Persistent Left Superior Vena Cava

  • Incidence: Uncommon, affecting approximately:
    • 0.3% of the general population.
    • 4.3-11% of patients with congenital heart disease (CHD).
  • Two Types:
    • Persistent left SVC connecting to right atrium via coronary sinus:
      • This is the more common anomaly of the SVC, accounting for about 90% of cases.
    • Persistent left SVC connecting to left atrium:
      • Found in the remaining 10% of cases.
      • Most individuals with this connection also have associated atrial septal defects (ASD) or heterotaxy syndromes.
      • Results in a small right-to-left shunt.
  • Etiology (Cause):
    • Failure of regression of the left anterior and common cardinal veins and the left sinus horn during development.
  • Course of Persistent Left SVC Draining into Right Atrium:
    • Originates at the junction of the left subclavian vein and the left internal jugular vein.
    • Passes lateral to the aortic arch.
    • Receives the left superior intercostal vein.
    • Located anterior to the left hilum.
    • Joined by the hemiazygos system.
    • Crosses the posterior wall of the left atrium.
    • Receives the great cardiac vein to become the coronary sinus (common).
  • Course of Persistent Left SVC Draining into Left Atrium:
    • Originates at the junction of the left subclavian vein and the left internal jugular vein.
    • Passes lateral to the aortic arch.
    • Receives the left superior intercostal vein.
    • Located anterior to the left hilum.
    • Joined by the hemiazygos system.
    • Passes between the left atrial appendage (anteriorly) and the left superior pulmonary vein posteriorly.
  • Associated Findings:
    • Absent or small left brachiocephalic vein (65% of cases).
  • Bilateral SVCs:
    • The abnormality effectively results in bilateral superior vena cavae.
  • Absent Right SVC:
    • In a small percentage of cases (10-18%), the right SVC may be absent.
  • Radiographic Findings:
    • Chest X-ray post-implantation of a tripolar RV defibrillation lead via a persistent left SVC demonstrates a typical "alpha" shaped loop of the lead in the right atrium.
    • This shape is due to the proximity of the coronary sinus orifice (where the lead enters) and the tricuspid valve.
    • The ICD generator is typically placed in a pectoral position, serving as the defibrillation anode (active can principle).
    • Lateral chest X-ray shows the lead following the path of the persistent left SVC along the posterior aspect of the left atrium.
    • The lead enters the heart through the coronary sinus at the bottom of the right atrium and passes the tricuspid valve near the peak of the loop in a more anterior and superior position.