Why do ASD present later in life?
You mean atrial septal defects?
The left atria is stronger than the right, so it's a left to right shunt, initially (Oxygenated blood getting more oxygenated kind of shunt.)
This is why, ASD is acyanotic at birth. It won't present till there is pulmonary hypertension (The lungs get fed up of the excess blood!)
This will cause a reversal of shunt - turning it into right to left. (Now, the deoxygenated blood is getting thrown into circulation!)
This reversal is also known as Eisenmenger's syndrome.
This is why, ASDs present late in life.
Okay.. So I think the compensatory mechanisms make up for the disturbances in circulation in early years but fail later hence the features appear later..
Also the atria contribute very little as compared to the ventricles.
Atrial defects are usually very small thus, less complications in infancy. And also murmurs heard in ASD are not very loud, so its difficult for a physician to detect it.
I think, it becomes complicated due to development of Eisenmenger syndrome in later years.
Yes.. And the patient hardly survive 5-6 yrs after development of Eisenmenger syndrome..
Sometimes, ASDs never get severe enough to present as a heart disease. A paradoxical embolus is the initial presentation of an ASD in some cases!