Define Patent Ductus Arteriosus. Describe its clinical features, investigations, management and complications.

Definition

• Patent Ductus Arteriosus (PDA) is the persistence, after birth, of the fetal ductus arteriosus — the vessel connecting the pulmonary artery to the aorta.
• Failure of its normal closure results in an acyanotic, left-to-right shunt (aorta → pulmonary artery).

Normal Closure & Risk Factors

• The ductus normally closes functionally within 1–3 days and anatomically by 2–3 weeks (rising oxygen and falling prostaglandins cause closure).
• PDA is common in preterm infants, in congenital rubella syndrome, and at high altitude.

Clinical Features

• A continuous 'machinery' murmur (systolic + diastolic) at the left infraclavicular / upper sternal area.
• Wide pulse pressure with bounding ('collapsing') peripheral pulses.
• A large PDA → heart failure, failure to thrive and recurrent chest infections; a small one is asymptomatic.

Investigations

• Echocardiography — diagnostic (shows the duct and shunt).
• Chest X-ray — cardiomegaly and pulmonary plethora in large shunts; ECG — LV/biventricular hypertrophy.

Management

• Preterm: fluid restriction and a prostaglandin inhibitor — indomethacin or ibuprofen — to close the duct; paracetamol is an alternative.
• Term / persistent PDA: device (catheter) closure or surgical ligation.
• Treat associated heart failure medically in the interim.

Complications of a Large Pda

• Heart failure and failure to thrive; recurrent chest infections.
• Pulmonary arterial hypertension → Eisenmenger syndrome if untreated.
• Infective endocarditis (endarteritis).

A Note on WHY the Duct Is Friend or Foe

• A concept of great practical importance is understanding why the ductus arteriosus, whose persistence is a disease in one child, is the only thing keeping another child alive.
• In fetal life the duct is essential — it shunts blood from the pulmonary artery to the aorta, bypassing the lungs.
• After birth, the rise in oxygen tension and the fall in prostaglandins normally cause it to close within a few days.
• If it fails to close in an otherwise normal heart, it becomes a PDA — a left-to-right shunt causing pulmonary over-circulation, heart failure and, eventually, Eisenmenger's — and it must be closed (with indomethacin/ibuprofen in the preterm, which inhibits prostaglandin synthesis; or by catheter device or surgery).
• But in a child with a duct-dependent lesion — transposition, critical pulmonary or aortic stenosis, coarctation, tricuspid or pulmonary atresia — the duct is the only route by which blood can reach the lungs or the body.
• When it closes in the first days of life, the baby collapses and dies.
• Hence the life-saving intervention: prostaglandin E1 infusion, which keeps the duct open and buys time until surgery.
• Understanding this explains why any collapsed neonate must be considered for prostaglandin.