The Fontan Procedure for Pediatric Tricuspid Atresia 

Updated: Mar 11, 2016
Author: Prema Ramaswamy, MD; Chief Editor: Jonah Odim, MD, PhD, MBA 

Overview

Background

The malformation of tricuspid atresia consists of a complete agenesis of the tricuspid valve with an absence of a direct communication between the right atrium and right ventricle. Tricuspid atresia is the third most common form of cyanotic congenital heart disease. It is also the most common cause of cyanosis with left ventricular hypertrophy.

The natural history of this condition is such that, without surgical intervention, only one third of patients survive to age 1 year and only 10% live to age 10 years.[1] The Fontan procedure, which was first performed in 1968 and then described in 1971, has changed the natural history dramatically and allowed survival into the third and fourth decades of life.[2]

History of the Procedure

The Fontan operation is named for Fontan, who was the first to describe an operation for patients with tricuspid atresia that could result in separate systemic and pulmonary circulations despite the absence of a ventricle, in this case, the right ventricle. Until that description, a pumping chamber was assumed to be essential to move the blood through the lungs. Although the Glenn operation, which involves the end-to-end anastomosis of the superior vena cava (SVC) to the right pulmonary artery, was described in 1958, it was primarily used as palliative surgery.[3] It was used to augment pulmonary blood flow as an alternate to the Blalock-Taussig shunt procedure. Patients remained cyanotic because the return from the inferior vena cava (IVC) still entered the heart and mixed with the pulmonary venous return. Moreover, the left ventricle continued to have the additional volume load of the IVC return.

Fontan was the first to completely bypass the right heart in a human subject and to channel both the IVC and SVC blood to the pulmonary arteries. He unsuccessfully attempted to bypass the right heart in healthy dogs. However, he reasoned that it may work in patients with tricuspid atresia because the right atrium is thicker and more muscular in humans than in canines and hence better able to perform a contractile function. He also believed that valved conduits were essential to prevent the blood from going in the opposite direction (ie, into the IVC). Therefore, he incorporated one valved homograft between the IVC and the right atrium and another valved homograft between the right atrium and the left pulmonary artery.

The final operation consisted of the classic Glenn SVC–to–right pulmonary artery operation as well as the right atrium–to–left pulmonary artery connection with the 2 homografts, as described. He published his results from the first three patients in 1971.[2]

Kreutzer et al (1973) offered a modification almost immediately.[4] They described a connection between the right atrial appendage and the main pulmonary artery accomplished by means of a pulmonary homograft or the patient's own pulmonary annulus but without a valved homograft at the IVC–right atrial junction. In this situation, the continuity of the pulmonary arteries is maintained.

Since these original articles were published, several other modifications have been described. These have greatly reduced the mortality and morbidity previously associated with tricuspid atresia. In addition, the Fontan-Kreutzer operation is applicable to all cardiac conditions where only a single functional ventricle is present.

Relevant Anatomy

The morphology of the atretic tricuspid valve is most often muscular but is occasionally an imperforate membrane. In rare cases, it is Ebstenoid, or it has no connection between the tricuspid valve and the right ventricle. Systemic venous blood entering the right atrium can exit the atrium only through an interatrial communication. In 80% of patients, this interatrial communication is a stretched patent foramen ovale. In most of the remainder, it may be a secundum atrial septal defect.

The right ventricle is small and hypoplastic when no ventricular septal defect is present. In the presence of a ventricular septal defect, the right ventricle may be better developed than it is without the defect, but even then it is smaller than normal. The most common ventricular septal defect in tricuspid atresia is muscular, but it is occasionally perimembranous.

Almost 100 years ago in 1906, Kuhne proposed a classification scheme for tricuspid atresia based on the great artery orientation.[5] Tandon and Edwards reevaluated and redefined this scheme in 1974, and this is the classification in general use at this time.[6] As mentioned before, this system is primarily based on associated anomalies.

The relationship of the great artery defines the type, as follows: Type I involves normally related great arteries, type II is D-transposition of the great arteries, and type III is L-transposition of the great arteries. The subtypes a, b, and c depend on the degree of pulmonary obstruction and, to a lesser degree, the presence of a ventricular septal defect. Subtype a is pulmonary atresia, b is pulmonic stenosis, and c is no pulmonary obstruction.

Type Ib is the most common; this is tricuspid atresia with normally related great arteries, a small ventricular septal defect, and pulmonic stenosis. Type I accounts for 80% of all cases, and type III is the rarest and responsible for 3-7% of all cases.

About 60% of patients with transposition of the great arteries may have additional cardiovascular abnormalities.[7] A persistent left superior vena cava (SVC) is seen in 15% of patients. Patients with tricuspid atresia, transposition of the great arteries, and large pulmonary flow (type IIc) are most likely to also have a coarctation of the aorta, hypoplasia of the aortic arch, and a patent ductus arteriosus. This is in contrast to patients with tricuspid atresia and normally related great vessels, an intact ventricular septum, or a small ventricular septal defect (type Ia or Ib). These patients tend to have a small patent ductus arteriosus and a large ascending aorta and isthmus. Juxtaposition of the atrial appendages is reported in 40% of patients with tricuspid atresia and transposition of the great arteries.[8]

Problem

The basic problem arises from the absent connection between the right atrium and pulmonary artery due to the absent tricuspid valve. Hence, the only egress to the blood entering the right atrium is into the left atrium through an interatrial communication. This combined venous return then enters the left ventricle and is pumped out into the aorta. Some of this blood finds its way into the pulmonary artery through a ventricular septal defect or a patent ductus arteriosus.

Pathophysiology

Because of the absence of the tricuspid valve and the lack of continuity between the right atrium and the right ventricle, venous blood returning to the right atrium can exit only by means of an intra-atrial connection. Because this situation leads to an obligate right-to-left shunt at the level of the atria, saturation of the left atrial blood is diminished, and hypoxia and cyanosis result.

The classification is discussed below. However, in the most common type (type Ib), left atrial blood enters the left ventricle and is pumped out into the aorta. Some of this blood may reach the lungs through a small ventricular septal defect or through a patent ductus arteriosus if the ventricular septum is intact. In most cases of tricuspid atresia, pulmonary blood flow is restricted, leading to reduced pulmonary venous return and hence additional cyanosis. In this scenario, the single left ventricle can easily handle the added volumes of the systemic and the pulmonary venous return.

On the contrary, in patients with tricuspid atresia, a large ventricular septal defect, and no pulmonic stenosis (type IIc or rare cases of type Ic), pulmonary blood flow is excessive. This can manifest as congestive cardiac failure early and predispose the patient to the pulmonary vascular disease late. Because of the large amount of pulmonary venous return, cyanosis may be difficult to detect. Also, this excessive pulmonary venous return can pose a volume burden on the single ventricle and contribute to congestive cardiac failure.

Etiology

The cause of tricuspid atresia is unknown. Although specific genetic causes of the malformation have not been determined in humans, data indicate that the FOG2 gene may be involved in the process. Mice in which the FOG2 gene is knocked out are born with tricuspid atresia.[9] The significance of this finding and its applicability in humans has yet to be defined.

Epidemiology

The true prevalence of the Fontan procedure for tricuspid atresia is unknown, but a rate reported in clinical studies was approximately 1.5%. An autopsy series revealed a prevalence of approximately 3%.[10] The calculated incidence is 1 case per every 10,000 live births. No sex dominance is known, and girls and boys are almost equally affected.

Presentation

Tricuspid atresia is usually detected in the neonatal period. Cyanosis is the most prominent feature, and this is due to the obligate intracardiac right to left shunt. However, the amount of pulmonary venous return modulates this sign. Cyanosis is most prominent in patients with restricted pulmonary blood flow (type Ib) and least noticeable in those with excessive pulmonary blood flow (types I and IIc). In the latter group, symptoms of congestive heart failure and pulmonary edema predominate. Examples are feeding and breathing difficulties, frequent respiratory infections, and growth failure. Clinical signs include tachypnea, tachycardia, and an enlarged liver.

Hypoxic-cyanotic spells may occur in infants with tricuspid atresia and diminished pulmonary blood flow, similar to those seen in tetralogy of Fallot. These episodes are potentially life-threatening and are indications for surgery.

Polycythemia is a consequence of the cyanosis and, as in other conditions with cyanosis, cerebrovascular accidents are a risk in infants with iron deficiency anemia. In older, nonsurgically treated children, brain abscesses may occur because the filtering function of the lungs is no longer operational in the presence of a right-to-left intracardiac shunt. These are uncommon at this time because children with tricuspid atresia undergo the Fontan procedure typically around age 2-4 years; this effectively separates the systemic and the pulmonary circulations.

The combination of cyanosis, polycythemia, and the artificial material used for modified Blalock-Taussig shunts predispose older patients receiving surgical palliation to bacterial endocarditis.

Indications

The treatment for tricuspid atresia is predominantly surgical. Because one of the requirements for a Fontan procedure is low pulmonary vascular resistance, this operation cannot be performed in neonates. Hence, an interim palliative procedure may be needed depending on the amount of pulmonary blood flow. Most infants with tricuspid atresia have restrictive pulmonary blood flow. Therefore, after initial medical stabilization is achieved with intravenously administered prostaglandin 1 (PGE1), the first surgical intervention is palliative pulmonary-to-systemic anastomosis to increase pulmonary blood flow and to improve systemic oxygenation. These aims are achieved by using a modified Blalock-Taussig shunt, which is a small polytetrafluoroethylene (PTFE) graft to connect the subclavian artery and a pulmonary artery.

In those few patients with no pulmonary obstruction, a pulmonary artery band may initially be required to prevent the onset of pulmonary vascular disease.

In patients with a balanced circulation secondary to pulmonary obstruction that is not severe, no immediate intervention may be required at birth. However, they may undergo a bidirectional Glenn procedure after about age 3 months, by which time the pulmonary vascular resistance decreases to low levels. This procedure is essentially an anastomosis between the SVC and the pulmonary artery. One of the major advantages of this procedure is that it results in volume unloading of the left ventricle. Early volume unloading improves exercise capacity in preadolescents with the Fontan procedure.[11] Furthermore, this may serve as a first stage for subsequent surgery involving total cavopulmonary anastomosis (ie, modified Fontan procedure).

Choussat et al (1977) delineated selection criteria to define an ideal candidate for a Fontan procedure.[12] They described the 10 following criteria, which are occasionally and facetiously referred to as the 10 commandments for an ideal Fontan operation.

  • Age older than 4 years

  • Sinus rhythm

  • Normal systemic venous return

  • Normal right atrial volume

  • Mean pulmonary artery pressure less than 15 mm Hg

  • Pulmonary arteriolar resistance less than 4 Wood units/m2

  • Pulmonary artery–aorta ratio more than 0.75

  • Left ventricular ejection fraction more than 0.60

  • Competent mitral valve

  • Absence of pulmonary artery distortion

Due to the several modifications of the operation that have followed its initial description, the absence of most of the above criteria is regarded as only relative contraindications. Current absolute contraindications are a pulmonary vascular resistance above 4 Wood units/m2, severe hypoplasia of the pulmonary arteries, and severe diastolic dysfunction of the left ventricle.

Contraindications

The Fontan operation has only a few absolute contraindications at this time: pulmonary vascular resistance more than 4 Wood units/m2, severe hypoplasia of the pulmonary arteries, and severe diastolic dysfunction of the left ventricle.

The age at which a Fontan is performed has been steadily lowered, and several centers perform it at age 2 years or even younger in patients with good anatomy and physiology.[13] The advantage of performing a Fontan operation at an early age is improving oxygenation, which may enhance somatic growth and neurodevelopmental outcomes. It also reduces the volume load on the single ventricle.

 

Workup

Laboratory Studies

CBC count

Determine if the patient has concomitant iron deficiency anemia because this, in the presence of cyanosis and polycythemia, can increase the risk of a cerebrovascular accident in an infant.

Thrombocytopenia is not uncommon in an older child with cyanosis.

Test of prothrombin time and activated partial thromboplastin time

The results may be abnormal because of polycythemia.

Serum electrolytes and liver function tests

Results may be abnormal because of medical therapy administered to treat congestive heart failure.

ABG analysis

This is a critical test in a cyanotic newborn to confirm hypoxia.

Moreover, when this test is repeated after 100% oxygen is administered over 10 minutes, it helps in differentiating cardiac causes of cyanosis from the common pulmonary ones. In the former situation, the partial pressure of oxygen (PO2) does not exceed 150 torr because of the obligate right-to-left shunt. This has been termed the hyperoxia test.

Imaging Studies

Chest radiography

Chest radiography is typically not helpful in diagnosing tricuspid atresia. In most patients, pulmonary vascular markings are diminished because of decreased pulmonary blood flow.

A right aortic arch is less common in tricuspid atresia than in tetralogy of Fallot, and it is seen in only 3-8% of patients.[7]

Electrocardiography

This is a useful test and helps narrow the differential diagnosis in a cyanotic newborn. The other 2 cyanotic heart diseases that are more common than tricuspid atresia (ie, tetralogy of Fallot and transposition of the great arteries), involve right ventricular hypertrophy. By contrast, tricuspid atresia involves left ventricular hypertrophy.

The typical ECG in tricuspid atresia demonstrates left ventricular hypertrophy and a superior left axis. Enlarged P waves suggestive of right atrial enlargement are also common.

Echocardiography

This is the primary modality for the diagnosis of tricuspid atresia. An echo-bright shelf is in the position the tricuspid valve normally occupies. Two-dimensional echocardiography can define the size and location of the chambers, great vessels, and the atrial and ventricular septal anatomy. Associated abnormalities, such as a left superior vena cava (SVC), juxtaposed atrial appendages, subaortic stenosis, and coarctation of the aorta, can also be well documented.

Blood-flow characteristics can be quantitated by using pulse and continuous-wave and color-flow Doppler methods. The pressure gradients across stenotic orifices, valves, and septal defects can be determined by using these techniques.

Fetal diagnosis is feasible and alters the outcome because of elective termination of a pregnancy.[14]

MRI

Although MRI is not used as ubiquitously as echocardiography in diagnosing tricuspid atresia, the advantages of MRI are improved delineation of extracardiac structures, such as the pulmonary artery anatomy, especially in older children.

Cardiac MRI might replace the role of cardiac catheterization before the stages of a Fontan surgery.[15]

Diagnostic Procedures

In neonates, cardiac catheterization is almost never required any longer as echocardiography offers excellent details of the intracardiac anatomy. In rare cases, in the presence of a restrictive atrial septal defect it may be used to perform a balloon septostomy.

The current role of cardiac catheterization is primarily to assess the anatomy and the resistance of the pulmonary vascular bed before a bidirectional Glenn (or hemi-Fontan) operation, which is based on the similar principle of directing blood in the SVC to the pulmonary arteries. Catheterization is also performed before the modified Fontan procedure is completed. With improvements in cardiac MRI, even this role has been challenged as being unnecessary in most patients.[15]

In older children and adolescents, arteriography is used to define details important to surgical management, including the following:

  • Number and relationship of the vena cavae

  • Size of the pulmonary arteries

  • Pulmonary artery vascular resistance

 

Treatment

Medical Therapy

Immediate therapy for newly diagnosed tricuspid atresia in a neonate depends on the degree of pulmonary blood flow. After the patient's airway and circulation are initially stabilized, the next priority is to determine the amount and stability of the pulmonary blood flow.

Neonates with either no or only tenuous forward flow across the pulmonic valve must be immediately given an intravenous infusion of prostaglandin 1 (PGE1), which relaxes the ductus and hence keeps it open. An important adverse effect of this drug is apnea, and intubation may be needed. The infusion of PGE1 drip is continued until palliative surgery in the form of modified Blalock-Taussig shunting is performed (usually in a few days).

Neonates with no pulmonary obstruction may develop signs of congestive cardiac failure within weeks. They benefit from anticongestive medications, such as furosemide, followed by a pulmonary artery band.

The risk of bacterial endocarditis and thromboembolism must be minimized. The former is done by inculcating good oral hygiene practices and by antibiotic prophylaxis prior to dental, GI, or urinary procedures. The latter is accomplished by ensuring a lack of iron deficiency anemia.

Myocardial function and integrity of the pulmonary vasculature must be preserved to optimize conditions for a Fontan operation. A recent report of 8 patients demonstrated an improvement in the clinical and hemodynamic status of patients with an elevated pulmonary vascular resistance with Bosentan. These patients were then able to undergo the Fontan operation.[16]

Surgical Therapy

As mentioned before, the Fontan operation cannot be performed in the neonatal period because of high pulmonary vascular resistance. Hence, palliative surgery is initially required.

Most infants have restricted pulmonary blood flow. For these patients, a modified Blalock-Taussig shunt procedure is the most common first operation. This consists of a small polytetrafluoroethylene (PTFE) tube graft, which typically measures about 3.5 mm in diameter in a term infant. This graft connects one of the subclavian arteries to the pulmonary artery to ensure controlled pulmonary blood flow and adequate oxygenation for a few months. See the image below.

Polytetrafluoroethylene (PTFE, Gore-Tex; W. L. Gor Polytetrafluoroethylene (PTFE, Gore-Tex; W. L. Gore & Associates, Newark, DE) patch used to fashion the lateral tunnel in the Fontan operation.

A possible complication of the shunt is stenosis and distortion of the pulmonary artery at the site of shunt insertion. It also adds to the volume load on the left ventricle.

Within a few months, treated infants outgrow their shunts and become increasingly cyanotic. Although some centers opt to complete the Fontan procedure at this time, the most common treatment is to perform a procedure that, although still palliative, can serve as a stage for the final completion. This operation is a bidirectional Glenn or a hemi-Fontan procedure. The principles in both are similar and involve a superior vena cava (SVC) to pulmonary artery anastomosis. The former operation consists of an end-to-side anastomosis between the cranial end of the SVC and the undetached right pulmonary artery near the bifurcation. This results in blood flow from the SVC into both the pulmonary arteries. The cardiac end of the SVC is ligated. In the hemi-Fontan, both the cranial and cardiac ends of the SVC are sutured to the superior and inferior surfaces of the right pulmonary artery. See the image below.

Hemi-Fontan procedure. Hemi-Fontan procedure.

Both of these operations result in volume unloading of the left ventricle, which has implications for the long-term function of the single left ventricle. Hence, the timing of this surgery is crucial, and it is commonly performed at age 4-8 months. The Blalock-Taussig shunt is ligated at the time of this surgery.

Neonates with increased pulmonary blood flow may present with severe congestive heart failure. Pulmonary artery banding may be required within a couple of months to decrease blood flow to the lungs and to ensure low pulmonary vascular resistance. These infants are also candidates for the bidirectional Glenn operation after about age 4 months.

In neonates with adequate oxygenation but enough pulmonic stenosis to protect the pulmonary vascular bed, no immediate operation is required. These patients can undergo the bidirectional Glenn operation as the first palliative procedure at about age 4 months. Infants who have undergone bidirectional Glenn surgery are still cyanotic because the inferior vena cava (IVC) return mixes with the pulmonary venous return. These infants typically have an oxygen saturation in the 85% range, immediately after surgery, but this soon decreases with the growth of the child, which subsequently reduces the portion of the venous return that the SVC contributes.

Venous return from the SVC is reported to be a maximum of 55% at age 2.5 years and then steadily decreases.[17] This accounts for the increasing cyanosis after this age. The recurrence of cyanosis, progressive polycythemia, and decreasing exercise tolerance indicate the need for completion of the Fontan procedure.

The outcome of the Fontan procedure requires unobstructed flow pathways and near-normal ventricular function. As mentioned before, only a few absolute contraindications to the operation remain, and the originally prescribed age of older than 4 years is no longer one of them. Several groups have reported good results in children as young as age 1 year.[13] However, most patients are aged 18-24 months old. Candidates most suitable are those with adequate and nonstenotic pulmonary arteries with a normal pulmonary vascular resistance, a normal sinus rhythm, normal mitral valve function, and good systolic and diastolic function of the left ventricle.

The principle of the Fontan operation is to connect both vena cavae to the pulmonary artery by bypassing the right ventricle. As Fontan originally described, it involved classic Glenn shunting (end-to-end SVC-to–right pulmonary artery anastomosis), a connection of the right atrium to the left pulmonary artery, and the interposition of 2 valved homografts (one between the IVC and the right atrium and one between the right atrium and the left pulmonary artery). See the images below.

Bidirectional Glenn procedure. SVC = superior vena Bidirectional Glenn procedure. SVC = superior vena cava.
Completion of the bidirectional Glenn operation. S Completion of the bidirectional Glenn operation. SVC = superior vena cava.

Since then, numerous other modifications have been proposed. One such modification, the atriopulmonary connection, was in wide use until it was abandoned. In this technique, the right atrial appendage was connected to the main pulmonary artery without any valved homografts. However, it resulted in severe dilatation of the right atrium and was accompanied by frequent atrial arrhythmias and serious thromboembolic complications.

The 2 modifications in current use are the lateral tunnel Fontan procedure and an extracardiac conduit between the IVC and the central pulmonary artery. Puga et al (1987) and the Boston group described modifications leading to the development of the lateral tunnel Fontan procedure to reduce the risk of pulmonary venous obstruction.[18, 19] These resulted in the atrial pathway being reduced to a lateral wall.

Lateral-tunnel Fontan procedure. Lateral-tunnel Fontan procedure.
Extracardiac Fontan operation. Extracardiac Fontan operation.

deLeval et al (1988) performed hydrodynamic studies in an atriopulmonary Fontan model and concluded that streamlining of blood flow would be beneficial.[20] They proposed a total cavopulmonary connection. As they described it, the operation consists of 3 parts: (1) end-to-side anastomosis of the SVC to the undivided right pulmonary artery, (2) construction of a composite intra-atrial tunnel with the use of the posterior wall of the right atrium, and (3) use of a prosthetic patch to channel the IVC to the enlarged orifice of the transected SVC that is anastomosed to the main pulmonary artery. Advantages they cited were that this is technically simple and reproducible in any atrioventricular arrangement and that it is performed away from the atrioventricular node. Also, most of the right atrial chamber remains at low pressure, which reduces the risk of early or late arrhythmias, and the reduction of turbulence prevents energy losses and should minimize the risk of atrial thrombosis.

Marcelleti in Italy and Laschinger et al in the United States first described the extracardiac conduit modification.[21, 22] The proposed advantages were the lack of requirement of aortic cross clamping; the absence of atriotomy; and the interatrial suture lines, which may decrease the late risk of arrhythmias and the risk of interatrial obstruction from the baffle.

Another notable advance in Fontan surgery was the surgical creation of a fenestration or a restrictive atrial septal defect, which allows communication between the 2 circulations and which helps maintain cardiac output at the expense of some cyanosis and hypoxemia.[23] It may substantially ameliorate postoperative pleural and pericardial effusions and low cardiac output. Although it was initially proposed for candidates considered to be at high risk, one study demonstrated that fenestration at the time of modified Fontan surgery improves short-term outcomes in standard-risk patients by decreasing pleural drainage, hospital length of stay, and the need for additional postoperative procedures.[24]

Preoperative Details

Detailed anatomic and hemodynamic assessment is necessary to decide on the patient's surgical care. Study of the systemic venous drainage is necessary. A careful search for a left SVC is important. The morphology and size of the right atrium must be ascertained.

A horizontal orientation of the atrial septum can lead to the diagnosis of a left juxtaposition of atrial appendage. Recognition of this anomaly is of clinical importance because the mouth of the juxtaposed atrial appendage could be confused to be an atrial septal defect.

The outlet chamber and its size and pressures must be assessed to determine if the ventricular septal defect is restrictive and if the pulmonary artery is stenotic. Of paramount importance is the size of the pulmonary artery and the pulmonary artery pressures because these are critical for a successful Fontan operation. The main ventricular chamber must be of adequate size. Therefore, study of the main chamber is warranted to assess its volume, contractility, and compliance, as well as function of the arteriovenous valve.

Intraoperative Details

The approach for intracardiac repair for tricuspid atresia is a median sternotomy incision made by using hypothermic cardiopulmonary bypass with cold cardioplegia. Systemic-to–pulmonary artery shunts are occluded when perfusion begins. The arterial blood is returned through the ascending aorta, and the venous blood is drained from the venous cannula directly inserted into the vena cavae. During the various stages of the Fontan operation, several authors speak of the importance of preserving the contractile and rhythmic function of the right atrium. Care must be taken to preserve the eustachian valve of the IVC.

In the lateral tunnel Fontan operation, a baffle is placed in the right atrium to convey IVC blood along the lateral wall of the right atrium to the SVC orifice. This baffle, which is fashioned from a PTFE (Gore-Tex; W. L. Gore & Associates, Newark, DE) tube graft is sutured to the lateral wall of the right atrium; this forms the lateral tunnel. If required, the baffle has a 4-mm fenestration punched into it. To complete the cavopulmonary anastomosis, the segment of the SVC still attached to the heart is connected in an end-to-side fashion to the undersurface of the right pulmonary artery. An alternate way to perform this step is by making an incision in the atrium in the region of the baffle, which can be connected to the pulmonary artery to complete the cavopulmonary anastomosis. An important consideration at this stage is to avoid compression of the pulmonary veins.

deLeval and colleagues have suggested that energy losses are minimized in a lateral tunnel Fontan procedure. Jonas et al (1988) pointed out its other advantage is that it minimizes the risk of the systemic venous pathway obstructing the pulmonary venous pathway.[19]

Over the last 10 years, interest in performing extracardiac Fontan surgery has increased. The goal is minimizing the atrial suture load, which may ultimately preserve atrioventricular synchrony and normal sinus rhythm in the long run. The latter goal is far from firmly established.

The extracardiac cavopulmonary anastomosis is also performed through a median sternotomy incision. In this variation, the IVC is transected at its entrance into the right atrium and a 22-mm to 24-mm PTFE (Gore-Tex; W. L. Gore & Associates) tube graft is interposed end-to-end between the IVC and the inferior surface of the right pulmonary artery. Here, a fenestration takes the form of a small tube graft interposed between the conduit and the right atrial appendage.

Modified ultrafiltration has also shown to be effective in reducing length of stay and duration of chest tube drainage.

Postoperative Details

It has been known since the early operations that fairly high atrial filling pressures (often a mean of >15 mm Hg) are required to maintain adequate cardiac output. The left atrial pressure can be decreased by improving left ventricular function with inotropes, such as dopamine, and with afterload reducing agents, such as milrinone. Pulmonary vascular resistance must be kept low. Therefore, every attempt must be made to maintain adequate oxygenation (PO2 >80 mm Hg), hypocarbia (PCO2< 40 mm Hg), and drug therapy to maximize pulmonary arterial dilatation. Atelectasis should be avoided at all costs. Early extubation improves pulmonary blood flow by reducing pulmonary end-expiratory pressure (PEEP).

The most common problem in the immediate postoperative period after a Fontan is the appearance of pleural and pericardial effusions. This is probably due to a combination of elevated systemic venous pressure and a general inflammatory response to cardiopulmonary bypass. Fenestration of the Fontan circuit, an idea a group at the Children's Hospital of Boston first proposed, dramatically decreased the incidence of pleuropericardial effusions from almost 40% to less than 13%.[23] Data from one study confirmed a reduction of days of hospital stay and effusions not only in high-risk patients but also in standard-risk patients.[24]

Follow-up

Close follow-up of the patient's weight is important because weight change may be the first evidence of fluid retention. This may be due to heart failure or may be an ominous first sign of protein-losing enteropathy wherein protein losses due to diarrhea results in hypoalbuminemia.

Patients need a close follow-up because arrhythmias can occur secondary to the surgery in the atria. Abnormalities in clotting and platelet reactivity have led to proposals to use low-dose aspirin and or warfarin (Coumadin). These therapeutic regimens are not standardized at this time.

One prospective, randomized study analyzed the safety and efficacy of acetylsalicylic acid and warfarin for thromboprophylaxis after the Fontan procedure.[25] One hundred eleven patients randomly received 5 mg/kg/d (no-heparin phase) of acetylsalicylic acid or warfarin started within 24 hours of heparin lead-in. Transthoracic and transesophageal echocardiograms were obtained at 3 months and again at 2 years after the Fontan procedure; 13 thromboses in the warfarin group and 12 in the acetylsalicylic acid group were noted, suggesting no significant difference between these groups in the first 2 years after Fontan surgery.

Hence, while there was no difference in the thrombosis rate or in the rate of major bleeding between the treatment regimens, the concerning aspect of the study is that despite anticoagulation, there was a cumulative thrombosis rate of 23% in the first 2 years post surgery. The optimal anticoagulant medications and the utility of routine transesophageal echocardiograms in detecting the thrombosis remain unanswered questions at this time.[25]

Another  study demonstrated that prophylaxis with either aspirin or warfarin was associated with a significantly lower rate of thromboembolic events, 20 years after the Fontan operation, although no difference was noted between these 2 treatment modalities.[26]

Complications

Complications related to the Fontan circulation include protein-losing enteropathy, reduced exercise capacity, thromboembolism, reduced somatic growth, and neurodevelopmental abnormalities.

Protein-losing enteropathy

The venous hemodynamics are altered, and central venous pressure is increased. This increased venous pressure in the inferior vena cava (IVC) territory has been implicated in the production of a dreaded complication (ie, protein-losing enteropathy), which typically first manifests years after a Fontan procedure. Its reported prevalence among patients who have undergone the Fontan procedure is 2.5-10%, with a postonset 5-year survival rate of approximately 50%.[27] Although its exact cause and pathophysiology remains unknown, fenestration may reduce its incidence.

Reduced exercise capacity

Exercise performance is substantially reduced in patients after the modified Fontan operation. This may be related to several factors, such as ventricular diastolic and systolic dysfunction, increased afterload due to the nonpulsatile nature of the vascular load, and the inability to augment the cardiac output due to lack of a pumping chamber. Mahle et al (1999) demonstrated that the mean percentage of maximal oxygen uptake is substantially lowered and that the mean half-time of oxygen uptake is notably prolonged in these patients.[11]

Minamisawa et al (2001) demonstrated that selected patients after the Fontan operation could safely undergo exercise training, improving their aerobic capacity in a 2-month to 3-month exercise training program.[28] They concluded that, although the increase in peak oxygen consumption after exercise training was modest, the improvement in oxygen use and participation in appropriate exercise may allow patients to increase their activity.

Thromboembolism

Rates of thrombosis after the Fontan operation are reported to be as high as 20% about 10 years after the procedure. Of interest, authors reporting this rate did not find a difference in freedom from thrombus between atriopulmonary and lateral tunnel Fontan operations. In addition, they found no difference between fenestrated and nonfenestrated Fontan surgeries.[29] This finding suggests that thrombus formation is inherent to the physiology after Fontan surgery, and it is likely not related to the type of modification performed. Abnormalities in the clotting factors and in platelet reactivity are implicated as a cause.[30]

Reduced somatic growth

Cohen et al[31] showed that patients with the univentricular heart are considerably underweight and shorter than the general population at all stages of palliative reconstruction. It has been suggested that early volume unloading procedures may lead to better somatic growth.[32]

Neurodevelopmental abnormalities

Two groups found that patients with Fontan circulation had a mean full-scale intelligence quotient (IQ) scores substantially lower than that of the healthy population.[33, 34] However, Goldberg et al[35] found that neurodevelopmental and behavioral outcomes in patients who have undergone the Fontan procedure are generally in the normal ranges.

Complications likely related to surgical technique

After Fontan completion, arrhythmias result from dysfunction of the sinus node, increased atrial pressure, and the presence of suture lines and scars. The incidence of atrial tachyarrhythmias and bradyarrhythmias increases with time. Cohen et al reported no difference in the incidence of early postoperative dysfunction of the sinus node between patients who underwent a lateral tunnel Fontan procedure and those receiving extracardiac Fontan completion.[31] They also reported that avoidance of surgery near the sinus node has no discernible effect on the development of early dysfunction of the sinus node.

However, Ovroutski et al found that 23 patients in an extracardiac Fontan cohort had a decreased incidence of atrial tachyarrhythmias and bradyarrhythmias relative to 24 patients who underwent a lateral tunnel Fontan procedure.[36] This issue is far from settled at this time.

Pulmonary arteriovenous malformations are an uncommon but important complication that can develop in one lung if hepatic blood flow is streaming to the other lung. One study reported that a Fontan modification involving a direct hepatic-vein-to-azygous-vein connection may help in the resolution of these malformations by directing the hepatic blood flow to the affected lung.[37]

Outcome and Prognosis

Technical and surgical advances have remarkably reduced immediate and long-term mortality rates. Gaynor et al (2002) reported a mortality rate of only 2% after a Fontan procedure.[38] Earing et al (2005) from the Mayo clinic also reported about a recent cohort.[39] Actuarial survival rates for the 203 early operative survivors at 5 years, 10 years, 15 years, and 20 years was 91%, 80%, 73%, and 69%, respectively.

In a multi-institutional study involving more than 2000 patients, age and weight at the time of the Fontan operation did not significantly impact postoperative outcomes. However, a lower weight-for-age z-score was associated with significantly increased postoperative mortality, Fontan failure, and length of stay, independent of other patient and center characteristics.[40] In a study of 312 patients with exercise testing, younger age at Fontan operation was associated with better exercise performance in adolescents.[41]

Concerns about the long-term functioning of a single ventricle remain. Some have suggested that the ideal volume for a single ventricle should be larger than the volume for a ventricle that operates in a 2-ventricular system. Given this information, Yeh et al (1999) suggested that the longevity of a Fontan operation is 30-40 years on average.[42] Patients with tricuspid atresia may fare better than other patients who undergo a Fontan operation because the remaining ventricle is a morphologically left ventricle.

In a study reporting the long-term outcomes of over 1000 patients after Fontan operation, 30-year survival was only 43%. Overall, 20% patients needed pacemakers or revisions, and 11% needed Fontan revisions or conversions. Clinically significant arrhthymias were noted in 44% and 9% developed protein losing enteropathy.[43]

In patients with a failing atriopulmonary Fontan connection and arrhythmias, marked improvement has been reported after conversion to a total cavopulmonary connection with arrhythmia surgery; the associated operative risk is low. However, after the lateral tunnel or the extracardiac Fontan connection begins to fail, the only option is heart transplantation.

Organ damage over time, the liver in particular, is  increasingly being recognized. In a report on 195 patients after a Fontan operation, Pundi et al found 21% with cirrhosis, with only a 57% 30-year freedom from cirrhosis. The 5-year survival after a diagnosis of cirrhosis was only 35%, hypoplastic left heart syndrome appeared to be associated with an increased risk of cirrhosis, and preoperative sinus rhythm was protective.[44]

Future and Controversies

Future directions include interventions early in the single-ventricle palliation pathway to prevent or minimize the incidence of protein-losing enteropathy, the development of new management strategies for protein-losing enteropathy, elucidation of neurodevelopmental outcomes, and early interventions to minimize morbidity to improve patients' quality of life.