Paradoxical Continuous Left-to-Right Ductal Shunt during Circulatory Collapse due to Ductal Closure in an Infant with Duct-Dependent Systemic Circulation.

Duct-dependent systemic circulation is accompanied by a right-to-left ductal shunt, at least during systole. Although observations of paradoxical continuous left-to-right shunts in duct-dependent systemic circulation have been reported, the mechanism remains unclear. We report a continuous left-to-right ductal shunt throughout the cardiac cycle during the initial recovery phase from circulatory collapse and right ventricular (RV) dysfunction due to ductal closure in an infant with hypoplastic left heart and severe aortic coarctation. Further recovery improved his RV function and changed the ductal flow from continuous left-to-right to bidirectional, which is usually seen in duct-dependent systemic circulation. Marked RV dysfunction may contribute to the continuous left-to-right ductal shunt. A continuous left-to-right ductal shunt should not be used to rule out duct-dependent systemic circulation.