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