Ostium Secundum ASD: The Most Common Atrial Septal Defect

Ostium secundum atrial septal defect (ASD) accounts for ~70–80% of all ASDs. It is a defect in the fossa ovalis region of the interatrial septum—caused by excessive resorption of the septum primum or inadequate growth of the septum secundum.

Key Features

• Location: Central septum, at the site of the foramen ovale.
• Hemodynamics: Left-to-right shunt (higher left atrial pressure) → right atrial/ventricular volume overload → pulmonary overcirculation.
• Gender: 2:1 female predominance.
• Associations: May occur with mitral valve prolapse, partial anomalous pulmonary venous connection (PAPVC).

Clinical Presentation

• Often asymptomatic in childhood; discovered incidentally (murmur, abnormal CXR/ECG).
• Adults: exertional dyspnea, palpitations (atrial arrhythmias), fatigue, paradoxical embolism risk.
• Physical exam: Fixed, wide splitting of S2; systolic ejection murmur at left upper sternal border (pulmonary flow); diastolic rumble at LLSB (tricuspid flow) if large shunt.

Diagnosis & Management

• Echo (TTE/TEE): Definitive—visualizes defect, shunt direction, chamber sizes, pulmonary pressure.
• Closure indicated if: Qp:Qs > 1.5, right heart enlargement, symptoms, paradoxical embolism, pulmonary hypertension (reversible).
• Device closure (percutaneous): Preferred for suitable anatomy (adequate rims).
• Surgical repair: For large defects, deficient rims, or associated anomalies.

Untreated large ASDs lead to Eisenmenger syndrome (irreversible pulmonary vascular disease). Early closure normalizes life expectancy.