Etiology

• Down syndrome

• Fetal alcohol syndrome

• Holt-Oram syndrome (hand-heart syndrome)

  • Autosomal dominant disorder

  • Characterized by ASD, a first-degree heart block, and abnormalities of the upper limbs (e.g., absent radial bones)

  • Affects ∼ 1/100,000 children

• Impaired growth or excessive resorption of the atrial septa in utero leads to atrial septal defects (absent atrial septa tissue).

  • Ostium primum atrial septal defect (ASD I): ∼ 15–20% (usually accompanied by other heart defects)

  • Ostium secundum atrial septal defect (ASD II): ∼ 70% (usually isolated)

• Typically a low-pressure, low-volume, minor left-to-right shunt (therefore, patients are asymptomatic)

• ASD → oxygenated blood shunting from LA to RA → ↑ O2 saturation in the RA → ↑ O2 saturation in RV and pulmonary artery

• In more severe defects, the shunts may lead to supraventricular arrhythmias, pulmonary hypertension, and/or Eisenmenger syndrome.

Types of atrial septal defects

(A) ASD II/ostium secundum atrial septal defect is the impaired growth of the septum secundum or excessive resorption of the septum primum. The defect is located in the fossa ovalis, in the cranial part of the atrial septum. (B) ASD I/ostium primum atrial septal defect is the incomplete fusion of the septum primum with the endocardial cushion (caudal part of the atrial septum, near the ventricular septum) (C) Sinus venosus ASD (rare defect) (D) Coronary venosus ASD (rare defect)

Cardiac hemodynamics in atrial septal defect

An atrial septal defect causes blood to flow from the left to the right atrium (left-to-right shunt; white arrow), resulting in volume overload of the right atrium and ventricle (1). As a result, there is dilation and compensatory hypertrophy (double-headed white arrows) of the right atrium and ventricle (2). In the late stages, Eisenmenger syndrome with shunt reversal (right-to-left shunt; white arrow) and cyanosis can occur (3).

Blue: structures that contain deoxygenated blood; Red: structures that contain oxygenated blood; Purple: structures that contain mixed blood