Tet spells

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Synonyms and keywords: hypercyanotic spell, hypercyanosis

Overview

Children with Tetralogy of Fallot may develop acute severe cyanosis or hypoxic “tet spells“. The spells are unpredictable and are associated with profound cyanosis and can be fatal.

Pathophysiology

The mechanism underlying these episodes is not entirely clear, but may be due to spasm of the infundibular septum and the right ventricular outflow tract. Whatever the mechanism, there is an increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the systemic circulation. The child will often squat during a Tet Spell to improve venous return to the right side of the heart. Squating increases the systemic vascular resistance and thereby shunts flow to pulmonary circuit.

Diagnosis

Symptoms

Prolonged crying

Physical Examination

Vitals

Tachypnea

Skin

Intense cyanosis

Heart

The ordinarily harsh murmur will be greatly diminished as blood is not flowing through the pulmonary vasculature.

Emergency Medical Management of Tet Spells

‘Tet spells’ cause acute hypoxia and may be treated with:

Beta-blockers such as propranololor esmolol. Beta-blockers cause relaxation of the right ventricular outflow tract and increases blood flow into the pulmonary vessels.
Morphine to reduce ventilatory drive
Phenylephrine to increase systemic afterload that in turn increases the flow across right ventricle and the pulmonary artery and decreases right to left shunting
There is data limited to case reports describing the use of dexmedetomidine.^[1] Care must be taken to titrate the drug starting at a very low dose of 0.1-0.125 mcg/kg/hour (without a bolus).^[2]
Procedures such as the knee-chest position which increases aortic wave reflection, increasing pressure on the left side of the heart, decreasing the right to left shunt thus decreasing the amount of deoxygenated blood entering the systemic circulation.^[3]

Oxygen is ineffective in treating hypoxic spells as the underlying problem is lack of blood flow through the pulmonary circuit and not alveolar oxygenation.
In case all these measures fail, an emergency Blalock-Taussig shunt might be needed.
General anesthesia can be considered

Prognosis

These spells can be fatal, and can occur in patients who are not cyanotic.

References

↑ Senzaki H, Ishido H, Iwamoto Y, Taketazu M, Kobayashi T, Katogi T, et al. Sedation of hypercyanotic spells in a neonate with tetralogy of Fallot using dexmedetomidine. J Pediatr (Rio J). Jul-Aug 2008;84(4):377-80.
↑ Chrysostomou C, Sanchez De Toledo J, Avolio T, Motoa MV, Berry D, Morell VO, et al. Dexmedetomidine use in a pediatric cardiac intensive care unit: can we use it in infants after cardiac surgery?. Pediatr Crit Care Med. Nov 2009;10(6):654-60.
↑ Murakami T (2002). “Squatting: the hemodynamic change is induced by enhanced aortic wave reflection”. Am. J. Hypertens. 15 (11): 986–8. PMID 12441219.

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[1] Senzaki H, Ishido H, Iwamoto Y, Taketazu M, Kobayashi T, Katogi T, et al. Sedation of hypercyanotic spells in a neonate with tetralogy of Fallot using dexmedetomidine. J Pediatr (Rio J). Jul-Aug 2008;84(4):377-80.

[2] Chrysostomou C, Sanchez De Toledo J, Avolio T, Motoa MV, Berry D, Morell VO, et al. Dexmedetomidine use in a pediatric cardiac intensive care unit: can we use it in infants after cardiac surgery?. Pediatr Crit Care Med. Nov 2009;10(6):654-60.

[3] Murakami T (2002). “Squatting: the hemodynamic change is induced by enhanced aortic wave reflection”. Am. J. Hypertens. 15 (11): 986–8. PMID 12441219.

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