being squeezed out by the huge size of the dilated right-sided chambers of the heart Bottom, The heart itself had Ebstein malformation of the tricuspid valve The pulmonary atresia itself is usually produced by an imperforate pulmonary valve, and the pulmonary arteries are typically of good size, being fed through the persistently patent arterial duct The problem lies with the tricuspid valve, which exhibits either severe Ebstein malformation (see Fig 43.8, bottom), or significant tricuspid valvar dysplasia.15 The consequence of the gross dilation of the heart is that the lungs become squeezed during fetal life, and do not develop properly hypoplastic lungs 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 The walls of the RV also become excessively thin Such myocardial thinning, existing as a consequence of ventricular dilation, should not be misinterpreted as representing the Uhl anomaly The latter lesion is the consequence of congenital absence of the myocardium in the parietal walls of the RV, and is found with normal tricuspid and pulmonary valves.42 Segmental Combinations In typical pulmonary atresia in the setting of an intact ventricular septum, there is usual atrial arrangement, with concordant atrioventricular, and potentially concordant ventriculoarterial connections, with the atretic pulmonary trunk arising from the morphologically right ventricle In exceedingly rare circumstances, pulmonary atresia can be found in the setting of an intact ventricular septum when the ventriculoarterial connections are discordant In this setting, because of the discordant connections, the atretic pulmonary trunk arises from the morphologically left rather than right ventricle Hence left ventricular hypoplasia dominates the picture, typically with the ventricle having a fibroelastotic lining as is the case in hypoplasia of the left heart with usual segmental combinations (see Chapter 69) This rare variant of pulmonary atresia with intact ventricular septum can be found either with concordant or discordant atrioventricular connections As far as we are aware, it has not been found in the setting of isomeric atrial appendages Clinical Diagnosis Prenatal Diagnosis Fetal echocardiography is now well established, and it has proved to be effective at detecting the lesion.17 Cases are usually detected because of an abnormal fourchamber view on echocardiography, but prenatal identification of tricuspid regurgitation, and even recognition of coronary arterial abnormalities, is now feasible.17,43–48 On the mainland of the United Kingdom, even by the early 1990s, two-fifths of all cases were diagnosed during fetal life.19 The proportion at the current time is likely to 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, and/or a “failed” pulse oximetry screening The arterial duct is the sole source of blood flow 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,39,49–52 but usually, as soon as the duct narrows, arterial desaturation increases, and visible cyanosis results Infants with severe tricuspid regurgitation may also show signs of congestive heart failure and respiratory distress Physical Findings The usual physical findings can be explained by the abnormal morphology Cyanosis has already been discussed Pulses and blood pressure are normal because systemic cardiac output is not impaired The jugular venous pulse is hard to evaluate in newborns, and is not a useful diagnostic sign Precordial motion is normal because a pure pressure overload of the RV does not usually result in an exaggerated left parasternal lift The second heart sound at the high left sternal border is soft and single, or is inaudible The first heart sound is normal, and an ejection sound is not present Several murmurs may be heard The most common is a soft high-pitched continuous murmur at the high left sternal border This murmur originates in the duct, and is usually quite subtle Occasionally, it may be heard only intermittently, disappearing when the duct narrows and cyanosis deepens, and appearing again as the duct opens and cyanosis lightens Some infants with pulmonary atresia have a soft high-pitched systolic murmur of tricuspid regurgitation at the low left sternal border The presence of this murmur correlates strongly with a relatively large RV,53 but lack of a murmur of tricuspid regurgitation does not rule out an RV of normal size When there is severe tricuspid regurgitation, there is often a soft, mediumpitched, mid-diastolic murmur at the low left sternal border, representing increased tricuspid flow Such a murmur is not heard in those with severe tricuspid stenosis alone because there is little or no flow across such a valve in the presence of pulmonary atresia Some infants with pulmonary atresia have no murmur In this situation, the only indication of congenital cardiac disease on physical examination is the severe cyanosis