An 18-year-old male athlete presents with a 2/6 midsystolic murmur at the right upper sternal border, 2nd intercostal space, paradoxical splitting of S2, and no change in the murmur with Valsalva. Dx?

• A. Bicuspid aortic valve (AS)
• B. Hypertrophic obstructive cardiomyopathy
• C. Mitral valve prolapse
• D. Pulmonic stenosis

Answer: (A)

Midsystolic, crescendo–decrescendo murmur at the aortic area (right upper sternal border, 2nd intercostal space) in an 18-year-old athlete points to aortic stenosis from a bicuspid aortic valve. The paradoxical splitting of S2 means the aortic component (A2) closes later than normal, a pattern seen when the outflow valve is narrowed and delays ventricular emptying. The murmur’s lack of change with Valsalva supports a fixed obstruction like a valve lesion rather than a dynamic process; maneuvers that reduce preload (like Valsalva) would markedly alter a dynamic lesion such as hypertrophic obstructive cardiomyopathy, but not this aortic lesion. Other causes of this murmur and S2 finding are unlikely given the location and age: mitral valve prolapse tends to have an apical late systolic murmur with a click and changes with maneuvers; hypertrophic obstructive cardiomyopathy sounds best at the left lower sternal border and worsens with Valsalva; pulmonic stenosis is left-sided as well. In young patients, bicuspid aortic valve is a common congenital cause of early aortic stenosis, matching these findings.