NBME 23 Closure of the mitral valve (NBME Answers)

+12
submitted by lfsuarez(141),

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yotsubato Then why the fuck is it describing a mitral valve sound in the tricuspid area +22

dr.xx it's describing a splitting S1 — consisting of mitral and tricuspid valve closure — that is best heard at the tricuspid (left lower sternal border) and mitral (cardiac apex) listening posts. +30

titanesxvi tricky question, I though what sound it is in the left sternal border, so I chose tricuspid valve, but what they where asking was, what is the first component of the S1 sound +4

titanesxvi tricky question, I though what sound it is in the left sternal border, so I chose tricuspid valve, but what they where asking was, what is the first component of the S1 sound +1

drzed It shouldn't matter where you hear a split sound. For example, no matter where you auscultate on the heart, the second heart sound in a healthy individual will always be A2 then P2 (whether you are at the mitral listening post or the aortic listening post) The key is recognizing that the right sided valves in healthy individuals will always close later (e.g. the heart sounds are S1 S2, but more specifically M1 T1 A2 P2). The reason for this is simple: if you take a breath in, you will increase preload on the right side of the heart, and thus the greater volume will cause a delayed closure of the valve. This is physiologic splitting, and is better appreciated in the pulmonary and aortic valves because they are under greater pressure, and thus louder, but it can also be heard in the first heart sound. +9

alexxxx30 yes agreed!! This question is mostly asking if you understand a few basic things regarding cardio physio. The left side of the heart is the higher pressure side so left sided valves will close first. The right side of the heart is the lower pressure side, which means right sided valves will open first. [Left closes first, Right opens first]...Secondly, it requires you to know what S1 and S2 sounds come from. S1 is the mitral/tricuspid valve closing and S2 is the Aortic/pulmonary valves closing. So really the question asks what is the first component of S1 (mitral or tricuspid closes first). And since we know that the left side will always close first, it must be mitral valve closure. Sorry if that was a long explanation. +10

jesusisking Thanks @alexxxx30, you the man! RIP Kobe +