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Pacemakers of the Heart (Nursing)

by Rhonda Lawes

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    00:01 Let's go back over this a little bit more before we get into dysrhythmias.

    00:04 But I want you to see in this presentation, how the electrical system works in pretty good detail.

    00:10 So if you study with us now, in this video, you'll be rock solid by the time you're done.

    00:15 So the SA node, the AV node, and the bundle of His or the AV bundle is a newer name for it.

    00:22 These are the pacemakers of the heart.

    00:24 Do you remember which one we consider the natural pacemaker? Yeah, it's the SA node.

    00:29 Good job.

    00:30 The first one.

    00:32 Now, it's the primary pacemaker.

    00:34 Its average is 70 beats a minute.

    00:36 So acrossed the normals.

    00:39 We're going to say that the average this is 70 beats a minute.

    00:42 Now the SA node is under both parasympathetic and sympathetic control.

    00:49 Now, we've got an arrow down and an arrow up.

    00:52 What does that mean? Well, when it's under parasympathetic stimulation, it will decrease the heart rate.

    00:58 When it's under sympathetic stimulation, it will increase the heart rate.

    01:02 So that's why we went ahead and just put those arrows in there but draw a little note or highlight whatever you find most effective to help yourself remember that.

    01:11 So the SA node is under both parasympathetic and sympathetic nerve control.

    01:15 Now the AV node is the next stop, right.

    01:18 It's considered an Ectopic pacemaker.

    01:21 Because did you hear me almost say pregnancy? Yeah.

    01:24 Now, an ectopic pregnancy is a pregnancy that happens outside of the uterus, where we much prefer they happen.

    01:31 Ectopic pacemaker is the same thing.

    01:34 It's really not the best idea for the AV node to be the pacemaker because it only goes at a rate of about 40 to 60 beats a minute.

    01:42 So that's why it's considered an ectopic pacemaker.

    01:45 We prefer the signal to come from the SA node at a higher rate.

    01:51 Now the third pacemaker remember, these are backup pacemakers, AV node, and bundle of His, or AV bundle.

    01:57 These are backup pacemakers if the SA node fails for some reason goes even slower, like 30 to 40 beats a minute.

    02:05 So what's important that you takeaway in this slide is you're reinforcing the path of electrical impulse from the SA node, the AV node, the...

    02:14 Right.

    02:15 The bundle of His or the AV bundle.

    02:18 So that's what I want you to do, try and close your eyes or look away from your notes and review that.

    02:23 Peak when you have to, but keep going till you don't have to look anymore.

    02:27 Once you have solid in your mind the order SA node, AV node, bundle of His or AV bundle, then go back and make sure you have the rates.

    02:35 So you have a fair idea of SA node is 70, AV notice 40 to 60, and bundle of His is 30 to 40.

    02:43 Those are important points before we take the next step.

    02:48 And we call that an autorhythmic? Right, the SA node is autorhythmic because it is the primary pacemaker.

    02:54 But what really is it? I mean, how do they do that? What's this group of cells? They are cardiomyocytes.

    03:00 And they're on the wall of the right atrium.

    03:03 So get a picture in your mind.

    03:05 Oh, you don't need to.

    03:06 We've got one for you right there.

    03:09 See where the SA node is? It's on the wall, the right atrium.

    03:13 And it's really close to where the superior vena cava enters the heart brings up blood.

    03:19 Now it's capable of spontaneously producing an electrical impulse that travels through the special cells to reach the atrial ventricular node.

    03:27 That's what the SA node does.

    03:30 So it can go off by itself.

    03:31 We know what the average rate is.

    03:33 It's a group of cells in the right atrium.

    03:39 So because they can do this, these are spontaneously depolarizing at about 100 times.

    03:43 Whoa...

    03:45 Wait a minute.

    03:46 Now, why does it say there that they depolarize about 100 times a minute? Because I remember very clearly, trying to make sure that I knew that it only goes at 70.

    03:57 So how does this happen? Did we have an error on our slide? No.

    04:02 It's just something super cool that your heart can do.

    04:07 Let me tell you how it works.

    04:08 Remember, the sympathetic and parasympathetic nerve fibers via the autonomic nervous system are constantly changing the heart rate.

    04:16 Why? Because it's responding to the stimuli in needs of the body.

    04:21 Okay, that doesn't get you fired up. I don't know what will.

    04:25 That is amazing.

    04:27 That its spontaneously set at 100.

    04:29 But your body has such exquisite control.

    04:33 The sympathetic and parasympathetic nerve fibers through the autonomic nervous system controls are constantly adjusting your heart rate.

    04:41 It's why we can run when we need to sleep when we need to.

    04:43 All those things my body needs to do.

    04:47 It's constantly adjusting it.

    04:50 Okay, so we know the SA node on its own.

    04:52 We'll be going about 100 beats a minute, but because the SA node is influenced by parasympathetic and the sympathetic nervous system, the average is around 70.

    05:04 And see that's where we get the rate for sinus rhythm comes from the SA node, the sinoatrial node.

    05:12 Sinus rhythm is 60 to 100.

    05:16 We haven't even looked at rhythm strips and you're already getting it.

    05:19 Good job.


    About the Lecture

    The lecture Pacemakers of the Heart (Nursing) by Rhonda Lawes is from the course Review: Anatomy and Physiology of the Cardiovascular System (Nursing).


    Included Quiz Questions

    1. Parasympathetic control decreases the beats per minute, and sympathetic control increases the beats per minute.
    2. Parasympathetic control increases the beats per minute, and sympathetic control decreases the beats per minute.
    3. The SA node is affected only by sympathetic activation.
    4. The SA node is affected only by parasympathetic activation.
    1. In the wall of the right atrium, by the superior vena cava
    2. In the wall of the left atrium, by the aorta
    3. At the junction of the atria and ventricles
    4. Deep in the ventricular myocardium
    1. 40–60/min
    2. 70–90/min
    3. 60–100/min
    4. 30–40/min
    1. Electrical signals are not properly conducted from the atria to the ventricles.
    2. Electrical signals are not properly conducted from the ventricles to the atria.
    3. The heart comes to a complete standstill.
    4. It occurs when the SA node is damaged.
    1. Purkinje fibers specialize in rapid electrical conduction and have fewer myofibrils than other myocardial cells.
    2. Purkinje fibers have excessive transverse tubules to slow down conduction.
    3. Purkinje fibers slow down electrical conduction and have more myofibrils than other myocardial cells.
    4. Purkinje fibers specialize in rapid electrical conduction and have more transverse tubules and myofibrils than other myocardial cells.

    Author of lecture Pacemakers of the Heart (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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