FIG 69.9 Aneurysmal floor of the intact oval fossa as seen from the right atrial aspect A four-chamber section of the heart is shown in at right in Fig 69.7 In some of these patients with an intact oval fossa, the pulmonary venous drainage can be abnormal because of the presence of a so-called levoatrial cardinal vein or because of fenestration of the walls that usually separate the left atrium from the cavity of the coronary sinus This provides an overflow for the left atrial return More usually, there is no such overflow when the atrial septum is intact The resulting increase in left atrial pressure produces increased left atrial hypertrophy, along with changes in the lungs, including arterialization of the pulmonary veins and lymphangiectasia, with a “cobblestone” appearance of the pulmonary surfaces seen at autopsy These are bad prognostic features In most instances, as stated, the oval foramen is patent and does not obstruct flow from left to right The primary atrial septum is frequently deviated into the left atrium Left ventricular endocardial fibroelastosis is seen only when the mitral valve is perforate Aortic atresia, when present, can result from an imperforate valve More usually, there is no evidence of persisting leaflets at the ventriculoarterial junction, with fibromuscular tissue interposing between the ventricular cavity and the blind-ending aortic root The aortic root itself is usually markedly hypoplastic, with the ascending aorta serving only as a conduit to feed the coronary arteries (Fig 69.10).13 Further distally, aortic coarctation is common, occurring in over four-fifths of patients.14 The obstructive shelf is typically in a preductal location but can be found paraductally Ductal tissue is not only incorporated into the stenosing shelf but also may extend proximally and distally, an important point for those undertaking surgical palliation of these patients Abnormalities of the coronary arteries, such as ventriculocoronary fistulas and abnormal tortuosity, are more common in the subgroup of patients with mitral stenosis and aortic atresia (Fig 69.11) Such coronary arterial fistulas, if present, are not necessarily associated with abnormalities of the right ventricular myocardium but can produce an increased risk of mortality at the first stage of a Norwood reconstruction.15 The conduction tissues are in their expected location, albeit with miniaturization of the left bundle branch in keeping with the size of the left ventricle FIG 69.10 Typical arrangement of the arterial pathways in the setting of hypoplastic left heart syndrome The pulmonary trunk feeds the descending aorta via the persistently patent arterial duct and provides retrograde flow to the minute ascending aorta, which serves as a conduit to feed the coronary arteries