Pathophysiology and natural history of atrial septal defect

Abstract

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.

Keywords: Atrial septal defect; natural history; physiopathology; pulmonary hypertension.

Figure 1

Schematic representation of the systemic and pulmonary circulations, in case of a large atrial septal defect. Atrial shunt occurs mostly during end systole and the beginning of diastole. Pressures in both atria are equalized, and the shunt only depends on the ratio of ventricular compliances.

Figure 2

Simulation by CircAdapt software (www.circadapt.org) of left (red) and right (black) ventricular pressure-volume loops without (dotted line) and with large atrial septal defect (solid line).

Figure 3

Natural history of patients with unoperated significant atrial septal defects, according to the age at evaluation: before 40 years old (A) and after 40 years old (B). The relative sizes of the circles represent the relative proportion of occurrence of cardiac adverse events. HF, heart failure; PHT, pulmonary hypertension; M, mortality.