A 4-month-old boy is brought to the cardiology clinic by his parents for continued follow-up of tetralogy of Fallot. The diagnosis was made during routine antenatal sonography, and the pregnancy and delivery were otherwise uncomplicated. The infant has been seen frequently in the clinic and has not had any cyanosis, respiratory distress, or difficulty feeding. The parents become concerned when their son's surgical plan is discussed because he does not have the clinical signs that other children with tetralogy of Fallot demonstrate. Which of the following is the major determinant of symptom severity in this condition?

Question

A 4-month-old boy is brought to the cardiology clinic by his parents for continued follow-up of tetralogy of Fallot.  The diagnosis was made during routine antenatal sonography, and the pregnancy and delivery were otherwise uncomplicated.  The infant has been seen frequently in the clinic and has not had any cyanosis, respiratory distress, or difficulty feeding.  The parents become concerned when their son's surgical plan is discussed because he does not have the clinical signs that other children with tetralogy of Fallot demonstrate.  Which of the following is the major determinant of symptom severity in this condition?

Quizplus · Accepted Answer

11ec160b_3aa0_a350_9249_0783930bb7e6_MD0001_00 Tetralogy of Fallot (TOF) is characterized by ventricular septal defect (VSD), overriding aorta, right ventricular outflow tract (RVOT) obstruction, and right ventricular hypertrophy. The VSD generally is large, which allows for equal pressure in the right and left ventricles. Therefore, it is the amount of RVOT obstruction that determines how much deoxygenated blood is delivered to the systemic circulation. Infants with significant RVOT obstruction shunt more deoxygenated blood across the VSD to the aorta and are more cyanotic. Infants with no or minimal RVOT obstruction, such as this patient, deliver more deoxygenated blood to the lungs and appear acyanotic. The degree of RVOT obstruction is dynamic and can increase suddenly, leading to profound cyanosis ("tet spells"). These can be caused by dehydration or hyperventilation but are usually idiopathic. (Choices A and D) Although the pulmonary valve is usually small and stenotic in TOF (contributes to RVOT obstruction), involvement of the aortic or tricuspid valves is unusual. (Choice B) Less than 25% of patients with TOF have extracardiac malformations. The most common associated syndromes include Down, Alagille, and DiGeorge. Pulmonary malformations are extremely rare. (Choice E) A VSD is universally present in TOF. The VSD invariably is large and does not determine the degree of cyanosis. Educational objective: In patients with Tetralogy of Fallot, the degree of right ventricular outflow tract obstruction is the major determinant of the degree of right-to-left intracardiac shunting and resulting cyanosis.

A 4-Month-Old Boy Is Brought to the Cardiology Clinic by His