A 5-Month-Old Boy Is Brought to the Emergency Department by His

A 5-month-old boy is brought to the emergency department by his mother because his lips turned blue for several minutes while playing earlier that evening. She reports that he has had similar episodes during feeding that resolved quickly. He was born at term following an uncomplicated pregnancy and delivery. He is at the 25th percentile for length and below the 5th percentile for weight. His temperature is 37°C (98.6°F) , pulse is 130/min, respirations are 42/min, and blood pressure is 83/55 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 90%. During the examination, he sits calmly in his mother's lap. He appears well. Which of the following is the major determinant of symptom severity in this condition?

A) Aortic valve insufficiency
B) Associated pulmonary malformations
C) Right ventricular outflow tract obstruction
D) Tricuspid valve insufficiency
E) Ventricular septal defect