Patients with right to left shunt have decreased pulmonary blood flow and can be intermittently or permanently cyanosed. The classic example is tetralogy of Fallot where a large VSD co-exists with an obstruction to blood flow from the RV to the PAs hence causing right to left shunt or ‘spells’. Like many things this is a spectrum of limited to severe right to left shunt
Conditions exhibiting right to left shunt:
Tetralogy of Fallot
Pulmonary atresia
Tricuspid atresia
Ebstein’s anomaly
Southampton Cardiac Anaesthesia 