Doppler echocardiography or catheterization, leads to increasing ventricular hypertrophy with decreasing ventricular diastolic compliance. 23 These two problems are important mortality risk factors for the Fontan operation. To avoid the problems engendered by banding, it may be reasonable for patients with tricuspid atresia or other forms of single ventricle who have subaortic muscle (double-outlet ventricle or transposed great arteries) to undergo a more extensive palliative operation33 : division of main pulmonary artery, anastomosis ·of its proximal end to the side of the ascending aorta (bypassing the subaortic obstruction), and establishing limited pulmonary blood flow with a 4-mm PTFE aortopulmonary shunt.

THE FONTAN OPERATION Since Harvey's epochal studies of the circulation in the seventeenth century, we have known that two ventricles are required as circulatory pumps: a right ventricle for the pulmonary circulation, and a left ventricle for the systemic circulation. Radical reorientation of this belief was required to bring tricuspid atresia into the category of correctable heart malformations. This conceptual leap was made by Fontan in 1971, when he reported three patients with tricuspid atresia in whom the right atrium was connected directly to the pulmonary arteries, and the two circulations were completely separated. 20 After this procedure, systemic venous return directly entered the pulmonary circulation, and the sole ventricle pumped pulmonary venous return to the body. A ventricular pump was not needed for the pulmonary circuit because pulmonary vascular resistance is normally so low that a difference of only 4 to 6 torr between mean pulmonary arterial and left atrial pressure is needed for the systemic venous return to traverse the pulmonary capillary bed. In the 18 years since Fontan demonstrated that this principle may be clinically successful, it has been applied to a wide variety of malformations in which there is only one functional ventricle. A successful outcome of Fontan's procedure requires that flow pathways throughout the circulation be unobstructed, and that both systolic and diastolic ventricular muscle function is nearly normal. The outcome of this operation is closely related to selection criteria. The Fontan procedure is contraindicated if pulmonary vascular resistance exceeds 4 units·m 2 , if severe hypoplasia of the pulmonary arteries is present, and if the patient is a young infant (pulmonary vascular resistance is high early in infancy). There are additionally a number of relative contraindications (Table 1). Patients who are between 1 and 2 years of age may safely undergo a Fontan operation only if all the other anatomic criteria are met because young children do not

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Table 1. Selection Criteria Absolute contraindications Early infancy PVR > 4 units' m 2 Severe hypoplasia of PAs Relative contraindications Age < 1-2 years Rp 2-4 units' m 2 Ppa> 15mm Hg LVEDP> 15 mm Hg Previous P A band Severe LV hypertrophy Moderately stenotic or deformed PAs Mitral insufficiency

tolerate high systemic venous pressures as well as older children. 44 If the pulmonary vascular resistance is 2 to 4 units·m2 , a child over the age of2 years may undergo a Fontan operation. Mean pulmonary artery pressure greater than 15 mm Hg is probably acceptable if the elevation is due to high levels of pulmonary blood flow that will be reduced by a corrective operation. 4 , 44 Left ventricular end-diastolic pressure greater than 15 mm Hg suggests left ventricular dysfunction and may contraindicate a Fontan operation, but if it is associated with a large volume overload (which it often is), these high end diastolic pressures may decline to normal levels immediately after a corrective operation.41 It has been found recently that severe left ventricular hypertrophy is a substantial risk factor for the Fontan operation, whether it is associated with left ventricular volume overload, subaortic obstruction, or pulmonary artery band. 36 A Fontan operation may safely be carried out in the presence of stenotic or deformed pulmonary arteries, provided these stenoses can be relieved at the time of corrective surgery .41,44 Mitral insufficiency is also acceptable, ifit can be relieved by valvuloplasty or valve replacement at the time of surgery. The Operation Itself The goals of the Fontan operation are to close all communications between the right and left heart and to connect the venae cavae with the pulmonary arteries. 59 There are certain critical technical requirements in achieving these goals. The pathway from the venae cavae into the pulmonary arteries must be widely open. The total cross-sectional area of the pulmonary arteries must be adequate; therefore, stenoses or deformities of the pulmonary arteries must be relieved at the time of operation. Because postoperative pulmonary artery pressure will vary directly with pulmonary venous pressure, pulmonary venous pressures must be kept low by insuring good preservation of left ventricular function during the operation, and assuring that mitral valve function is normal, or nearly so. All intracardiac shunts must be closed,

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including surgical shunts that were created for palliation, and all atrial septal and ventriculopulmonary communications. Many variations in operative technique have been used since Fontan's original operation. An example of a currently used operation for tricuspid atresia with transposed great arteries (Fig. 6) is illustrated. Several other modifications are being widely used. Postoperative Management There is no pump for the pulmonary circuit, and cardiac output depends entirely on pulmonary blood flow so the physiologic approach

B Figure 6. A variant of the Fontan operation in a patient with tricuspid atresia and associated transposition of the great arteries (aorta cut away to show details of operation). A, The main pulmonary artery is divided, and the opening is extended into the right pulmonary artery behind the superior vena cava. The superior vena cava is divided, and the incision is extended into the base of the right atrial appendage. B, The proximal stump of the main pulmonary artery has been oversewn, the upstream end of the superior vena cava has been anastomosed to an opening in the right pulmonary artery, and the atrial septal defect has been closed with a patch. C, The large opening in the pulmonary artery has been sewn to the large opening in the superior vena cava and right atrium. Now, both the inferior and superior venae cavae drain directly into the pulmonary arteries, and no communications remain between the right and left sides of the heart.

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to management of patients who have just undergone a Fontan operation must focus on maintaining pulmonary blood flow. 58 The following formula describes the relations between flow, pressure, and resistance:

Q = p

P pa -

PIa

Rp

In the early postoperative period, cardiac output (Qp) can be increased by several maneuvers affecting these variables. The pulmonary artery pressure (P pa) can be increased by increasing the blood volume. The left atrial pressure (Pia) can be decreased by improving left ventricular function through use of inotropic agents like dopamine, and after-unloading agents like nitroprusside or amrinone. Normal sinus rhythm may maintain a low left atrial pressure, so using atrioventricular sequential pacing may be helpful for a patient not in sinus rhythm. Finally, the pulmonary vascular resistance (Rp) can be kept low by hyperventilation (hypocarbia and alkalosis are potent pulmonary vasodilators) and hemodilution (hematocrit around 30 per cent). The most common problem after a Fontan operation is fluid retention. The reasons for the pleural or pericardial effusions that usually accompany the Fontan operation are not entirely clear but probably are related to the general inflammatory response to cardiopulmonary bypass, and to the elevated systemic venous pressure that is always a consequence of the Fontan operation (right atrial pressure in the early postoperative period is usually 12 to 18 mm Hg). Whatever the cause, nearly all patients after a Fontan operation have pleural effusions that require from several days to several months of pleural drainage. In some patients, the pleural drainage gradually becomes chylous after a few days. Persistent effusions lasting more than 3 weeks are seen in 30 to 40 per cent of patients. 6 Pleural effusions can sometimes be controlled by intermittent thoracentesis but usually require continuous chest tube drainage until the effusion stops. Chylous effusions may be treated in the same way as serous effusions. In addition, it is usual practice to institute a low-fat, mediumchain triglyceride diet; the benefit of this diet has not been well documented. In persistent cases, thoracic duct ligation may control chylous effusions, but a pleuroperitoneal shunt47 may be a simpler and effective way to treat persistent effusions. Pericardial effusions may be treated with intermittent pericardiocentesis. Recurrence after two or three pericardiocenteses, however, suggest the need for a pericardial window, and this may occur in 10 per cent of patients. 6 Pericardial window usually controls the pericardial effusion. Any patient who has persistent pleural or pericardial effusion should undergo recatheterization; nearly half these patients may be found to have a correctable cause of their effusions. 2 Postoperative Results The operative mortality rate is closely related to selection criteria. For patients who are ideal candidates, the mortality rate is less than 5

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per cent. 21 ,32 The risk of the operation increases with an increasing number of risk factors 41 ,44 and may be as high as 20 to 30 per cent. 36 Perioperative mortality is usually related to compromised pulmonary blood flow, residual shunts, or inadequate cardiac output. Late mortality is approximately 10 per cent of survivors, usually occurs in the first 5 years after operation, and is most often related to residual obstruction or intracardiac shunts 59 (Fig. 7). Thrombus in the right atrium or pulmonary artery is a particularly dangerous late complication, often fatal. The thrombi may be treated by surgical excision,17 or treated with streptokinase. 13 They may be associated with protein-losing enteropathy. Protein-losing enteropathy is associated with chronic diarrhea and hypoalbuminemia, as well as generalized edema. The mechanism of this complication is probably related to the higher-than-normal systemic venous pressure, resulting in increased lymph production in the drainage area of the inferior vena cava and obstruction to lymph drainage because of high pressure in the superior vena cava and thoracic duct. 30 Consequent intestinal lymphangiectasia may lead to loss of albumin, lymphocytes, and immunoglobulin into the gastrointestinal tract, thus leading to the hypoalbuminemia, generalized edema, and immunologic abnormalities associated with this disorder. Interestingly, high superior vena caval pressure is probably a more important etiologic factor than high inferior vena caval pressure, because proteinlosing enteropathy has not been seen in patients with isolated inferior vena caval hypertension, but has been described in patients with isolated superior vena caval hypertension. 30 Treatment of this disorder is with a supplementary low-fat, medium-chain triglyceride diet, which may not cause improvement for several months. If the patient shows no progress after several months on this diet, insertion of inflow valves between the venae cavae and the right atrium has been beneficial in a few cases. 9 Arrhythmias occur commonly after Fontan procedures. The actuarial incidence of supraventricular tachycardia is approximately 25 per cent 5 years after operation, and is 37 per cent at 7.5 years. 52 Arrhythmias are sometimes fatal in the late postoperative period, especially if they occur when atriopulmonary obstruction is present. 28

Other Figure 7. Causes of late mortality. These complications are often caused by obstruction at some point between the venae cavae and the pulmonary arteries, or by residual intracardiac shunts.

Right heart failure

Ventricular failure

Sudden death, arrhythmias

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Hospital mortality Late mortality

NYHA III-IV

Figure 8. The outcome of the Fontan operation relates closely to selection of patients for operation. The hospital mortality rate ranges from fewer than 5 to over 20 per cent, depending on the number and severity of risk factors. Among late survivors, 92 per cent are in class I or II. (Key: NYHA = New York Heart Association.)

Cerebral infarction has been reported late after Fontan procedures. This event may be associated with arrhythmias, thrombocytosis, or congestive heart failure. 42 Reoperation for residual intracardiac lesions is required for approximately 15 per cent of patients after a Fontan operation, most commonly in the first year after operation. Reoperation may be needed for obstructed atriopulmonary communication (particularly neointimal proliferation in a Dacron conduit), a residual shunt, a dehisced patch, subaortic stenosis, or increasing insufficiency of an atrioventricular valve.B, 22, 36, 40 Patients who survive the operation generally do very well. Ninetytwo per cent are in New York Heart Association class I or II (Fig. 8), and ninety-seven per cent attend school or work at a regular job. 32 Most are on no medications. The first patient to have a Fontan operation underwent the procedure in 1968. Twenty years later, this patient is married and carries out the usual activities of a housewife. 22 Patients who have undergone a Fontan operation have singular physiology. The right atrial pressure is higher than in a normal heart, and the pulmonary blood flow is less pulsatile. The early postoperative period is fraught with dangers that are related to preoperative anatomy and physiology and the peculiarities of the new physiology of these patients. Nevertheless, the survival rate is high, and among the longterm survivors, clinical functioning of the patient is very good, at least for 10 to 15 years of follow-up. As our understanding of the physiologic derangements induced by this operation improves, it is likely that early postoperative problems will become fewer, and a greater variety of patients with only one ventricle will be treated with operations based on the Fontan principle.

REFERENCES 1. Arciniegas E, Farooki ZQ, Hakimi M, et al: Results of two-stage surgical treatment of

tetralogy of Fallot. J Thorac Cardiovasc Surg 79:876, 1980 2. Am GM, Chin AJ, Murphy JD, et al: Modified Fontan operation: correctable causes of low cardiac output, persistent pleural effusions, late onset effusions, and

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