In a child who has undergone repair of tetralogy of Fallot, when are hypercyanotic episodes most likely to occur?

In a child who has undergone repair of tetralogy of Fallot, when are hypercyanotic episodes most likely to occur?

• A. Before repair
• B. After repair
• C. Only in adolescence
• D. Only with infection

Answer: (A)

Tet spells happen when a child with tetralogy of Fallot develops a sudden increase in right-to-left shunting across the VSD due to infundibular (RVOT) obstruction, leading to rapid, profound cyanosis. This mechanism relies on the presence of the obstructed outflow and the unrepaired defect. Before repair, the RVOT obstruction is still causing limited pulmonary blood flow, so these spells are most likely to occur during episodes that worsen obstruction (crying, feeding, agitation, or dehydration). After repair, the outflow obstruction is relieved and the shunt is reduced, so the tendency for these spells drops dramatically. Occasional spells can occur after repair only if there is residual or new RVOT obstruction, but that’s much less common. Hence, hypercyanotic episodes are most likely before repair.

Tet spells happen when a child with tetralogy of Fallot develops a sudden increase in right-to-left shunting across the VSD due to infundibular (RVOT) obstruction, leading to rapid, profound cyanosis. This mechanism relies on the presence of the obstructed outflow and the unrepaired defect. Before repair, the RVOT obstruction is still causing limited pulmonary blood flow, so these spells are most likely to occur during episodes that worsen obstruction (crying, feeding, agitation, or dehydration). After repair, the outflow obstruction is relieved and the shunt is reduced, so the tendency for these spells drops dramatically. Occasional spells can occur after repair only if there is residual or new RVOT obstruction, but that’s much less common. Hence, hypercyanotic episodes are most likely before repair.