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Key Features

  • Four common forms

    • Ostium secundum defect (midseptum) (80% of cases)

    • Ostium primum defect (low septum)

    • Sinus venosus defect (upper or lower septum), often associated with partial anomalous pulmonary venous connection

    • Coronary sinus defect (unroofed coronary sinus)

  • Shunt due to oxygenated blood from higher-pressure LA shunting into RA, increasing RV output and pulmonary blood flow

  • Prolonged high flow through pulmonary circulation often leads to elevated pulmonary pressure, but severe pulmonary hypertension with cyanosis (Eisenmenger physiology) uncommon (about 15%)

  • Patent foramen ovale is responsible for most paradoxical emboli especially if associated with redundant septal tissue (septal aneurysm)

Clinical Findings

  • Most small or moderate atrial septal defects (ASDs) are asymptomatic for long periods

  • Direction of left-to-right at the atrial level depends on respective compliance of atria (which depend on ventricular compliance)

    • Normally, LV compliance worsens with age, and left-to-right shunt increases with age

    • If shunt results in a reduced RV compliance over time, then left-to-right shunt may be lessened and even reverse

    • If it reverses, cyanosis is present

  • Large shunts can produce exertional dyspnea or cardiac failure

  • Moderately loud systolic ejection murmur in the second and third interspaces due to increased pulmonary artery flow; S2 widely split, does not vary with breathing

  • In very large left-to-right shunts, a tricuspid rumble may be heard due to the high flow


  • ECG

    • Incomplete or complete right bundle branch block

    • Right axis deviation, RV hypertrophy

    • With sinus venosus defects, the P axis is leftward due to abnormal atrial activation

  • Chest radiograph

    • Large pulmonary arteries

    • Increased pulmonary vascularity

    • Enlarged RA and RV

    • Small aortic knob with all pre-tricuspid valve cardiac left-to-right shunts

  • Echocardiography is diagnostic

    • Saline injection (bubble contrast) demonstrates the right-to-left component of the shunt (occurring in essentially all) and Doppler flow can demonstrate shunting in both directions

    • Transesophageal echocardiography is helpful when transthoracic echocardiography quality is not optimal, and it improves the sensitivity for small shunts and provides a better assessment of PFO anatomy

  • Both CT and MRI can elucidate the atrial septal anatomy and demonstrate associated lesions

  • Cardiac catheterization

    • Can determine size and location of the shunt

    • Can measure the pulmonary pressure and pulmonary vascular resistance (PVR)


  • Small shunts (< 1.5:1) do not require intervention

  • If the pulmonary systolic pressure is > two-thirds the systemic pressure, the pulmonary hypertension may preclude ASD closure

  • Testing with transient balloon occlusion of the shunt and with pulmonary vasodilators may be required in the presence of pulmonary hypertension

  • Percutaneous devices can close most secundum ASDs without surgery

  • Ostium primum, sinus venosus ASDs, and coronary sinus ASDs require surgery

  • If predominantly a right-to-left shunt, closure probably not effective (consistent with Eisenmenger physiology)

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