PDA and Fetal Circulation

• Systemic circulation: Low Vascular Resistance.
• Pulmonary circulation: High Vascular Resistance (R-L PDA shunt).
• PDA carries most of the RV output.
• Diverts blood away from high resistance pulmonary circulation to aorta, then to the low resistance placenta circulation.
• Bypass fluid filled lungs. 

Prostaglandin

• Hormone the body releases while baby is in utero.
• Some cardiac defects are ductal dependent and the baby will need prostaglandins to keep ductus open to stay alive: Pulmonary Atresia with intact ventricular septum, TOF with Pulmonary Atresia, Tricuspid Atresia with Pulmonary Atresia, Aortic Atresia (Hypoplastic Left Heart Syndrome), Transposition of Great Arteries with intact ventricular septum.
• Ibuprofen: thought to possibly cause premature ductal closure in-utero. 

Pre-Natal Circulation and PDA

• Systemic circulation: High Vascular Resistance.
• Pulmonary circulation: Low Vascular Resistance (R-L PDA shunt).

Post-Natal PDA

• Lungs inflate and pulmonary resistance drops.
• Blood will flow through low resistance system (L-R PDA shunt).
• Within 10-15 hours of birth there is an initial contraction of the medial smooth muscle wall of the PDA (Closure Reflex in response to increased O2 levels). 
• 2-3 weeks permanent sealing of the ductus by connective tissue and it forms the ligamentum arteriosum.
• Indomethacin: constricts ductal tissue.

  Given to premature infants to close ductus, otherwise ligated.

Conditions Associated w/PDA

• Maternal Rubella-most likely will find PDA and PPS (peripheral pulmonary stenosis).
• High Altitude Birth-elevations of 9,900 feet or higher have an increased risk of PDA of 18-20%.
• Prematurity-highest chance of having PDA.

Hemodynamics of Persistent Fetal Circulation

• Cyanosis in absence of CHD.
• Infants < 1750 grams: 45% have PDA.
• Infants < 1200 grams: 80% have PDA.
• LAE in proportion to degree of L-R shunt
• Pulmonary resistance remains high which keeps ductus arteriosus open.
• PHTN: The ductus will shunt right to left. 

PDA Small Shunt

• Asymptomatic.
• Diastolic Velocity >1.5m/s.
• Narrow PDA (obstructive)-RV will be normal.
• Wide PDA (hypertensive)- RVH, increased PAP (Aorta and PA in free communication. The systolic pressure of both will be nearly equal).

PDA Moderate/Large Shunt

• Diastolic Velocity <1.5m/s.

• Congestive heart failure.

• Dyspnea.

• Poor weight gain.

• Lower respiratory infection.

• Persistence of large PDA can result in pulmonary over circulation and volume overload of the left heart. 

PDA Murmur

• Continuous machinery murmur.
• Left sternal border or beneath left clavicle.
• Ductus murmur may be absent: Preterm infant w/respiratory distress syndrome, large ductus w/CHF, very large and short ductus. 

PDA Associated Conditions

• Interrupted aortic arch
• Pulmonary atresia
• Aortic atresia
• Bi-directional shunts (d-transposition)
• Coarctation of Aorta
• VSD 

Hemodynamics of PDA

• Shunt is between great arteries.
• Hemodynamic burden is carried by MPA-> pulmonary circulation-> LA->LV->AO.
• LV volume overload LVE and hyperkinesis of ventricular walls.

Medical Management of PDA

• Treat CHF (digitalis, diuretics).
• Indomethacin to close ductus (up to 3 doses). May be asked to echo after last dose.
• Administration of oxygen to close ductus.
• Infective endocarditis prophylaxis.

Surgical Management of PDA

• Ligation or division.
• Transcatheter closure: coil or device.

PDA 2D Echo

• Best View is high left parasternal short axis and suprasternal notch.
• Record and measure LV and LA sizes (You will see LVE and LAE).
• LA/Ao ratio by M-mode will be helpful to determine presence of PDA.
• If PDA closes on its own or medically then need to evaluate descending aorta to rule out isthmus narrowing or coarcation.
• Evaluate the following after device implantation: Possible LPA obstruction, Descending aorta obstruction, Evaluate for residual shunting.

PDA and Doppler

• Determine direction and pressure gradient across ductus using CW.
• Peak velocity in late systole.
• R-L shunting: flow below baseline.
• L-R shunting: flow above baseline.
• Large PDA may have diastolic flow reversal seen in descending abdominal aorta as blood shunts back to PA.

PDA and Pulmonary Artery Systolic Pressure

• Need to know systolic BP.
• Obtain CW Doppler across ductus to obtain peak pressure gradient.
• Systolic BP-PDA gradient= Pulmonary Artery Systolic Pressure.