Friday, February 27, 2015

Study group discussion: Mechanism of tet spells

Can anyone explain why crying causes cyanosis in Tetralogy of Fallot? I don't get the concept crystal clear.

In TOF, patient has the suck rest suck cycle. Starts sweating and cyanotic in breast feeding because he can't do the work of suckling. I think it's grade 2 dyspnea according to NYHA.

But how cyanosis and crying are related?

Increased catecholamines during crying causes increased right to left shunt.

Crying causes decrease in the pulmonary blood flow, increased right to left shunt and systemic desaturation that lead to cyanosis.

It also leads to peripheral vasodilation and further increase in R-L shunt when crying. There is release of catecholamines too which contributes as well.

But shouldn't catecholamines cause vasoconstriction?

Same doubt!

Yup, catecholamines causes vasoconstriction. Increased catecholamines causes decreased pulmonary blood flow and increased right to left shunt. That leads to activation of mechanoreceptors in right ventricle that inturn leads to peripheral vasodilation. Sorry if I'm confusing you all!

Ohh.. I get it. Basically, the pulmonary resistance increases.. Which causes shunting of blood, right? And the mechanism for vasodilation is different?

Yes. The mechanism is different.

They're called tet spells, right?

Yes, known as tet spells.

So it all begins with the catecholamines? Are they the main player here?

Yup it all begins with catecholamines.

So this phenomenon happens in a normal child too and it is aggravated in TOF due to pulmonary stenosis?

Obviously, due to pulmonary stenosis and ventricular septal defect.

Here's a link on tet spells!

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