A 1-month-old boy is brought to the emergency department by his mother after she noticed that he had developed bluish skin and lips after a fit of crying. The patient was born at term without complications. He has been feeding, stooling, and urinating normally. On physical examination, a systolic ejection murmur is noted at the left upper sternal border and a holosystolic murmur at the left mid-sternal border. Tetralogy of Fallot is suspected. The patient is positioned with his knees to his chest and is given 100% oxygen while cardiology is consulted.
Which of the following would not be expected to be found in the suspected underlying condition?
B) Pulmonary regurgitation
Tetralogy of Fallot (TOF) includes four major features: right ventricular outflow tract obstruction, malalignment ventricular septal defect, overriding aorta, and concentric right ventricular hypertrophy. Pulmonary stenosis is a frequent finding in TOF, but pulmonary regurgitation is not.
In the vignette, the systolic ejection murmur at the left upper sternal border is due to pulmonic stenosis, and the holosystolic murmur at the left mid-sternal border is due to the ventricular septal defect.
The physiologic consequences of TOF depend mainly on the degree of right ventricular outflow obstruction. The ventricular septal defect (VSD) typically is large and unrestrictive, so the pressure in the right ventricle reflects that of the left ventricle. If the resistance to blood flow across the obstructed right ventricular outflow tract (RVOT) is less than the resistance to flow through the aorta into the systemic circulation, blood shunts from the left ventricle and into the pulmonary bed. This is predominantly a left-to-right shunt resulting in acyanosis. When the degree of RVOT obstruction increases, resistance to blood flow into the pulmonary bed increases. If the RVOT obstruction is significant enough to increase resistance, blood crosses the VSD from right ventricle to left ventricle and exits through the aorta. This right-to-left shunt results in desaturated blood entering the systemic circulation, resulting in cyanosis.
Infants with mild to moderate right ventricular outflow tract obstruction and balanced pulmonary and systemic flow may be asymptomatic and acyanotic initially and present with hypercyanotic spells (also called “tet” spells) when the RVOT obstruction is abruptly increased such as during a fit of crying.
Key Learning Point
Tetralogy of Fallot is a condition described by the simultaneous presence of ventricular septal defect, right ventricular hypertrophy, right ventricular outflow obstruction, and ventricular septal defect. Depending on the severity of this condition, presentation can range from cyanosis in the immediate newborn period to cyanosis with agitation or hypovolemia (“tet” spells) to gradually developing cyanosis to signs of heart failure 1-2 months after birth.
