AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Background

Tetralogy of Fallot (TOF) with absent pulmonary valve is a rare congenital anomaly characterized by features of TOF with either rudimentary ridges or the complete absence of pulmonic valve tissue. Congenital absence of the pulmonary valve with an intact ventricular septum occurs but is much less common. The absence of mature pulmonary valve tissue leads to severe pulmonary regurgitation. This is often associated with massive dilatation of the pulmonary arteries, which is characteristic of this syndrome.

An interesting feature of this anomaly is that the ductus arteriosus is frequently absent. However, when the pulmonary valve is absent and the ventricular septum is intact, a normal ductus arteriosus generally coexists (Yeager, 2002).

Pathophysiology

TOF consists of a malalignment ventricular septal defect, infundibular pulmonary stenosis, overriding aorta, and right ventricular hypertrophy (see Image 1). The absence of a functioning pulmonary valve gives rise to pulmonary regurgitation (insufficiency) that may result in aneurysmal dilation of the main and branch pulmonary arteries, which can compress the tracheobronchial tree. In addition to compression of the larger bronchi, Rabinovitch et al (1982) described abnormal tufts of the smaller pulmonary arteries that compress the intrapulmonary bronchi. They further reported a reduction of the number of alveoli. This may explain why surgical relief of the larger airway compression alone is not always effective in reversing the severe obstructive respiratory disease.

The pulmonary valve annulus is usually hypoplastic, and this results in some degree of pulmonary stenosis. The stenosis is typically mild, and the pathophysiology in this condition is such that, after the immediate neonatal period, a net left-to-right shunt is observed. This and the airway obstruction due to the dilated pulmonary arteries are the hallmarks of the condition. In the immediate neonatal period, cyanosis may be present, which is a result of increased pulmonary vascular resistance causing a right-to-left shunt at the level of the ventricular septal defect. After the fall in pulmonary vascular resistance, respiratory difficulties are the most prominent symptom in severe cases.

Frequency

United States

TOF is the most common cause of cyanotic heart disease and may occur at a rate of 1-3 cases per 1000 live births. However, TOF with absent pulmonary valve is rare, and approximately 3% of patients with TOF have the absent pulmonary valve syndrome.

Mortality/Morbidity

Mortality and morbidity rates in patients with TOF with absent pulmonary valve syndrome far exceed those of patients with normal physiology who have typical TOF. Patients are at risk for hypoxemia, heart failure, respiratory failure, and combinations of these events. The size of the pulmonary valve annulus and, therefore, severity of pulmonary regurgitation substantially influence patient morbidity and mortality. Patients with a smaller, more stenotic annulus are subject to risks akin to those of typical TOF. Patients with a large annulus and, therefore, more severe pulmonary regurgitation are at greater risk of morbidity and mortality. Patients with severe bronchial obstruction develop symptoms in the early neonatal period. As the airways increase in size and strength, these symptoms may decrease. However, this usually cannot be expected to occur until approximately age 9 months.

• Hypoxemia: The newborn may demonstrate significant cyanosis until pulmonary vascular resistance falls, after which the degree of hypoxemia reflects the severity of pulmonary annular stenosis. A larger pulmonary annulus produces less stenosis, and, therefore, intracardiac shunting may primarily be left-to-right, resulting in minimal cyanosis. The patient with more severe annular hypoplasia presents more similarly to the patient with typical TOF.
• Heart failure: CHF can occur as a result of a large left-to-right ventricular shunt. This contributes to an enlarged left atrium, which, along with dilated pulmonary arteries, results in airway compression. The presence of significant tricuspid regurgitation also increases the risk of heart failure.
• Respiratory failure: In patients with more severe pulmonary regurgitation, aneurysmal dilation of pulmonary arteries can cause air trapping due to bronchial compression. This process can be localized or diffuse and may be severe.

Age

TOF with absent pulmonary valve can be accurately diagnosed based on fetal echocardiography findings. Galindo et al report that many fetuses with absent pulmonary valve syndrome have an increased nuchal thickness in the first trimester, and this may help with earlier recognition of the defect. They found the 22q11 microdeletion to be the most common associated karyotype anomaly, and it was present in 21% of their patients. Their results confirmed that the outlook for these patients remains extremely poor, as only 2 of 14 patients ultimately survived (Galindo, 2006). Other authors have reported similar prognosis findings (Volpe, 2004; Moon-Grady, 2002). Symptoms are noted soon after birth in patients in whom fetal detection failed to reveal the condition. In early infancy, patients fall into 2 groups: those with severe respiratory problems in whom medical management fails in the first year of life and those with less severe respiratory symptoms.

CLINICAL

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History

In a fetus, severe pulmonary regurgitation may cause heart failure, and this may result in fetal hydrops and intrauterine death. According to some suggestions, only fetuses in which the ductus is restrictive or absent are able to survive to term (Yeager, 2002). In fetuses that survive to term, respiratory symptoms develop soon after birth. Cyanosis may be present early because of the high pulmonary vascular resistance.

• Cyanosis usually does not progress as it does in typical TOF in patients with an intact pulmonary valve. As the pulmonary vascular resistance falls, the cyanosis decreases as the left-to-right shunt increases.
• Patients may present in severe or critical respiratory distress due to tracheal or bronchial obstruction early in infancy.

Physical

• Cyanosis, if present, is mild in most cases. The newborn may demonstrate more significant cyanosis because of both higher hemoglobin concentration and higher pulmonary vascular resistance. Stenosis can predominate in patients with a significantly hypoplastic pulmonic annulus. Such patients, therefore, demonstrate more cyanosis.
• • Respiratory distress may be evident with variable auscultatory findings consistent with atelectasis, hyperinflation, or consolidation.
  • CHF evidenced by increased heart rate, respiratory rate, hepatomegaly, and cardiomegaly, with an increase in the pulmonary blood flow, is noted after the normal fall in the pulmonary vascular resistance.
  • The precordium is hyperactive with a right ventricular lift.
• Cardiac auscultation reveals the following:
• • The first heart sound is normal. The second sound is single because of the absence of the pulmonic component. The aortic component may be accentuated.
  • The murmur in this condition is characteristic and is a systolic and diastolic (to-and-fro) murmur best heard in the pulmonic area. The murmur is rough in quality and radiates widely over the lung fields. A short pause between the systolic and diastolic components is noted; this helps differentiate this murmur from that of a patent ductus arteriosus.

Causes

Etiologic factors are not known in most cases. Absent pulmonary valve syndrome has been reported in association with chromosomal abnormalities that involve chromosomes 6 and 7 (Tiller, 1988; Horigome, 1991). More recently, the association with a deletion of the 22nd chromosome and Di George syndrome has also been reported in about 25% of cases (Miyabara, 1994; Iserin, 1998; Volpe, 2004; Galindo, 2006).

Emmanoulides et al (1976) were the first to highlight the association of this condition with the absence of the ductus arteriosus. They proposed a pathogenetic link between the lack of the ductus arteriosus and pulmonary artery dilation and the absent pulmonary valve. They argued that, because most of the blood that enters the pulmonary artery does not have the usual egress through the ductus arteriosus, the blood returns to the right ventricle through the somewhat stenotic pulmonic annulus and, thus, contributes to the dilation of the pulmonary arteries, as well as the possible nondevelopment of the pulmonic valve. This blood then crosses the ventricular septal defect to feed the lower resistance placental circulation through the left ventricle. This has been challenged on the basis that TOF with absent pulmonary valve syndrome occasionally presents with a ductus arteriosus (Ettedgui, 1990). This group suggested poststenotic dilation as the mechanism for the dilated pulmonary arteries.

Others have postulated that agenesis of the ductus arteriosus results from obliteration of a still immature artery slightly later in development rather than from complete failure of a sixth arch artery to develop (Bergwerff, 1999). Rabinovitch et al have suggested that some congenital weakness of the pulmonary arteries may be present, although the histological findings are not specific. Some authors believe that the described changes are the result of increased wall stress similar to the changes seen in pulmonary hypertensive arteriopathy. No such wall abnormalities have been demonstrated in peripheral pulmonary arteries.

In fetuses with a ductus arteriosus, the direction of flow through the ductus is controversial. Lakier et al thought the flow was from the pulmonary artery to the descending aorta because of lower placental resistance. However, others dispute this and contend that the flow of blood occurs from the aorta into the pulmonary artery, and, as no pulmonic valve is present, the diastolic pressures between the aorta and the ventricles equalize, thus leading to ventricular dysfunction and impairment of the diastolic filling of the ventricles (Smith, 1959; Yeager, 2002). If the ventricular septum is intact, this affects only the right ventricle and may be the pathogenetic mechanism of membranous tricuspid atresia described in association with absent pulmonary valve and intact ventricular septum (Freedom, 1979: Yeager, 2002). Yeager et al suggest that TOF with dysplastic pulmonary valve may be more common than apparent from clinical experience but that it is generally lethal in a fetus with a large

ductusarteriosus,as the function of both ventricles is adversely effected. Only fetuses in which the ductus is restrictive or absent are able to survive to term.

DIFFERENTIALS

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Other Problems to be Considered

Absent pulmonary valve may occur in isolation without the presence of a ventricular septal defect. This rare anomaly usually causes severe distress at birth, especially when associated with a patent ductus arteriosus, as it can result in severe right ventricular dysfunction (Yeager, 2002).

A pulmonary artery may arise directly from the aorta. Absence of the left pulmonary artery has been reported. A nonrestrictive ductus arteriosus is more likely to be present in this scenario (Casteneda, 1994).

WORKUP

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Lab Studies

• Obtain a hemogram (CBC) to determine hemoglobin and hematocrit levels.
• An arterial blood gas study can provide useful information in a sick infant.

Imaging Studies

• Chest radiography
• • Chest radiography usually demonstrates aneurysmally dilated central pulmonary arteries with otherwise normal peripheral pulmonary vascularity. Cardiomegaly results from dilation of the right ventricle, particularly its outflow tract (infundibulum).
  • Other pulmonary parenchymal abnormalities may be evident (eg, atelectasis, pneumonic infiltrate, lobar emphysema, hyperinflation). The air trapping may cause a herniation of a lobe.
  • A right aortic arch may be found in some patients.
• Echocardiography
• • Echocardiography is usually diagnostic in this condition. Findings similar to those of TOF include the characteristic large ventricular septal defect, enlarged anteriorly displaced aorta, and right ventricular hypertrophy.
  • The conal septum is displaced anteriorly, but the right ventricular infundibulum is patent and may be dilated if the degree of pulmonic regurgitation is substantial.
  • The pulmonary annulus demonstrates some degree of hypoplasia, and pulmonary valve leaflets are not observed.
  • The pulmonic trunk (main pulmonary artery) and proximal right and left pulmonary arteries are dilated in proportion to the degree of pulmonic regurgitation. This is also true for the right ventricle, which is enlarged and demonstrates paradoxical septal motion.
  • Doppler echocardiography demonstrates turbulence through the right ventricular outflow tract. Pulmonary regurgitation is readily identified. Ductus arteriosus is rare. Flow across the ventricular septal defect is not turbulent because the defect is large and unrestrictive. Flow is generally bidirectional.

Other Tests

• Electrocardiography
• • Right ventricular hypertrophy is present.
  • Patients demonstrate greater left ventricular forces than typical for TOF, and some show actual left ventricular enlargement.
  • Right atrial enlargement may also be present.

Procedures

• Cardiac catheterization
• • Echocardiography in the typical patient provides all of the information necessary to plan surgical repair. Unusual anatomy or the presence of some complicating additional defects may suggest the need to perform catheterization in order to plan surgical intervention.
  • Abnormal pulmonary artery distribution and branching with possible peripheral pulmonary stenosis may be identified.
  • Catheterization may be appropriate in patients with absence of the left pulmonary artery or origin of a pulmonary artery directly from the aorta.
  • Right ventricular angiography demonstrates the stenotic pulmonic annulus with the dilated right and left pulmonary arteries. This has been called the "Mickey Mouse" appearance.

TREATMENT

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Medical Care

Pulmonary complications are the common cause of infant mortality.

• Exacerbation of emphysematous changes and atelectasis from minor respiratory embarrassment, such as an upper respiratory infection, may cause severe problems in the affected neonate. Respiratory syncytial virus infection is particularly hazardous for these patients.
• Placing the infant in a prone position may be beneficial for respiratory effort. However, this sleeping position is not recommended unsupervised because it increases risk of sudden infant death syndrome. It has been reported to be helpful both preoperatively and postoperatively (Heinemann, 1993; Takabayashi, 2005). Takabayashi et al have recommended its use along with bilateral pillows to avoid compression of the sternum.
• Maturation of the tracheobronchial tree in infants older than one year reduces pulmonary obstructive symptoms, presumably by strengthening the underlying cartilaginous structures.
• Patients with severe bronchial obstruction present a distinct management problem. If an infant develops respiratory acidosis with retention of carbon dioxide, assisted ventilation may be indicated; however, mechanical ventilation in these patients is of great concern because once a patient is dependent on positive pressure ventilation, weaning from the respirator can be very difficult. If used, pressure settings should be as low as possible.

Surgical Care

In asymptomatic infants and those with only mild symptoms, surgery is usually deferred until later in childhood. Surgical repair techniques vary in accordance with the particular anatomy in a given patient, especially the severity of pulmonary artery dilation.

• Definitive repair includes the elimination of bronchial compression. Therefore, any intracardiac surgery needs to be accompanied with excision of the main, right, and left pulmonary arteries (Stellin, 1983). However, this is not always uniformly helpful because, as mentioned above, abnormalities may be present at the pulmonary arteriolar level.
• Another area of controversy is whether to insert a valve in the pulmonic position via a homograft and the type of homograft that is best suited. Currently, most centers advocate the use of an aortic homograft (Karl, 1986; Snir, 1991; Castaneda, 1994). Of course, repair also includes closure of the ventricular septal defect.
• Other approaches have been suggested to reduce the bronchial compression. One such approach includes translocation of the pulmonary artery anterior to the aorta and away from the airways (Hraska, 2005).
• In a recent article, external stenting of the airway along with intracardiac repair, another ingenious approach, was described (Sakamoto, 2005). This group placed a separate graft and patch around the respiratory tract. They point out that suturing the first graft on the border region between cartilaginous portion and membranous portion is important and not to encircle the trachea completely, as this may then hamper growth of the airway. They argue that external stenting of the airway was likely to be more effective that endobronchial stenting.
• Repair in the critically ill neonate is urgent, high risk, fraught with postoperative complications, and carries a high mortality rate (50%).

Consultations

• Consultation with a pediatric cardiologist and a pediatric cardiothoracic surgeon is essential.

MEDICATION

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No specific medications for this disease are indicated. Anticongestive therapy is of limited benefit in the treatment of heart failure.

Drug Category: Inotropic agents

Positive inotropic agents increase the force of contraction of the myocardium and are used to treat acute and chronic CHF. Some may also increase or decrease the heart rate (ie, positive or negative chronotropic agents), provide vasodilatation, or improve myocardial relaxation. These additional properties influence the choice of drug for specific circumstances.

Drug Category: Diuretic agents

These agents promote excretion of water and electrolytes by the kidneys. They are used to decrease pulmonary or systemic edema.

FOLLOW-UP

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Further Outpatient Care

• Surgical repair aneurysmal pulmonary arteries in infants does not necessarily eliminate respiratory symptoms. These patients require close and regular outpatient follow-up.
• Patients in whom repair is successful require regular outpatient visits to monitor right ventricular function, hemodynamics of the homograft, if used, and cardiac rhythm stability.

Transfer

• Transfer to a tertiary care facility with pediatric critical care specialists, pediatric cardiologists, and pediatric cardiothoracic surgeons is expected.

Complications

• Airway compromise is the predominant concern.
• Consider atelectasis, pneumothorax, and pneumonia.

Prognosis

• Neonates with severe respiratory distress soon after birth are most at risk for early death.
• Infants who require surgery early in life have a worse prognosis than those repaired at a later date.
• Prognosis is directly related to the degree of tracheobronchial obstruction secondary to pulmonary artery dilatation.

Patient Education

• For excellent patient education resources, visit eMedicine's Heart Center. Also, see eMedicine's patient education article Tetralogy of Fallot.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Failure to refer a patient with cardiopulmonary embarrassment to a specialty center constitutes a departure from standard of care.
• Failure to recognize the presence of a cardiac defect by failing to perform a satisfactory physical examination in a patient with symptoms of respiratory distress is a pitfall.

MULTIMEDIA

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Media file 1:  Drawing showing absence of the pulmonary valve with features of tetralogy of Fallot. Note the small nubbins of tissue at the pulmonary valve annulus in the center of the drawing. Characteristic muscular right ventricular hypertrophy and infundibular pulmonary stenosis are present. A right aortic arch, a ventricular septal defect with overriding aortic valve, and massively dilated main and branch pulmonary arteries are present.
	View Full Size Image
Media type:  Illustration

Media file 2:  Pulmonary artery branching in a healthy person and in a patient with absent pulmonary valve syndrome.
	View Full Size Image
Media type:  Illustration

REFERENCES

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• Castaneda AR, Jonas RA, Mayer JE. Tetralogy of Fallot. Cardiac Surgery of the Neonate and Infant, WB Saunders. 1994;232-233.
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• Sakamoto T, Nagase Y, Hasegawa H, et al. One-stage intracardiac repair in combination with external stenting of the trachea and right bronchus for tetralogy of Fallot with an absent pulmonary valve and tracheobronchomalacia. J Thorac Cardiovasc Surg. Dec 2005;130(6):1717-8.
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• Snir E, de Leval MR, Elliott MJ, Stark J. Current surgical technique to repair Fallot's tetralogy with absent pulmonary valve syndrome. Ann Thorac Surg. Jun 1991;51(6):979-82. [Medline].
• Stellin G, Jonas RA, Goh TH, et al. Surgical treatment of absent pulmonary valve syndrome in infants: relief of bronchial obstruction. Ann Thorac Surg. Oct 1983;36(4):468-75. [Medline].
• Takabayashi S, Shimpo H, Miyake Y, et al. Postoperative prone position management of tetralogy of fallot with absent pulmonary valve syndrome. Jpn J Thorac Cardiovasc Surg. Mar 2005;53(3):150-3. [Medline].
• Tiller GE, Watson MS, Duncan LM, Dowton SB. Congenital heart defect in a patient with deletion of chromosome 7q. Am J Med Genet. Feb 1988;29(2):283-7. [Medline].
• Volpe P, Paladini D, Marasini M, et al. Characteristics, associations and outcome of absent pulmonary valve syndrome in the fetus. Ultrasound Obstet Gynecol. Nov 2004;24(6):623-8. [Medline].
• Yeager SB, Van Der Velde ME, Waters BL, Sanders SP. Prenatal role of the ductus arteriosus in absent pulmonary valve syndrome. Echocardiography. Aug 2002;19(6):489-93. [Medline].

Article Last Updated: Jul 28, 2006