Pathophysiology and natural history of atrial septal defect.

Atrial septal defects are among the third most common types of congenital heart disease. This group of malformations includes several types of atrial communications allowing shunting of blood between the systemic and the pulmonary circulations. The nature of shunting across the defect in patients with atrial septal defect is of particular interest. Understanding the underlying mechanisms of interatrial shunts and their natural history will help selecting the best timing for closure, before irreversible cardiac and pulmonary injury occur. This review describes the different pathophysiologic mechanisms involved in the direction and magnitude of blood flow through atrial septal defects. The natural history of an individual born with an isolated atrial septal defect is then discussed, including the impact of a longstanding shunt on survival.