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S3 and S4

by Carlo Raj, MD

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    00:01 Before we move on, let us take a look at some S3 and S4 issues. First and foremost what does S3 mean to you? S3 is always going to take place after S2 and that is nice because chronological order. So take a look at the picture down below. Then you will notice that there is a little red line with S3, you see there? And that S3 right there is following your S2. What is exactly happening here? How are you referring to S2 as? S2 is a diastolic heart sound because you just close your aortic and pulmonic valves during diastole. And in the mean time what happens afterward? The mitral valve opens and blood is gushing into left ventricle.

    00:46 Are you picturing this? You have to picture this in your head or otherwise it is just bunch of words that makes no sense. So all of this blood is rushing into the left ventricle during diastole, the mitral valve has opened and if the left ventricle is too large as it may occur with pathology such as congestive heart failure. Could occur physiologically? Sure. Really, what kind of patient? A patient that is a well-conditioned athelete. Isn't their heart a little bit more efficient in terms of increasing preload and having increased contraction? That is why they are athletes. They are able to properly have enough blood and oxygen being supplied to the skeletal muscle. "So Dr. Raj, you're telling me that S3 could be found in normal individuals?" That's exactly right. Who are these individuals? Athletes, may be pregnant ladies. What happens to plasm volume in a pregnant woman? It increases up to as much as 50 percent. That is a lot of volume in your plasm I am telling you. And what may then happen to left ventricle? Well that left ventricle might then become overwhelmed with fluid during diastole and you may create an S3. Hope that is clear? So it could be found normally in children for the same reason, athletes, reasons we just talked about and pregnant woman. An S3. However, in the United States a 35-year-old who is obese, hearing S3. That is pathology. You are thinking about left ventricular dysfunction, a systolic dysfunction. That is what happens with congestive heart failure? Let's continue. There is athletes. S4 is a little bit of a different story.

    02:35 It is regrouped. So S3 could be found in normal individuals, yes. We are going to hear S3 after S2.

    02:39 What is an S2? An S2 is a diastolic heart sound. What happened at S2? Closure.

    02:45 Closure of whom? A2, P2, followed by mitral valve opening, left ventricle is too large. You create an S3. What about S4? Take a look at the bottom picture. You've an S4, where is it? It is before S1. Regroup, tell me about S1. S1 is a sytolic or diastolic heart sound? It is a systolic heart sound. How do you know, Dr. Raj? Because during systole, you have closure of the mitral followed by closure of the tricuspid. Welcome to S1.

    03:16 What happen right before S1? It is the fact that you are at late diastolic. Think about this.

    03:23 I am asking you what happened at the beginning or right before closure of that mtiral valve.

    03:30 Late diastole, what does that mean to you? Atrial kick, right. SA node depolarized the atria kicks. This is part of diastole. Is that clear? Atria is going to kick. It is acute part of late diastole and is kicking the blood into left ventricle. What if the left ventricle is thickened? What if it is stiff? Like what? There is something called hypertrophy. You've heard of that before. You have heard of hypertension. You've heard of that before. That's a lot of pressure on your left ventricle and at some point left ventricle is then going to respond physiologically. It is going to go through an adaptation process.

    04:09 What is that called? Hypertrophy. What kind? Concentric, we will talk about this. Not to worry. Over and over again, a concentric hypertrophy is when the sarcomeres are going to duplicate in parallel. Why? In this case, it is pressure overload. What caused that excess pressure? Hypertension being the most common.

    04:26 So with all that pressure taking place in left ventricle undergoing concentric hypertrophy, a thickened left ventricle wall. Tell me about the compliance of this left ventricle. Take your time. Tell me about the compliance. It is decreased, right? Decreased compliance, what does that mean? It has becomed stiffened. Now during that kick, the blood is having a hard time getting into left ventricle. What are you going to create? You are going to create an S4. Look at the term bolded here. Always abnormal S4, what does it mean? Indicates a stiff left ventricle. Example, hypertension. What's another one? A pressure type of overload on left ventricle, aotric stenosis. What kind of hypertrophy? Concentric. What does that mean to you? The sarcomeres are duplicating how? In parellel.

    05:14 Causing what? Narrowing of the left ventricle. I'm going to take you one step furthee, you ready? Of course, you are. You are born ready. So that left ventricle on thickening, this is a diastolic dysfunction. That chamber becomes very small and if that chamber becomes very small you can’t fill it up doing diastole, is that clear? That is the diastolic dysfunction.

    05:33 What then happens to left atrium, please? You see the last line right here. This is dilated what? Left atrium. How come? The left atrium is having a hard time kicking left ventricle. Therefore left atrium is going to do what? It is then going to get dilated. So what does S4 mean to you? Always pathologic. What does it mean to you? It means that you have a stiff left ventricle.

    05:54 Now is it possible for you to have congestive heart failure in which blood remains back in left ventricle? Think about what I am just saying. Congestive heart failure, you have a dying heart. Blood then remains back in the left ventricle. Are you with me? So you are creating what kind of issue? You are creating an issue where the blood is contributing to stiffnes. So could you have an S4 with congestive heart failure? Sure you can. That is not a good sign though.


    About the Lecture

    The lecture S3 and S4 by Carlo Raj, MD is from the course Heart Sounds: Basic Principles with Carlo Raj.


    Included Quiz Questions

    1. S4
    2. S1
    3. S2
    4. S3
    1. 35-year-old man with obesity
    2. 35-year-old female athlete
    3. 32-year-old pregnant woman
    4. 15-year-old boy
    5. 22-year-old male basketball player
    1. It is created by an accentuated atrial contraction prior to S1.
    2. It may be normal.
    3. It indicates a large volume of blood in the left ventricle.
    4. It is due to a dilated ventricle.
    5. It occurs immediately after S2.

    Author of lecture S3 and S4

     Carlo Raj, MD

    Carlo Raj, MD


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    Repetitions help solidify info.
    By Corissa S. on 26. May 2021 for S3 and S4

    I like that Dr. Raj verbally retests you again and again to help you memorize.