A hypercyanotic spell can be subtle, as most spells are mild and self limited. A typical spell occurs in the morning when the infant awakens. Mild dehydration is present due to the overnight fast, thereby, reducing circulating blood volume. Activity after awakening causes systemic vasodilation. If the parent decides to bathe the infant, warm water results in further systmic vasodilation.
"Tet" Spell Mechanism
As "tet" spell begins, hypoxemia causes the infant to become anxious, activity decreases and hyperpnea develops. Vasoconstriction occurs in the skin, creating a pale, slightly gray-blue color and obscuring recognition of significant cyanosis. An experienced examiner can recognize that the systolic ejection murmur of right ventricular outflow tract obstruction becomes shorter and less loud, as flow into the pulmonary artery decreases. The episode may cease spontaneously as the infant is fed, removed from the bath, comforted by the parent or put down to rest. When the episode is mild, the parent may not recognize that an unusual event has occurred. Patients can manifest behaviors that are therapeutic. The infant who assumes the knee-chest position and the toddler who learns to squat are in fact treating themselves by constricting blood flow to the legs, increasing systemic vascular resistance, thereby, decreasing the right-to-left shunt. Parents must be questioned carefully, because an infant who manifests subtle spells may one day develop an unremitting spell with potentially disastrous results.