In this section, pulmonary stenosis is taken to mean primarily valvular pulmonary stenosis in hearts with intact ventricular septum. Valvular pulmonary stenosis may coexist with infundibular pulmonary stenosis, but obstruction of the right ventricular outflow tract in association with a ventricular septal defect is considered elsewhere.

Neonates with critical valvular pulmonary stenosis are dependent upon patency of the ductus arteriosus for pulmonary blood flow. The pulmonary valve is most often a uniform cone of fibrous tissue with a central or eccentric orifice considerably smaller than the pulmonary annulus itself. Two or three fibrous ridges radiate from the central orifice to the annulus, dividing the valve tissue into two or three leaflets that correspond to the two or three, usually well developed sinuses of Valsalva. The leaflet tissue is in general thicker than that of a normal, non-stenotic pulmonary valve. In hearts with critical pulmonary stenosis, the right and left pulmonary arteries are usually well developed, though moderate to severe branch pulmonary artery hypoplasia is occasionally seen. Similarly, it is rare for the cavity of the right ventricle to be severely reduced in size, though a mild to moderate reduction of right ventricular cavity size relative to normal is most common.

Neonates with critical pulmonary stenosis generally present within the first few days of life with irritability, tachypnoea, and hypoxaemia which is due to right to left shunting at the atrial level but will become extreme and be associated with metabolic acidosis if the ductus arteriosus begins to close. Radiographic examination of the chest reveals clear to hyperlucent lung fields and a large cardiac silhouette. Two-dimensional echocardiography is diagnostic, revealing the thickened, immobile pulmonary valve as well as defining the size of the right ventricular cavity and the degree of tricuspid valve regurgitation. Initial medical therapy consists of ensuring the patency of the ductus arteriosus, for example by infusion of prostaglandin E&sub1;.

Relief of pulmonary valve stenosis is the goal of surgery, and this can be accomplished using a variety of adjunctive techniques. Closed pulmonary valvotomy, open valvotomy with temporary venous inflow occlusion, and open valvotomy with cardiopulmonary bypass with or without cardioplegia all give good results. A small increment in the effective cross-sectional area of the valve orifice results in significant augmentation of antegrade flow from the right ventricle to the pulmonary arteries. Only rarely is a transannular right ventricular outflow tract patch required in the initial management of critical pulmonary stenosis of the newborn. Similarly, it is uncommon that a systemic to pulmonary artery shunt is required to augment pulmonary blood flow.

Percutaneous balloon valvotomy is an important non-surgical method of treatment of critical pulmonary stenosis in the neonate. This is accomplished in the cardiac catheterization laboratory and is with increasing frequency supplanting surgical valvotomy as the initial method of management of critical pulmonary stenosis. Since the vast majority of neonates with critical pulmonary stenosis can be stabilized by ensuring patency of the ductus arteriosus prior to palliative or definitive therapy, the hospital mortality for this group has in recent years been reduced to between 5 and 10 per cent.

The spectrum of pulmonary valve stenosis presenting after the neonatal period ranges from mild to moderate valvular obstruction that may remain relatively stable throughout life, to severe pulmonary stenosis associated with suprasystemic right ventricular pressure. The pulmonary valve is generally made up of two or three leaflets which are relatively well developed in contrast to those of the neonate with critical pulmonary stenosis. There may be complete or partial commissural fusion. The leaflet tissue is generally thicker than in normal valves, and the pulmonary artery wall may be pulled inward or tethered at the site of commissural cusp attachment. Some patients, particularly among those with Noonan's syndrome, have pulmonary valve dysplasia wherein the valve tissue itself is very thickened and the leaflets are quite rigid. Immobility of the leaflets due to thickening and rigidity, rather than commissural fusion, results in the significant pressure gradient between the right ventricle and the pulmonary arteries. Pulmonary valvular stenosis of any type may be accompanied by secondary infundibular hypertrophy resulting in infundibular stenosis.

About one-third of patients with valvular pulmonary stenosis and intact ventricular septum are asymptomatic when first evaluated. The diagnosis is suspected after auscultation of an ejection type of systolic murmur. Among those with symptoms, dyspnoea on effort is the most common complaint. Cyanosis at rest or with exercise results from right to left shunting at the atrial levels, which is the consequence of diminished compliance of the right ventricle relative to that of the left ventricle. Untreated valvular pulmonary stenosis may eventuate in the development of right ventricular failure. More importantly, infants in whom right ventricular pressure is elevated to near systemic levels at rest are at risk for sudden death. The electrocardiogram generally shows prominent P-waves associated with right atrial enlargement, and elevation of the height of the R-wave in the right precordial leads, together with incomplete right bundle branch block. Radiographic examination of the chest is non-specific, but often shows an enlarged cardiac silhouette due primarily to prominence of the right atrium. As in neonates with critical pulmonary stenosis, two-dimensional echocardiography is diagnostic. Cardiac catheterization may be undertaken for complete haemodynamic evaluation, but most importantly to provide access for balloon pulmonary valvotomy which is efficacious except in cases where the valve is severely dysplastic.

If relief of valvular pulmonic stenosis is not achieved at cardiac catheterization, it can be reliably accomplished by surgical means. Cardiopulmonary bypass with mild to moderate hypothermia is the most commonly used form of circulatory support. The pulmonary valve is generally exposed by means of a vertical arteriotomy in the proximal main pulmonary artery. Incision of fused commissures back to the level of the annulus often provides complete or near complete relief of valvular obstruction. When there is tethering of the wall of the main pulmonary artery to the commissural attachments, these should be incised. If the leaflets remain significantly immobile despite commissurotomy, as in instances of severe pulmonary valvular dysplasia, then partial or complete pulmonary valvectomy may be necessary. The resulting pulmonary insufficiency is well tolerated, as long as right ventricular function is not significantly compromised, there is a competent tricuspid valve, and the pulmonary vascular resistance is not significantly elevated. For patients with simple valvular pulmonary stenosis who present after the neonatal period, hospital mortality for relief of pulmonary stenosis by surgical means or by percutaneous balloon valvotomy approaches zero. The results are somewhat less uniform in patients with Noonan's syndrome, and in those with severe degrees of hypoplasia of the pulmonary annulus or of the right ventricular cavity.

Pulmonary atresia with intact ventricular septum is a congenital heart malformation in which there is no luminal continuity between the right ventricular chamber and the pulmonary arteries. Hearts with pulmonary atresia and intact ventricular septum include a spectrum of morphology with regard to both the nature of the junction of the right ventricle and the pulmonary trunk, and the degree of development of the right ventricle and the tricuspid valve. Generally, the right and left pulmonary arteries and the main pulmonary artery are normal or near normal in size. Almost invariably, the ductus arteriosus is the exclusive source of pulmonary blood flow.

Most often, right ventricular cavity size is reduced and the wall is significantly hypertrophied. The right ventricle may have an infundibulum which ends blindly in a well developed but imperforate pulmonary valve plate. Alternatively, the atresia may be ‘muscular’. In such cases, there is no identifiable valve or valve-like tissue between the most distal portion of the right ventricle and the main pulmonary trunk. There is a high degree of correlation between the diameter of the tricuspid valve, and right ventricular cavity size. While right ventricular cavity size is less than normal in over 90 per cent of patients, those with normal or near normal size of the tricuspid annulus (and a concomitant moderate to significant degree of tricuspid incompetence) can be expected to have the most developed right ventricular chambers. This construction makes sense, as chamber development is undoubtedly related to the volume of blood flowing into and out of the right ventricle, despite atresia of the outflow tract. Another important aspect of morphology is the presence of coronary artery–right ventricular fistulae which are present in between one-third and one-half of patients with pulmonary atresia with intact ventricular septum. In the most extreme cases, there are intrinsic abnormalities such as stenoses or occlusion of the principal coronary arteries, resulting in a partially or completely right ventricular dependent coronary circulation.

Nearly all infants with pulmonary atresia and intact ventricular septum will present during the first few days of life with cyanosis. Progressive closure of the ductus arteriosus is associated with increasing hypoxaemia and metabolic acidosis. Radiographic examination of the chest typically discloses clear lung fields with normal or diminished pulmonary vascular markings. The cardiac silhouette may be normal or enlarged. The electrocardiogram is not particularly helpful, as there may be electrocardiographic evidence of right ventricular hypertrophy despite diminished right ventricular cavity size. Two-dimensional echocardiography is diagnostic. This study should provide information regarding the dimensions of the tricuspid valve, the presence and degree of tricuspid insufficiency, right ventricular cavity size, and the nature of the right ventricular outflow obstruction. Frequently, right ventricular–coronary artery fistulae can be appreciated by two-dimensional echocardiography and colour flow mapping. Cardiac catheterization, however, is necessary to define with confidence the nature of the coronary circulation and the potential for its dependence upon the right ventricle and ventricular–coronary fistulae. Without treatment, patients with pulmonary atresia with intact ventricular septum succumb as a result of severe hypoxia and metabolic acidosis. Virtually all patients can be stabilized by maintenance of patency of the ductus arteriosus, for example with infusion of prostaglandin E&sub1;

Choice of initial surgical procedure for patients with pulmonary atresia with intact ventricular septum depends upon the degree of development of the tricuspid valve and right ventricular cavity, and on the nature of the coronary circulation (including the presence or absence of right ventricular–coronary fistulae and the potential for a right ventricular dependent coronary circulation). Though not invariably true, it is generally the case that those patients with the larger tricuspid valves and right ventricular chamber sizes are less likely to have significant fistulae between the right ventricle and the coronary circulation. If the tricuspid valve and right ventricle are well developed, and decompression of the right ventricle does not pose a risk of coronary ischaemia as a consequence of a steal from the coronary circulation via ventricular–coronary fistulae, then a procedure to establish antegrade flow from the right ventricle to the pulmonary artery trunk is undertaken. This may be incision or excision of the pulmonary valve plate if present, or establishment of continuity between the right ventricle and pulmonary artery trunk by means of a transannular patch or even a ventriculoarterial conduit. As right ventricular compliance remains markedly diminished for a period of time even after decompression, it is virtually always the case that patients having pulmonary atresia with intact ventricular septum will require an additional source of pulmonary blood flow at the time of initial surgery. This may be accomplished by construction of a systemic to pulmonary artery shunt, or by assuring prolonged patency of the ductus arteriosus, as for example by formalin infiltration of the wall of the ductus. This initial procedure may be accomplished with or without extracorporeal circulatory support. At The Children's Hospital of Philadelphia, we prefer to place a transannular right ventricular outflow tract patch without the use of cardiopulmonary bypass, and to maintain patency of the ductus arteriosus by formalinization of its wall (Fig. 1) 1714. This formalinized ductus generally remains patent over a period ranging from several weeks to a few months. As the compliance of the right ventricle improves over time, the degree of right to left shunting at the atrial level through the foramen ovale gradually diminishes. With this operation, some patients achieve a ‘normal’ circulation utilizing four cardiac chambers without any cardiac level shunts. Other patients require an additional procedure later to achieve additional relief of right ventricular outflow tract obstruction and to eliminate surgically potential for right to left shunting at the atrial level.

Those patients with the smallest tricuspid valves and least well developed right ventricular chambers, and those in whom connections between the right ventricular chamber and coronary arteries together with intrinsic abnormalities of the coronary arteries result in a right ventricle dependent coronary circulation, are ultimately best served by a modification of Fontan's procedure. As such, their initial surgical management does not include decompression of the right ventricle, but rather they are helped by construction of a systemic to pulmonary artery shunt. After a period of maturation, when the pulmonary vascular resistance has fallen, they undergo a modification of Fontan's operation in one or two stages.

For patients with pulmonary atresia and intact septum, palliative or definitive surgery is required during the neonatal period. Without surgical treatment, about 50 per cent of babies die within the first month of life and nearly all die before 12 months of age. Construction of a systemic to pulmonary artery shunt alone is not associated with growth of the tricuspid valve and right ventricular chamber, and thus should be reserved for those patients who will ultimately be managed by means of a modification of Fontan's procedure. For those with a right ventricle that is judged to have the potential for eventually managing all of the systemic venous return, a procedure to optimize antegrade flow from the right ventricle to the main pulmonary artery trunk (such as a transannular outflow tract patch) should be combined with a procedure to provide an additional, but temporary, source of pulmonary blood flow, such as formalinization of the ductus or construction of a Blalock Taussig shunt. In a multi-institution study prepared by the Congenital Heart Surgeons Society, survival was 81 per cent at 1 month after the first intervention and 64 per cent at 4 years. This group of patients represented the entire spectrum of right ventricular morphology, and they were managed with a variety of treatment plans.

Congenital valvular aortic stenosis is a form of left ventricular outflow tract obstruction caused by abnormal development of the aortic valve cusps and the aortic annulus. Critical aortic valve stenosis of the neonate is a condition in which the severity of obstruction at the level of the aortic valve results in a systemic circulation that is dependent upon flow from the right ventricle, via the ductus arteriosus. More commonly, valvular aortic stenosis becomes evident after the newborn period. The majority of patients with stenosis severe enough to warrant operative intervention in infancy and childhood have a bicuspid aortic valve. The larger of the two cusps frequently contains a central thickened ridge or raphe representing the rudimentary commissure between two fused cusps. There is usually fusion peripherally at one or both commissures. In about 30 per cent of cases, the valve is tricuspid, with thickening of the leaflets and variable degrees of fusion at the commissures. Rarely, the valve has a unicuspid configuration with only one commissure. With severe valvular aortic stenosis, there is virtually always concentric hypertrophy of the left ventricle. Some neonates present with a very extreme degree of hypertrophy and with fibrosis of the endocardium and subendocardium. Endocardial fibroelastosis may be present as a result of ischaemia of the developing myocardium. In some instances, severe aortic valve stenosis in the neonate may be associated with varying degrees of stenosis or hypoplasia of the mitral valve, and a smaller than usual left ventricular cavity. These cases should be considered part of the spectrum of hypoplastic left heart syndrome.

Neonates with critical aortic stenosis present with poor systemic perfusion, pallor, tachypnoea, tachycardia, and a mild degree of cyanosis. The murmur of aortic stenosis may be unimpressive because of diminished flow from the left ventricle. Spontaneous narrowing of the ductus arteriosus is associated with a profound hypoperfusion state and metabolic acidosis, and progresses rapidly to death unless supportive therapy to re-establish patency of the ductus arteriosus is undertaken (i.e. infusion of prostaglandin E&sub1;).

Clinical signs of aortic stenosis presenting in older infants and children include an ejection systolic murmur at the base of the heart radiating to the carotid vessels and accompanied by a systolic ejection click. There may be a third or fourth heart sound present. The electrocardiogram usually shows severe left ventricular hypertrophy and there may be a left ventricular strain pattern as well. In neonates and infants with severe aortic stenosis, radiographic examination of the chest usually reveals increase in heart size. This may not be so in older children, though left ventricular prominence and prominence of the ascending aorta may be present. Two-dimensional echocardiography is diagnostic. In neonates with critical aortic stenosis and in infants with severe congestive heart failure, the Doppler derived estimate of the left ventricular outflow tract gradient is of little importance, as flow may be significantly diminished. In neonates and infants with severe valvular aortic stenosis, cardiac catheterization adds little diagnostic information. However, percutaneous balloon valvotomy is increasingly being utilized as the initial treatment of many patients in this category.

Surgical valvotomy can be accomplished in neonates and infants using a variety of techniques. As with critical valvular pulmonary stenosis, a relatively small increment in the effective valve orifice can result in significant diminution in the degree of obstruction. It is of course of paramount importance in valvular aortic stenosis to achieve relief of obstruction while creating a minimum amount of incompetence of the valve. Valvotomy can be effectively accomplished under direct vision via an incision in the ascending aorta during cardiopulmonary bypass with or without cardioplegic arrest. Alternatively, valvotomy can be accomplished via an incision in the ascending aorta during a brief period of inflow stasis, or ‘blindly’ by passing dilators through the apex of the left ventricle and advancing them antegrade through the aortic annulus. Using these various techniques, mortality rates as low as 10 per cent and as high as 65 per cent have been reported for surgical palliation of neonates.

Aortic valvotomy in older children is generally accomplished using cardiopulmonary bypass with a moderate degree of hypothermia and aortic cross-clamping with cardioplegic myocardial protection. The goal of the operation is to minimize the degree of obstruction at the level of the aortic valve without creating a significant degree of insufficiency. This goal is usually accomplished by incision of fused commissures out to the level of the annulus, and often by removal of nodular and fibrous excrescenses from the valve leaflets themselves in order to enhance their mobility. One cannot overemphasize the importance of avoiding incision of the raphe in the congenitally bicuspid aortic valve, as this is certain to result in a significant degree of aortic insufficiency. Reintervention is likely to be necessary in the majority of patients who undergo aortic valvotomy early in childhood. In a long-term study performed at the National Institutes of Health (excluding those who underwent initial valvotomy as neonates and infants), about 90 per cent of children and young adults were free from reintervention for at least 10 years after the initial operation. The actuarial estimate of freedom from reintervention by 20 years after the initial operation was 60 per cent, and by 40 years was only 10 per cent. Reintervention appears to be required earlier and more frequently when the initial valvotomy has been performed during the neonatal or infant period.

Aortic atresia is the developmental anomaly in which the aortic valve is imperforate. This is virtually always associated with a hypoplastic ascending aorta. The systemic circulation is dependent upon flow from the right ventricle through the ductus arteriosus into the aorta. Flow in the ascending aorta is retrograde and includes only the flow to the coronary arteries. In the vast majority of cases, aortic atresia is associated with atresia or hypoplasia of the mitral valve, and absence or severe hypoplasia of the left ventricle. This is known as hypoplastic left heart syndrome, and is the fourth most common congenital cardiac anomaly presenting in the first year of life. It is the most common cause of death due to cardiac disease in infancy.

In rare instances, aortic atresia is associated with an unrestrictive ventricular septal defect. In these cases, normal left ventricular development can occur. Thus, a primary myocardial abnormality is unlikely to be the cause of hypoplastic left heart syndrome.

Physical examination typically shows a mildly cyanotic infant with tachypnoea and tachycardia. Depending on the degree of patency of the ductus arteriosus at the time of evaluation, peripheral pulses may be normal, diminished, or absent. Progressive closure of the ductus arteriosus is associated with a profound hypoperfusion state leading rapidly to death. Re-establishment of patency of the ductus arteriosus by means of an infusion of prostaglandin E&sub1; is life saving. The electrocardiogram generally shows right atrial enlargement and right ventricular hypertrophy. Radiographic examination of the chest is non-specific. Cardiomegaly is common and pulmonary vascular markings may be prominent. Two-dimensional echocardiography is diagnostic in this lesion. Cardiac catheterization may be destabilizing to the critically ill neonate and adds little if any important physiological information.

Being the most common cardiac anomaly associated with a single dominant ventricle, aortic atresia or hypoplastic left heart syndrome lends itself ultimately to reconstruction by means of a modification of Fontan's operation. This, however, cannot be accomplished in the neonate because of the prohibitively high pulmonary vascular resistance. Initial surgical palliation is embodied by three basic principles. (1) The aorta must be associated directly with the right ventricle in a fashion guaranteeing unobstructed flow from right ventricle to the systemic circulation, with growth potential obviating further aortic surgery. (2) Pulmonary blood flow must be regulated for proper growth and development and maturation of the pulmonary vasculature, in order to avoid the development of pulmonary vascular obstructive disease and to minimize the volume load on the right ventricle. (3) A large interatrial communication is necessary to avoid pulmonary venous hypertension and its consequences.

The initial palliative procedure, as described by Norwood, is accomplished utilizing deep hypothermia and circulatory arrest. Extracorporeal circulation is established with a bypass loop between the right atrium and the main pulmonary artery. The right and left branch pulmonary arteries are occluded with tourniquets and patency of the ductus arteriosus is maintained thus assuring adequate systemic perfusion. The branch vessels of the aortic arch are occluded with tourniquets in preparation for circulatory arrest. After removal of the right atrial cannula, septum primum is excised, ensuring a large and unrestrictive interatrial communication. The main pulmonary artery is transected immediately proximal to the origin of the right pulmonary artery. The distal main pulmonary artery is oversewn with a patch to ensure continuity between the right and left pulmonary artery branches. The ductus arteriosus is ligated and transected at its entrance into the thoracic aorta. The incision is extended distally on to the thoracic aorta and proximally into the aortic arch and ascending aorta. The entire aortic arch is augmented with a gusset of cryopreserved pulmonary artery homograft. Proximally, the transected main pulmonary artery is anastomosed to the ascending aorta and the homograft gusset is then sewn to the remainder of the proximal main pulmonary artery. Pulmonary blood flow is provided by a systemic to pulmonary artery shunt. This may be a central shunt placed between the reconstructed aorta and the confluence of the pulmonary arteries, or a modified Blalock Taussig shunt interposed between the innominate artery and right pulmonary artery (Fig. 2) 1715. Postoperatively, the critical balance between systemic and pulmonary blood flow is maintained through judicious control of ventilatory parameters, as the pulmonary vascular resistance is exquisitely sensitive to alterations in carbon dioxide tension and pH.

Currently, hospital survival following initial palliative surgery for hypoplastic left heart syndrome is at a level of 80 to 90 per cent at selected centres. These patients eventually undergo a modified Fontan procedure with results similar to those for other cardiac malformations characterized by a single ventricle. Some believe that hypoplastic left heart syndrome is best managed by heart replacement. Neonatal heart transplantation, though severely limited by the shortage of available donors, has provided excellent results at a few selected centres.

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