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Second Degree AV Block (Nursing)

by Rhonda Lawes

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    00:01 Now let's look at a Second Degree AV block.

    00:04 Remember 1st-degree is usually no big deal.

    00:08 2nd-degree is getting a little more intense and 3rd-degree is the worst.

    00:13 Now, do you remember how many types of 2nd-degree AV block there are? Good.

    00:21 There's two.

    00:22 And I love how easy that is to remember.

    00:25 I wish everything was but let's enjoy it while we got it.

    00:28 So 2nd-degree atrioventricular blocks are occasional, non-conducted P waves and a prolonged RR interval.

    00:39 Okay, that's really critical.

    00:41 So underline that in your notes.

    00:44 It's occasional, non-conducted P waves with prolonged R to R intervals.

    00:51 So we've got the two types Mobitz type I which is also called Wenckebach and Mobitz type ll.

    00:59 2nd-degree AV block that means occasional non-conducted P waves with prolonged R to R intervals.

    01:06 And you've got Mobitz type I which is also known as Wenckebach and Mobitz type II.

    01:12 So of course, we're going to start with Mobitz type I, one of the two types of 2nd-degree atrioventricular blocks.

    01:20 This one is known as Wenckebach.

    01:22 Now, let me talk about what's cool about this one, I love it when you find a strip with this, because the PR interval gets longer, longer, longer, until you have a P wave with no QRS.

    01:34 So look at that strip.

    01:36 If you pause the video and you measured it, the PR interval gets longer, longer and then you see a P wave right where it's supposed to be.

    01:45 But there's no QRS after it.

    01:48 This is one of the important reasons we ask you to always make sure, are the P waves their one to one for every QRS? Do they all look the same? This is so you don't miss a type of block or other dysrhythmia.

    02:00 So Wenckebach gets longer, longer, longer until there's a P wave and no QRS.

    02:07 So what's going on? What's happening? Well, in a Mobitz type I, there's an intermittent conduction block within the AV node.

    02:17 And that's why you have a failure to conduct the impulse from the atria into the ventricles.

    02:23 Okay, so let's check that out.

    02:26 You've got a PR interval, right? So that means the impulse is going through the atria, it's making it to the ventricle, that's the QRS, then the second B, you've got a PR interval, right? We've got a P wave.

    02:38 So it's going through the SA node, AV node, it's making it through the ventricles.

    02:43 Now we've got a P wave.

    02:44 So it's moving through the SA node, oh, it didn't make it through the ventricles.

    02:50 So if you picture in your mind what's going on in the heart, see how it matches up with what you see in the ECG.

    02:58 So can you pause the video and think, why is there a P wave without a QRS? How would I explain that? Okay, great.

    03:10 Did you remember there's an intermittent conduction block within the AV node, that's why it's an AV block, that results in a failure to conduct an impulse from the atria to the ventricle.

    03:23 So it just kind of gets stopped there.

    03:25 That's why you have a P wave, but no QRS and Wenckebach or Mobitz type I.

    03:31 So we usually don't have to treat this, we treat it depending on the patient's condition.

    03:37 If they're stable, they're able to maintain a stable blood pressure, they're not complaining of any problems, then it's usually considered just a benign condition that rarely causes hemodynamic instability.

    03:49 Asymptomatic patients, we don't do anything with, we leave them alone, and we just keep an eye on it.

    03:54 And check on that when we see them for care.

    03:57 Symptomatic patients, the really the only way to fix this is a pacemaker.

    04:01 So most people with Mobitz type I or Wenckebach are fine.

    04:07 It's benign, they're able to have a stable blood pressure.

    04:10 It's not a problem.

    04:12 If they're symptomatic, then the next step for treatment would be a pacemaker.

    04:16 Now back to our chart.

    04:18 So this is a great study tool if you use it right.

    04:22 Remember, we're going to lay this out for you as we continue through this video series.

    04:27 But the best thing you can do for your study is that you cover up these boxes and use it as a way to ask yourself and then check the answer.

    04:37 So you see we started with 1st-degree, we've already talked about that.

    04:40 Remember, it's technically not a block.

    04:42 The only difference between normal sinus rhythm and a 1st-degree block is the PR interval, just a little bit longer than normal.

    04:50 So we don't usually have to treat this.

    04:52 Now 2nd-degree type I or Wenckebach is also usually benign.

    04:58 But the difference is we don't just have a consistently long PR interval, we have a PR interval that progressively lengthens, and then you have a P wave and no QRS.

    05:10 So usually this one doesn't need treatment.

    05:13 And if the patient is symptomatic, then we'll use a pacemaker to treat the 2nd-degree Mobitz type I, but that is not the norm.

    05:22 Usually, the patient is stable, and we don't have to do anything with it.

    05:27 Now let's go on to 2nd-degree AV block Mobitz type II.

    05:32 This is a little bit different than the Wenckebach.

    05:35 Now, look at the strip.

    05:37 The P waves are at a constant rate, you see that? All the way across the strip, we've got the P waves just rocking along, right? The PR interval.

    05:49 Try and measure that right now.

    05:50 Pause the video and look at the PR interval.

    05:54 Hey, that's different than Mobitz type II, because there's no prolongation of the PR interval like we saw in Mobitz type II.

    06:03 Now remember, a study strategy is comparing similarities and differences.

    06:08 So write in your notes, what do you see right now that's a similarity between type I and type II and what do you see that's different? Now let's talk about the R to R intervals as something we normally look at.

    06:21 But look at this strip.

    06:22 That looks a little scary, doesn't it? Yeah, as a student, this would be really scary.

    06:27 But know as a nurse, we would be looking at the whole patient and assessing them for their blood pressure, how they're feeling, we would make sure they were hemodynamically stable.

    06:39 So look at the R to R interval.

    06:41 Now here we just have a couple, but if you look at those, they're the same.

    06:45 So the R to R interval is stable before the dropped beats.

    06:50 So it's the same before the dropped beats, but you just have to have a couple hours together to actually measure that.

    06:58 So the Mobitz type II can sometimes happen secondary to a disease involving the His-Purkinje system.

    07:06 Now there's a failure to conduct impulses from the atria into the ventricles.

    07:11 Ah, this is different, right? 1st-degree AV block, there's an occasional or intermittent block.

    07:19 But this one, there's a failure to conduct it from the atria into the ventricles.

    07:24 Now the block happens somewhere after the AV node and within the bundle of His.

    07:31 Let's go through that one more time.

    07:33 I know you will have this clear.

    07:35 It's all about location, location, location.

    07:40 So there's something going on usually secondary to a disease or heart disease in this patient that would cause them to have Mobitz type II.

    07:51 We know that we have P waves, but we don't have QRS complexes.

    07:56 So we know that the impulse isn't making it from the atria into the ventricle.

    08:00 That's why we don't have the QRS impulses.

    08:04 But we also know that the block occurs after the AV node and within the bundle of His or within the bundle branches.

    08:13 So that's where Mobitz type II happens.

    08:17 And that's why you end up with a strip that looks like P waves, but not as many QRS complexes.

    08:26 So do you wonder why there's no change to the PR interval? I bet you've already got this answer.

    08:32 Think about what the PR interval represents.

    08:36 Remember, the impulse starts from the SA node, then when it goes to the ventricles, the block hasn't happened yet.

    08:47 That's why we have a PR clear interval.

    08:50 So the block happens after the AV node.

    08:54 So the His-Purkinje system like an all or nothing conduction system.

    08:58 So there's no changes in the PR interval.

    09:01 It's made it through the block happens after the AV node.

    09:07 So to clarify, in Mobitz type II, there are no changes to the PR interval.

    09:14 So no changes in the PR interval in Mobitz type II, are there changes in the PR interval in Mobitz type I? Yes. So that's one of the differences.

    09:26 Because in Mobitz type II, there are no changes in the PR interval even after the non-conducted P waves.

    09:34 So that is a classic difference between I and II that you want to help keep in mind.

    09:40 But use our pictures.

    09:42 Use the pictures to remember what's being represented on the strip, and these will be much easier for you to master.

    09:50 Now that you have the picture in your mind that that impulse is getting blocked after the AV node.

    09:56 What do you think could possibly cause that? Well type II blocks, Mobitz type II blocks, they kind of let us know there's some type of structural damage to the AV conduction system.

    10:07 Now why this is more serious than Mobitz type I is that Mobitz type II often deteriorate into complete heart block, and that one is the most serious of all.

    10:20 So this is a big deal.

    10:23 In 1st-degree AV blocks, we usually don't treat it.

    10:27 In 2nd-degree AV blocks Mobitz type I, we also usually don't have to treat that.

    10:33 If they are symptomatic, we'll use a pacemaker.

    10:36 In Mobitz type II, this patient is going to require either a transvenous pacemaker or a permanent pacemaker.

    10:44 Now how do we pick? Well, the transvenous pacemaker is transvenous through the vein, right? We just use that until the patient can go for a permanent pacemaker.

    10:55 But pacemaker is the treatment of choice for patients who are symptomatic with Mobitz type I.

    11:03 And for patients with Mobitz type II because we know this rhythm could deteriorate into complete heart block.

    11:11 So when this is recognized, they definitely need a pacemaker.

    11:16 So back to our chart, you've got 1st-degree secondary type I, 2nd-degree type ll.

    11:23 So I is not that big a deal.

    11:25 II is usually benign, but 2nd-degree type II, we know because they have an increased risk to roll down into 3rd-degree heart block, this one requires treatment.

    11:39 Now when you compare the PR intervals, the 1st-degree is greater than 20.

    11:43 In 2nd-degree type I, they get longer, longer, longer until there's a P wave and no QRS.

    11:50 But in 2nd-degree type II, that PR interval is constant, except for the dropped QRS.

    11:58 Now we don't really need to treat I rarely.

    12:02 II, we most often do not have to treat it.

    12:04 So 2nd-degree type I, we don't have to treat.

    12:08 But 2nd-degree type II will receive an internal pacemaker.


    About the Lecture

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


    Included Quiz Questions

    1. It has an occasional non-conducted P waves
    2. It has a prolonged PR intervals
    3. It consists of two types
    4. It has three types
    5. It has a regular PR intervals
    1. AV block is occasional
    2. AV block is constant
    3. AV block is continuous
    4. AV block is regular
    1. Mobitz type 1
    2. Wenckebach
    3. Mobitz type 11
    4. Mobitz type 3
    5. Menckebach
    1. Pacemaker
    2. No treatment if patient is asymptomatic
    3. Cardiac medications
    4. Cardizem drip
    5. Digoxin
    1. >0.20s
    2. >0.30s
    3. >0.12s
    4. >0.25s
    1. Constant PR interval except for dropped QRS
    2. Irregular PR interval except for dropped QRS
    3. The PR interval is more than 0.20 seconds
    4. The PR interval is more than 0.30 seconds

    Author of lecture Second Degree AV Block (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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