Coanda effect on ductal flow in the pulmonary artery.

The Coanda effect (the tendency of a jet stream to adhere to a boundary wall), and the relevant anatomy, may explain the location of ductal jets within the main pulmonary artery. With the usual insertion of the duct close to the left pulmonary artery, during right ventricular ejection, the ductal jet adheres to the left wall of the main pulmonary artery. When right ventricular ejection is absent in pulmonary atresia, the ductal jet streams down the right wall of the pulmonary artery to the pulmonary valve, reverses, and maintains a parallel column back toward the bifurcation. If the reversed flow is mistaken for ejection from the right ventricle, the diagnosis of pulmonary atresia may be missed.