Persistent fetal circulation: Causes

In utero fetal circulation is different from adult circulation in 4 primary ways:

1. Umbilical venous blood bypasses the liver by way of the ductus venosus
2. Blood is shunted from right atrium to left atrium through the foramen ovale
3. Blood ejected from the right ventricle bypasses the lungs by traveling through the ductus arteriosus and into the systemic circulation
4. Blood travels back to the placenta by way of the umbilical artery

The high pulmonary vascular resistance (PVR) of the fetus is responsible for the shunting of blood away from the lungs and through the foramen ovale and ductus arteriosus. As the alveoli are first exposed to oxygen after birth, the PVR decreases resulting in increased flow in the adult circulatory pattern, and eventual closure of the foramen ovale and ductus arteriosus.

There are 3 main categories of etiologies of persistent fetal circulation (PFC) in the newborn:

1. Congenital heart defect Any congenital heart defect which results in elevated pulmonary artery or RV pressures will have PFC in order to allow adequate cardiac output. The effect this will be R –> L shunt and cyanosis.
2. Primary PFC Hypertrophy and increased muscularization of the walls of the pulmonary vessels results in persistently elevated PVR. Poor prognosis.
3. Secondary PFC Most commonly seen in infants with lung disease, where hypoxia and acidosis leads to pulmonary vasoconstriction and persistently elevated PVR. Causes include:

• Meconium aspiration (most common)
• Hyaline membrane disease
• Diaphragmatic Hernia
• Sepsis syndrome (often related to GBS, listeria, E Coli, H influenzae B)
• Pulmonary embolism

Updated definition 2020:

In utero fetal circulation is different from adult circulation in 4 primary ways:

1. Umbilical venous blood bypasses the liver by way of the ductus venosus
2. Blood is shunted from right atrium to left atrium through the foramen ovale
3. Blood ejected from the right ventricle bypasses the lungs by traveling through the ductus arteriosus and into the systemic circulation
4. Blood travels back to the placenta by way of the umbilical artery

The high pulmonary vascular resistance (PVR) of the fetus is responsible for the shunting of blood away from the lungs and through the foramen ovale and ductus arteriosus. When the alveoli are first exposed to oxygen after birth, the PVR decreases resulting in increased flow in the adult circulatory pattern, and eventual closure of the foramen ovale and ductus arteriosus. When these events do not occur as planned, PVR and right ventricular pressures remain elevated causing right to left ductal and/or atrial shunting after birth. This condition is known as persistent fetal circulation (PFC).

There are 3 main categories of etiologies of PFC in the newborn:

1. Congenital heart defect:Any congenital heart defect which results in elevated pulmonary artery or RV pressures will have PFC in order to allow adequate cardiac output. The effect of this will be R –> L shunt and cyanosis.
2. Primary PFC:Hypertrophy and increased muscularization of the walls of the pulmonary vessels results in persistently elevated PVR. This typically carries a poor prognosis.
3. Secondary PFC:Most commonly seen in infants with lung disease, where hypoxia and acidosis leads to pulmonary vasoconstriction and persistently elevated PVR. Causes include:

• Meconium aspiration (most common)
• Bronchopulmonary dysplasia
• Diaphragmatic Hernia
• Sepsis syndrome (often related to GBS, listeria, E Coli, H influenzae B)
• Pulmonary embolism