A 2-hour-old boy has developed worsening cyanosis over the past few minutes. The infant was delivered vaginally at term after an uncomplicated pregnancy. Birth weight was 4.1 kg (9 lb). Apgar scores were 7 and 8 at 1 and 5 minutes, respectively. Oxygen is administered by hood but does not relieve the cyanosis. Further examination shows tachypnea, subcostal retractions, a normal first heart sound, a single and loud second heart sound, and no murmur. Which of the following is the most likely cause of the infant's cyanosis?

Question

A 2-hour-old boy has developed worsening cyanosis over the past few minutes.  The infant was delivered vaginally at term after an uncomplicated pregnancy.  Birth weight was 4.1 kg (9 lb).  Apgar scores were 7 and 8 at 1 and 5 minutes, respectively.  Oxygen is administered by hood but does not relieve the cyanosis.  Further examination shows tachypnea, subcostal retractions, a normal first heart sound, a single and loud second heart sound, and no murmur.  Which of the following is the most likely cause of the infant's cyanosis?

Quizplus · Accepted Answer

11ec25c8_d62f_17da_bc81_9354bd0c546a_MD0003_00 D-transposition of the great vessels (TGV) is a congenital cyanotic heart defect that commonly presents in the neonatal period. Abnormal rotation of the great vessels during cardiac development results in an aorta arising from the right ventricle and the pulmonary artery from the left ventricle ("arterial switch"). As a result, deoxygenated blood coming from the body goes to the right atrium and ventricle and is cycled back to the body through the aorta. Oxygenated blood from the lungs is returned to the lungs by the left side of the heart through the pulmonary artery. Characteristic findings include cyanosis within 24 hours of life, a single S2 on auscultation (absent pulmonary component of S2 because the aorta is anterior to the pulmonary artery), and a narrow mediastinum ("egg on a string") on x-ray. Abnormal rotation After delivery, mixing of deoxygenated and oxygenated blood is necessary for survival and typically occurs through a patent ductus arteriosus or ventricular septal defect (both of which cause murmurs) or through a patent foramen ovale (which is likely the case in this patient). This infant most likely is mixing through a patent foramen ovale as there is no murmur on examination. If there is inadequate mixing, the infant will rapidly develop severe cyanosis and pulmonary edema and die unless a shunt is created (ie, emergency atrial septostomy). Therefore, if TGV is suspected, prostaglandins should be initiated to keep the ductus arteriosus patent to optimize inter-circulatory mixing, and echocardiography should be obtained. (Choices A, C, E, and H) Atrial septal defect, dextrocardia, patent ductus arteriosus, and ventricular septal defect are acyanotic congenital heart diseases. (Choice B) Coarctation of the aorta can present with pallor, diaphoresis, and diminished femoral pulses once the ductus arteriosus closes. Coarctation may also present with differential cyanosis that is more prominent in the lower extremities. (Choice D) Hypoplastic left heart syndrome may present with tachypnea, cyanosis, no murmur, and a single S2; however, presentation is typically delayed until a few days after birth when the ductus arteriosus closes. (Choice F) Tetralogy of Fallot can cause a single S2 but typically has a significant systolic murmur from the pulmonary stenosis as well as a ventricular septal defect murmur (depending on the size of the ventricular septal defect). The presentation can range from birth to a few years depending on the degree of right ventricular outflow obstruction and pulmonary blood flow. Educational objective: Transposition of the great vessels is a congenital cyanotic heart defect that typically presents within the first 24 hours of life with cyanosis and a single loud S2. References: Transposition of the great arteries. (http://www.ncbi.nlm.nih.gov/pubmed/21849902)

A 2-Hour-Old Boy Has Developed Worsening Cyanosis Over the Past