Pulmonary vascular disease in congenital shunts and fetal circulation
THE CONTEXT
Persistent high pulmonary flow from a left-to-right shunt can cause irreversible pulmonary vascular disease. The target also describes the routes of blood flow in fetal circulation.
Progression and clinical findings
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Persistently increased pulmonary flow from a left-to-right shunt raises pulmonary vascular resistance, followed by pulmonary hypertension.
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Progressive vascular changes include obliteration of distal arterioles and are irreversible. Central cyanosis and digital clubbing develop at this stage.
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Chest radiography shows enlarged central pulmonary arteries with peripheral pruning of pulmonary vessels.
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Electrocardiography and echocardiography show right ventricular hypertrophy. Advanced disease can produce right ventricular dilatation.
Fetal blood flow
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Oxygenated blood arrives through the umbilical vein and enters the inferior vena cava through the ductus venosus. It streams through the right atrium and open foramen ovale into the left atrium, then through the left ventricle into the aorta.
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Venous blood from the superior vena cava crosses beneath the main blood stream into the right atrium. After partial mixing with oxygenated blood, it enters the right ventricle and pulmonary artery.
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High pulmonary vascular resistance limits blood flow to the fetal lungs. Most blood passes through the ductus arteriosus into the descending aorta.
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The aortic isthmus lies in the aortic arch before its junction with the ductus arteriosus. This constriction limits oxygen-rich blood flow to the descending aorta, so organs such as the kidneys and intestinal tract receive less oxygen-rich blood.