NBME 23 β-Myosin (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 3/Question#12 (reveal difficulty score)
A 39-year-old man comes to the physician for ...
β-Myosin 🔍 / 📺 / 🌳 / 📖
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submitted by ∗yotsubato(1208)

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Murmur that is louder with reduced venous return => Hypertrophic cardiomyopathy

HOCM is due to mutations encoding sarcomeres such as myosin binding protein C and beta myosin heavy chain.

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btl_nyc So I thought this was Marfan's because the murmur from HOCM is at the left sternal border, but Marfan's is a defect in fibrillin, not in collagen. +4

arcanumm To help rule out Marfran's, it is stated that there are "no history of major medical illness," which I wouldn't expect them to put if there was a syndrome going on. (they also tend to give body habitus descriptors at least) +

dul071 This isn't HOCM, rather it's simply Mitral stenosis. He has a murmur that radiates at the apex which happens to be the Mitral area. Despite everything his BLOOD PRESSURE AND PULSE are normal. The heart is over working to keep the vitals normal and as a consequence, it is undergoing hypertrophy which dictates the answer +

dna_at @dull071 I don't think this is MS. That would be 1) diastolic and not systolic, 2) less likely to cause LVH. I believe as others said it is just HOCM leading to MR, which is what we are hearing. MR secondary to HOCM would still increase in intensity with less preload as there would be more LVOT obstruction (thus more regurgitation) +1

fatboyslim @dul071 and @dna_et: HOCM causes a systolic murmur because the intraventricular septum hypertrophies to a point where it obstructs LV outfow, especially when there is less preload in the LV because the septum has less resistance against it to compress the LV. It causes a "sub-aortic narrowing", causing a systolic murmur. It is WORSENED with LESS preload (unlike most heart murmur) and SOFTENED with INCREASED preload or INCREASED afterload (increased afterload makes the LV have to pump harder and that pushes the septum away -> less subaortic narrowing). +

fatboyslim *interventricular +

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submitted by ∗krewfoo99(115)

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Wouldnt the HCOM murmur be best heard in the aortic area?

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krewfoo99 Correction: Shouldnt it be heard best in the left upper sternal border? +

usmlehulk In FA 2018 page 303. patients with HOCM presents with MItral regurgitation due to impared mitral valve closure. Hence this explains the murmur. +1

xw1984 I think this was mentioned in Gojian's lecture, around Austin-Flint murmur +

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submitted by ∗maxillarythirdmolar(45)

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FA 19, pg. 305 - May see Mitral regurgitation due to impaired mitral valve closure.

I always find it important to remember that once you get pathology somewhere in the heart, you can expect pathology everywhere behind it, over time.

So in this case you start with HCM -> Mitral regurg -> LA dilation -> A.fib -> LA/LV failure -> Pulm edema -> RHF -> etc.

It's always a matter of time.

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mario wrong q bro @ maxillarythirdmolar +

usmile1 nope right question. he just went even deeper into the answer. +1

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