In patients with tricuspid atresia, blood is shunted from the right atrium to the left atrium through what structure?

In patients with tricuspid atresia, the normal flow of blood is disrupted due to the absence of a functional tricuspid valve, which prevents blood from flowing from the right atrium to the right ventricle. As a result, blood from the right atrium must find an alternative route to reach the left side of the heart.

The patent foramen ovale is a key structure in this scenario. It is a remnant of fetal circulation that allows blood to flow between the right atrium and left atrium. In the case of tricuspid atresia, the presence of a patent foramen ovale facilitates the necessary shunting of deoxygenated blood from the right atrium into the left atrium, allowing some oxygenated blood to circulate through the systemic circulation.

This physiological adaptation is critical in helping maintain some level of oxygen delivery to the body despite the anatomical abnormalities associated with tricuspid atresia. While other congenital anomalies like a ventricular septal defect or an atrial septal defect could also allow for shunting, the specific question regarding the default structure facilitating this shunt in the absence of a functioning tricuspid valve indicates the relevance of the patent foramen ovale in this context.