• In the fetus, of the total right ventricular output, 85% goes through the ductus.
  • Persistent fetal circulation means that the fetal ductal right to left shunt persists after birth.
  • Ductus dependent circulations are left sided obstructions, right sided obstructions and TGA.
  • Ductus histology peculiarities are intimal cushions and prominent smooth muscle.
  • Functional closure of ductus begins within 15 hours and ends within 2 weeks.
  • Anatomical closure of ductus usually occurs within 3 weeks.
  • Persistent patency of ductus means that it is patent for more than 3 months in a full term baby.
  • The main constrictor of the ductus is oxygen and the main dilator is PG-E2.
  • In the early fetal life, ductus is more responsive to PG-E2 while in late fetal life, it is more sensitive to oxygen.
  • Immediately after birth, ductus flow is bidirectional. This becomes left to right soon. This flow decreases to become nil within 48 hours.
  • In the preterm baby, the ductus may close any time within 1 year.
  • In the full term baby, the dutus may close any time within 3 months.
  • In the preterm baby, ductus may decrease cerebral blood flow by stealing circulation from the aorta into the pulmonary artery.
  • With first trimester rubella, heart disease occurs in two-third of babies, one-third of whom will be having a patent ductus arteriosus.
  • The ductus may be highly restrictive, moderately restrictive or non-restrictive. If highly restrictive, there is no hemodynamic problem. If moderately restrictive, there is left to right flow causing left ventricular volume overload. Pulmonary artery pressure is not much increased due to gradient across the PDA. So, pulmonary vascular resistance does not increase. If non-restrictive, first there is left to right shunt and left ventricular volume overload since systemic vascular resistance is more than pulmonary vascular resistance. Then, since pulmonary artery is having systemic pressure, pulmonary vascular resistance increases. When it exceeds systemic vascular resistance, right to left shunt occurs.
  • Only 5% of PDAs are non-restrictive.
  • With non-restrictive PDA, right ventricle is exposed to systemic pressure.
  • With non-restrictive PDA, right ventricle is not exposed to supra-systemic pressures.


  • Less common mechanisms of ductal closure are healed vegetations and thrombus.
  • PDA is 2 to 3 times more common in females.
  • Female prevalence increases with age.
  • It is more common in siblings and offspring.
  • With maternal rubella, PDA co-exists with pulmonary artery stenosis.
  • In rubella syndrome, birth weight is low.
  • Patency of ductus is 6 times more at high altitude.
  • Commonest cause of death due to the ductus is heart failure.
  • Less common causes of death are ductal rupture, pulmonary artery rupture and ductal dissecting aneurysm.
  • Non-patent ductal aneurysm can rupture, cause pressure symptoms, cause embolisms and can get infected.
  • Infective endarteritis does not occur with a non-restrictive ductus.
  • Infective endarteritis occurs at pulmonary end or at the site of jet impinging on the pulmonary artery wall.
  • Preterm with non-restrictive ductus can have cerebral hemorrhage due to increased pulse pressure.
  • PDA may cause symptoms during the first year of life.
  • Moderately restrictive PDA causes heart failure in the third decade of life.
  • In Eisenmenger PDA, exercise causes leg fatigue but not dyspnoea because desaturated blood goes to the legs, but not to the respiratory center and carotid bodies.
  • In Eisenmenger PDA, the right ventricle does not have supra-systemic pressure. So, there is no angina from right ventricular strain.
  • With maternal salicylate ingestion, ductus closure can cause massive tricuspid regurgitation and right to left atrial shunt in the neonate.

Physical appearance

  • PDA may be associated with trisomy 18, Char syndrome and maternal rubella.
  • Trisomy 18 is characterized by lax skin, clinodactyly (overlapping fingers) and rocker bottom feet.
  • Char syndrome is inherited as a defect in chromosome 6 and is characterized by abnormal face and hands.
  • With differential cyanosis of Eisenmenger PDA, the left hand may also be slightly cyanotic and have finger clubbing.
  • With neonatal right to left shunt via PDA, a line demarcates cyanosis below and no cyanosis above. This line extends from above the left shoulder to below the right axilla.

The arterial pulse

  • The classical wide pulse pressure may be absent in preterm due to steal effect into the pulmonaries.
  • With Eisenmenger, the pulse volume returns to normal. But even in this situation, wide pulse pressure can occur due to pulmonary regurgitation.

The jugulars

  • With Eisenmenger, a wave is not prominent as would be expected, as right ventricular pressure is never suprasystemic.

The precordium

  • Moderately restrictive VSD- LV impulse is hyperdynamic. RV impulse is not prominent.
  • Non-restrictive VSD- Before Eisenmeger, LV impulse is hyperdynamic, after Eisenmemger, LV impulse is not prominent. RV impulse is always heaving. Loud P2.


  • The continuous murmur may not be present in late diastole and early systole.
  • The classical character description is rough and thrilling.
  • Maximum intensity of the murmur is at or just after the second heart sound.
  • Highly restrictive PDA- murmur has high frequency.
  • Moderately restrictive PDA- murmur has coarse quality with eddy sounds- called machinery murmur.
  • Murmur is loudest in first or second left intercostal space and left infracalvicular area.
  • The murmur may rarely be intermittent due to ductal angulation or valve.
  • The murmur is said to have “systolic reinforcement”.
  • With rise in pulmonary vascular resistance, the diastolic part disappears first and then the murmur disappears altogether.
  • With Eisenmenger PDA, the findings are differential cyanosis + findings of pulmonary hypertension (loud P2, pulmonary ejection sound, single or closely split S2).
  • A normal newborn may have a systolic murmur due to ductal flow before ductal closure.
  • In a newborn destined to have PDA, first there is a systolic murmur only. This then becomes a continuous murmur when pulmonary vascular resistance falls.
  • Infants with large left to right shunt across a PDA may have a to-and-fro over the cranium.
  • With a large left to right shunt across a PDA, A2 may be delayed to cause a paradoxical split.


  • Superior axis can occur in rubella syndrome.


  • With a large left to right shunt across the PDA, aorta distal to the ductus shows diastolic flow reversal.