Like a hole in the heart

Commencing placement on paediatrics and neonatology has highlighted conditions that relate to premature birth. One such condition is patent ductus arteriosus (PDA). To understand this condition it is crucial to first understand the circulation within the foetus.

Just to quickly recap the human blood circulation; blood from the body returns to the heart via the inferior and superior vena cava where it enters the right atrium of the heart. The blood then flows through the tricuspid valve into the right ventricle where it is pumped into the pulmonary artery through the pulmonary valve. The pulmonary artery carries the blood to the lungs to allow oxygenation of the blood and removal of waste products such as carbon dioxide. The oxygenated blood returns to the heart via the pulmonary veins into the left atrium and then into the left ventricle via the mitral valve (or bicuspid valve) before the blood is pumped around the body exiting the heart through the aorta.

When the foetus is in the womb it gains its oxygen and nutrients as well as removing waste products through the placenta. The placenta acts as a store for oxygen and nutrients to allow the foetus to develop. The oxygenated blood in the foetus is gained from the placenta via the umbilical vein which runs in the umbilical cord. The umbilical vein joins the inferior vena cava via the ductus venosus, bypassing the liver. This enters into the right atrium, but as the lungs are not functional in a foetus the blood travels into the pulmonary artery where it enters into the aortic arch directly through the ductus arteriosus which connects the two arteries. Supplying the foetus with oxygen and nutrients before the blood returns to the mother via the two umbilical arteries back to the placenta.

Babies that are born preterm, 25-38 weeks gestation, are at increased risk of having a patent (open) ductus arteriosus where this connection between the pulmonary artery and aorta remains open. This means that oxygenated blood that is within the aorta is forced back into the pulmonary artery due to the aorta having higher pressure. This results in additional fluid returning to the lungs. This increases the lung pressure which increases the amount of energy needed to inflate the lungs. This excess energy use can lead to faltering weight gain as well as dyspnoea (shortness of breath) and tachycardia (increased heart rate) in the neonate (baby in the first 28 days of life).

This condition does not necessarily need treatment as some neonates do not suffer from adverse symptoms. In other cardiac conditions in neonates treatment can be commenced to keep the PDA open to allow overcome a more severe abnormality. Surgically closing the ductus arteriosus by either tying it shit or use of an intravascular coil or plug leading to a clot blocking the vessel. Non-steroidal anti-inflammatories (e.g. special forms of ibuprofen) can act as medical treatment for closing the vessel as they inhibit the production of prostaglandins, these lipid compounds stop the closure of the ductus arteriosus.

#medicine #anatomy #physiology #paediatrics #heart

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