Congenital Heart abnormalities

Question 1

What is the foetal blood pathway?

Answer 1

Umbilical vein-> liver and ductus venosus-> IVC-> RA where blood is mixed, 25% to RV and 75% through fossa ovalis-> pul trunk has ductus arterious to shunt blood to aorta, thus aorta contains medium oxygen content. The umbilical arteries take blood back to placenta

Question 2

What changes at birth?

Answer 2

1- Pulmonary pathway resistance lowers (due to first breath)
2-blood leaving RV leaves heart now through the pulmonary artery, not the DA
3- this means more blood in LA, LA pressure rises
4- umbilical vein is clamped, so RA pressure drops
5-LA pressure greater then RA, foramen ovale flap closes
6-SM in the DA contracts due to high oxygen tension.

Question 3

Outline the series of events that occur with an untreated atrial septal defect

Answer 3

• During filling, Blood will flow from LA to the more complaint, thin RA/RV. This is a LA to RA shunt.
• Volume load on RV (2-3 times more than normal)
• After time, pulmonary arterioles thicken due to large flow, and thus lung resistance increases.
• Pul. A. pressure rises, meaning RV hypertrophy occurs
• this can lead to heart failure/death OR the shunt will reverse (as LV is less compliant)
• This means systemic blood flow is greater than pulmonary, insufficent oxygenation (eisenmengers)

Question 4

How does a ventricular septal defect alter blood flow

Answer 4

Same as atrial septal defect but the shunt is LV to RV.
(low resistance pulmonary pathway or higher systemic for LV)
Due to pulmonary arterioles thickening, and large volume load on RV and LV, hypertrophy of both ventricles occurs. (more prominent in RV)
Can get RV to LV shunt