Question: Role of ductus arteriosus in transposition of great vessels

[drwatson1575]

In utero, the ductus ateriosus shunts oxygenated blood from the pulmonary trunk to the aorta to maintain systemic circulation. In transposition of great vessels, the aorta is exiting the right ventricle with oxygenated blood. What role does the ductus arteriosus perform in this situation?
The left heart+pulmonary circulation is at a higher pressure. Will this lead to atresia of the ductus arteriosus or do the circulating prostaglandins maintain it?

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[Step Up]

Don't need the PDA post delivery. You do, however, need mixing at the ventricular or atrial level with a VSD or ASD.

 

[drwatson1575]

Don't need the PDA post delivery. You do, however, need mixing at the ventricular or atrial level with a VSD or ASD.

My question: why do we need it in utero/before delivery?

 

[takk]

If there is an associated ASD/VSD then the above is true; however if you have TGA w/ intact ventricular septum (as in a significant proportion of these kids) then your PDA/PFO are the sole mixing locations and starting prostaglandins to keep the duct open is lifesaving until more definitive treatment can occur (balloon septostomy etc)

 

[drwatson1575]

Looks like I am having trouble wording my question. I apologize.
Why would a fetus require a ductus arteriosus (not PDA) when they have TGA since oxygenated blood directly enters the aorta from the right ventricle?

 

[drwatson1575]

Looks like I am having trouble wording my question. I apologize.
Why would a fetus require a ductus arteriosus (not PDA) when they have TGA since oxygenated blood directly enters the aorta from the right ventricle?

Could the ductus arteriosus play a role in shunting blood that passes through the foramen ovale in this situation?
I might be over thinking this.

 

[MonkeyRalph]

I'll attempt to answer your question, with the caveat that every patient has differences (such as intact ventricular septum versus VSD, or restrictive atrial septum versus nonrestrictive) so everyone will not follow these rules...

The fetal circulation includes some components of streaming (i.e. a large proportion of caval flow is directed across the atrial septum to the LA by the Eustachian valve, then the LV). Typically, the LV ejects that blood to the aorta and it essentially all goes to the body (in addition to the RV blood that's pumped R to L across the PDA). However, in TGA, that blood goes from the LV to the PA and since the PVR is so high, not all of that blood can reasonably flow through the collapsed lungs, so a proportion of it flows across the PDA into the aorta to mix with the RV blood that's going directly to the body. Of course, after birth, the PDA is not a good site for mixing, but can temporize things until the kid can get a septostomy.

 

[drwatson1575]

I'll attempt to answer your question, with the caveat that every patient has differences (such as intact ventricular septum versus VSD, or restrictive atrial septum versus nonrestrictive) so everyone will not follow these rules...

The fetal circulation includes some components of streaming (i.e. a large proportion of caval flow is directed across the atrial septum to the LA by the Eustachian valve, then the LV). Typically, the LV ejects that blood to the aorta and it essentially all goes to the body (in addition to the RV blood that's pumped R to L across the PDA). However, in TGA, that blood goes from the LV to the PA and since the PVR is so high, not all of that blood can reasonably flow through the collapsed lungs, so a proportion of it flows across the PDA into the aorta to mix with the RV blood that's going directly to the body. Of course, after birth, the PDA is not a good site for mixing, but can temporize things until the kid can get a septostomy.

Thank you!!! The human body just continues to blow my mind!!
That makes a lot of sense. I do have a follow up question regarding the foramen ovale. So, even though the Left Heart/ Left Atrium is at a higher pressure the foramen ovale will stay open?

 

[MonkeyRalph]

Thank you!!! The human body just continues to blow my mind!!
That makes a lot of sense. I do have a follow up question regarding the foramen ovale. So, even though the Left Heart/ Left Atrium is at a higher pressure the foramen ovale will stay open?

The direction of atrial level shunting is dependent on the ventricular diastolic pressures. I don't think anyone has ever studied the difference in RV versus LV diastolic pressure in fetuses with TGA versus normal anatomy, but presumably, if the PDA is wide open, even though the LV is pumping to the PA, where PVR is higher, that will not necessarily make the LV pressure any higher than the RV that's pumping directly to the aorta (cuz the duct is nonrestrictive in utero), so it shouldn't necessarily be much different from a fetus with normal great arteries (as far as diastology goes), although I have no data to support that.

 

[drwatson1575]

The direction of atrial level shunting is dependent on the ventricular diastolic pressures. I don't think anyone has ever studied the difference in RV versus LV diastolic pressure in fetuses with TGA versus normal anatomy, but presumably, if the PDA is wide open, even though the LV is pumping to the PA, where PVR is higher, that will not necessarily make the LV pressure any higher than the RV that's pumping directly to the aorta (cuz the duct is nonrestrictive in utero), so it shouldn't necessarily be much different from a fetus with normal great arteries (as far as diastology goes), although I have no data to support that.

Thank you!!
Could you please explain "the duct is nonrestrictive in utero"?

 

[Stitch]

Thank you!!
Could you please explain "the duct is nonrestrictive in utero"?

Restrictive refers to resistance to blood flow. The ductus is about the size of the great vessels in utero and immediately after birth. In fact it's sometimes challenging for surgeons to identify the aorta/PA when doing a ductal ligation. After birth the ductus becomes 'restrictive' as it shrinks down. That's normally a good thing unless you depend on it for survival.

You may also hear restrictive in terms of a small ASD that isn't enough to allow blood mixing or pressure relief in congenital heart disease. Hypoplastic left heart with a restrictive ASD is more difficult to manage than one with an unrestrictive ASD due to the back pressure on the pulmonary vasculature.

 

[drwatson1575]

Restrictive refers to resistance to blood flow. The ductus is about the size of the great vessels in utero and immediately after birth. In fact it's sometimes challenging for surgeons to identify the aorta/PA when doing a ductal ligation. After birth the ductus becomes 'restrictive' as it shrinks down. That's normally a good thing unless you depend on it for survival.

You may also hear restrictive in terms of a small ASD that isn't enough to allow blood mixing or pressure relief in congenital heart disease. Hypoplastic left heart with a restrictive ASD is more difficult to manage than one with an unrestrictive ASD due to the back pressure on the pulmonary vasculature.

Thank you!!