resistance are made, correcting for the proportion of blood flow that would normally go to the anomalously connected lobe or lobes, it appears that this resistance is the same in the normally and anomalously connected regions of lung.141 Therefore it is not the vascular resistance that determines preferential flow to the anomalously connected lobe or lobes The left-to-right shunt at atrial level has the same consequences on the right heart and pulmonary circulation as does an atrial septal defect Pulmonary hypertension is rare except in some infants with scimitar syndrome who exhibit arterial but not venous muscularity in both lungs.142 Presentation and Symptoms Presentation is as for an atrial septal defect except that some asymptomatic patients may present with an unexpected abnormality on chest radiograph (see later) Presentation with heart failure occurs rarely, as with interatrial defects at the oval fossa.140 Patients with scimitar syndrome can present with recurrent pneumonia, wheezing, or hemoptysis The physical signs in patients with an associated atrial septal defect are as for the atrial septal defect In those patients with an intact atrial septum, the signs are as for atrial septal defect with left-to-right shunt of comparable size except that the second heart sound, though widely split, often varies normally with respiration.127,140 Sinus arrhythmia is common This is presumably because changes in intrathoracic pressure affect the atria to different degrees, as in normal individuals This contrasts with what happens in the presence of a large atrial septal defect Therefore, if a patient has the pulmonary ejection systolic murmur of an atrial septal defect and yet has physiologic splitting of the second heart sound, the diagnosis is more likely to be partially anomalous connection with intact atrial septum rather than an atrial septal defect Investigations Chest Radiography The general appearances of the heart and pulmonary vessels will be exactly as for an atrial septal defect with a comparable left-to-right shunt But the anomalous pulmonary vein may also be evident A snowman appearance would suggest return to the left vertical vein; in older patients with return to the inferior caval vein, the anomalous pulmonary vein is usually visible.138,140 We have already highlighted the importance of this appearance as seen in the scimitar syndrome.143 The hypoplasia of the right lung, pulmonary sequestration, and secondary right-sided location of the heart usually accentuate the scimitar sign as seen in the frontal projection of the right lung It is formed by the anomalous right pulmonary vein (Fig 28.25), though rotation of the heart to the right may completely obscure the scimitar in infants.142 Exceptionally, such a scimitar may be formed by a common right pulmonary vein that descends toward the diaphragm but ascends to connect normally to the left atrium144–146 or to the left atrium and the inferior caval vein.144 FIG 28.25 Chest radiograph showing scimitar syndrome There is only mild hypoplasia of the right lung; consequently the bulk of the heart is still in the left chest (Courtesy Dr Simon Rees, National Heart Hospital, London, United Kingdom.) Electrocardiography When the partially anomalous connection is associated with an atrial septal defect in the oval fossa, or the atrial septum is intact and the anomalous connection is supracardiac or to the right atrium, the electrocardiogram is identical to that of an atrial septal defect Specifically, V1 shows an rsr′ or rsR′ (rarely a QR) pattern Partial return to the inferior caval vein with intact atrial septum is characterized by a terminal s or S wave in V1.140 Echocardiography As with TAPVC, echocardiography is the primary means of defining pulmonary venous anatomy in these patients As with all patients, echocardiographers should persistently attempt to identify pulmonary venous connections from all portions of the lung into the heart Increased or atypical flow in the superior or inferior caval veins should alert one to the possibility of partially anomalous pulmonary venous connection (Figs 28.26 and 28.27) Partially anomalous venous connection is the Achilles heel of the echocardiographer, particularly when associated abnormalities mask its clinical effects There are three problems First, even when all four pulmonary veins are normally connected, they may not be imaged In particular, fusion of two pulmonary veins on one side into a common pulmonary vein may not be recognized, although it is a common normal variant Second, some patients have more than four pulmonary veins For example, if a patient has a right middle lobe draining normally to the left atrium but a right upper lobe draining to the superior caval vein, the echocardiographer may visualize four pulmonary veins entering the left atrium and erroneously assume that completely normal pulmonary venous connections are present (Fig 28.28) Third, the great clue to the diagnosis of TAPVC, namely a collecting pulmonary venous channel (or confluence), is almost invariably missing in partially anomalous connection In short, partially anomalous venous connection can be positively and reliably diagnosed, particularly if it is via a left vertical vein (Fig 28.29), but it can rarely, if ever, be ruled out, even using colorflow mapping and transesophageal echocardiography.146 Surgeons should be aware of this caveat in diagnosis Partially anomalous pulmonary venous connection is occasionally identified by fetal echocardiography.115