Pulmonary stenosis
Right ventricular outflow tract (RVOT) obstruction at the level of the pulmonary valve
Pulmonary annulus may be stenotic or normal.
Treatment is often with balloon valvotomy versus surgical valvotomy.
Recurrent stenosis and insufficiency is common with surgical or balloon valvotomy.
Pulmonary atresia (PA) with intact ventricular septum (IVS)
Complex defect with complete absence of communication between right ventricle (RV) and pulmonary arteries
Characterized by varying degrees of RV and tricuspid valve hypoplasia
Multiple surgical interventions common in childhood
Surgical treatment strategies based on size and development of RV and tricuspid valve
Pulmonary stenosis (PS) at the valvar level accounts for 8 to 10 percent of all congenital heart defects. In most patients, the pulmonary valve is found to be dome-shaped, with commissural fusion and variable subvalvar right ventricular outflow tract (RVOT) obstruction. The pulmonary annulus may be normal in size or smaller than predicted, and a patent foramen ovale (PFO) or atrial septal defect (ASD) is usually present. Clinical presentation is variable. Although severe PS may present in the newborn period, most of these lesions do not manifest significant signs and symptoms until later in childhood. Clinical findings are directly related to the severity of the RVOT obstruction and the degree of shunting across the atrial septum. Timing of intervention is based on severity of clinical findings and is indicated when an RVOT gradient exceeds a mean of 50 mm Hg. Although balloon valvotomy has become the initial therapeutic intervention in most patients, surgical valvotomy still remains an important form of intervention in a subset of these patients. Both catheterization with balloon valvotomy and surgical valvotomy are associated with low morbidity and mortality and excellent long-term survival.
Pulmonary atresia (PA) with intact interventricular septum (IVS) is an uncommon defect, representing between 1 and 3 percent of all congenital heart lesions. By definition, there is no communication between the right ventricle (RV) and the pulmonary arteries and no antegrade pulmonary blood flow through the RVOT. Consequently, a patent ductus arteriosus (PDA) is essential for early survival. The defect presents with varying degrees of hypoplasia of the RV and tricuspid valve, and often involves RV-to-coronary artery fistulas (45 percent). In addition, the tricuspid valve may have an Ebstein malformation (10 percent), and a right ventricle-dependent coronary circulation (RVDCC) is found in 10 to 15 percent of patients.
In neonates with PA/IVS, surgical classification of RV hypoplasia into mild (more than two-thirds of normal), moderate (one-third to two-thirds of normal), and severe (less than one-third of normal), as well as accurate assessment of the TV annular diameter, is useful in directing surgical management. A similar classification strategy is used for surgical management in older children. This allows patients to be stratified into those who will most likely achieve a biventricular repair and those who are best suited for a single ventricle pathway.
PS with IVS is characterized by RVOT obstruction at the level of the pulmonary valve. The pulmonary valve is typically dome-shaped, with commissural fusion of the leaflets and a small central orifice. The pulmonary annulus may be either normal in size or smaller than predicted by the patient’s weight. The RV is usually of normal size and morphology but may develop RV hypertrophy very early in life. This progression of RV hypertrophy may lead to further obstruction of the RVOT at the infundibular level.
The initial pathologic description of PS is credited to Morgagni in 1761. The first attempt at surgical treatment of this lesion is attributed to Doyen in 1913. In his report, Doyen described a transventricular valvotomy using a tenotomy knife with an unsuccessful outcome.1 In 1948, Sellors and Brock reported successful blunt valve dilatation using a transventricular approach.2 Several successful cases of open pulmonary valvotomy using systemic hypothermia and ventricular fibrillation also followed. Open pulmonary valvotomy with the use of cardiopulmonary bypass was successfully introduced in 1955. This remained the primary treatment for patients with PS until the technique of balloon valvotomy was introduced by Semb and associates in 1979. In 1982, Kan and associates at the Johns Hopkins Hospital first reported successful percutaneous balloon valvotomy in a patient with PS.3 Balloon valvotomy has since become the mainstay of initial therapy for PS and has succeeded surgical therapy as a primary intervention in most patients.
Obstructive lesions of the RVOT are found in 25 to 30 percent of children with congenital heart disease. Isolated PS at the level of the pulmonary valve with an intact IVS accounts for approximately 8 to 10 percent of all congenital heart defects, with a slightly higher incidence in females. Without intervention, the onset of hypoxia and heart failure in neonates carries an extremely high mortality. There is a reported increased incidence of 2 to 4 percent in siblings of patients with this particular defect.
The etiology of this lesion is unknown. Failure of the pulmonary valve leaflets to form and separate adequately during embryonic development results in limited mobility and stenosis of the valve. The consequent turbulence of blood flow across this region during subsequent growth and development leads to dysplasia and fibrous distortion of the valve leaflets and further increases the degree of stenosis. RV hypertrophy develops secondarily and is directly related to the severity of the obstruction. Rarely, neonates may present with enlarged RVs and cardiomyopathy, associated with a very poor prognosis despite early intervention.
Neonates who present with critical PS in the newborn period develop severe cyanosis and congestive heart failure. The clinical findings are directly related to the severity of the stenosis as well as to the degree of right-to-left shunting across the interatrial septum. On physical examination, most children with PS present with a harsh holosystolic ejection murmur, an ejection click, and a palpable thrill over the pulmonic valve region. These neonates often appear irritable, tachypneic, and cyanotic due to shunting at the atrial level. Although severe PS may present in the newborn period, most of these lesions do not manifest significant clinical findings until later in childhood. The timing of intervention is usually determined by the severity of clinical findings and is indicated for a documented mean gradient of 50 mm Hg or greater across the RVOT. The results of treatment and long-term outcomes are directly related to the size of the RV and the patient’s age at presentation.
In patients with PS, an electrocardiogram typically reveals right-axis deviation, prominent P waves, and RV hypertrophy. On the chest radiograph, prominent pulmonary artery (PA) shadows secondary to poststenotic dilatation may be observed. The cardiac shadow is usually normal except in severe cases with associated congestive heart failure. Transthoracic echocardiographic examination establishes the severity of the stenosis, the gradient across the RVOT, and the size of the ASD. Cardiac catheterization is performed to obtain additional diagnostic information, and in many patients to perform therapeutic intervention with a balloon valvotomy.
The differential diagnosis includes all congenital heart defects that have RVOT obstruction as an anatomic finding. They include defects such as tetralogy of Fallot, PS with ventricular septal defect (VSD), PA/IVS, and all morphologic cardiac abnormalities characterized by infundibular obstruction. Echocardiography can easily delineate these defects in most patients and identify those with isolated PS with an IVS.
The medical management of these patients is similar to that for any neonate or child with RVOT obstruction. In the neonate with severe PS and cyanosis, ductal patency must be maintained with prostaglandin infusion, and pulmonary vascular resistance must be reduced to ensure adequate pulmonary blood flow. Systemic hypotension is avoided as it may result in reduced ductal flow to the pulmonary arteries and lead to increased hypoxemia. These patients may also have dynamic obstruction in the infundibular region secondary to RV myocardial hypertrophy. Inotropic agents must therefore be used with caution as increased contractility may, in turn, worsen functional obstruction across the RVOT. This will result in further compromise of pulmonary blood flow. After initial stabilization, percutaneous intervention with balloon valvotomy is often performed. If this is unsuccessful in relieving the obstruction, surgical valvotomy can be then performed as either an open technique using cardiopulmonary bypass or with a transventricular approach using a dilator without bypass.
Open pulmonary valvotomy is performed through a median sternotomy using cardiopulmonary bypass and bicaval cannulation. If present, the PDA is ligated or snared prior to the initiation of cardiopulmonary bypass. An aortic cross clamp is applied, and antegrade cardioplegia is administered through the aortic root to achieve myocardial arrest. If no ASD is present, cardioplegic arrest may be omitted and the procedure performed with the heart beating. Otherwise, the PFO or ASD is closed through a right atriotomy, either with primary suture closure or with a patch of autologous pericardium. A vertical pulmonary arteriotomy is then performed on the anterior wall of the main PA and extended down to the level of the pulmonary valve. The stenotic valve is inspected, and the fused commissures are carefully identified and incised with a No. 11 scalpel or fine vascular scissors. The incisions in the valve tissue should extend to the edge of the annulus (Fig. 70-1). Any valvular adhesions to the PA wall are sharply incised. A partial valvectomy may be necessary to remove thickened valve tissue or dense fibrous scarring on dysplastic leaflets. The infundibulum is then inspected through the valve for any subvalvular stenosis, and sharp infundibular resection may be performed if necessary. A dilator may be used to size the valve annulus and dilate the annular tissue. A transannular patch may be required if the annulus is small. The arteriotomy may be closed primarily or with a patch of autologous or bovine pericardium to reduce the risk of any residual obstruction.
If no ASD is present, a pulmonary valvotomy may be performed through a median sternotomy using an off-pump transventricular technique. A purse-string suture is placed in the anterior wall of the RV. An angiocatheter connected to a pressure transducer is first introduced through the purse-string suture into the RV and then into the PA. Using the same technique, progressively larger metal dilators are then introduced through the RV wall and across the valve membrane. If the valve does not dilate easily, a long vascular clamp can be used to initially disrupt the valvar tissue. After adequate dilation is achieved, the purse string is tied and reinforced. If adequate relief of obstruction is not achieved, then open valvotomy may be performed with cardiopulmonary bypass, while a systemic-to-pulmonary shunt may be added to augment pulmonary flow for persistent cyanosis.
Most patients with PS are operated on electively and require routine pre- and postoperative care. In neonates, the management of acidosis, electrolyte derangements, and congestive heart failure should be aggressively pursued prior to surgery. Following surgical correction, there is often a residual gradient across the RVOT. Inotropic support should be used cautiously in the postoperative phase in order to avoid exacerbation of any residual infundibular obstruction. Mild and moderate residual gradients often resolve with age and the patient’s growth.
Both balloon valvotomy and surgical valvotomy are associated with low morbidity and mortality rates and excellent long-term survival. Each has a significant incidence of recurrent stenosis, requiring additional early or late intervention. There is also a significant incidence of pulmonary valve insufficiency following both procedures. Mild-to-moderate pulmonary insufficiency is tolerated remarkably well by most patients, and its long-term clinical importance is a current topic of investigation. Although early mortality is not reportedly increased in patients with significant pulmonary insufficiency, the development of RV enlargement, RV dysrhythmias, and abnormal RV response to exercise may lead to increased long-term morbidity and mortality in these patients. Although overall survival following surgical treatment of isolated PS remains excellent, many patients undergo late reintervention after 30 years of follow-up.4 Therefore, these patients should be followed in the long term for the need of possible late reintervention or pulmonary valve replacement.
A multi-institutional study by Hanley and associates reported a 30-day survival of 89 percent and a 4-year survival of 81 percent for all modes of intervention in neonates with critical PS.5 Of note, 26 percent of these patients required reintervention within 2 years for residual stenosis (defined as a gradient greater than or equal to 30 mm Hg). Following successful pulmonary valvotomy (after either initial intervention or reintervention), RV size approaches normal in more than 90 percent of these patients.
A report by Rao and associates on 80 patients treated initially with balloon valvotomy with follow-up between 3 and 10 years showed a freedom from repeat balloon valvotomy or surgery of 88 and 84 percent at 5 and 10 years, respectively.6 Furthermore, surgical reintervention in older children is associated with minimal morbidity and mortality and excellent short- and long-term outcomes.
PA/IVS is a congenital defect characterized by lack of communication between the RV and pulmonary arteries (PAs), resulting in no antegrade blood flow from the RVOT to the pulmonary arteries. A PDA is essential for maintaining adequate pulmonary blood flow and for early survival. Unlike PA with VSD, aortopulmonary collateral arteries are rarely found in patients with PA/IVS. The defect presents with varying degrees of hypoplasia of the RV and tricuspid valve and often involves fistulas from the RV cavity to the coronary arteries. Morphologically and functionally, the hypoplastic tricuspid valve usually varies in direct correlation with the size of the RV chamber. Coronary artery fistulas are present in up to 45 percent of cases and are more common in patients with severely hypoplastic RVs and small but competent tricuspid valves.7 In addition, it should be noted that an Ebstein’s malformation of the tricuspid valve might be present in 10 percent of cases.8 These patients may present with marked cardiomegaly due to right atrial (RA) enlargement, severe tricuspid regurgitation, and a relatively large RV size.
Surgical treatment of this PA/IVS was historically associated with very high morbidity and mortality. The low incidence of this defect combined with its extreme morphologic variability delayed the development of a standardized approach to surgical therapy.
The original Greenwold classification9 of PA/IVS described this defect by two types of RVs: Type I with a hypoplastic RV and Type II with a normal or dilated RV. A further refinement of this classification was offered by Goor and Lillihei who described the tripartite morphology of the RV (a sinus inlet part, a trabecular part, and a conus or outlet portion) and used this as a basis for surgical therapy.10 Bull and associates introduced as part of the pre- and intraoperative decision-making process the actual annular diameter of the tricuspid valve.11 More recently, the surgical approach to PA/IVS has been based on a quantitative Z-score assessment of the tricuspid valve diameter.12 The Z-score is determined by comparing the estimated diameter of the tricuspid valve (as measured by echocardiography) to the expected “normal” size and calculating the difference of the two values in standard deviations. In 1989, Billingsley and associates from UCLA introduced a surgically oriented classification of mild, moderate, and severe hypoplasia of the RV that is used today by many centers.13
Current surgical approaches to patients with PA/IVS are primarily based on the degree of RV hypoplasia and the degree of TV hypoplasia. In most patients, the degree of hypoplasia of these two structures correlate quite well and this facilitates the classification of these patients for purposes of surgical management. With a more systematic approach to this defect, increasing surgical experience, and improved diagnostic modalities, long-term outcomes have steadily improved.14,7,15
In contrast to other forms of RVOT obstruction, PA/IVS is an uncommon congenital cardiac malformation, representing between 1 and 3 percent of all congenital heart defects.16 Without early surgical intervention, children with PA/IVS have an extremely high mortality rate. The natural history in untreated patients is a 50 percent mortality rate at 2 weeks of life and a mortality of approximately 85 percent at 6 months.17 Death occurs as a consequence of severe hypoxemia and progressive metabolic acidosis secondary to closure of the ductus arteriosus and subsequent loss of pulmonary blood flow. In general, most children with PA/IVS will require multiple surgical interventions beginning in the neonatal period and continuing to one or more interventions later in life.
The etiology of this defect remains unknown. A failure of formation of a patent pulmonary valve during embryonic development results in a completely obstructed RVOT. The obstruction varies in form and may be a relatively thin tissue membrane at the end of a well-formed infundibulum or a thick muscular wall with a poorly formed, or absent outflow tract. Since the ventricular septum remains intact, forward blood flow through the RV is precluded. The growth and development of the RV and tricuspid valve (TV) in utero are severely compromised by this lack of forward flow. Both structures tend to follow a similar pattern of hypoplasia, which is reflected by the TV annular size and the reduced size and volume of the RV chamber. RV-to-coronary artery fistulas are present in 45 percent of cases and are more common in those patients with a severely hypoplastic RV and a small competent TV.13 In 10 percent of patients, the coronary circulation may be dependent on RV pressure for perfusion by way of fistulous communications associated with severe proximal coronary artery stenosis. Pulmonary blood flow in the neonate is dependent almost entirely on a PDA, as aortopulmonary collaterals are uncommon with this defect. Ebstein’s malformation of the TV is seen in 10 percent of patients, adding significantly to the severity of the defect. Although no specific genetic pattern of inheritance has been identified, PA/IVS has been reported in siblings and associated with trisomy 18 or 21.8
Although prenatal diagnosis is increasing for this defect, most neonates with PA/IVS are still diagnosed shortly after birth. The diagnosis is often prompted by varying degrees of hypoxia and cyanosis within the first week of life. Physical examination is often remarkable for prominent venous pulsations. A significant systolic murmur may be indicative of tricuspid regurgitation. This must be differentiated from the continuous machinery murmur of a PDA. Prostaglandin E1 (PGE1) therapy should be initiated as early as possible to maintain ductal patency. Neonates with hypoxia and poor perfusion in spite of medical management should be evaluated for the presence of a restrictive ASD. In this case, balloon septostomy should be performed urgently to relieve the obstruction at the atrial level. Neonates with severely hypoplastic RVs may also require open atrial septostomy. Classification of the defect is determined by echocardiography. Cardiac catheterization and an appropriate operative procedure are selected based on assessment of RV morphology, TV size, the development of the RVOT, and the coronary circulation.
In neonates with PA/IVS, an electrocardiogram usually shows progressive evidence of RA enlargement with prominent P waves. The pattern of RV hypertrophy that is present in most neonates is absent. A chest radiograph is usually unremarkable at birth but may later reveal an increased heart shadow secondary to RA and left ventricular (LV) enlargement. The lung fields are usually clear with normal to diminished vascular markings. Echocardiography remains the initial diagnostic study to identify the anatomic abnormalities and assess RV morphology. The size of the ventricular cavity, valve dimensions and function, and the nature of the RVOT obstruction are also evaluated. Because of the complexity and morphologic variability of PA/IVS, the anomaly must be defined by both echocardiography and right/left heart catheterization. Catheterization should determine the size and competency of the TV, the degree of RV hypoplasia, the size of the pulmonary arteries, the coronary anatomy and presence of coronary sinusoids and fistulas, and ventricular function. Selective coronary injections and an injection into the RV are also required for a complete evaluation. RV-to-coronary artery fistulas are frequently accompanied by the development of fibrous intimal hyperplasia, resulting in stenosis or complete obstruction of the native coronary circulation. The presence of obstructive lesions in the proximal coronaries may produce a RVDCC. Such patients are at high risk for myocardial ischemia as desaturated blood from the RV perfuses a significant portion of the myocardium. An even greater risk of myocardial ischemia is incurred by the reduction of diastolic aortic pressure resulting from the creation of a systemic-to-PA shunt. In such patients, decompression of the RV by either an outflow tract patch or a pulmonary or tricuspid valvotomy is poorly tolerated and may lead to acute myocardial infarction and intraoperative demise. The presence or absence of a RVDCC by catheterization must be established in a neonate prior to determining the operative strategy.
The differential diagnosis encompasses all congenital heart defects with PA. This includes such defects as PA with VSD and single-ventricle defects associated with PA. Echocardiography can easily delineate these defects in most patients and correctly identify those with isolated PA/IVS. Cardiac catheterization is performed in almost all neonates with PA/IVS to confirm the diagnosis and to define and evaluate the anatomy.
Previous surgical experience has indicated that the surgical management of patients with PA/IVS should be based primarily on an anatomic classification system that specifically defines the degree of RV hypoplasia and the TV annular size. A variety of surgical strategies has been proposed in the past for the treatment of these infants.18–23 We and others have found classification of the RV hypoplasia to be an accurate and consistent approach to surgical therapy.24,7,25–27 Using this approach, neonates with PA/IVS are initially separated into three groups of mild, moderate, and severe RV hypoplasia.
In patients with mild RV hypoplasia, the TV and RV cavity are approximately two-thirds or greater of the calculated normal size and the RVOT is well developed. This usually correlates with a Z-score for the TV between 0 and −2. In patients with moderate RV hypoplasia, the TV and the RV cavity are approximately one-half of calculated normal size (with a range of one-third to two-thirds of normal) and the pulmonary outflow tract is usually developed enough to perform an effective pulmonary valvotomy. This usually correlates with a Z-score for the TV of −2 to −4. In patients with severe RV hypoplasia, the TV and RV cavity are one-third or less of calculated normal size and the pulmonary outflow tract is not amenable to an effective pulmonary valvotomy. This usually correlates with a Z-score for the TV of −4 to −6. This approach is not based on any single anatomic component such as RV volumes or the size of the tricuspid annulus but instead assesses the overall RV morphology and the degree of both TV and RV hypoplasia.
During the initial evaluation of patients with PA/IVS, special attention must be paid to the anatomy of the coronary circulation. Abnormalities of the coronary circulation are often found in the severely hypoplastic group and dictate which surgical management options are indicated.28,14 During fetal development, RV hypertension may cause intramyocardial sinusoids to develop. These sinusoids may branch extensively into blind channels or communicate by fistulas with the coronary artery circulation. The morphology of these sinusoids and their specific communications are extremely variable and can change over time. Proximal coronary artery stenoses or obstructions may develop in a coronary artery supplied by these intramyocardial sinusoids. If the distal coronary artery flow is dependent on these sinusoids for adequate myocardial perfusion, they are termed RVDCC.29 Decompression of the RV in these patients is contraindicated and may lead to acute myocardial ischemia and death. The preferred management strategy for these patients is single-ventricle palliation to a Fontan procedure.30
Almost all neonates with PA/IVS will require surgical intervention early in life in order to survive. Treatment with PGE1 maintains pulmonary flow through the PDA and allows time for medical stabilization, diagnostic evaluation, and surgical decision-making. Once the anatomy and morphology of the defect is defined by echocardiography and right/left cardiac catheterization, classification is determined and an appropriate operative strategy initiated. Delay in surgical treatment is hazardous and will reduce early survival.
The surgical approach to most patients is based on the degree of RV hypoplasia and TV measurements (Table 70-1). Initial surgical management of most neonates with PA/IVS involves the establishment of a reliable and adequate source of pulmonary blood flow while optimizing the potential for growth and development of the RV and TV in order to achieve a biventricular repair later in life.
| Classification of RV Hypoplasia | RV Morphology | Treatment |
|---|---|---|
| Mild |
|
|
| Moderate |
|
|
| Severe |
|
|
Neonates with PA/IVS and mild RV hypoplasia with a TV Z-score of 0 to −2 are best treated with a pulmonary valvotomy, insertion of an aorta-to-PA shunt, and ligation of the ductus arteriosus. Occasionally, there are patients in whom a pulmonary valvotomy alone will restore adequate pulmonary blood flow. Experience has shown that initial valvotomy alone often fails to produce effective palliation despite favorable anatomy. In most instances, it is preferable to perform a small shunt to ensure adequate pulmonary blood flow and promote subsequent growth of the branch PAs.
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