• SVC type-
    • 80%
    • SVC overrides atrial septum to drain into both RA and LA
    • Upper margin of ASD is devoid of atrial septal tissue
    • Right upper and middle pulmonary veins may drain into SVC
  • IVC type-
    • 20%
    • Right pulmonary veins may drain into IVC


  • Right horn of sinus venosus gives rise to SVC and IVC. This process is defective.


  • The left to right shunt is small.

Clinical features

  • Due to the small shunt
    • S2 has wide variable split
    • No tricuspid MDM


  • Ectopic atrial rhythm with superior P axis is diagnostic. This is not always present.

Chest X-ray

  • Ampullary dilation of SVC may be present due to anomalous pulmonary drainage.


  • SVC straddling ASD

Cardiac catheterization

  • Catheter takes acute turn at a high plane.
  • SVC higher oxygen saturation than innominate vein.


  • First a tunnel is made to drain the anomalous pulmonary vein into LA.
  • Then ASD is closed.