On examination, the child is severely cyanotic. The precordium is active but there is a very short, short murmur. So here s a child with a typical presentation of tetralogy spell. And what usually happens with a child playing is it decreases his systemic resistance so that there is a tendency for more blood from the right ventricle out the aorta and at the same time can increase the obstruction dynamically of the right ventricle outflow tract, increase sympathetic tone with play activity etc. to obstruct even further the pulmonary flow. The pathology we talked about, increased outflow obstruction, decreased peripheral resistance, this may be triggered by acidemia or anemia.
Spells often occur in the early morning.
It s thought to be associated with a sort of relative acidemia. And certainly has the tendency to occur in children who are anemic with tetralogy of Fallot.