Skip to Main Content



  • Often asymptomatic and discovered on routine physical examination.

  • With an ASD and left-to-right shunt: RV lift; S2 widely split and fixed.

  • Echocardiography/Doppler is diagnostic.

  • ASDs should be closed if there is evidence of an RV volume overload regardless of symptoms.

  • A PFO, present in 25% of the population, rarely can lead to paradoxical emboli. Suspicion should be highest in patients who have cryptogenic stroke before age 55 years.


Knowing how the atrial septum develops embryologically helps in understanding the different anatomic lesions that create a communication between the atria (eFigure 10–18). Embryologically, the septum primum separates the two atria, first moving inferiorly toward the endocardial cushions. The ventricular septum forms by moving upward from the ventricles to the endocardial cushions at the same time. If the atrial septum does not make it all the way, the residual defect in the septum primum (ostium primum) results in the primum ASD. If the septum primum makes it all the way to meet the ventricular septum, a hole or holes (fenestrations) form in the middle of the septum (creating the ostium secundum). A second septum then moves down the right side of the first and normally covers the ostium secundum hole. If it does not cover the hole or holes, a secundum ASD is present. The septum secundum normally completely covers the right side of the atrial septum except for an oval defect in it inferiorly (the foramen ovale). After birth, the returning blood from the lungs increases the left atrial pressure and the two septi fuse in 75% of the population. If the septae do not fuse, a patent path from the RA to the LA persists (the PFO). The most common form of ASD (80% of cases) is persistence of the ostium secundum in the mid-septum. A less common abnormality is persistence of the ostium primum (low in the septum). In most patients with an ostium primum defect, there are mitral or tricuspid valve “clefts” as well as a ventricular septal defect (VSD) as part of the atrioventricular (AV) septal defect (eFigure 10–19). A sinus venosus defect is a hole, usually at the upper (or rarely the lower) part of the atrial septum, due to failure of the embryonic superior vena cava or the inferior vena cava to merge with the atria properly. The superior vena cava sinus venosus defect is usually associated with an anomalous connection of the right upper pulmonary vein into the superior vena cava. The coronary sinus ASD is rare and is basically an unroofed coronary sinus that results in shunting from the left atrium (LA) to the coronary sinus and then to the RA.

eFigure 10–18.

Atrial septal anatomy. A: Embryologically, the septum primum (first septum) divides the atrium by migrating to the ventricles. The gap preceding the septal migration is the ostium primum. B:...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.