Adult Echocardiography Practice Exam

A patient with pulmonary atresia and a small right ventricle has an atrial shunt. Which direction would the shunt typically travel?

1. Left to right

2. No shunt because of pulmonary atresia

3. No shunt because right ventricle is not dilated

4. Right to left

The correct answer is: Right to left

In the context of pulmonary atresia combined with a small right ventricle, the presence of an atrial shunt would typically show a right-to-left flow direction. Pulmonary atresia is a condition where the pulmonary valve does not form properly, obstructing flow from the right ventricle to the pulmonary artery. Given that the right ventricle is small and unable to support sufficient blood flow to the pulmonary circuit, the function of the atrial shunt (often an atrial septal defect or patent foramen ovale) is to allow blood to bypass the non-functioning right ventricle and the blocked pulmonary route. In this scenario, oxygen-poor blood from the right atrium moves directly into the left atrium through the atrial shunt, resulting in deoxygenated blood entering systemic circulation. This represents a right-to-left shunt, where blood is diverted away from the pulmonary circulation, leading to lower oxygenation levels in the body. This understanding is critical in managing patients with this condition, as it highlights the importance of shunt dynamics and the impact on systemic oxygen delivery.