The 'Upstairs-Downstairs' heart with complete main pulmonary artery agenesis and PDA-dependent pulmonary circulation:...

Superior-inferior ventricular arrangement is an exceedingly rare form of congenital cardiac malposition, representing fewer than 0.1% of all congenital heart diseases, and is almost invariably associated with complex intracardiac anomalies. We report a 3-year-old male who presented with persistent cyanosis, exertional dyspnea, and failure to thrive. Prospective ECG-gated CT angiography demonstrated situs solitus with levocardia. A superior-inferior ventricular arrangement was present, with the morphologic left ventricle positioned superior to the morphologic right ventricle. The great arteries were normally related, with a left-sided aortic arch. A large ventricular septal defect was identified. Pulmonary atresia was present, characterized by the absence of the right ventricular outflow tract, pulmonary valve, and main pulmonary artery. Native confluent branch pulmonary arteries were present and received pulmonary blood flow through a large patent ductus arteriosus supplying the left pulmonary artery, with additional small systemic-to-pulmonary collateral vessels. The morphologic right ventricle was dilated and hypertrophied, with associated enlargement of the right atrium. Pulmonary venous drainage was normal, and no abnormalities of the systemic venous drainage were identified. This case underscores the critical role of cardiac CT angiography in comprehensive anatomical delineation of rare and complex congenital cardiac malformations, with direct implications for surgical planning and prognostication.