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Retired NBME 20 Answers

nbme20/Block 3/Question#12 (reveal difficulty score)
A 46-year-old man has dyspnea, orthopnea, and ...
Mitral regurgitation ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: DDX murmur

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submitted by โˆ—breis(56)
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Patient has Midsystolic murmur heard at the cardiac apex. there is also a LEFT ATRIAL abnormality. Echo shows LEFT ATRIUM is enlarged.

Mid systolic... enlarged left atrium...

Best choice: Mitral Regurg

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hpsbwz  Why is it regurg instead of stenosis? +3
minhphuongpnt07  Vague question requires a lot clinical reasoning. mitral regurgitation: holosystolic murmur( this cv: midsystolic), enlarged LA, LV Mitral stenosis: diastolic murmur, enlarged LA, normal LV. only best explanation I can think of: early stage Mitral regur, that's why the murmur is not holosystolic but midsystolic and LV still adequately handle the situation +4
dickass  @hpsbwz it's regurgitation because the murmur is SYSTOLIC, when the mitral valve is not supposed to make any sound. mitral valve leaks in systole, which causes blood to back up, which causes the left atrium to work harder and eventually hypertrophy. Mitral stenosis would be a DIASTOLIC sound, which is when the left atrium normally contracts. +9
themangobandit  I'm still confused as to why mitral regurg has an enlarged left atrium. Are we supposed to think that it was mitral stenosis for a time, the high LA pressure led to hypertrophy, and then became mitral regurg? That's how it works in rheumatic fever, right? +
shapeshifter51  I agree that mitral regurgitation is a holosystolic murmur heard best heard over the apex. However, with the murmur being found in the mitral valve area of auscultation it was the only answer choice that could result in LA enlargement and normal LV. Ruled out mitral valve stenosis since it is a diastolic murmur. +1
weenathon  @themangobandit I believe mitral regurg could cause an enlarged left atrium from the increased amount of blood flooding back into the left atrium with each systole causing increased pressure on the wall. +
rockodude  why is LV size normal? doesnt cause MR cause increased preload and overload over time leading to enlarged LV? +



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