A 4-year-old boy is being evaluated for failure to thrive, shortness of breath, and exercise intolerance. The parents first became aware of his symptoms after the patient started preschool a few weeks ago. His teacher mentioned that the patient seemed to tire faster than the other children when playing outside. Cardiac examination shows bounding peripheral pulses and a palpable thrill below the clavicle near the left upper sternal border. On auscultation, a continuous murmur is best heard over the same region. After discussion with the parents, a thoracotomy is scheduled to correct the patient's condition. During the procedure, the surgeon should plan on ligating a derivative of which of the following embryologic structures?
Aortic arch vascular derivatives | |
Aortic arch | Adult derivative |
First |
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Second |
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Third |
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Fourth |
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Sixth |
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This patient most likely has a patent ductus arteriosus (PDA). The ductus arteriosus is an embryonic derivative of the sixth aortic arch that allows fetal blood to pass directly from the pulmonary artery to the proximal descending aorta (bypassing the pulmonary circulation). This vessel usually closes shortly after birth, secondary to decreased prostaglandin E2 (PGE2) levels and increased oxygen concentration. Patency of the ductus after birth results in a left-to-right shunt that can cause left ventricular volume overload and symptoms of heart failure (eg, failure to thrive, respiratory distress). Physical examination will show a continuous "machinery-like" murmur and palpable thrill over the left infraclavicular region due to turbulent blood flow through the PDA.
Pharmacologic closure of a PDA can be achieved by PGE2 synthesis inhibitors (eg, indomethacin) in premature infants. However, older patients usually require surgical ligation or percutaneous PDA occlusion.
(Choice A) The bulbus cordis forms the beginning of the ventricular outflow tract in the embryonic heart. This structure forms the smooth portions of the left and right ventricles adjacent to the aorta and pulmonary artery, respectively.
(Choice B) The fourth aortic arch on the left forms the arch of the aorta between the left carotid artery and ductus arteriosus. Abnormalities during development can result in coarctation (narrowing) of the aorta, which can present with continuous murmurs over the back due to collateral formation.
(Choice C) The primitive atrium receives blood from the sinus venosus in the embryonic heart and transmits it to the primitive ventricle. The primitive atrium forms the rough portions of the left and right atria.
(Choice D) The sinus venosus is an embryologic structure within the heart that receives blood from the vena cava. In adults, this structure forms the smooth portion of the right atrium, known as the sinus venarum.
Educational objective:
The ductus arteriosus is derived from the sixth embryonic aortic arch. A patent ductus arteriosus (PDA) causes left-to-right shunting of blood that can be heard as a continuous murmur over the left infraclavicular region. Indomethacin (a PGE2 synthesis inhibitor) can be used to close a PDA in premature infants, but surgical ligation is often necessary in older patients.