Patent ductus arteriosus

Question 1

Definition

Answer 1

Persistent communication between aorta & proximal left pulmonary artery after birth. The patent ductus arteriosus doesn’t constrict as normal to form the ligamentum arteriosum.

Question 2

Pathophysiology

Answer 2

Ductus arteriosus remains open & doesn’t constrict within a few hours of birth to form ligamentum arteriosum.

• Abnormal left-to-right shunt exists from aorta→ pulmonary artery (since left-sided pressures are higher)
• Leads to increased pulmonary flow leading to right heart failure & Eisenmenger’s syndrome (right sided pulmonary heart pressures increase> systemic pressures, shunt reverses & deoxygenated blood is shunted from right to left resulting in cyanosis)

Question 3

Why does ductus arteriosus remain open during fetal development? Fetal circulation wrt DA?

Answer 3

Ductus arteriosus is kept open by the vasodilator prostaglandin E2 (produced by placenta).
IN THE FETUS:

• Lungs are non-functional. Oxygenated blood from the placenta (via umbilical vein) is shunted from RA→ LA across the foramen ovale to bypass the lungs & then to the left ventricle and the aorta. Blood that continues into the RV travels to the pulmonary artery then is shunted into the aorta via the ductus arteriosus.

Question 4

Why does ductus arteriosus close at birth?

Answer 4

The ductus arteriosus usually closes at birth as the main source of oxygenated blood after birth, is from the lungs. At this point the foramen ovale closes and the ductus arterious becomes a ligament, called the ligamentum arteriosus.

The lungs also start to release a small peptide called bradykinin, which constricts the smooth muscle wall of the ductus arteriosus.

Question 5

Clinical manifestations

Answer 5

Signs

• continuous “machine murmur” - heard during systole AND diastole (due to blood moving form aorta into pulmonary artery)
• Eisenmenger’s syndrome causing differential cyanosis - blue toes & clubbing but pink fingers & no clubbing (when pulmonary pressures > systemic pressures, the shunt reverses & blood is shunted from right→ left through the patent ductus arteriosus. This results in deoxygenated blood passing to the systemic circulation- specifically the lower body- causing cyanosis in the lower extremities. The upper body receives oxygenated blood from branches of the aortic arch PROXIMAL to the PDA (brachiocephalic trunk , left common carotid & left subclavian)hence no cyanosis here.)
• dyspnoea, failure to thrive

Question 6

Explain why a patent ductus arteriosus leads to differential cyanosis & what this is?

Answer 6

Eisenmenger’s syndrome causing differential cyanosis - blue toes & clubbing but pink fingers & no clubbing (when pulmonary pressures > systemic pressures, the shunt reverses & blood is shunted from right→ left through the patent ductus arteriosus. This results in deoxygenated blood passing to the systemic circulation- specifically the lower body- causing cyanosis in the lower extremities. The upper body receives oxygenated blood from branches of the aortic arch PROXIMAL to the PDA (brachiocephalic trunk , left common carotid & left subclavian)hence no cyanosis here.)

Question 7

Investigations

Answer 7

Echocardiogram = diagnostic

& CXR & ECG (may be normal for small shunts, provide additional info)

Question 8

Management

Answer 8

1st line = Indomethacin (prostaglandin inhibitor, prostaglandins are vasodilators that help keep ductus arteriosus open) OR ibuprofen (NSAID that inhibits prostaglandin synthesis) to induce duct closure

2nd line (if duct does not close)= surgical ligation