CHAPTER SUMMARY AND CENTRAL ILLUSTRATION
This chapter discusses the various types of congenital cardiac shunt lesions, their anatomy, physiologic impact, epidemiology, clinical presentation, work-up, and management. In congenital shunt lesions, a fundamentally important link exists between anatomy and physiology, such that the location of a shunt dictates its physiologic impact and likely sequelae. As a general rule, shunts upstream of the tricuspid valve (including atrial septal defects and accompanying partially anomalous pulmonary venous return) lead to volume overloading of the right atrium and right ventricle with consequences related to right-sided chamber dilatation and dysfunction. By contrast, shunts downstream of the tricuspid valve (including ventricular septal defects and patent ductus arteriosus) result in volume loading of the left atrium and left ventricle with accompanying consequences. Each lesion has unique associations with other cardiac abnormalities and genetic syndromes. Fundamentally important to all cardiac shunts is the downstream impact of pulmonary overcirculation on the pulmonary vascular bed. Changes in pulmonary vascular physiology, including the development of pulmonary arterial hypertension, play a major role in dictating prognosis and therapeutic decision-making.
eFig 66-01 Chapter 66: Shunt Lesions
Atrial septal defects (ASDs) are a group of lesions characterized by an abnormal communication between the right and left atria. There are several different types of ASDs1 that, while etiologically and anatomically distinct, are physiologically similar to one another. In patients with ASDs, the physiologic impact of lesion-related shunting on the myocardium and pulmonary vascular tissues largely drives management decisions. Due to the heterogeneity in anatomy and physiologic sequelae, individualized decision-making is necessary to determine the timing, appropriateness, and technique employed for ASD closure.
Secundum ASDs occur in the region of the fossa ovalis (Fig. 66–1). Embryologically, secundum ASDs are the result of either an excessively large ostium secundum, or diminished growth of the septum secundum. Either or a combination of both processes lead to the presence of a defect in the midportion of the interatrial septum, which may be multiple (Figs. 66–2 and 66–3).
The different types of atrial septal defects.
Embryology of the atrial septum. (A) The ostium primum is closed by the septum primum that fuses with the endocardial cushion. (B) A portion of the septum primum then involutes creating the ostium secundum. (C) The septum secundum develops adjacent to the septum primum. This septum does not form an uninterrupted sheet, but has a persistent defect in its center called the foramen ovale. (D) The foramen ovale normally does not overlap with the ostium secundum, leading to the formation of a one-way ...