Step I coarc vs PDA

[lilmisty]

Do both Coarc and PDA cause pressure differences between upper and lower extremities? I had a uworld question where PDA was causing differential cyanosis (and not a coarc), and then I got another question were coarc was causing the pressure differences between upper and lower extremities. Someone got any idea?

 

[Handinhand]

You should still get normal perfusion distal to a coarct, because what else is distal to a coart? The kidneys. If your kidneys are being under-perfused they're going to increase your pressures until they are happy. You will still have a pressure gradient between upper and lower extremities because your subclavians are going to be proximal to the coarct.

With a PDA, no matter how hard your left heart works, your right heart is still going to be a lower pressure circuit than your periphery, so it's always going to steal blood flow -- that's just physics, and because your subclavians are proximal to the PDA, they are going to perfuse fine still while your legs get the short end of the stick.

 

[Fungi121]

Okay i'm confused too. I just did one where baby girl (idk like 9 months) with hypotension and a murmur with decreased femoral pulses presents....coarc or PDA? answer was coarc but IDK why?!

 

[thehundredthone]

Do both Coarc and PDA cause pressure differences between upper and lower extremities?

No. Only coarctation does.

Okay i'm confused too. I just did one where baby girl (idk like 9 months) with hypotension and a murmur with decreased femoral pulses presents....coarc or PDA? answer was coarc but IDK why?!

See my response above.

I had a uworld question where PDA was causing differential cyanosis (and not a coarc), and then I got another question were coarc was causing the pressure differences between upper and lower extremities.

Herein lies the problem. Differential blood pressure and differential cyanosis are two completely different things.

Coarctation is a partial block in the aorta, the pressure wave gets attenuated at the block and hence your pulses beyond this point, i.e. the lower limbs in a post subclavian coarctation, will be weak and delayed.

A reversed PDA (i.e. elevated right heart pressures) causes admixture of deoxygenated blood beyond the subclavian vessels hence only the lower extremities are affected, causing a differential central cyanosis. It has nothing to do with the perfusion of the lower limbs.