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NBME 24 Answers

nbme24/Block 4/Question#11 (37.1 difficulty score)
A 53-year-old woman comes to the physician ...
Fixed cardiac output in spite of increased demandπŸ”
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 +10 
submitted by neonem(550),
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guillo12  What does "fixed cardiac output" signify? +1  
usmleuser007  "fixed cardiac output" might mean that with the stenosis (ie. narrowed aortic valve) there is a limited or rather reduced cardiac output. Exercise would not increase cardiac output because the stenosis is caused by a mechanical (physical) rather than a biochemical process. Therefore, At any given moment the heart can not increase its output no matter how forcefully it contracts. +7  
fallot4logy  why not option A?arterial compression ? +3  
sunshinesweetheart  @fallot4logy LVH does not lead to coronary artery compression. only reallyyyy rarely will pulmonary artery dilation cause coronary artery compression. plus that would cause angina but probably wouldnt decrease cerebral bloodflow to syncope. her murmur + LVH point us toward aortic stenosis which does cause those --> fixed CO +2  
drpatinoire  @fallot4logy LVH can cause coronary artery compression, but typically leading to coronary ischemia after exercise (i.e. stable angina in this patient). The question is asking what leads to her syncope. Syncope actually means her brain is lacking blood supply abruptly. +5  
rainlad  how do we rule out mitral valve prolapse in this case? +  
spow  @rainlad murmurs at the right upper sternal border are aortic in nature. Mitral murmurs are heard at left 5th intercostal at the midaxillary line. +  



 +7 
submitted by usmile1(103),
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cbreland  Great, same thought process, murmur made me think of aortic stenosis, supported by the LV hypertrophy in stem. Then you have syncope during exercise because the heart is not able to keep up with the demands of the body +  



 +0 
submitted by aneurysmclip(134),

described a classical murmur of AS (late peaking, mid systolic, radiates to carotids b/l), no lesions on angio graph, ECG - LVH d/t AS most likely. its relieved on rest, rule our b) coronary spasm, an LVH wouldn't compress coronary artery (think a bit of anatomy). Mitral valve prolapse would a mid systolic click. im sure no one picked vasopressor induced hypotension; vasopressors increase blood pressure, this pt bp is 120/80 and a transient increase wouldn't lead to syncope.

the explanation of the right answer is given in other comments, just some thoughts of mine for wrong answers