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USMLE Step 1 Questions
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An 18-year-old male has dyspnea on exertion. A wide, fixed S2 split can be heard as well as a grade 2/6 systolic murmur in the left second intercostal space. What is the likely diagnosis?
Correct Answer: A. Atrial septal defect
Right-to-left shunts cause cyanosis immediately (near birth), so tetralogy of fallot (D) and transposition of the great vessels (E) can be immediately eliminated. A patent ductus arteriosus (C) also presents early and can be eliminated. A bicuspid aortic valve (B) would result in a systolic ejection murmur and paradoxical split of S2. However, an atrial septal defect can cause a fixed A2-P2 split with a murmur at the left second intercostal space (site of pulmonic valve). Although small atrial septal defects are often asymptomatic, larger ones can lead to a left-to-right shunt in the atria. The increased blood flow in the right side of the heart results in fixed wide splitting (due to increased duration of flow through the pulmonic valve, causing the valve to close later) and a systolic murmur in the second left intercostal space (because the increased flow over the valve is turbulent).
1. QuestionCategory: Pathophysiology
An 18-year-old male has dyspnea on exertion. A wide, fixed S2 split can be heard as well as a grade 2/6 systolic murmur in the left second intercostal space. What is the likely diagnosis?Correct