A Tet spell, also known as a hypercyanotic spell, is a sudden, life-threatening episode that results in a profound drop in the amount of oxygen circulating in the blood. This condition is strongly associated with the congenital heart defect Tetralogy of Fallot (ToF), which is why the episodes are commonly referred to as “Tet spells.” Recognizing a spell and acting immediately is important, as the rapid decrease in oxygen saturation can lead to serious complications if not quickly resolved.
The Physiological Cause
Tetralogy of Fallot is characterized by four specific structural heart defects that collectively disrupt normal blood flow. These defects include pulmonary stenosis (narrowing of the outflow tract from the right ventricle to the pulmonary artery), a ventricular septal defect (VSD), an overriding aorta, and right ventricular hypertrophy. The combination of the narrowed pulmonary artery and the VSD creates a delicate balance of blood flow to the lungs and the rest of the body.
A Tet spell is triggered when this balance is suddenly disrupted, often by events like crying, feeding, or defecation. These triggers lead to a sudden increase in the dynamic muscular obstruction below the pulmonary valve, causing a spasm in the right ventricular outflow tract (RVOT). This spasm severely restricts blood flow into the lungs.
The increased pressure in the right ventricle forces a greater volume of deoxygenated blood to cross the VSD into the left ventricle and then out to the body. The resulting hypoxemia and the child’s distress trigger rapid, deep breathing, known as hyperpnea, which further decreases the systemic vascular resistance. This decrease in resistance makes it easier for deoxygenated blood to bypass the lungs, creating a vicious cycle of worsening cyanosis.
Identifying the Signs
Recognizing a Tet spell quickly is the first step in effective intervention. The most obvious sign is a rapid and marked increase in cyanosis, which presents as a sudden deepening of the blue or grayish tint to the child’s skin, lips, and nail beds. The child will often exhibit extreme and inconsolable irritability, frequently initiating the spell with prolonged, panicked crying.
This distress quickly escalates into hyperpnea, characterized by noticeably rapid and deep breathing as the body attempts to compensate for the lack of oxygen. In a clinical setting, the heart murmur associated with the right ventricular outflow obstruction may also soften or temporarily disappear. If the spell is not quickly resolved, the child may become limp, unresponsive, or even lose consciousness, indicating profound hypoxia.
Emergency First Steps
The immediate response to a suspected Tet spell focuses on breaking the vicious cycle of shunting and hypoxemia. The primary action is to remain calm and immediately place the infant in the knee-chest position, bringing the baby’s knees up tightly against their chest. For older children, they may instinctively squat down on their own, as this position achieves the same physiological effect.
The knee-chest or squatting position works by sharply increasing the systemic vascular resistance (the pressure in the blood vessels supplying the body). This increased resistance makes it more difficult for blood to flow out to the body and instead redirects it through the narrowed pulmonary artery, thereby increasing blood flow to the lungs.
While positioning the child, comfort and soothe them to reduce their anxiety and crying. Crying and agitation release catecholamines, which can worsen the dynamic spasm in the right ventricular outflow tract. If a spell does not quickly resolve after performing the knee-chest maneuver, emergency medical services must be called immediately. Caregivers should be prepared to administer supplemental oxygen if prescribed.
Clinical Treatment and Long-Term Prevention
Upon arrival at a medical facility, the clinical team will initiate several interventions designed to stabilize the child and terminate the spell. Initial clinical treatment often includes administering a fluid bolus, typically a crystalloid solution, to increase the volume of blood returning to the heart. Increasing this preload helps maximize the amount of blood available for pulmonary circulation.
Medications are quickly employed to address the underlying physiological issues. Morphine is commonly given to sedate the child, which reduces anxiety, decreases the hyperpnea, and helps to break the cycle of catecholamine release that fuels the RVOT spasm. If the spell persists, a vasoconstrictor like phenylephrine may be administered to immediately increase the systemic vascular resistance, forcing more blood toward the lungs. Beta-blockers, such as propranolol, are also used to reduce the contractility of the heart muscle, thereby decreasing the dynamic obstruction in the RVOT.
The long-term prevention of Tet spells centers on definitive surgical repair of the Tetralogy of Fallot defect. This complete repair typically involves closing the VSD with a patch and widening the narrowed pulmonary outflow tract, which eliminates the primary cause of the shunting. The timing of this surgery is determined by the child’s general health and the frequency and severity of the spells, but it is often performed in early infancy. Until surgical repair can be safely performed, prophylactic medication, usually an oral beta-blocker, may be prescribed to reduce the frequency and intensity of the spasms.