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Congenital Cardiac Right to Left Shunts

Congenital Cardiac Right to Left Shunts

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Congenital Right to Left Shunts
Healthy Heart Typically, post-natal systemic and pulmonary circulation run in parallel and maintain separation between low and high oxygen blood. When separation is incomplete, low and high oxygen blood mix, which produces systemic blood with insufficient oxygen concentrations.
Review fetal circulation & adult circulation
Right to Left Shunts
  • Diagnosed prenatally or soon after birth.
  • Are characterized by early cyanosis.
    • So-called "blue babies" have hypoxemia because systemic blood bypasses the lungs.
The Great Vessels
  • The aorta carries blood with a high oxygen concentration to the body tissues.
  • The pulmonary trunk carries blood with a low oxygen concentration to the lungs.
  • Ductus arteriosus
    • Allows blood to flow from pulmonary trunk to aorta, bypassing the lungs.
    • The ligamentum arteriosus is the adult remnant of the ductus arteriosus.
Persistent Truncus Arteriosus
  • Caused by a malformed or absent aortico-pulmonary septum that fails to form separate outflow tracts for systemic and pulmonary circulations.
  • Thus, blood from each ventricle enters the common vessel, largely bypassing the lungs.
  • The defect is attributed to disturbances in secondary heart field or cardiac neural crest formation, and, therefore, is often associated with ventricular septal defect (recall the aorticopulmonary septum contributes to the membranous portion of the interventricular septum.
Transposition of the Great Vessels
  • Occurs when the conotruncal ridges fail to spiral, and the aorticopulmonary septum creates two distinct vessels.
  • The right ventricle continuously pumps low-oxygen blood to the body through the aorta, while the left ventricle continuously pumps high oxygen blood to the lungs through the pulmonary trunk.
  • Thus, blood from the right heart never enters the lungs for re-oxygenation, and blood from the left heart never reaches body tissues.
  • Newborn viability depends on accompanying septal defects and patent ductus arteriosus to provide opportunities for blood mixing.
Tricuspid Atresia
  • The right atrioventricular valve, aka, tricuspid valve, doesn't properly form. Instead of ensuring unidirectional blood flow from the right atrium to the right ventricle, it blocks flow.
  • Associated characteristics are septal defects and/or patent ductus arteriosus that allow blood mixture, and a hypoplastic (smaller than usual) right ventricle.
  • Corrective surgeries are necessary to establish healthy blood flow.
Tetralogy of Fallot
  • Venous blood from the right heart and mixed blood from the left heart are pumped through the pulmonary trunk and aorta.
Characterized by 4 defects:
    • Pulmonary stenosis (narrowing of pulmonary trunk)
    • Rightward displaced aorta, with opening over right ventricle (aka, overriding aorta)
    • Ventricular septal defect, specifically, of the membranous portion
    • Right ventricular hypertrophy, which occurs in response to increased work load to pump blood through stenotic pulmonary trunk
Total Anomalous Pulmonary Venous Return
  • Characterized by pulmonary veins that drain into the right atrium via the coronary sinus, superior vena cava, brachiocephalic vein, etc.
Example:
  • Paired right and left pulmonary veins also draining into the right atrium via the coronary sinus.
    • In this case, viability requires an accompanying shunt that allows oxygenated blood to reach the left side of the heart.

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