Clinical Diagnosis Presentation The increasing frequency of antenatal diagnosis of transposition allows the clinical team to deliver the infant in a specialist center or arrange prompt transfer for those born outside of such centers.23 As a result, time-sensitive and potentially lifesaving interventions such as the initiation of a prostaglandin infusion and balloon atrial septostomy can be expedited and the potential for hemodynamic instability reduced.24 Most newborns with transposition have a normal birth weight.25 They have been noted to have smaller occipitofrontal circumferences at birth than controls, which may reflect the abnormal hemodynamics in utero, with relatively desaturated blood circulating to the brain and upper body.26,27 Undiagnosed infants can present with cyanosis, with or without clinical evidence of circulatory insufficiency As discussed, QEP and QES depend on the extent of circulatory mixing In the extreme, some infants may present shortly after birth with cyanosis and circulatory collapse, which is most often related to inadequacy of the interatrial communication Infants with a widely patent arterial duct and a large unrestrictive ventricular septal defect may present with only minimal cyanosis and, instead, later develop signs of pulmonary overcirculation Clinical examination during infancy reveals a variable degree of cyanosis, which is incompletely responsive to supplemental oxygen The adequacy of the peripheral pulses generally reflects the overall circulatory state Infants with real or pending circulatory collapse will tend to be profoundly desaturated, with globally reduced peripheral perfusion, cool extremities, and weak pulses Decreased pulses noted only in the lower extremities should alert the clinician to an associated coarctation or interruption of the aorta An upper to lower extremity blood pressure gradient may be present Cardiac auscultation typically reveals a single second heart sound attributable to the relative positions of the aortic and pulmonary valves There may be an audible continuous murmur from the arterial duct or a systolic murmur related to a ventricular septal defect Large septal defects will eventually result in findings consistent with pulmonary overcirculation including tachypnea, dyspnea, hepatomegaly, feeding difficulty, and failure to thrive Chest Radiography The chest radiograph may or may not be abnormal Cardiac size is often normal, whereas the pulmonary vascular markings may be reduced, normal, or increased, reflecting the volume of flow to the lungs In approximately one-third of neonates, the mediastinum is narrow, a result of the anteroposterior relationship of the arterial trunks This classic finding has been described as resembling an “egg on a string.” Electrocardiography In most newborns, the electrocardiogram is normal During early infancy prior to surgical intervention, the electrocardiogram may begin to reflect right ventricular hypertrophy and later demonstrate right-axis deviation A superior axis in the neonatal period suggests associated abnormalities of the tricuspid valve, particularly straddling or overriding Fetal Imaging In the modern era, transposition is being diagnosed more frequently in utero than it has in the past; however, even recent series demonstrate that less than half of patients have an antenatal diagnosis.23,28 The efficacy of fetal screening is based on the premise that early detection will provide opportunities for parental choice and allow optimal neonatal care and preoperative management In some series, reductions in both preoperative and postoperative morbidity, as well as mortality, have been demonstrated in neonates after an antenatal diagnosis of transposition.24,28 However, the data are mixed, with other studies reporting no such benefit.29,30 In mothers referred for comprehensive fetal echocardiography performed by specialist sonographers, the lesion can be detected with high levels of accuracy (Fig 37.10, Video 37.1).30 A systematic segmental approach is recommended.31 A detailed assessment of the adequacy of intracardiac mixing, particularly at the atrial level, is usually performed Restriction to flow at the atrial level is a highly specific predictor of the need for emergency neonatal care, but its sensitivity is too low to permit detection in all fetuses.32 Findings of a small oval foramen relative to the total septal length and reversal of flow through the arterial duct during diastole have been associated with the need for an early atrial septostomy.33,34 There are mixed data regarding whether increased mobility of the flap of the septum primum is similarly predictive Four-dimensional fetal echocardiography may provide an advantage over cross-sectional imaging in that it creates an en face view of the four cardiac valves, thus enhancing the definition of the spatial relationships of the great arteries and, in turn, improving the probability of predicting an abnormal distribution of the coronary arteries.35 Cardiac magnetic resonance may be used to detect reductions in flow at the atrial and ductal levels and excessive flow through aortopulmonary collateral arteries.36 FIG 37.10 Fetal echocardiogram demonstrating the aorta (Ao) arising from the right ventricle (RV) and the pulmonary artery from the left ventricle (LV) Note the parallel orientation of the great vessels, not seen in normally connected hearts LPA, Left pulmonary artery; RPA, right pulmonary artery Postnatal Echocardiography The echocardiographic examination of the neonate with transposition requires a complete assessment of the anatomy, using a sequential approach, an examination of the circulatory physiology, particularly of the adequacy of mixing, and an estimation of the ability of the left ventricle to support the systemic circulation Echocardiographic confirmation of the diagnosis requires