PDA

Question 1

Normal anatomy PDA

Answer 1

• Bifurcation of main PA → ventral aspect of descending Ao btw L subclavian and intercostal arteries
  o Distinct muscular cylinder btw 2 elastic arteries

Question 2

Function of DA during fetal life

Answer 2

o Allow blood flow to bypass lungs during fetal life

Question 3

Histo DA

Answer 3

• 98% smooth muscle + subadventitial elastic fibers +adventitial loose collagen
  o Circumferential distribution of muscle mass

Question 4

What happens after birth

Answer 4

o Constriction in response to ↑ arterial O2 tension → close w/I min to hrs after birth
o Apobiosis: non inflammatory muscle degeneration starts after 48h
 Complete cytolysis after 1mo → ligamentum arteriosum
* Remnant adventitial elastic fibers

Question 5

Difference in Hu DA

Answer 5

intimal cushions of fetal DA contribute to closure = not in dogs

Question 6

Gross pathology

Answer 6

• Most dogs: funnel shaped ductus
  o Narrowest segment at PA
  o Internal orifice is narrowed by fibrous ridge from maximal contraction of small amount of ductus muscle
• Intra-aortic wall segment: ductus course w/I wall of Ao before opening in Ao lumen
  o Separated from the lumen by thin flap
  o May bulge and form aorto-ductal aneurysm
   Caused by lack of ductus muscle in Ao wall segment
   Size varies inversely w length of surgical segment → larger aneurysm = shorter surgical segment

Question 7

Histopathology changes

Answer 7

• Shorter ductus
• Hypoplasia of ductal muscle mass AT PA END
  o Primary abnormality
  o Muscle present: contraction and degeneration → partial constriction and ductal closure
   Asymmetric: Failure to encircle lumen precluded complete closure
• Replacement by non contracting, Ao like elastic segments AT AO END
  o Secondary abnormality → from absence of ductus muscle promoter/inducer
• Both abnormalities contribute to failure to close
  o Hypoplastic muscle: ↓ strength to close against systemic BP
  o Elastic segment prevents sphincteric action

Question 8

Histo lesions grades

Answer 8

• 6 grades based on presence/extent of elastic tissue
• Grade abnormality inversely related to ductus length

Question 9

Breed predispositions and epidemio

Answer 9

Toy, miniature Poodles, Collies, Pomeranians, Shetland Sheep dogs, Maltese, English Springer Spaniel, Keeshond, Yorshire Terrier

o Females > males

Question 10

PE and clinical evaluation: type 1

Answer 10

small PDA
 Asymptomatic L to R shunt
 High frequency continuous murmur only at L base, faint/no thrill
 Normal HR, pulse, CTX, ECG
 Sx not urgent but recommended for normal life span

Question 11

PE and clinical evaluation: type 2

Answer 11

medium PDA
 Asymptomatic L to R shunt
 Coarse continuous murmur at L base + thrill
 Pulse normal to slight bounding
 Echo: Mild to moderate L heart enlargement before 1y
 CTX: Borderline ↑ pulmonary vascular marks
 ECG: R wave >3mV
 Sx recommended but can wait couple weeks

Question 12

PE and clinical evaluation: type 3a

Answer 12

large PDA before CHF
 ↓ exercise capacity
 Coarse continuous murmur and thrill + systolic murmur at L apex from MR
 Bounding pulses
 CTX: medium to large ductal aneurysm, left enlargement, significant ↑ pulmonary vascular marks
 Echo: marked L enlargement before 6mo
 ECG: Sx recommended w/o delay

Question 13

PE and clinical evaluation: type 3b

Answer 13

large PDA +CHF
 Same as 3a + dyspnea from pulmonary edema
 ECG: Afib ca be present
 Sx: clear CHF prior

Question 14

PE and clinical evaluation: type 4

Answer 14

large PDA + PH → R to L shunting
 Hind leg weakness, collapse with exercise
 Differential cyanosis: limited to caudal body
 Pulses normal to weak
 Polycythemia
 Usually no murmur
* Split, prominent S2 can be present
 ECG: R axis deviation from RVH

Question 15

Angio classification: Type I

Answer 15

o Gradually tapered from Ao → point of insertion on PA
o No abrupt change in diameter
o Angle typically <15

Question 16

Angio classification: Type II

Answer 16

o Abrupt/marked distal narrowing of >50% ductal diameter
o Type IIA: constant dimension of proximal portion
 Most common
o Type IIB: conical chape, angle from 30-60 degrees

Question 17

Angio classification: Type III

Answer 17

o Tubular appearance w/o attenuation of ductal diameter (<20%)
o Common in German Shepherd
o Difficult for KT occlusion