Friday, 19 November 2010

MRCP revision battle 54.3: Patent ductus arteriosus

The ductus arteriosus is a connection between the pulmonary trunk and the descending aortic arch allowing blood flow in the fetus to avoid the fluid-filled lungs.

It should close shortly after birth, being mostly closed within 48 hrs and fully closed within 3 weeks, leaving the ligamentum arteriosum in its place.

Closure is due to 2 mechanisms:
  1. exposure of infants lungs to oxygen promotes bradykinin production which promotes PDA closure
  2. loss of maternal prostaglandins encourages closure

Closure is more likely to fail (=patent ductus arteriosus) in:
  • premature infants
  • infants exposed to rubella in 1st trimester
  • infants at high altitude

Features of patent ductus arteriosus include:
  • machinery murmur
  • wide, collapsing pusle
  • apical heave

If it does not close the infant may fail to thrive or develop heart failure.
Many cases however will be asymptomatic.
5% of patients with PDA go to develop pulmonary hypertension and Eisenmengers.

  • indomethacin (a prostaglandin antagonist) causes closure in 90%
  • surgical treatment is also an option

In some cases (eg transposition of the great vessels) keeping the ductus arteriosus open may be beneficial to the infant, in which case IV prostaglandin E1 is given.

On to the cardiac axis...