First Degree AV Block (Nursing)

by Rhonda Lawes, PhD, RN

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    00:01 Hi, welcome to our video series on electrocardiograms.

    00:05 In this particular part, we're going to look at first, second and third degree atrioventricular blocks.

    00:12 Well, sometimes students think, "Oh, this is so overwhelming." But I promise you it's really not.

    00:20 Each one of these blocks follows very specific rules.

    00:24 So if you've hung with us in our other videos where we've gone through the seven steps, this will not be as difficult as you may have heard that other people think it is.

    00:34 So let's start with this first picture.

    00:37 It's normal sinus rhythm.

    00:40 Now we look at this normal sinus rhythm in every one of our videos when we talk about how to recognize specific ECG rhythms.

    00:48 But let's take a quick moment to some key points that are going to matter when we look at these blocks.

    00:55 Well, you know that we have a P wave for every QRS, right? We're very thorough, we always check that out.

    01:01 If I plotted the distance from P to P to P to P to P to P, it's the same in normal sinus rhythm.

    01:08 If I measured the distance between the R waves.

    01:12 the very top of the peak of the QRS, R to R to R to R to R, it's also the same.

    01:20 Those are hallmarks of a normal sinus rhythm.

    01:23 Once you have that clear in mind, the blocks make a lot more sense.

    01:28 So here's the seven steps that I'm talking about, that we've discussed in each of our videos.

    01:34 Now, if you need a little more time with these, just watch the introductory videos that we spend a lot of time walking through each step.

    01:43 So once again, let's recap.

    01:45 Remember, the electrical impulse travels from the atria to the ventricles, and its trajectory is what gets documented on the ECG strip.

    01:54 Now at first, the electrical impulse gets created in the SA node or the sinoatrial node, then it starts traveling towards the AV node or the atrioventricular node.

    02:05 This causes contraction of the musculature of the atria and formation of the P wave.

    02:11 Now when the impulse reaches the AV node, it doesn't just pass through it, it gets delayed.

    02:17 This delay is documented in the ECG strip as the PR segment.

    02:22 So the PR segment corresponds to the passage of the impulse through the AV node.

    02:29 Next we have the QRS complex.

    02:31 The QRS complex represents ventricular contraction which is caused by the migration of the impulse from the AV node to the Purkinje fibers.

    02:41 Moving on, we can see the T wave which is caused by repolarization or relaxation of the ventricles.

    02:48 And as previously mentioned, the interval between ventricular depolarization and repolarization gets documented as the ST segment.

    02:58 Finally, we have the U wave which is believed to be the product of delayed repolarization of the Purkinje fibers.

    03:04 But remember, this wave may or may not be present on an ECG strip that you are interpreting.

    03:13 So we've begun to talk about why this ECG is normal sinus rhythm.

    03:17 Let's see what you can recall.

    03:19 P waves, one for every QRS.

    03:22 The rhythm is regular.

    03:24 Sometimes it can vary during respirations.

    03:26 But for the most part, this will be very regular.

    03:30 Now the P wave is positive in lead I and lead II and it's biphasic or a little bumpy appearing in lead V1.

    03:39 The rate ranges between 60 and 100.

    03:43 Now let's dig into the atrioventricular blocks, right? The AV blocks, sometimes you'll see it written as AVB.

    03:52 Okay, now we've got a chart for you here.

    03:55 And this is a great way to orient yourself.

    03:58 There are three types of AV blocks.

    04:01 They're not really cleverly named as you'll notice.

    04:05 They're 1st-degree, 2nd-degree and 3rd-degree.

    04:10 Okay, so as we're building our scaffolding, we'll know we're talking about atrioventricular blocks, and that refers to the atrioventricular node.

    04:19 We have three types of blocks, 1st-degree, 2nd-degree and 3rd-degree.

    04:26 And just so you keep in mind, 1st-degree is no big deal.

    04:31 3rd-degree is the worst one, okay? That's the most significant problems.

    04:36 1st-degree, not a big deal if they're not having symptoms.

    04:40 3rd-degree, that's a big deal.

    04:43 2nd-degree, somewhere in the middle, it depends on what else is going on with your patients.

    04:49 But since it's 2nd-degree, it's easy for you to remember there are two types of 2nd-degree.

    04:57 Now there's a lot of numbers going on here.

    04:59 But 2nd-degree is type I or type II.

    05:03 They both used that funny word before it Mobitz.

    05:06 So 2nd-degree has two types Mobitz type I and Mobitz type II.

    05:13 Now let me ask you a couple questions to see if you can pause and recall the information about the types of AV blocks.

    05:20 So look away from the screen and see if you can answer these questions.

    05:25 How many types of AV blocks are there? Right.

    05:30 There's three.

    05:32 What are the names of the 3 categories of atrioventricular blocks? Good.

    05:40 1st-degree, 2nd-degree, 3rd-degree.

    05:43 Which is the most serious category for AV blocks? Cool.

    05:49 3rd-degree.

    05:50 Which category has two types of blocks? Right.

    05:56 2nd-degree and they are Mobitz type I and Mobitz type II.

    06:01 So that exercise that you and I just did together is a great way for you to study.

    06:06 Look away for your notes, ask yourself some questions, you're forcing your brain to stop process and recall and try and retrieve information so that you can make strong connections in your neocortex.

    06:19 So it'll be there when you need it on a test and when you're caring for a patient.

    06:25 So this strip is normal sinus rhythm with 1st-degree AV block.

    06:31 Remember that one is not such a big deal, your heart rates still going to be between 60 and 100.

    06:38 The rhythm is regular.

    06:39 So so far, nothing different than normal sinus rhythm, because it is normal sinus rhythm, it just has a little bit of a block.

    06:49 Now the P wave may be buried, might be a little difficult to find.

    06:53 So just keep that in mind, that's why your T wave might look a little different.

    06:57 But the PR interval, put a star by that.

    07:00 That's the difference between normal sinus rhythm and normal sinus rhythm with a 1st-degree AV block.

    07:08 So this one is pretty easy to recognize.

    07:11 The PR interval is greater than 20.

    07:14 Okay, the QRS is still normal.

    07:17 So the only thing that's different from a normal sinus rhythm strip to a normal sinus rhythm strip with 1st-degree AV block is the PR interval is longer than normal.

    07:30 Because remember, the PR represents the passage of that impulse through the AV node.

    07:35 When the PR is greater than 20, this tells us that there's a delay outside of what normally happens in the conduction system.

    07:44 Now something important to keep in mind is that the stimulus always reaches the ventricles.

    07:50 So technically, it's not a block.

    07:53 So for 1st-degree AV block treatment isn't usually required.

    07:57 The patient's healthcare team will monitor the patient and look at the cardiac rhythm over time to see if it worsens or further issues develop.

    08:06 So remember, the only difference between normal sinus rhythm and normal sinus rhythm with a 1st-degree AV block is which measurement? Right.

    08:16 The PR interval will be greater than 0.20.

    08:20 So we've got a chart for you here.

    08:22 Let's go over that again.

    08:23 If it is a 1st-degree block, it's technically not a true block but we still use that verbage.

    08:29 The only thing different is the PR interval is longer and it usually does not require treatment.

    08:36 They'll just keep a regular checkup on the patient to make sure things are still staying at a first degree AV block.

    About the Lecture

    The lecture First Degree AV Block (Nursing) by Rhonda Lawes, PhD, RN is from the course Analysis of Abnormal ECG Strips (Nursing).

    Included Quiz Questions

    1. 1st degree
    2. 2nd degree
    3. 3rd degree
    4. 4th degree
    5. 5th degree
    1. 3rd degree
    2. 2nd degree
    3. 1st degree
    4. 5th degree
    1. Treatment is not usually required
    2. Pacemaker
    3. Antidysrhythmic
    4. Calcium channel blockers
    1. Regular rhythm
    2. PR interval >0.20s
    3. Irregular rhythm
    4. Heart rate >100 bpm
    5. PR interval >0.12s

    Author of lecture First Degree AV Block (Nursing)

     Rhonda Lawes, PhD, RN

    Rhonda Lawes, PhD, RN

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