A 9-month-old boy is brought to the ED by his mom due to sudden-onset rapid breathing and bluish discoloration of the lips while crying. His mother says these episodes have happened several times before, often during feeding or agitation, and improve when he is placed in a squatting position. On examination, he is cyanotic. Respiratory rate is elevated. Cardiac auscultation reveals a harsh systolic murmur at the left upper sternal border. Oxygen saturation is 78% on room air and does not improve significantly with supplemental oxygen. Which of the following is the most likely cause of this patient’s acute presentation?
Decreased pulmonary vascular resistance
Increased systemic vascular resistance
Sudden increase in left ventricular oxygen demand
Sudden increase in right-to-left shunting across the interatrial septum
Worsening of right ventricular outflow obstruction
Increased systemic vascular resistance
Sudden increase in left ventricular oxygen demand
Sudden increase in right-to-left shunting across the interatrial septum
Worsening of right ventricular outflow obstruction
