A 17-year-old girl is evaluated due to decreased exercise tolerance and fatigue. She has no known medical conditions and takes no medications. Blood pressure is 110/60 mm Hg and pulse is 88/min. The lungs are clear on auscultation. Cardiac examination reveals a parasternal heave, and a widely split second heart sound is heard throughout the respiratory cycle. A systolic ejection murmur is present at the left upper sternal border. Distal pulses are normal. Echocardiography of this patient is most likely to demonstrate which of the following findings?

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11ec160b_38c3_5731_9249_a1cea885bd13_MD0001_00 This patient with decreased exercise tolerance and a widely split second heart sound (S2) likely has an atrial septal defect (ASD). ASD is a congenital heart defect caused by abnormal septal tissue growth between the right and left atria. Immediately after birth, a left-to-right shunt develops through the ASD due to decreased pulmonary vascular resistance and increased systemic vascular resistance. The right atrium, right ventricle, and pulmonary circulation therefore receive increased blood volume (ie, venous return to the heart plus blood delivered via the shunt). Over time, this right-sided volume overload leads to right atrial and right ventricular dilation (Choice C). However, the left-sided heart chambers do not enlarge because excess blood delivered to the left atrium is able to escape through the ASD and return to the right heart (Choices A and D). The increased blood flow through the pulmonic valve with ASD causes a systolic ejection murmur best heard along the left sternal border at the second intercostal space. Similarly, increased right-sided blood volume leads to prolongation of right ventricular emptying and delayed closure of the pulmonic valve; this causes wide and fixed splitting of S2 (communication between the atria eliminates respiratory variation of splitting). A parasternal heave due to a hyperdynamic right ventricle may also be present. Most patients with ASD can accommodate right ventricular volume overload without symptoms until adolescence or adulthood. They may then have symptoms of right-sided heart failure (eg, exertional dyspnea, fatigue), as seen in this patient. Additional complications of uncorrected ASD include atrial arrhythmias and Eisenmenger syndrome due to shunt reversal from pulmonary hypertension. (Choice E) In contrast to ASD, a ventricular septal defect (VSD) causes blood from the left ventricle to enter the right ventricle, leading to a high volume of blood traversing the pulmonary circulation and left atrium. As a result, left atrial enlargement is particularly common. Large VSDs with a high fraction of shunted blood can also cause ventricular volume overload with enlargement of the right and left ventricles. Eventual right ventricular failure (due to pulmonary hypertension) can lead to right atrial enlargement. Educational objective: Atrial septal defects cause right-sided volume overload resulting in right atrial and ventricular enlargement. Excessive right-sided blood flow causes a characteristic systolic ejection murmur (ie, pulmonic flow murmur) and wide and fixed splitting of S2. __________ References: Atrial septal defect. (http://www.ncbi.nlm.nih.gov/pubmed/30571061) Pathophysiology and natural history of atrial septal defect. (http://www.ncbi.nlm.nih.gov/pubmed/30305945)

A 17-Year-Old Girl Is Evaluated Due to Decreased Exercise Tolerance