Fallot's tetralogy why is it right to left shunting? - USMLE Forums
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Old 03-03-2011
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Heart Fallot's tetralogy why is it right to left shunting?

VSD is a left-to-right shunt!

So why is it in fallot's tetralogy considered to be a right-to-left shunt ??
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Old 03-03-2011
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VSD is a L-> R shunt when that is the only anomly present in the heart. Systemic pressures are more the pulmonic pressures and that causes the L->R shunt.
In tetraology of fallot you have pulmonary stenosis and this causes inc. pressure in RV. Remember, blood still flows high pressure to low pressure, so now tht we have inc RV pressure, shunt will be R->L
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Old 03-03-2011
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Thanks alot..it has been tickling my mind for a while
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Quote:
Originally Posted by DoctorB View Post
VSD is a L->R shunt when that is the only anomly present in the heart. Systemic pressures are more the pulmonic pressures and that causes the L->R shunt.
In tetraology of fallot you have pulmonary stenosis and this causes inc. pressure in RV. Remember, blood still flows high pressure to low pressure, so now tht we have inc RV pressure, shunt will be R->L
Nice explanation. Also remember that this is the same concept for Eisenmenger's syndrome; in VSD, ASD, and AV, a left to right shunt can reverse to become a right to left shunt if the pressure in the right heart becomes higher than that in the left side.
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Old 03-05-2011
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Quote:
Originally Posted by hope007 View Post
VSD is a left-to-right shunt!

So why is it in fallot's tetralogy considered to be a right-to-left shunt ??
cuz of pulmonary artery stenosis...it increases the right ventricular pressure, leading to R-L shunt...
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