A 14-year-old girl is brought to the office to establish medical care. The patient recently immigrated to the United States with her parents from Vietnam. Vital signs are within normal limits. Phonocardiogram obtained at the left upper sternal border is shown below. Which of the following is the most likely underlying cause of this patient's heart murmur?

Question

A 14-year-old girl is brought to the office to establish medical care.  The patient recently immigrated to the United States with her parents from Vietnam.  Vital signs are within normal limits.  Phonocardiogram obtained at the left upper sternal border is shown below.  Which of the following is the most likely underlying cause of this patient's heart murmur?

Quizplus · Accepted Answer

11ec160b_3c88_4e9f_9249_cbf10fedffa1_MD0001_00 This patient has an early-peaking systolic murmur and wide and fixed splitting of S2. These findings are characteristic of an atrial septal defect (ASD), a common congenital heart lesion involving an abnormal connection between the right and left atria. After birth, pulmonary vascular resistance decreases and systemic vascular resistance increases, creating a left-to-right shunt through the ASD. As a result, the right atrium and ventricle receive increased blood volume (ie, venous return to the heart plus blood delivered via the shunt) as compared to normal. Increased blood flow into the pulmonary arteries across the pulmonic valve creates an early-peaking, midsystolic ejection murmur best heard over the left second intercostal space (ie, pulmonic flow murmur). In addition, increased blood flow through the tricuspid valve may cause a diastolic rumble best heard at the lower left sternal border (not present in this patient). It is notable that the blood flow through the ASD itself is low velocity and does not typically cause a murmur. Increased blood flow across the pulmonic valve also accounts for the characteristic ASD finding of a widely split, fixed S2. Under normal conditions, S2 is split only during inspiration due to increased venous return to the heart, resulting in delayed pulmonic valve closure (P2) relative to aortic valve closure (A2). With ASD, increased right ventricular volume further delays P2, and the communication between the left and right atria maintains high right-sided blood volume throughout the respiratory cycle, eliminating respiratory variation of splitting. (Choice A) Aortic stenosis causes a crescendo-decrescendo systolic murmur over the right second intercostal space. A2 may be delayed until after P2 (paradoxical splitting) due to the increase in left ventricular ejection time. (Choice B) Ventricular septal defect creates a holosystolic murmur along the lower left sternal border due to a high-pressure, left-to-right shunt from the left to the right ventricle. Splitting of S2 may be widened but is usually not fixed. (Choice D) Aortic insufficiency is characterized by regurgitant blood flow through the aortic valve, resulting in a decrescendo diastolic murmur along the sternal border. Splitting of S2 is usually not affected. Educational objective: Atrial septal defects result in increased right-sided blood flow due to left-to-right shunting and characteristic findings of a systolic ejection murmur (ie, pulmonic flow murmur) and widely split, fixed S2. __________ References: Atrial septal defect (ASD). (http://www.ncbi.nlm.nih.gov/pubmed/30571061)

A 14-Year-Old Girl Is Brought to the Office to Establish