A 2-month-old infant presents with recurrent episodes of deep cyanosis while crying. During examination the child instinctively squats, which relieves the symptoms. A harsh systolic murmur is heard at the left upper sternal border. What is the most likely underlying mechanism of the cyanotic spell?
A
Sudden increase in pulmonary vascular resistance
B
Infundibular spasm causing increased right-to-left shunt
C
Closure of ductus arteriosus
D
Acute mitral valve obstruction