Pacemakers of the Heart (Nursing)

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.