Full transcript
0:00in this video I'm going to be teaching
0:01you guys about the three types of Av
0:03blocks that are very high yeld for step
0:05one basically on step one the test
0:08writers know that you cannot interpret
0:10EKGs because you're really just
0:11beginning in your kind of clinical path
0:13so there's only a limited number of EKGs
0:16that are fair game and because the pool
0:18is so small AV blocks are so high yield
0:22because again aside from sinus rhythm
0:24aib or a flutter the three AV blocks are
0:27really really fair game so you're
0:30probably going to be asked a question on
0:31them and that's why they're high yield
0:32and that's why we're going over them
0:33today so before we go into the AV blocks
0:36here is normal you have a p-wave a QRS
0:39complex and a t-wave what we're going to
0:42be concerning ourselves with today is
0:43really the PR interval that is the
0:45distance from the beginning of the
0:46p-wave to the beginning of the
0:48QRS now normally on a normal EKG in
0:51normal sinus rhythm the PR interval is
0:55less than 200 milliseconds which is five
0:57little boxes on an EKG and this this
1:00example of normal it looks like we've
1:02got about maybe three and 1 half to four
1:04blocks so this is normal if it was
1:07greater than five blocks or greater than
1:10200 milliseconds then it would be
1:12prolonged and we would have to think
1:14about an AP block so again this is
1:17normal so we're going to start with the
1:19first deegree AV block and before I do
1:21that I just want to say what it is and
1:23what the presentation will be on the
1:24exam so an AV block is just as the name
1:27implies it is a block in the conduction
1:29system down from the SA node to the AV
1:31node so the hisper kingi system never
1:33gets activated correctly and therefore
1:36the heart can't beat efficiently so
1:38think about it on the test you might be
1:40given a clinical vignette where a
1:41patient is experiencing dizziness
1:43Syncopy a slow heartbeat whatever the
1:47case is it's all related to the fact
1:49that the heart can squeeze and give you
1:50that nice good ejection fraction in time
1:53because of the electrical conduction
1:55abnormality so a first-degree AV block
1:58looks like this and basically what you
2:00have in a first-degree AV block is just
2:02prolonged PR intervals they are constant
2:05they are prolonged and that's it so
2:08whereas in the normal I showed you a
2:10nice pretty little PR interval that was
2:12less than five boxes a first deegree AV
2:14block is a PR interval that's greater
2:17than 200 milliseconds or greater than
2:20five little boxes and I've drawn in
2:21these reddish arrows to illustrate that
2:23to you now for second deegree AV blocks
2:26there's two types the first one is
2:28called mobitz one also Al known as Winky
2:30boach and the second one is known as
2:32mobitz 2 now you do have to know the
2:35difference but I have a nice little
2:36memory hook or pneumonic for you that'll
2:37help you out a winky boach looks like
2:42this and what happens is the PR interval
2:45gets progressively longer before a QRS
2:48is dropped so usually there's about two
2:51to four beats and then you drop a beat
2:53or you drop a QRS so what we see here in
2:57the example and I've again drawn in
2:58those little red arrows to to show you
3:00is that PR interval lengthens lengthens
3:02gets longer and then you drop a beat
3:05because the conduction abnormality you
3:07you conduct the heart's trying to
3:09squeeze and the signal goes through
3:11delayed heart tries to squeeze signal
3:12goes through even more delayed same
3:14thing happens and then the signal never
3:16makes it down to the hisper kingi system
3:17and you never get that QRS which
3:20represents ventricular
3:22depolarization so the way that you
3:24remember this is longer longer longer
3:27drop that is a win Bo longer longer
3:31longer drop that is a winky boach okay
3:34so what you're looking for in winky
3:35boach again the pr intervals are still
3:37greater than 200 milliseconds because
3:39they're prolonged but you're getting PR
3:41intervals that are progressively
3:43elongated before a beat is dropped that
3:46is winky boach another way that to
3:48remember this is some people say winky
3:50boach gives you warning just think of
3:51those W's winky boach gives you warning
3:54the pr intervals are gradually
3:55lengthening and they're warning you yo
3:57man I'm about to drop a beat check check
3:59out my EKG that's wanky boach that's
4:02also known as mobitz type 1 now mobitz
4:04type 2 is a little bit different in a
4:07mobitz type 2 the PR interval is
4:10lengthened it stays lengthened it's not
4:12getting progressively longer they stay
4:15elongated but then a beat is dropped so
4:17the way that you can think of a mobitz
4:19type 2 it's almost like a first-degree
4:21AV block that has a dropped beat in it
4:24because the PR interval is still greater
4:26than 200 milliseconds and it's still
4:27constant but somewhere Downstream drop a
4:30beat now look in the example here that
4:32green down arrow shows you where a QRS
4:34complex should be but the beat is
4:36dropped meanwhile the PR interval is
4:39still lengthened as you can see by the
4:40green little ticks that's a mobitz type
4:43two so again winky boach gives you
4:45warning longer longer longer drop that
4:47is a winky BL mobitz type 2 is just a
4:50prolonged PR interval that drops a b you
4:53need to know the differences but these
4:55are just two subtypes of a second
4:56deegree AV block now the last one we
4:58need to talk about is is a third degree
5:00AV block and I've dedicated an entire
5:02slide to it because it's really
5:03important that You' be able to pick this
5:04out because this is probably the highest
5:07yield in my opinion so a third degree AV
5:09block is one where the Atria and the
5:12ventricles contract independently of one
5:14another they both work they both squeeze
5:17but there's such an abnormality in the
5:19conduction system that they basically
5:21say hm I'm just going to do my own thing
5:23so the Atria are squeezing The ventricle
5:25are squeezing and there's no connection
5:27between them now because of this the e G
5:29has a very characteristic finding what
5:31you'll tend to see are a couple things
5:35first constant P2P intervals and
5:37constant Q toq intervals what does this
5:39mean so even though the Atria and the
5:41ventricles are Contracting independent
5:43of one another the interval between
5:46themselves is still constant so let's
5:48look in the second EKG strip I have on
5:50this slide look at the bottom arrows
5:53where you see the p waves they are all
5:55at constant intervals even though the
5:57Atria are doing their own thing like
5:58little Rebels that they are they're
6:00constant look at the intervals P to P to
6:03P to P to P it's all the same interval
6:06because even though the Atria is doing
6:07its own thing it still has rhyme and
6:08reason to it in itself look at the top
6:11where the r waves are they're still at
6:13constant intervals even though they are
6:15beating independent of the p waves they
6:18are at constant intervals now that's
6:21very characteristic of a third degree AV
6:23block the other thing that's very
6:24characteristic that you have to keep in
6:26mind is that because the p waves and the
6:28QRS complex are going to be appearing
6:30independent of one another it's possible
6:33that p waves are buried within QRS
6:35complexes and it might be hard for you
6:37to find p waves so if you look at the
6:39first strip on this slide in some of
6:42these examples it looks kind of funky
6:44right I mean we can't really discern p
6:47waves QRS and t- waves the reason that
6:49this is is because you're having some
6:51overlap if you will where the p waves
6:54are almost entirely buried in the QRS
6:56complex look at the second QRS beat in
6:58the first ryth strip you see that little
7:01thing right in front of it that's a
7:02p-wave that's basically buried in the
7:04QRS now this is kind of easy to spot
7:07because I've pointed it out to you but
7:08on the test it's possible that you're
7:10given a rhythm strip they're going to be
7:12braed cardic again because it's an AV
7:14block the patient's going to have
7:15dizziness maybe they fainted whatever
7:17and then they show you this weird strip
7:18and you're like I don't know what this
7:20is because I don't see p waves these are
7:22really big long QRS complexes what the
7:24hell am I looking at just relax look at
7:27the intervals if the P2P is constant in
7:29the Q to Q's constant you're already on
7:30the right path if you can't find p waves
7:33maybe they're buried in the QRS
7:35complexes if that's the case you've got
7:37yourself a third degree AV block so now
7:40let me just summarize what we've gone
7:41over today AV blocks are conduction
7:44abnormalities in the heart where signals
7:47are not properly propagated down from
7:48the SA node through the AV node into the
7:50hisper kinchy system because of this
7:52people with AV blocks experience braic
7:54cardia dizziness and Syncopy a
7:57first-degree AV block is one such that
7:59the PR interval is greater than 200
8:00milliseconds or greater than five little
8:02boxes on an EKG there are no dropped
8:04beats in a first-degree AV Block in a
8:07second degree AV block there are two
8:09types the first type is a mobitz type
8:11wand also known more commonly as a wnky
8:14boach in a winky boach the pr intervals
8:17get progressively longer before dropping
8:19a beat on EKG the P the PR interval will
8:22be greater than 200 MCS and get longer
8:24for a few beats before a QRS complex
8:26completely disappears The pneumonics
8:28remember this is that winky gives you
8:29warning or longer longer longer drop
8:33that is a winky Bop in ait's type 2 the
8:36PR interval is greater than 200
8:37milliseconds it's constant it doesn't
8:39get progressively longer it stays
8:42elongated but then you drop a beat a
8:45second degree AV block is basically like
8:46a first deegree AV block with a dropped
8:48B and lastly a third degree AV block as
8:51you see here on this slide is one where
8:53the atrian ventricles are Contracting
8:55independent of one another the P2P
8:57intervals are constant the Q toq
8:58intervals are also constant but because
9:01they are independent of one another
9:03often times the p waves are buried in
9:04the QRS complexes and it makes EKGs
9:07really hard to read because of this
9:09these are high yield all right guys go
9:11through this once or twice it's high
9:13yield it's going to be helpful and I
9:14wish you the best of luck