MEDizzy - An 18-year-old college freshman is being evaluated for a

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Introduction to clinical medicine

An 18-year-old college freshman is being evaluated for a heart murmur heard at health screening. She reports an active lifestyle, no past medical history, and no cardiac symptoms. She has a midsystolic murmur that follows a nonejection sound and crescendos with S2. The murmur duration is greater when going from supine to standing and decreases when squatting. The murmur is heard best along the lower left sternal border and apex. Her electrocardiogram is normal. Which of the following is the most likely condition causing the murmur?

ExplanationMitral valve prolapse is characterized by a midsystolic non - ejection sound (click) followed by a late systolic murmur that crescendos and terminates with S2. A decrease in venous return induced by standing will move the click closer to S1 and increase the duration of the murmur. Squatting will increase venous return and shorten the duration of the murmur. The murmur of hypertrophic cardiomyopathy behaves in a similar fashion, but there would be no nonejection click, and left ventricular hypertrophy would be expected on electrocardiography (ECG). Aortic stenosis is best heard at the right second intercostal space radiating to the carotid and is crescendo–decre - scendo in character. Congenital pulmonic stenosis is crescendo–decrescendo in character and is heard best in the second to third left intercostal space. If severe, there is a paraster - nal lift right ventricular overload on ECG. Tricuspid regurgitation causes a holosystolic, not midsystolic, murmur that increases with inspiration.