NBME 23 Closure of the mitral valve (NBME Answers)

Retired NBME 23 Answers

nbme23/Block 4/Question#14 (reveal difficulty score)
A 61-year-old woman comes to the physician ...
Closure of the mitral valve 🔍 / 📺 / 🌳 / 📖
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+14 upvote downvote
submitted by ∗lfsuarez(160)

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First heart sound (S1) is generated by two heart valves: the mitral valve and tricuspid valve. Nearly simultaneous closing of these valves normally generates a single S1 sound. Splitting of the S1 sound is heard when mitral and tricuspid valves close at slightly different times, with usually the mitral closing before tricuspid

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yotsubato Then why the fuck is it describing a mitral valve sound in the tricuspid area +29

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. +40

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 +5

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. +16

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. +16

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

yesa @drzed unless it's paradoxical splitting Ex] aortic stenosis, then it is aortic valve closing first at S2. +

This video explains it https://www.youtube.com/watch?v=kvQ2IU3ILRo&list=PL3n8cHP87ijDnqI8_5WQlS4tN37D6P4dH&index=8&t=52s

+/- uasid(68)

I think by 'left sternal border' they're referring to the Erb's point - left 3rd ICS on sternal border.

Even I got it wrnong thinking tricuspid area is being described!

+/- abhishek021196(119)

+4 upvote downvote
submitted by ∗gh889(154)

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Great video on S1 and it's split!!

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+3 upvote downvote
submitted by ∗rolubui(17)

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The way I remember it, S1: Mitral & tricuspid bc blood goes from atria to ventricles then from ventricles to outside the heart --> S2. Now, when you have a Split S1 the way I think about is that when you inhale you have extra blood coming into the right side of the heart so the tricuspid valves closes later and causes a split S1 upon respiration. Hope that helps.

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+1 upvote downvote
submitted by ∗yogi(19)

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Q: Split S1 heard over Left sternal border - tricuspid area. First component of S1? A: anything (MC in RBBB) that causes delayed closure of tricuspid valve compared to mitral valve- will cause split S1 with delayed T1 and early M1 heard at Tricuspid area.

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+1 upvote downvote
submitted by usmlehulk(7)

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Please read the last sentence of the question. I think the split might be because of Rbb,. this causes the mitral and tricuspid valve to close at different times.

-so which of the following best explains the first component of the heart sound (split S1). Should be the mitral valve closure before the tricuspid valve.

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