The presentation of cyanotic spells with activity (feeding) are most consistent with Tetralogy of Fallot (TOF), a congenital cardiac defect characterized by (1) pulmonic stenosis, (2) ventricular septal defect, (3) overriding aorta, and (4) right ventricular hypertrophy.
TOF is a cyanotic congenital cardiac abnormality and is the result of a failure of neural crest cell migration through the primitive truncus arteriosus and bulbus cordis. Patients can present immediately after birth or later in childhood depending on severity, specifically the degree of pulmonic stenosis. Cyanosis results from increased right to left shunting (through the VSD) during times of exertion. Older children (ages 2-5) will often be noted to squat during these episodes (effectively increasing systemic vascular resistance and resulting in less right to left shunting through the VSD).
Saenz et al. report, "Tetralogy of Fallot is the most common CHD seen beyond infancy, with surgical repair usually undertaken when the child reaches three years of age...The classic clinical presentation is the “tet spell," characterized by hyperpnea, irritability, cyanosis and decreased murmur intensity."
Kirby and Waldo review the role of neural crest cells and cardiovascular patterning, "(1) participation in the patterning of the pharyngeal arches and their derivatives, including the aortic arch arteries, which will become the great arteries of the thorax, and (2) migration of a discrete population of neural crest cells into the cardiac outflow tract and participation in formation of the outflow septum."
Image A shows components of Tetralogy of Fallot (the overriding aorta is not labelled).
Answer 1: Atrial septal defect (ASD), a non-cyanotic heart lesion, is not a component of TOF. ASDs often do not present until reversal of the left to right shunt due to development of secondary pulmonary hypertension (Eisenmenger syndrome).
Answer 3: Tricuspid atresia is a cardiac defect in which the tricuspid valve is missing or abnormally developed, blocking blood flow from the right atrium to the right ventricle. A cyanotic lesion, it will present with bluish skin from birth.
Answer 4: Coarctation of the aorta is a narrowing of the aorta that results in decreased blood pressure in the legs compared to the arms. It can present with leg pain on exercise.
Answer 5: Transposition of the great vessels (aorta and the pulmonary artery) is another cyanotic congenital cardiac abnormality that will present at birth or shortly thereafter. Without immediate treatment, it is universally fatal.
Saenz RB, Beebe DK, Triplett LC. Caring for infants with congenital heart disease and their families. Am Fam Physician. 1999 Apr 1;59(7):1857-68. Review. PubMed PMID: 10208705.
Kirby ML, Waldo KL. Neural crest and cardiovascular patterning. Circ Res. 1995 Aug;77(2):211-5. Review. PubMed PMID: 7614707.
PMID:10208705 (Link to Abstract)
USMLE World Step 1 QBank Question #1705. Copyright © USMLEWorld, LLC 2012