Ventricular Septal Defect... L-to-R shunt or R-to-L shunt?

[SuperSaiyan3]

If somebody can clear up this contradiction, I would owe you a big one.

Alright, so according to Wikipedia, "VSD is an acyanotic congenital heart defect, aka a Left-to-right shunt, so there are no signs of cyanosis."

http://en.wikipedia.org/wiki/Ventricular_septal_defect#Symptoms

But in my study book, it says that in the case of tetralogy of fallot, VSD can cause a right to left shunt as the RV pressure gets greater than LV pressure.

Also, wikipedia contradicts itself in saying...: "A right-to-left shunt occurs when : Ventricular septal defect (an abnormal hole between the ventricles)"

http://en.wikipedia.org/wiki/Right-to-left_shunt

This is actually just driving me insane. I've researched it on other websites and some say L-to-R and others say R-to-L. I feel like this is gonna rip my brain apart unless somebody can clear it up for me!!

please please please and thank you.

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[ChrisKnight]

It depends.

Normally, a VSD will cause a left-right shunt.

However, in the case of Tetralogy of Fallot, there is unequal splitting of the truncus arteriosus, so you have an overriding aorta and a stenotic pulmonary trunk. This prevents right sided blood from entering the pulmonary circulation, and thus creates a right-left shunt.

By the way, you don't need to know this for the MCAT, so all of this is a big waste of time.

 

[Charles_Carmichael]

Yea, you definitely don't need to know this for the MCAT.

My limited understanding of ToF is that the extent and direction of shunting depends on the amount of pulmonary obstruction. If there's only a slight pulmonic obstruction/stenosis, there would be left-to-right shunting because the pressures are higher in the LV compared to the RV.

More commonly though, there's a decent bit of pulmonary stenosis (valvar and subvalvar) that causes right-to-left shunting due to greater pressures in the RV relative to the LV.

Maybe a med student or someone better versed in this can contribute. Hope this helps.

 

[SuperSaiyan3]

hey thanks for the replies lads. That clears it up well for me. Makes sense that if the pressure got built up by a pulmonary stenosis, a R-to-L shunt would occur. So normally VSD is a L-to-R shunt... gotcha. I guess that's the case no pulmonary shunt is occurring.

hahah yeah this has nothing to do with the MCAT. I'm just studying for my Pathophysiology class final exam on Monday and my prof tends not to answer emails on weekends so I was pretty much screwed unless somebody could explain it for me.

Thankfully I remembered this forum offers some pretty good study help. Thanks again for the help!

 

[coffeebythelake]

For VSD, ASD, and PDA... These are initially acyanotic heart conditions. Initially, it is a L->R shunt because the resistance in the pulmonary circulation is lower than the resistance in the systemic circulation. However, prolonged shunting causes the pulmonary vessels (which are very delicate) to become constricted as a compensatory response to the high pulmonary pressures. The shunt reverses to R->L, and result in a cyanotic condition. When this happens, it is called Eisenmenger syndrome, and there is irreversible damage to the lungs.

For ToF... the overriding aorta is lower pressure than the stenotic pulmonary artery, so blood is shunted R->L across the VSD. Result is a cyanotic condition.

 

[SuperSaiyan3]

For VSD, ASD, and PDA... These are initially acyanotic heart conditions. Initially, it is a L->R shunt because the resistance in the pulmonary circulation is lower than the resistance in the systemic circulation. However, prolonged shunting causes the pulmonary vessels (which are very delicate) to become constricted as a compensatory response to the high pulmonary pressures. The shunt reverses to R->L, and result in a cyanotic condition. When this happens, it is called Eisenmenger syndrome, and there is irreversible damage to the lungs.

For ToF... the overriding aorta is lower pressure than the stenotic pulmonary artery, so blood is shunted R->L across the VSD. Result is a cyanotic condition.

excellent reply. Cleared it up 100% thank you guys!

 

[ksmi117]

SDN is not for homework help. Closing.