A 3-month-old boy is rushed to the emergency department for evaluation of cyanosis. The baby appeared "bluish-pale" during a bottle feeding this morning and still appears "dusky." The parents say that this color change has occurred during crying or feeding for the past few days. The patient also seems to tire and breathe faster after a few minutes of feeding. Review of systems is negative for fever, coughing, choking, and gagging. Temperature is 36.7 C (98 F); blood pressure is 84/50 mm Hg in the right arm, 85/55 mm Hg in the left arm, 88/58 mm Hg in the right leg, and 87/52 mm Hg in the left leg; pulse is 155/min; and respirations are 54/min. Pulse oximetry shows an oxygen saturation of 80% on room air. The infant is crying and the cyanosis is most prominent in the lips and tongue. Auscultation reveals a single S2, and a harsh crescendo-decrescendo systolic murmur is heard at the left upper sternal border. The abdomen is soft, nontender, and nondistended. No digital clubbing is present. Capillary refill is <2 sec. Which of the following is the most likely diagnosis in this patient?
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This patient has the life-threatening "tet" spells of tetralogy of Fallot. The key anomalies of this congenital heart condition include:
The presentation depends on the severity of the RVOT obstruction. The presence of pulmonary stenosis or atresia and infundibular spasm restricts pulmonary blood flow. In addition, exertion, feeding, and agitation can increase pulmonary vascular resistance, resulting in complete RVOT obstruction. The diversion of blood from the right ventricle into the aorta instead of the pulmonary artery results in acute hypoxemia and cyanosis ("tet" spell). Another clinical finding is a harsh, crescendo-decrescendo systolic ejection murmur over the left upper sternal border due to pulmonary stenosis. The single S2 comprises the normal aortic and the inaudible pulmonary components.
Acute management involves knee-chest positioning to increase systemic vascular resistance as well as inhaled oxygen to stimulate pulmonary vasodilation and systemic vasoconstriction. These mechanisms promote right ventricular blood to flow into the pulmonary artery instead of into the aorta.
(Choice A) Coarctation of the aorta causes upper body hypertension and lower body hypoperfusion. Lower extremity hypotension and cyanosis can be seen in severe cases. This patient has central cyanosis and normal blood pressure in all extremities.
(Choice B) D-transposition of the great arteries presents with immediate cyanosis. The cyanosis is due to the aorta arising from the right ventricle and the pulmonary artery arising from the left ventricle, resulting in two parallel circulations.
(Choice C) Hypoplastic left heart syndrome presents with central cyanosis and heart failure in the newborn period as the underdeveloped left ventricle cannot support the systemic circulation. Although these patients typically have a single S2 due to the lack of an aortic component, murmurs are often inaudible.
(Choice D) Most VSDs are acyanotic in infancy due to left-to-right blood flow through the defect. The holosystolic murmurs of small to medium VSDs are best heard at the left lower sternal border. Large, unrestrictive VSDs can cause cyanosis but usually no murmur as turbulence is minimal.
Educational objective:
Tetralogy of Fallot presents with hypercyanotic "tet" spells due to obstruction of the right ventricular outflow tract during exertion. The harsh crescendo-decrescendo systolic murmur over the left upper sternal border reflects turbulence at the stenotic pulmonary artery.