Patent Ductus Arteriosus

Question 1

What is the origin of the ductus ateriosus?

Answer 1

• In foetal heart, initially 6 pairs of aortic arches - system becomes greatly modified as loses its symmetry as development continues
• Ductus arteriosus originates from distal portion of left 6th aortic arch

Question 2

Ductus arteriosus circulation?

Answer 2

• In foetal circulation, DA provides vital communication between aorta and pulmonary artery
• Function of DA to direct blood away from inactive foetal lungs
• As blood travels from RV to MPA, blood shunted to descending aorta by DA
• Shunting from PA to aorta occurs as pulmonary vascular resistance is very high

Question 3

Closure of the ductus arteriosus?

Answer 3

• Normally spontaneously closes within 72hrs following birth
• Release of bradykinin triggered by high oxygen content of blood which occurs upon initial inflation of lungs
• Bradykinin causes muscular contraction of walls of ductus arteriosus
• Obliteration can take 1-3 months and forms ligament arteriosum

Question 4

What is a PDA?

Answer 4

• Persistent of ductus arteriosus
• Aortic pressure > PA pressure so shunting from aorta to PA
• Increased pulmonary venous return = dilatation of LA and LV

Question 5

Where is a PDA best seen with echo?

Answer 5

• Best imaged from high PLAX view of PA (ductal view)
• High PSAX at level of PA bifurcation
• SSN - long axis with slight counter-clockwise rotation
• CFI useful to identify PDA borders to measure

Question 6

PDA shunt direction?

Answer 6

• Shunt from higher pressure aorta to lower pressure PA
• CW: continuous flow above baseline

Question 7

QP in PDAs?

Answer 7

• QP = pulmonary venous volume to or from lungs (will be greater than QS as QP includes blood flow from the lungs as well as blood shunted across PDA)
• QP = SV LVOT
• Can also be calculated from SV across MV or ascending aorta

Question 8

QS in PDAs?

Answer 8

• QS = systemic volume to or from the body
• QS = SV RVOT
• Can also be calculated from SV across MPA or TV

Question 9

QP and QS in PDAs?

Answer 9

QP and QS OPPOSITE to how we calculate in VSD and ASD
QP:QS > 1/5:1 haemodnamically significant

Question 10

PASP in PDAs?

Answer 10

• PASP can be estimated from peak systolic PDA velocity
• Peak systolic PDA velocity reflects pressure difference between aorta and MPA in systole
• PASP = SBP - 4(Vpda)^2

Question 11

Significance of low PDA velocity?

Answer 11

• Higher PDA velocity better = means PA pressures are low
• In the setting of low velocity PDA signal = PA pressures elevated
• Low PDA velocity bad

Question 12

Surgical closure methods for PDA?

Answer 12

Surgical legation of PDA

Question 13

Percutaneous closure methods for PDA?

Answer 13

Spring coil or Amplatzer device

Question 14

Echo post PDA closure?

Answer 14

1. Assessment of LV size and systolic function – to see if this had normalised and LV cavity size is decreased
2. Detection of any residual shunts
3. Evaluation of position of coil or device (if closed via these methods)

Question 15

Echo post coil closure?

Answer 15

• Small residual shunt may be seen between aorta and pulmonary artery - not uncommon
• May take a few weeks or several months for endothelialisation to occur before duct is totally closed off