Atrial Septal Defect in Infancy

The atrial septum was evaluated in necropsy specimens from subjects who died under the age of one year. Observations indicated that when an atrial septal defect (ASD) was present, there was commonly an associated condition. In the vast majority, the ASD was at the fossa ovalis and took the form of valvular incompetent foramen ovale. The findings strongly support the concept that an ASD at the fossa ovalis found in symptomatic infants is acquired secondary to the effects of an underlying anomaly. Overloading of the left or right atrium appears to be the mechanism resulting in the formation of an acquired ASD. In infants with various anomalies that cause overloading of the left atrium, such as left-to-right shunts from ventricular septal defect and left-sided inflow obstruction, the incidence of a defect at the fossa ovalis was 18% and 29%, respectively. A similar type of ASD was found in 31% of the cases with right-sided inflow or outflow obstruction.