Hi, I'm Maureen Canectel. I've been a cardiology PA since 2005, and I've worked in cardiac electrophysiology since 2008. I transitioned to full-time PA education in 2016, where I really enjoy teaching modules specific to cardiology and cardiac electrophysiology. I'm very excited to be here with you today as part of MedAxium to deliver an educational series about cardiac electrophysiology and topics specific to that. So let's get started. Today we're going to talk about EKGs. This presentation will be broken into two separate slideshows, so let's go ahead and get started. We are going to discuss how to take a systematic approach to EKG interpretation, utilize clinical information, differentiate between things that are more benign versus life-threatening, and also focus on a little bit of the pathophysiology and how it relates to the EKG pronoun. One of my goals with EKGs is to help you become confident in things that you must be competent in. So there are a lot of things with the EKG that it's simply okay to be familiar with, and then there's other things that you cannot miss, things like SC segment elevation or high-grade AV block. Those are things that you must be competent in as a provider, so I will point those things out as we work through our lectures today. It's imperative to take a systematic approach to the EKG. It can be overwhelming when you first pick up a 12-lead EKG, but if you are careful to always follow a system and follow a pattern, you're much less likely to miss things. The approach I use is to look at the rate, rhythm, axis, look for ischemia and infarction, and evaluate for signs of block. I would like for you to review things like rate, rhythm, and axis in a bit more detail in your EKG text, but I will cover an overview of that today. We'll spend a bit more time talking about things like infarction and block, as well as SVT. We'll finish by looking at dangerous EKGs that you should be able to recognize at a glance. So we start with rate. There are a couple different ways we can evaluate the heart rate on an EKG. I'll go over two of those on the next slide. Rhythm, we simply want to know is the rhythm regular or is it irregular, and this is where we really focus on the P-wave and its relationship to the QRS. The axis, is it normal left or right? We are not going to discuss axis and degrees during the lectures, but I strongly encourage you to read about that in your text. Heart block, things like PR interval, the QRS duration, and the QTC should be covered here. And then finally, ischemia or infarction, where we look at the ST segment and the T-wave. Let's start with rate. Two ways we can do this very quickly. We look at the rhythm strip that's along the bottom of a 12-lead EKG. We find a QRS that falls on a thick, dark line, and we count over. We count over 300, 150, 100, 75, 60, and we're counting along those dark lines until we come to the next QRS, and then we can very easily estimate what the heart rate is, 65 beats per minute or so in this strip. Now, what if the heart rate is irregular or if the heart rate is very slow, like less than 40 beats per minute? Well, another quick way we can calculate the rate is to count up all the QRSs in a standard rhythm strip of an EKG, which is going to be 10 seconds, and we multiply that by six. That's a very easy and quick way to calculate the heart rate. Once you've determined the rates, you should know if it's normal, too fast, or too slow. Then we look at the rhythm. Determining the rhythm, really what we're asking ourselves is, is it regular or is it irregular? We're going to look for a pattern to QRS complexes. The reason that's helpful is because it can give us a nice built-in differential diagnosis. If I have a pattern that is irregular, but it's regularly irregular, maybe then I should consider things like atrial or ventricular bigeminy or trigeminy, or a MOBITS type 1 heart block, or things like blocked PACs. If it's irregularly irregular, I should immediately think about atrial fibrillation. Once you establish if it's regular or irregular, we want to look at the PR interval. Try to evaluate the relationship of the P wave to the QRS, because oftentimes that's going to hold the key to our diagnosis. Let's look at some examples and try to apply that here. If we determine the rate in this first example here, very quickly we can say it's about maybe 140 or so beats per minute. I start with this QRS and count 300, 150, 100, so I can see it's fast. My next step is to look at the P wave and I evaluate the relationship of the P wave to the QRS. I see normal P waves occurring before every QRS. Now with just two steps, I can say that this looks like sinus tachycardia. The bottom EKG, I can look at those same things, so same steps, but I see now that this heart rate is slow. I can start with this QRS and say 300, 150, 100, 75, 60, 50, 40, so maybe it's 45 or so beats per minute. Then I look at the P wave that's before it and I see a normal looking P wave before every QRS and I can simply call this sinus bradycardia. Things that are regular but not sinus, the QRS is very fast, it's narrow, and it's regular. Then the next step, let's look at the P wave. I can't really see a P wave, so again, with just two steps, I can look at this and say the rate is too fast, I don't really see a P wave, I think this is some type of SVT, and now you're well on your way to your diagnosis. Alternatively, maybe the QRS is very wide, so in this example, I can see the QRS is wide, it's very fast, and I still don't really see readily identifiable P waves, so this appears to be ventricular tachycardia. A final example of a regular rhythm would be atrial flutter, so I can see that the QRSs are following a pattern, they're very regular, and then when I evaluate the P wave and its relationship to the QRS, I immediately see these sawtooth P wave patterns that's consistent with atrial flutter. I'll point out here though, remember the atrial flutter isn't always regular, it is oftentimes irregular as well. Examples of irregular rhythms would be things like atrial ectopic beats, so overall the rhythm seems like it appears to be regular, but then it's got periods of irregularity to it, so there's my differential diagnosis where I'm thinking, well, it seems to be following a pattern, and so when I look at the EKG, I'm immediately drawn to the components of where there's a PAC, so there's a beat coming a little bit early, I evaluate the relationship of the P wave to that QRS that's coming in early, I can pick out that that's a PAC. In the bottom example here, I can see that those PACs are coming in groups, so it is a regularly irregular rhythm, but when I look a little closer, I can identify these as PACs and that's the source of that irregular rhythm. Same thing applies to ventricular ectopic beats, I see that this one's coming in early and this one and this one, so it gives a nice pattern when I'm listening to a patient, when I'm auscultating, or when I'm evaluating their rhythm strip, and I can see that it is regularly irregular, and this is ventricular trigeminy on top where every third beat comes in early, and this is ventricular bigeminy where every other beat comes in early, so regular versus irregular helps me narrow down my differential diagnosis, and finally the classic irregularly rhythm is atrial fibrillation. The QRSs are not following a pattern, they are irregular, and I cannot see any identifiable P wave because I just see a fibrillatory baseline, so this is atrial fibrillation. Okay, so we've covered rate, rhythm, axis. So with axis, all I really want to know is if the Q, I want to know if the axis is normal, if it's left, or if it's right. So if we think back to Eindhoven's triangle, and we've all learned about that and how we create this axis wheel, it's really created by the intersection of leads one and AVF, and so if we also recall on Eindhoven's triangle, lead one kind of has this positive deflection over on the left, and lead AVF, we think of that as positive at the feet. So if I look at the QRS complex in lead one and AVF, and I see if it's upright or if it's negative or downright, then I look at where those two overlap, that tells me where the mean axis is. So what am I asking about with axis? I want to know the mean general electrical conduction flow through the heart. So if I take that axis wheel, and I just kind of superimpose it on my chest like this, I know that my heart, the base of my heart starts up here, and I have the apex down here, and so electricity should spread this way, right down towards that normal quadrant. If there's something that shifts the axis to the left, it's going to push it up this way, and if it shifts it to the right, it's going to push it over this way. So there are very classic findings that we can look for, and there are characteristic things that can do that, things like MIs or bundle branch blots, hypertrophy, all of that can shift the general direction of electrical flow one way or the other from that normal quadrant. So I can look at, let's look at an example. I can look at the QRS in lead one and see that it is positive. So I can use this little diagram over here, and if the QRS in lead one is positive, I know that the axis is going to point somewhere over to the patient's left. Then I look at the QRS in lead AVF, and this example is also positive. So I know that the axis is going to point somewhere down towards the patient's feet. So it's going to be somewhere in one of these two quadrants. So then I ask myself, where does this overlap with this? And it overlaps right here in the normal axis quadrant. You may have heard this described as the two thumbs up method, or I say QRS in lead one is positive, and the QRS in lead AVF is positive. So I know it's two thumbs up, it's a normal axis. And I can use these same concepts to look at left or right axis. So let's say the QRS in lead one is negative or down, and the QRS in lead AVF is positive or up. What is the axis? Right axis deviation, because my right thumb is up. If it's just the opposite, QRS in lead one is up, QRS in lead AVF is down, then it's a left axis deviation. So I can use the two thumbs up method, or I can also use these diagrams here and say, which side is that axis going to point to in each one? And then where do those two things overlap? Wherever they overlap, that's where the axis falls. You can take this one step further in your book and determine the axis in degrees as well, which is helpful for things like hemiblocks. So why do we care about axis deviation? Well, in left axis deviation can occur if there's a left bundle branch block, because now I have all of my depolarization is going to shift towards the left to kind of passively depolarize a blocked left bundle. Things like obesity can do it. So if someone's really big, they have that increased abdominal tissue that's going to push up on the diaphragm, and that'll shift your axis to the left. Same concept with left ventricular hypertrophy is with the left bundle branch block. With left ventricular hypertrophy, I got a big, thick left ventricle, and I recruit additional electrical vectors to depolarize over towards the left. With right axis deviation, we can just think of just the opposite. So right bundle branch block, right ventricular hypertrophy. People with COPD sometimes have a right axis deviation, and think of it this way. Their lungs are really big and hyperinflated, and so you essentially stretch your mediastinum in a vertical direction, and it's like you take the tip of the apex of the heart, and you just pull it down, and that shifts it to the right as well. So axis deviation is an important component of the EKG interpretation. Let's move into heart block now. So the different types of heart block we're going to make sure we evaluate for a first degree AV block, where the PR interval is going to be more than 200 milliseconds. So a normal would be less than 200 milliseconds, but in a first degree AV block, it's going to be greater than 200 milliseconds. And a QRS is greater than 120 milliseconds. That can occur with bundle branch blocks. A QT prolongation should be evaluated in this step, where we're going to look at the QT interval, and that should be less than half the RR interval if it's in normal circumstances, but it's going to be longer than that if there's QT prolongation. So I'll show you an example of that if they'll make a little bit more sense. And then we have second degree type one and two, along with third degree AV block. So first degree AV block, a helpful tip is to remember that one large box on the EKG, so one large box would be any one of these, so from here to here is one large box, is 200 milliseconds. So if I've got a first degree AV block, then that PR interval is greater than one large box. So I can eyeball this very quickly, find the start of a QRS complex that falls on a thick dark line, and find the start of the P wave that's just before it. If it's more than one large box, I can quickly identify that as a first degree AV block. So first degree AV blocks are usually asymptomatic, and the QRS is normal unless there's some additional type of heart block. This occurs because there's a delay in the spread of an impulse from the sinus node to the AV node. Next is a QRS duration that is more than three small boxes. So one small box is 40 milliseconds, so if I have three of those, then that's greater than 120 milliseconds, and that's the very first step in evaluating for a bundle branch block. So a lot of people want to jump straight to the QRS morphology and call things a bundle branch block, but you got to remember the QRS has to be consistently wide in order for there to be a bundle branch block present. Then we look at the QRS morphology and leads V1 and V6. So one thing I want you just to remember is with the chest leads, it's a lot more straightforward. The chest leads we place, the precordial leads, as opposed to the limb leads we look at with a 12 lead EKG, and I always say what you see is what you get with the chest lead. So wherever you put that lead, it's going to tell you exactly what's happening in that part of the heart. So the leads we look at are the far right chest lead V1 and the far left chest lead V6, and I can see electricity moving towards me if that complex is positive, and as electricity moves away from it in that lead, it'll look negative, and that's really the basis for what we look for with bundle branch blocks. So we have our right bundle and our left bundle's got an anterior and a posterior fascicle, and so with the left bundle branch block, there's a lot more tissue that has to be covered, so we see a bit more changes on the EKG. So let's look at each of these. With the right bundle branch block, I've got a delay here or a blocking of the conduction in the right bundle. So what happens is I have to have passive depolarization from the left bundle all the way across over to the right, and that's what causes that wide QRS. So I can look at the far right chest lead, and what I see if there's a right bundle branch block, I have passive depolarization from left to right. So that right chest lead V1 is going to see everything coming towards it, which is why we see two positive deflections in lead V1. So with lead V1, I have right and left ventricular activation, but it's all passive, so lead V1 sees it as positive. Now lead V6, I'm going to have a positive and a negative component. So the positive component in lead V6 is the intrinsic activation of the left bundle, and then the negative component, which is the S wave in V6, is electricity moving away to passively depolarize over to the right. So the classic EKG finding step one is the QRS is consistently wide. It's greater than three small boxes, all throughout the EKG. And then in lead V1, I see an R and an R prime, which some people call bunny ears. They look like bunny ears. So R, R prime in V1 and V2. And then in V6, I see an R wave with a broad S wave. And so that's really characteristic of a right bundle branch block. And what that means by broad is it doesn't just come down and go back up to baseline. It goes down, it kind of swoops back over to baseline there in V6. And another clinical pearl, you'll typically see a broad S wave in lead one as well with the right bundle branch block, which we have a nice example of right here, that broad S wave. So that's the right bundle branch block. A left bundle branch block with this one, step one, QRS is wide. And then I look at lead V1 and V6 again with lead V1, that's my right chest lead. So if all the electricity is going from right to passively depolarize the left, it makes sense that lead V1 is very negative. So it's going to see the strong negative deflection in lead V1. And then in lead V6, because everything is coming towards it, I see a very strongly positive QRS complex there. So left bundle branch block, the QRS is wide. It's more than three small boxes. And then in V1, I have a very negative QRS complex. In V6, a very positive QRS complex. So that is diagnostic of a left bundle branch block. So let's move on to other types of heart blocks. Second degree AV block type one. This is also called a Wenckebach and it's called a Mobitz one. So lots of different names for this one. But what we see here is a progressively lengthening PR interval from cycle to cycle prior to a dropped QRS. So remember when we talked about PACs and PVCs, I said, your eyes are kind of drawn to that beat that comes in early, but also to that little pause that comes after it. So similar to this, a Mobitz type one, your eyes are going to be drawn to this drop beat right here. So what you see is a P wave with nothing after it. So you have to be patient and really evaluate the whole EKG. You want to look at the PR interval just after and just before. And the PR interval just after the drop beat should be shorter than the PR interval that's happening just before it. And that's precisely what we see here. So I have a progressively lengthening. It's like you're standing, talking to someone and moving farther and farther away. Well, eventually they're not going to be able to hear you. And that's what happens with the AV node. It drops that beat and then the cycle repeats itself. So we can confirm that by following this strip through. So I see a PR interval that's short and then it gets longer, longer. And now I have a P wave with nothing after it. And the cycle repeats. You want to make sure you can differentiate a second degree type one from a second degree type two, because the second degree type one patients aren't terribly symptomatic unless they're dropping a lot of beats. But patients with second degree type two tend to be more symptomatic. So we call this an infrahissian block because it occurs below the bundle of hiss. And because of that, it tends to be associated with a wider QRS complex, as you can see here. With the second degree type two, there's a fixed PR interval that doesn't change throughout the strip. And then unpredictably, you'll have a dropped QRS. So your eyes are drawn right here to this drop beat. And then when we look at the PR interval after and the PR interval before, they're the same. And I can confirm that by looking at the PR interval throughout the remainder of that rhythm strip. And I'll see it doesn't change. So second degree type two, much more concerning because we don't know when they're just going to start dropping two or three beats at a time. It's very unpredictable because it's occurring lower in the conduction system. So these patients generally are going to get a pacemaker as long as there's not some easily reversible cause. Third degree AV block is defined by AV dissociation. So with a third degree AV block, you'll see regular appearing P waves following a pattern, and you'll see regular appearing QRS complexes following a pattern, but they're not connected. So if you just very quickly look at this, you might be tempted to call it a left bundle branch block because you say, oh, the QRS is wide and I see negative deflection in V1 and a positive deflection in V6, but you have to look at the EKG in its entirety. And when you do that, you'll start noticing the P waves here. So if you just look at, let's say just this complex right here, this P and this QRS, you might say that looks totally normal because it kind of does. I mean, it's a little long, but it doesn't look terribly abnormal, but then you have to offer an explanation for this. Well, what's this P wave right here? What's that doing there? And that's when you should start thinking, maybe this is complete heart block. So what I do is I take my calipers and I'll find two P waves that are right next to each other. And I'll measure that interval, that cycle length. So I measure that atrial cycle length, and then I'm going to just move my calipers across the page to the next P wave. And what you'll find is those P waves will march out perfectly across the page. They don't change because the atria are just marching away doing their thing and they don't know what's happening below. But in third degree AV block, the AV node is not conducting. There's a blocked impulse. And so what happens is an escape rhythm has to take over. And that's why it's regular. That's also why it will typically have either a left bundle or a right bundle branch block appearance with complete heart block. That just tells you the location of where in the ventricle that escape rhythm is coming from. So a third degree AV block, you'll see an atrial rate that is regular, a ventricular rate that's regular, the atrial rate is faster than the ventricular rate, and there's no communication between the two. There's no association between A and B. So that's complete heart block. So we will end this session right here and we'll start back up with another PowerPoint where we're going to focus on the remainder of our EKG topics. Thank you. Thank you.

EKG interpretation

systematic approach

heart block

rate

rhythm

axis