A 2-day-old infant is dusky and irritable. He was born to a 22-year-old primigravida with sporadic prenatal care. Delivery was uncomplicated, and Apgar scores were 7 and 8 at 1 and 5 minutes, respectively. His temperature is 36.7 C (98 F), blood pressure is 70/30 mm Hg, pulse is 148/min, and respiratory rate is 68/min. Physical examination shows a cyanotic and irritable newborn with mild-to-moderate respiratory distress. Auscultation reveals a continuous, machine-like murmur appreciated between the scapulae. Serum lactate is elevated. Echocardiogram shows the aorta lying anterior, inferior, and to the right of the pulmonary artery. Failure of which of the following embryologic processes is most likely responsible for this patient's condition?

Question

A 2-day-old infant is dusky and irritable.  He was born to a 22-year-old primigravida with sporadic prenatal care.  Delivery was uncomplicated, and Apgar scores were 7 and 8 at 1 and 5 minutes, respectively.  His temperature is 36.7 C (98 F), blood pressure is 70/30 mm Hg, pulse is 148/min, and respiratory rate is 68/min.  Physical examination shows a cyanotic and irritable newborn with mild-to-moderate respiratory distress.  Auscultation reveals a continuous, machine-like murmur appreciated between the scapulae.  Serum lactate is elevated.  Echocardiogram shows the aorta lying anterior, inferior, and to the right of the pulmonary artery.  Failure of which of the following embryologic processes is most likely responsible for this patient's condition?

Quizplus · Accepted Answer

11ec160b_3737_aea2_9249_a7ccd9050d1c_MD0001_00 The clinical and echocardiographic findings in this cyanotic neonate are consistent with transposition of the great arteries (TGA). The etiology of TGA is due to linear (rather than spiral) development of the aorticopulmonary septum in utero, resulting in an anteriorly positioned aorta connected to the right ventricle and a posteriorly positioned pulmonary artery connected to the left ventricle. Therefore, pulmonary and systemic circulations are abnormally separated and exist as 2 parallel circulations. TGA is incompatible with life unless there is another coexisting connection, such as a patent foramen ovale, septal defect, or patent ductus arteriosus (PDA), to allow mixing of oxygenated pulmonary circulation blood with the systemic circulation. Patients may be normal on initial presentation but will become cyanotic, tachypneic, and tachycardic as the PDA (machine-like murmur) begins to close, which typically occurs at age 1-3 days. Elevated lactate in this patient signifies anaerobic metabolism in the presence of poorly oxygenated blood. (Choice A) Failure of apoptosis of the tissue between the digits can result in syndactyly. (Choice B) Failure of fusion is seen in hypospadias (failure of urethral folds to fuse). (Choice C) A branchial cleft cyst results from failure of obliteration of the second branchial cleft. The cysts usually present as a draining sinus at the angle of the mandible. (Choice D) The membranous portion of the interventricular septum results from proliferation of endocardial cushions. Failure of this proliferation leads to a membranous ventricular septal defect (VSD) that can present as a holosystolic murmur if small, or cyanosis if large. However, the aorta should lie posterior to the pulmonary artery (the normal configuration). (Choice E) Failure of conotruncal septation results in persistent truncus arteriosus, which can present with cyanosis and respiratory distress, although an echocardiogram will show a single arterial trunk overriding a large VSD. Educational objective: An echocardiogram showing an aorta lying anterior to the pulmonary artery is diagnostic of transposition of the great arteries (TGA). This life-threatening cyanotic condition results from failure of the fetal aorticopulmonary septum to spiral normally during septation of the truncus arteriosus. __________ References: Clinical presentations of critical cardiac defects in the newborn: Decision making and initial management. (http://www.ncbi.nlm.nih.gov/pubmed/21189937)

A 2-Day-Old Infant Is Dusky and Irritable