Morphogenesis

As for many types of congenital heart disease, the morphogenesis of the lesion is unclear, although the morphology dictates that the insult producing the atresia must have occurred after the completion of ventricular septation. There is some evidence as to the timing of this developmental insult. Several groups have examined various morphological features, including the size and morphology of the pulmonary valve, and the topology of the arterial duct. ^20–22 The angle subtended by the duct to the postductal descending aorta may be an indicator of whether the pulmonary arterial pathways became atretic earlier or later in gestation. In normal hearts, the duct runs almost parallel with the transverse arch, forming an obtuse angle with the postductal aorta ( Fig. 30-2 ). In pulmonary atresia in the setting of deficient ventricular septation, the duct may originate more proximally on the aortic arch than normal, is usually sigmoid in shape, and subtends an acute angle to the postductal aorta. This led to the hardly surprising suggestion that the atresia develops early in these lesions during cardiac morphogenesis, at or shortly after partitioning of the outlets of the developing heart, but before closure of the embryonic interventricular communication. ²¹ In those in whom the ventricular septum is intact, the duct subtends a highly variable angle to the postductal aorta. Patients with better developed right ventricular cavities tend to have ducts subtending normal angles, whilst in those with severely hypertrophied ventricles, and ventricular-to-coronary fistulous connections, it tends to be acute ²³ (see Fig. 30-2 ), supporting the notion that those with smaller and hypertrophied right ventricles suffered their developmental insult earlier in gestation than did those with ventricles having better developed cavities. ²⁴ This notion has now been supported by evidence from fetal echocardiography, where progression from pulmonary stenosis to atresia has been documented during later pregnancy. ^9,17

These echocardiograms show the variation in ductal angle. A, A normal angle between the arterial duct and the descending aorta (DAO), of greater than 90 degrees, in a patient with a tripartite right ventricle and an imperforate pulmonary valve. B, An acute angle, of less than 90 degrees, in a patient with unipartite right ventricle and muscular atresia. The arrows superimposed on these echocardiograms show the variation in ductal angle. AO, aorta; LA, left atrium.

(From Daubeney PE, Delany DJ, Anderson RH, et al: Pulmonary atresia with intact ventricular septum: Range of morphology in a population-based study. J Am Coll Cardiol 2002;39:1670-1679.)

Previously, it was assumed that atresia of the pulmonary valve was the primary morphogenetic event, leading to right ventricular hypertension, and development of the fistulous communication with the coronary arteries. More recently, several groups have suggested that, at least in those with fistulous connections, the primary disease may be one of persistence of these communications, ²⁵ or abnormal morphogenesis of the right ventricle, ²⁶ rather than the pulmonary valve itself. As fistulous communications have been identified from 13 weeks gestation onwards, and as it is known that the embryonic interventricular communication closes in the ninth week, Chaoui and colleagues have doubted that this leaves enough time for right ventricular hypertension to cause the development of fistulas. ²⁵ Their argument goes on to state that, as prenatal afterload is higher in the right ventricle compared to the left, ^27,28 blood would preferentially pass through the fistulous communications, rather than the pulmonary valve, leading to pulmonary stenosis and atresia. As an alternative they suggested that there may be a primary insult at right ventricular level, leading to both pulmonary atresia and to persistence of the communications from the right ventricle to the coronary arteries, ²⁵ a concept also supported by Bonnet and colleagues. ²⁶ The concept has now been further extended by Gittenberger-de Groot and her colleagues, ^29,30 who refute the suggestion that the pulmonary valve is the site of the primary abnormality. Her group propose that the primary anomaly in this subset of patients is lack of ingrowth of the developing coronary arteries even prior to development of pulmonary atresia, since the coronary vasculature develops from the epicardium, and not from the intertrabecular spaces. ^31,32 They also highlighted the role of cells migrating from the neural crest in this process of vascular development. ³⁰ The likely morphogenesis has been summarised neatly by Bonnet and colleagues as a ‘primitive alteration of a mechanogenic transduction pathway, crucial for right myocardial remodelling during embryogenesis’. ²⁶

Aetiology

The underlying abnormality in this condition has not been elucidated. Both congenital and acquired aetiologies have been proposed. ^21,33 Some thought that the coronary arterial pathology seen represented an endarteritis, ³⁴ while others proposed that a prenatal inflammatory disorder may cause the development of atresia. ²¹ This has not been supported by any histological evidence of an acute or subacute disorder, either pre- or postnatally. ^2,15,17 There is some evidence showing that the lesion can be acquired during fetal life in association with twin-to-twin transfusion. ³⁵ Twinning studies have also demonstrated an excess of congenitally malformed hearts in monozygotic twins, often in only one of the set of twins, ³⁶ leading to the suggestion that the twinning process itself may lead to increased congenital cardiac malformations, possibly due to loss of laterality in one twin. Furthermore, siblings have been described, both having the lesion, suggesting an autosomal recessive trait, with doubt being expressed as to whether the disease can really be acquired. ³⁷ It seems likely, therefore, that the morphological entity represents a common endpoint for a range of underlying disorders, both hereditary and acquired during fetal life.

Tricuspid Valve

Almost invariably, the right ventricular inlet valve is abnormal. ^38,41–47 Abnormalities can include dysplasia, Ebsteinoid displacement, and a wide range of annular size, ranging from tiny to hugely dilated. Often the valve shows all three abnormalities to a variable degree. At a functional level, there is a continuum from severely stenotic to freely regurgitant.

Tricuspid stenosis at its most severe may be due to an obstructed muscularised annulus with dysplasia of the valvar leaflets and their supporting tension apparatus. ⁴⁵ The free edges of the leaflets may be thickened and nodular, the cords reduced in number, and shortened with fibrous thickening. The papillary muscles can be underdeveloped with abnormal attachments. ⁴⁷ Even the most severely stenotic tricuspid valve is likely also to have a degree of regurgitation. ⁴⁵

Tricuspid regurgitation at its most severe may be accompanied by a grossly dilated annulus, with displacement and severe dysplasia of the tricuspid valvar leaflets ( Table 30-2 ). ^23,37 At its extreme, the tricuspid valve may be devoid of all leaflet tissue, leaving an unguarded tricuspid valvar orifice, and leading to a hugely dilated and thin-walled right ventricle. ^47–50 Ebstein’s malformation is seen in about one-tenth of cases ^23,49 (see Table 30-1 ), and can be found with both hypoplasia ( Fig. 30-3 ) and dilation of the right ventricular cavity. In the setting of a dilated cavity, there is sail-like enlargement of the antero-superior leaflet, whereas when the ventricle is hypoplastic, the changes are confined to downward displacement of an often dysplastic septal leaflet. ⁴⁷ Whereas Ebstein’s malformation usually leads to a regurgitant valve, the displaced valve may also be virtually imperforate when the cavity is hypoplastic. ⁴⁴

In this heart with obliteration of the apical component, and hypoplasia of the outlet component, the tricuspid valve shows evidence of Ebstein’s malformation, with the septal leaflet hinged away from the atrioventricular junction ( yellow dotted line ).

Severe tricuspid regurgitation, whether due to dysplasia or Ebstein’s malformation, can lead to functional pulmonary atresia. ^51–53 This occurs when the right ventricle is unable to generate sufficient pressure to open an anatomically normal pulmonary valve. Distinguishing functional from true atresia can be difficult. It normally relies on the fact that there is a degree of diastolic regurgitation through the pulmonary valve that can be seen echocardiographically ^54–56 or angiographically. ⁵⁷

The size of the tricuspid valve correlates well with the size of the right ventricular cavity ^{23,38,43,44,47,58–60} (see Table 30-2 ), unlike the situation in critical pulmonary stenosis. ⁶¹ This correlation, and the importance of the right ventricular inlet in surgical repair, has led to several groups advocating use of the dimensions of the tricuspid valve as a guide to surgical management. ^60,62–74 This is usually based on the z score, the number of standard deviations a measurement departs from the mean normal. Several nomograms are available for these derivations. ^75,76 Caution must be adopted, nonetheless, in interpreting these z scores, as they are not always comparable. Some depend on normal data obtained from echocardiographic studies, ⁷⁵ while others come from postmortem studies of formalin-fixed hearts. ⁷⁷

Right Ventricle

Although the initial classification of the right ventricle was into small as opposed to normal or dilated categories, ⁷⁸ this concept has now been refined to acknowledge the continuum in right ventricular size. ^44,79 When the right ventricle is said to be hypoplastic, it is not the ventricle itself that is hypoplastic, but rather the ventricular cavity that is obliterated by the severe muscular hypertrophy. Using the observations of Goor and Lillehei, that normal right ventricle has three parts, ⁸⁰ Bull and colleagues proposed the tripartite approach to categorisation of pulmonary atresia with intact ventricular septum, and this was subsequently used as the basis for surgical decision-making. ^63,81 Patients were categorised as to the degree of mural hypertrophy present, giving the following options:

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  All three portions of the right ventricle cavity being well-formed, with minimal mural hypertrophy ( Fig. 30-4 ).

  
  

  
  

  
  

  

  
  

  
  

  In this heart, the pulmonary valve is imperforate, but all three parts of the ventricular cavity are well-formed. Note the relatively normal tricuspid valve.

  
  
  
  
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  Muscular overgrowth of the apical trabecular portion. The cavity in this setting is effectively formed by the inlet and outlet components, with the infundibulum still extending to the undersurface of the imperforate valve, but through a very narrow channel. The inlet component also becomes hypoplastic, with the tricuspid valve usually tethered by short cords to the margins of the obliterated apical component ( Fig. 30-5 ). Although the cavity effectively has only two components, all three initial parts of the morphologically right ventricle are readily identified.

  
  

  
  

  
  

  

  
  

  
  

  In this heart, mural hypertrophy has obliterated the apical component of the right ventricle, the cavity being represented by the hypoplastic outlet and inlet components. Note the abnormalities of the tricuspid valve.

  
  
  
  
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  Muscular overgrowth of both apical and outlet portions. It is this process that produces the severest examples of the lesion, with the cavity in this setting effectively represented only by the hypoplastic inlet component ( Fig. 30-6 ). Even with this arrangement, nonetheless, all three portions of the right ventricle are present, with the cavities of the apical trabecular and outlet parts being obliterated.

  
  

  
  

  
  

  

  
  

  
  

  Mural hypertrophy in this heart has squeezed out the apical and outlet components, leaving the ventricular cavity represented only by the inlet.

  
  

Management of these patients, be it by surgical or interventional catheterisation techniques, requires selection of patients with suitably sized right ventricles in early life. Numerous attempts have been made to assess the adequacy of the right ventricle in order to guide the optimal strategies for management. ^{6,38,60,62,65,71,72,81–94} Owing to the fact that the walls of the right ventricle are usually severely hypertrophied, with sometimes bizarrely irregular cavities, quantification of size may be inaccurate, particularly when assessed using methodologies designed for the left ventricle. ^38,95 The advantage of the tripartite approach to classification ³⁸ is that, following angiography, the ventricles can be relatively easily grouped into subtypes. This may be more clinically relevant than estimations of volume. Thus, about three-fifths of cases have the so-called tripartite arrangement, about three-tenths have bipartite cavities, and just under one-tenth have the unipartite form. ²³ The disadvantage of this classification is that it is qualitative, and perhaps over-simplistic. ⁴⁰ Deciding how much muscular overgrowth of the apical region of the right ventricle is needed to make a right ventricle bipartite as opposed to tripartite is very subjective. Furthermore, there is a great deal of variability in size within a subtype. So-called tripartite right ventricles can range from having severely hypoplastic to hugely dilated cavities. It has also been observed that the degree of muscular hypertrophy can increase over time, both pre- and postnatally. ^17,39 Despite these limitations, the partite classification is of considerable use. Its ultimate utility may be as one of several morphological markers for the state of the right ventricle, that can be used in combination as independent risk factors for analysis of procedural outcomes.

Dilation of the right heart occurs in just under one-twentieth of cases, ²³ and is caused by a tricuspid valve with either severe Ebstein’s malformation ( Fig. 30-7 ), or significant tricuspid valvar dysplasia, ¹⁵ both these lesions leading to severe tricuspid regurgitation. The dilation of the cavity occurs during fetal life, so that, at birth, the heart fills the entirety of the thoracic cavity, producing the so-called wall-to-wall arrangement ¹ (see Fig. 30-7 ). The right ventricle is still tripartite because none of its portions are overgrown with muscle. It is also very thin-walled, particularly the atrialised portion if there is tricuspid valvar displacement. ⁹⁵ These hearts may have minimal inlet and trabecular myocardium, superficially resembling hearts with Uhl’s anomaly. ^96,97 They should not, however, be described in this fashion, since the changes are the consequence of right ventricular dilation, whereas the anomaly described by Uhl is due to congenital absence of the right ventricular parietal musculature. The dilated ventricles seen with pulmonary atresia have low pressures, and hence do not develop right ventricular to coronary arterial fistulous connections (see Table 30-2 ). The consequence of the gross dilation of the heart is that the lungs become squeezed during fetal life, and do not develop properly. All the component parts are present, but they are unable to expand in appropriate fashion because almost all the space within the thorax is occupied by the heart. ¹⁵

A, A typical wall-to-wall heart. The lungs are not seen, being squeezed out by the huge size of the dilated right-sided chambers of the heart. B, Opening the heart shows marked displacement of the hingelines of the leaflets of the tricuspid valve away from the atrioventricular junction ( red dotted line ), the hallmark of Ebstein’s malformation.

When the right ventricle is very hypertrophied, often in conjunction with tricuspid stenosis, there may be suprasystemic right ventricular pressure, assuming insignificant tricuspid regurgitation (see Table 30-2 ). It is these hearts that typically are associated with numerous fistulous communications between the ventricular cavity and the coronary arteries, and which can exhibit a right ventricular dependent coronary arterial circulation.

At a histological level, a wide range of abnormalities of the right ventricle have been found, including subendocardial and transmural ischaemia, fibrosis, infarction, so-called spongy myocardium, myocardial disarray, and endocardial fibroelastosis. ^{1,2,29,39,44,46,95,98–106} There is an inverse relationship between endocardial fibroelastosis and the presence of fistulous coronary arterial connections, albeit that the reason for this is unknown. It may be that the endocardial fibroelastosis blocks the communications during their development, or alternatively that the communications may decompress the right ventricle, hence preventing the development of endocardial fibroelastosis. ^103,107 Ischaemic changes to the right ventricle can be seen even in the absence of fistulous connections. ¹⁰⁴

At a functional level, it is not surprising that the right ventricle shows disorders of both systolic and diastolic function. ^105,108,109 Even after complete biventricular repair, diastolic abnormalities have been documented, with antegrade diastolic flow occasionally being found in the pulmonary trunk. ¹⁰⁹

The Right Ventricular Infundibulum

As with the tricuspid valve and the right ventricle, there is a wide spectrum of morphology of the infundibulum. This can range from a patent infundibulum of normal size extending to an atretic valvar membrane ¹¹⁰ ( Fig. 30-8 ), to its complete obliteration by muscular hypertrophy (see Figs. 30-6 and 30-9 ). The latter arrangement produces the so-called unipartite arrangement of the ventricular cavity ³⁸ (see Tables 30-1 and 30-2 ). Membranous atresia is found in three-quarters of cases, and muscular in the remainder. ²³ In the cases with a well-formed infundibulum, the pulmonary valvar remnant shows evidence of the initial three leaflets, fused along their zones of apposition into a fibrous plate, ^{44,58,110–112} with raphes showing the sites of fusion ( Fig. 30-8B ), albeit on occasion the zones of fusion can suggest an initial bifoliate, or even a quadrifoliate valve.

A, An infundibulum ( arrow ) that is patent to the level of an imperforate valve. B, When viewed from the arterial aspect there is evidence that the valve initially possessed three leaflets, the sites of attachment to the sinutubular junction being readily apparent ( stars ).

In these images, from patients with muscular atresia and unipartite ventricle, the pulmonary trunk has been dissected to show the evidence of sinuses of Valsalva, but absence of any leaflets of the pulmonary valve (A) and minimal formation of the leaflets (B) .

When the outlet component is also obliterated, it is not possible to trace a patent infundibulum to the ventriculo-arterial junction, although evidence of the channel initially present can be seen in dissected hearts (see Fig. 30-6 ). When examined from the arterial aspect, it can be seen that the pulmonary trunk retains its origin from the right ventricle (see Fig. 30-9 ), so that the ventriculo-arterial connections remain effectively concordant. The blind-ending pulmonary trunk originates above the triradiating sinuses, with remnants centrally showing that, initially, the root did support valvar tissue (see Fig. 30-9 ). Assessment of the size of the right ventricular outflow is of great importance when contemplating either surgical or catheter manoeuvres to enlarge the outlet component. Indeed, several groups have advocated taking the size of the outflow tract as a means of determining the best strategy for management. ^{38,63,81,83,85,86,88,91,113}

Pulmonary Arteries

The pulmonary arteries are usually confluent, and supplied by a left-sided arterial duct. ³⁷ Should systemic-to-pulmonary arteries be encountered, then suspicion should be raised that, initially, there was an interventricular communication, but that the hole between the ventricles closed during fetal life. The pulmonary trunk is usually mildly hypoplastic or of normal size ( Fig. 30-10A ), although it may, rarely, be small or even no more than a thread-like solid cord ( Fig. 30-10B ). The dimensions of the pulmonary trunk and arteries may be unrelated to the size of the right ventricular cavity. ^44,111 Even those with a tiny right ventricle can have a pulmonary trunk of near-normal size. When the right ventricle is excessively dilated, the pulmonary arteries tend to be severely hypoplastic, with greatly reduced volumes of the pulmonary parenchyma.

The figures show the variability in dimensions of the pulmonary trunk. Usually it is no more than mildly hypoplastic (A) , but it can rarely be a solid cord (B) . Note that in both instances pulmonary arterial supply is through the persistently patent arterial duct.

Left Ventricle and Mitral Valve

The mitral valve is usually normal, but dysplasia has been documented. ^112,114 The left ventricle is often dilated, with a degree of mural hypertrophy, ^112,114 and may exhibit disorders of systolic and diastolic function. ^{105,108,115–118} With a severely hypertensive right ventricle, the ventricular septum may bulge into the left ventricular outflow tract, thus providing the substrate for subaortic obstruction, ^44,112,114 particularly after the Fontan procedure, ¹¹⁹ but only rarely before. ^23,120

At a histological level, abnormalities of the left ventricle may comprise myocardial disarray, non-compacted myocardium, and endocardial fibroelastosis. ^44,101,105 An increase in collagen in the subendocardial layer has been implicated as suggesting chronic ischaemia, indicating that the left ventricle may be the limiting factor for long-lasting intervention. ¹¹⁴ Abnormalities of contractility and efficiency noted in patients after the bidirectional Glenn and total cavopulmonary procedures, unrelated to fistulous connections, have also been related to the impact of the high-pressure residual right ventricle impairing left ventricular performance. ¹¹⁸ Abnormalities of the aortic valve have been reported, even critical aortic stenosis. ¹²¹ They are rare, but if severe, presage a poor outcome. ^{112,122–124}

Coronary Arterial Circulation

What sets this lesion apart from most other congenital cardiac disorders is the high incidence of coronary arterial abnormalities. ^23,60 These changes were first described in 1926, in a 14-month-old who had intermuscular spaces with free communications between the right ventricular cavity and the coronary arteries. ¹²⁵ Over the next 50 years, appreciation of their significance changed from innocent bystanders to a major potential cause of myocardial ischaemia. ¹²⁶ The abnormalities involve disorders of origin and distribution of the coronary arteries, fistulous connections to the right ventricle, absence of proximal connections to the aorta, stenoses or interruption, and hugely dilated ectatic segments. Although some use the term ventriculo-coronary connections synonymously with coronary artery fistulas, a distinction should be drawn between blind-ending sinusoids that may connect to the myocardial capillary bed, but not the coronary arteries, and those connections which are direct communications to the coronary arteries. ^30,103 Only in the latter setting is it expected to find histological abnormalities of the coronary arteries themselves.

The ventriculo-coronary fistulous connections can be single or multiple, and tend to communicate with the anterior interventricular or the right coronary arteries, less commonly to the circumflex artery. ^23,127 There is a wide spectrum of histopathological changes, found in both the intra- and extramural coronary arteries. These range from mild degrees of intimal and medial thickening, known as myointimal hyperplasia, to loss of normal morphology, with replacement of the arterial wall by fibrocellular tissue. ³⁷ The process can cause severe distortion of the arterial structure, leading to endothelial irregularity, severe stenosis, or obliteration of the lumen.

Right Ventricular Dependent Coronary Arterial Circulation

As awareness of ventriculo-coronary arterial connections developed, so did an appreciation that surgical outcomes could be influenced by their presence and extent. Thus became established the concept of the right ventricular dependent coronary arterial circulation. In the normal situation, flow through the coronary arteries is mediated by the aortic diastolic pressure. Where there are ventriculo-coronary fistulous connections, exposure of the coronary arterial system to the high right ventricular pressures can result in stenoses and distortions, such that the aortic diastolic pressure is insufficient to drive flow into the arteries. The territory distal to the stenosis is then perfused retrogradely in systole by the right ventricle. Thus, the coronary arterial circulation is, at least, in part dependent on the right ventricle. Continued exposure of the arteries to the high pressures generated by the right ventricle then leads to further damage, thus compounding the problem. The consequence is that any intervention, resulting in decompression of the right ventricle, whether surgical or catheter, will lead to loss of coronary arterial perfusion, myocardial ischaemia, infarction, and possibly even death. ² As summarised by Freedom and colleagues in their excellent review, ² and listed in decreasing order of severity, the problems include:

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  Atresia of the aortic orifices of both coronary arteries ^128–132

  
  
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  Atresia of the aortic orifice of the left coronary artery ¹³³

  
  
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  Proximal interruption or occlusion of the main stem of the left coronary artery, its anterior interventricular or circumflex branches, or the right coronary artery ( Fig. 30-11 ), combined with fistulous communications from the right ventricle

  
  

  
  

  
  

  

  
  

  
  

  This image shows a magnification of the base of the heart. Note that the right coronary artery (RCA) is atretic at its origin from the aorta. The territory of the anterior interventricular (intervent.) artery is fed primarily from the right ventricle by two prominent and ectatic fistulous communications. The pulmonary trunk (PT) is also grossly hypoplastic.

  
  
  
  
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  Important stenosis of the main stem of the left coronary artery, its anterior interventricular or circumflex branches, or the right coronary artery, in combination with fistulous communications from the right ventricle. Less severe abnormalities could also progress with time.

  
  
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  Presence of a huge fistulous communication from the right ventricle to a coronary artery ( Fig. 30-12 ). Although this situation is rare, decompression of the right ventricle in this setting would result in a massive steal, and hence result in coronary arterial insufficiency.

  
  

  
  

  
  

  

  
  

  
  

  In this heart, mural hypertrophy has obliterated the apex and narrowed significantly the outlet component. A, A fistulous communication is present in the anterior wall of the right ventricle. B, This feeds the ectatic anterior interventricular artery.

  
  

In two large series, the frequency of such a circulation has been documented at one-twentieth and one-tenth. ^23,60,72 Other studies have documented higher frequencies, ^92,93,127 but this may partly reflect the degree to which its presence is sought. There is also controversy as to how much myocardium must be jeopardised before the arrangement is termed a right ventricular dependent coronary arterial circulation. ^60,134–136 If it is to be of clinical value, of course, the right ventricular dependent coronary arterial circulation must be predicted prior to any attempted decompression.

Prenatal Diagnosis

Fetal echocardiography is now well-established, and has proved to be effective at detecting the lesion. ¹⁷ Cases are usually detected because of an abnormal four-chamber view on echocardiography, but prenatal identification of tricuspid regurgitation, and even recognition of coronary arterial abnormalities, is now feasible. ^17,137–142 In the mainland of the United Kingdom, even by the early 1990s, two-fifths of all cases were diagnosed during fetal life. ⁹ The proportion must now be even higher. This has changed the natural history of the disease, leading at least in the United Kingdom to selective termination of pregnancy, fetal intervention, and planned delivery.

Postnatal Diagnosis

After birth, infants present with cyanosis in the neonatal period. The arterial duct is the sole source of flow of blood to the lungs, although this channel rarely remains widely patent for more than a few days. Very rarely, patients may be found with systemic-to-pulmonary collateral arteries, ^23,143–146 but usually, as soon as the duct narrows, arterial desaturation increases, and deep cyanosis results. Closure of the duct may be intermittent at first, and cyanosis may wax and wane. Infants with severe tricuspid regurgitation may also show signs of congestive heart failure.

Electrocardiography

The electrocardiogram is usually abnormal, and reflects the abnormal morphology. The frontal plane axis is less rightward than normal, usually between 30 and 90 degrees. Most newborns have an adult praecordial pattern, rather than the usual right ventricular hypertrophy ( Fig. 30-13 ). Less commonly, the pattern of right ventricular hypertrophy is present. It must be noted that the electrocardiographic patterns of right ventricular hypertrophy, or of left ventricular predominance, do not reliably predict right ventricular size. ST–T wave changes suggestive of myocardial ischaemia are occasionally present and may be related to the abnormal coronary arteries. ¹²⁶ The tall peaked P waves of right atrial enlargement may be present.

Electrocardiogram demonstrating right atrial enlargement and left ventricular predominance that is abnormal for a term newborn infant.

Chest Radiography

There is no characteristic radiographic appearance. The abdominal organs are normally positioned, and the heart is left-sided. The bronchi are normally lateralised, and the aortic arch is left sided. Pulmonary vascular markings are not increased, but the distinction between normal and decreased markings is difficult at best in the neonatal period, which is when most infants with pulmonary atresia present. The cardiac contour is not distinctive, and there is a wide range of cardiac size, from normal to wall-to-wall ( Fig. 30-14 ). Although the very largest hearts occur when there is severe tricuspid regurgitation, the size of the heart is not a reliable predictor of the size of the right ventricular cavity.

Chest radiographs in two patients with pulmonary atresia and intact ventricular septum. A, Moderate cardiomegaly, right atrial enlargement, and decreased pulmonary vascular markings. B, Marked cardiomegaly in an infant with Ebstein’s malformation of the tricuspid valve and severe tricuspid regurgitation.

Echocardiography

Cross sectional echocardiography is the diagnostic investigation of choice. As well as confirming the diagnosis, it is important also to document all the morphological features systematically, and then use the findings to determine the optimal strategy for treatment. In the first instance, the atrial arrangement should be confirmed. The right atrium will often be dilated. Any prominent venous valves should be noted. The oval foramen is usually widely patent before, but not always after, construction of a systemic-to-pulmonary shunt. ¹⁴⁸ Next, the morphology of the tricuspid valve should be assessed, documenting any dysplasia or displacement of the leaflets ( Fig. 30-15 ). The degree and velocity of regurgitation should be recorded ( Fig. 30-16 ). The diameter of the valvar orifice should be measured, and converted to a z score using published nomograms. ^75,76 The measured orifice may not represent the effective orifice, particularly where there is limited opening due to tethering or raised filling pressures.

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