S1 and S2

by Carlo Raj, MD

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    00:00 Let's spend a little bit at a time with these heart sounds. I'm going to make a noise for you, the gallops and there were two sounds that you head "lerup" with that first noise and with the second sound, you also heard two specific sounds and I am enunciating "lerup" and "darup" on purpose. Now let us walk through depolarization of the heart, shall we? We begin at the base. We begin at the right atrium. It then travels through the atria, then you arrive where? AV node. From the AV node, what do you do? You go to the bundle of His and then you go through the bundle branches. How many do you have? Through the entire ventricular septum, you have two bundle branches, left and right. Physiologically, which bundle branch do you travel through first? Left bundle branch, isn't it? If it is a left bundle branch that you travel through first with depolarization, what is that going to control? It controls the mechanical activity of your valves on your left side in order how would they then close mitral S1, then aortic S2. Is that clear? So you pay attention with the closure of the valves on the left side due to depolarization passing through your left bundle branch. Hope that is clear. Now with that said, then you move on to the right side. Then you have the right bundle branch. So therefore subsequently, remember that your nodes with atrial activity fall through what type of action potential? Close your eyes. What kind of action potential, please? It would be 403. Remember those, 403. 4, funny, that's your sodium channel. And 0, what is that? Calcium.

    01:47 And then you have phase III, which is potassium, 403. But then, if you are dealing with mechanical activity, what kind of action potential is that? That is the one with the plateau, isn't it? 0, 1, 2, 3, 4.

    02:00 Now with both of those in mind, all we are going to do is keep repeating and if your physio is not strong then you are having a hard time following me. But this could also be a point in which "Maybe I didn't understand my actual potential as well and I need to go back and review." And you want to make sure that you have that down because later on in pharmocology those are things that come into the play over and over again. We will do a little bit of that. Now we have actual closure and we have S1. We have mitral and then tricuspid now as far as the type of heart sound that you want to pay attention to and know everything about would be S2.

    02:39 But just to make sure they were clear. S1 will be mitral closure first, then followed by tricuspid, is that clear? S1, S2. S1 and then S2 would be A2, P2. We will come then in a second. Now with S1, I need you to understand when these atrial-ventricular valves are closing. Atrial-ventricular valve, that's the other name for these mitral and tricuspid, aren't they? Of course it is. When would they close? That is your next big question. Do they close during systole or diastole? Take your time. Systole, right? Think what happens during systole. The left ventricle is about to create all these pressures so that it is then going to eject blood into the aorta if the right ventricle is trying to eject the blood into the pulmonary artery, isn't it? And so, therefore, you have to open up the aortic and pulmonic valves. Once again the question to you, is are you going to create any heart sounds with opening? Never. And during systole what then happens to the mitral and tricuspid? It closes. So from henceforth I want you to think of S1 as being a systolic heart sound with the closure of the mitral and tricuspid. Is that clear? Good. Then we take a look at S2. With S2, once again what side of the heart are we dealing with first? Left side. And with S2, it is the closure of the aortic followed by the pulmonic. So now we have A2, P2. Clear? Now your next question is that if there is closure of these aortic and pulmonic valves, A2, P2, then when does this occur? During diastole. Is that clear? During diastole, what happens? My blood has just been ejected from my left ventricle and right ventricle and to the aorta and pulmonary artery respectively. There goes the blood what has to happen next so that you prevent any blood regurgitating back into the respective ventricles. You have to close them. Welcome to A2, P2. Now as I said, we will walk through the pathophys of S2 because that is where the focus should be. Once you have understood everything that we are going to refer to in the next couple of slides, then you come back and take a look at S1. You do that in order, you are being in great shape.

    About the Lecture

    The lecture S1 and S2 by Carlo Raj, MD is from the course Heart Sounds: Basic Principles with Carlo Raj.

    Included Quiz Questions

    1. SA node, AV node, bundle of His, left bundle branch, right bundle branch
    2. AV node, SA node, bundle of His, left bundle branch, right bundle branch
    3. Right bundle branch, left bundle branch, bundle of His, AV node, SA node
    4. SA node, AV node, bundle of His, right bundle branch, left bundle branch
    5. SA node, AV node, left bundle branch, right bundle branch, bundle of His
    1. Mitral, tricuspid, aortic, pulmonary
    2. Tricuspid, aortic, pulmonary, mitral
    3. Pulmonary, aortic, tricuspid, mitral
    4. Mitral, pulmonary, aortic, tricuspid
    5. Aortic, pulmonary, mItral, tricuspid

    Author of lecture S1 and S2

     Carlo Raj, MD

    Carlo Raj, MD

    Customer reviews

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    so clear.
    By S C. on 17. August 2021 for S1 and S2

    very clearly explained important and salient points. Would help with further pathological findings.