hey everyone it's sarah with registernursern.com and in this video i'm going to be going over ekg interpretation basics and as always whenever you get done watching this youtube video you can access the free quiz that will test you on this material so let's get started an ecg also known as an ekg stands for electrocardiogram an electrocardiogram assesses the electrical conduction system of the heart and the whole role of the electrical conduction system is to get your heart to contract and pump blood throughout your body so to help us really understand how to interpret an ekg we first have to go back to the basics and talk about how the blood flows through the heart and apply that to how the electrical conduction system causes that to happen so first let's look at the heart blood flow everything starts on the right side of the heart and blood that needs to be replenished with oxygen will enter into the right atrium when the right atrium becomes full it will be stimulated by the electrical conduction system and cause it to contract and will send blood down through the tricuspid valve into the right ventricle the right ventricle will become full and whenever it receives stimulation from the electrical conduction system it will contract and send blood up through the pulmonic valve into the pulmonary artery where the blood is going to go into the lungs and gas exchange is going to occur and then that blood is going to get oxygenated again enter in to the left side of the heart through the pulmonary vein it will go down through the left atrium left atrium receives the electrical signal to contract once it's full and it will contract and send the blood through the mitral valve into the left ventricle and the left ventricle will contract whenever it receives signal up through the aortic valve and into the aorta and then it will go through your body and replenish your tissues with fresh oxygenated blood but in order for this process to occur smoothly we need the electrical conduction system to send off these electrical signals that target the cells of the atria and the ventricles so they will contract and relax so in order for the electrical conduction system to do this it has to cause repolarization and depolarization of these specialized heart cells so these are two terms that you really want to make sure that you understand whenever you're studying ekg interpretation because they really lay the foundation for understanding this pqrst complex so here i have a heart cell it's resting meaning it's not really doing anything it's just hanging out until it's told to do something so whenever you have a resting heart cell it is negatively charged on the inside and we can refer to this as it's being polarized and this cell the reason that it's like that is because there's a different concentration of ions on the inside compared to the outside and this cell membrane around the cell is really not permeable right now it's impermeable specifically to sodium there's a lot of sodium outside the cell and it would love to get on the inside so whenever this cell receives a jolt a jolt of electricity from this electrical conduction system it really changes that cell membrane and causes it to be more permeable so that sodium is like hey i can get inside that cell now so the sodium goes inside the cell and it changes its state from being negative to less negative so a little bit more positive because sodium is positive and it causes depolarization and whenever the cell becomes depolarized it causes it to contract so the next step after contraction is relaxation so after we have contraction it relaxes we get repolarization it's going back to its negative state so what you want to take away from this is that depolarization leads to contraction so whenever i'm saying atrial depolarization i'm talking about atrial contraction the contraction of the atria whenever i'm talking about repolarization i'm talking about relaxation and to help you remember that to keep those two straight remember that the word relax starts with re repolarization starts with re so whenever i refer to ventricle repolarization i'm talking about the relaxation of the ventricles so now let's look at the specific parts of the electrical conduction system normally everything should start here in the sa node the sa node stands for cyanoatrial node and it's located in the right atrium in the upper part of it and we like to refer to this as the pacemaker of the heart because it causes your heart to bead at a rate of 60 to 100. now the sa node is responsible for making the atria contract so it causes when it fires it causes atrial depolarization so whenever the electrical signals leave here goes through these internal pathways over here we have a pathway so it can actually get over here to this left atrium because it's a little bit over there called bachmann's bundle and then it goes down and hits the av node av node that stands for atrioventricular node and we refer to this node as the gatekeeper and why do we call it that well the av node helps delay or slow down impulses for just a little bit because it's allowing these atria to fully empty themselves and allow the blood to go into the ventricles because we don't want there to be leftover blood in the atria before the ventricles contract and we don't want the atrium ventricles contracting together because we would have problems so signal will leave here it will go down to the bundle of his so now we're ready for ventricle depolarization so what's that going to lead to that's going to lead to contraction of the ventricles so it goes down through a bundle of hiss it's going to go down through the bundle branches you have right bundle branch you have left bundle branch and then it's going to hit the purkinje fibers so whenever this system occurs the electrical conduction system shooting from sa node all the way to the kenji fibers we can pick this up and we can look at it and we can see it as our pqrst complex so if everything's occurring normally like it should everything's coming from our sa node originating there it's firing the way it should we should have on our ekg strip a beautiful normal sinus rhythm with all of its parts measuring perfectly and forming perfectly but if there's an issue with this system we can get dysrhythmias we can get like atrial flutter atrial fibrillation vtac etc so now let's see the heart in action how it actually contracts and relax whenever it is stimulated by this electrical conduction system and creating this pqrst complex by looking at this animation first the sa node fires and this causes atrial depolarization which causes the atria to contract then the signal goes down to the av node and notice the av node does not fire until those atria are empty and the blood is in the ventricle then it's time for ventricular depolarization so the signal travels down through the bundle of his to the bundle branches and then the purkinje fibers causing ventricular contraction followed by the relaxation of the ventricles so now let's look at this pqrst complex in detail and apply it to ekg strip paper now whenever you're analyzing a patient's rhythm and you're trying to interpret what kind of rhythm this is you're going to have a lot of these pqrs pqrst complexes are ekg on ekg strip paper and you want to be familiar with the ekg strip paper because it's made up of small boxes that are contained within large squares and each box represents a measurement of time and whenever you're starting out analyzing these rhythms you want to be familiar with the basics like how to measure certain parts of this complex what each part of this complex should look like is it regular irregular it's rate and so forth so i want you to memorize the following information on this ekg strip each small square that you see represents 0.04 seconds of time and each large square it contains five small squares so it represents 0.20 seconds of time and the reason you want to memorize this is because you will be analyzing these small squares to determine the duration of certain parts of that pqrst complex next you want to memorize the pqrst complex and all the little extras found within it so first let's look at the p wave the p wave represents atrial depolarization so this leads to the contraction of the atria which is created by the sa node so whenever those atria contract it creates this little wave now right after the p wave and before the qrs complex we can find the pr segment and the pr segment demonstrates the delay the av node created remember it was the gatekeeper so it gave the atria time to dump its blood into the ventricles before the ventricles contracted also found in this area is the pr interval and i really want you to remember the pr interval because we measure this and it's very important in determining if your patient has a heart block so the pr interval starts at the beginning of the p wave and extends to the beginning of the qrs complex so it's different than the pr segment the pr segment was after the p wave the pr interval is before the p wave to the beginning of the qrs complex and this demonstrates the amount of time it takes for the electrical signal to go from the atria to the av node and if it's taking too long if we have a long pr interval this could indicate a heart block next is the qrs interval or also known as the qrs complex and this represents ventricular depolarization so this is leading to the contraction of the ventricles also found in this but you can't see it is atrial repolarization where the atria are relaxing but the ventricles are so large that whenever the atria relax it's overshadowed by the ventricles so you're really only seeing ventricle depolarization here then we have the j point and this is the point where the qrs complex meets the st segment and the st segment represents the completion of ventricular depolarization and the beginning of ventricular repolarization and this segment should be flat hence it should be isoelectric meaning flat so there should be no depression of it or elevation and isoelectric is a word that is used to describe straight across lines of the pqrst complex that represents that the heart cells are resting they're not contracting and causing electrical activity so none is being transmitted to the ekg then here we have the t-wave the t wave represents the beginning of ventricular repolarization so relaxation and the ventricles are so big that whenever they relax it creates this t wave and then after the t wave you usually have a flat line which is representing ventricular repolarization is complete it's a flat line isoelectric and then the cycle starts immediately again where you get a new p wave qrs complex t wave and it just keeps going on now sometimes after the t wave you may see a u wave it's not the case in a lot of patients but in some patients and it may be happening because your patient's potassium level is low like in hypokalemia and then lastly here is the qt interval the qt interval starts at the beginning of the qrs complex and ends after the t wave and this demonstrates the time it takes for electrical signals to cause the ventricles to contract and then rest so now let's recap all that information and look at this pqrstc complex and see how depolarization and repolarization is occurring in each part of that complex so here section one is the p wave that represents atrial depolarization beginning so we have the contraction of the atria then two that was our pr segment that was atrial depolarization complete so it's done then three was our qrs complex and it represented ventricular depolarization beginning and in there but you can't really see it is atrial repolarization it's relaxing then four is our st segment and that is ventricular depolarization completing then we have five which represented our t wave and that is ventricular repolarization beginning and then six is that flat isoelectric line and this is ventricular repolarization complete so now that we've identified all the parts of the pqrst complex and where repolarization and depolarization is occurring let's now talk about how each part should measure and what each part should look like because this will help us analyze a rhythm first let's look at the p wave so p wave should always be present in a rhythm if it's normal and there should be one p wave in front of one qrs complex and they should be up like this they should be round they shouldn't be flat and their measurement should be less than 0.12 seconds so no more than three squares so whenever you're looking at the p wave look at those squares that it's taking up and count them because remember each small square represents 0.04 seconds next look at the pr interval the pr interval again starts at the beginning of the p wave and extends to the beginning of the qrs complex and you're looking at its measurement it should be about 0.12 to 0.20 seconds so about three to five boxes any more than that you may be thinking heart block here we have a picture of a first degree heart block and notice that that pr interval is more than 0.20 next look at the qrs complex it should be behind every p wave and it should look like this it shouldn't be very wide or narrow here we have v-tac notice how wide that qrs complex is whenever you measure it it should be no more than 0.12 seconds and you want to start measuring at the q wave to the end of the s wave then there's the st segment this starts at the end of the s wave and stops at the start of the t wave it should be flat shouldn't be elevated or depressed and if it is it should be no more than one millimeter and here is an example of an abnormal st segment here we have st elevation here we have st depression followed by this is the t wave and the t wave should come after the qrs complex and should be round and in the upright position in most leads and lastly the qt interval with this you're looking at the measurement typically it's anywhere between 0.35 to 0.44 seconds and men have shorter intervals than women and it really varies depending on if it's a fast heart rate or a slow heart rate fast heart rates have shortened qt intervals and a prolonged one could increase the risk of ventricular dysrhythmias like torsoda plant now let's apply this information we have learned about this pqrst complex and analyze a rhythm so to do this you want to use an ekg strip that's at least six seconds long and how you know if you have a six second strip is you're going to count those large squares and count 30 squares 30 squares equals 6 seconds and we're going to go through a check off of questions that we're going to answer and based on the answers we get we're going to take that information and apply it to what kind of rhythm we're dealing with so the first thing you want to look at are the p waves and we're thinking of the three r's we're thinking of regularity of those p waves the ray and the resemblance first regularity ask yourself are the p waves occurring at the same regularity as the consecutive p waves on that ekg strip and the p waves represent atrial so with your calipers you can start at the first p wave spread it out to the second p wave and just go from p wave to p wave and make sure that they're all lining up the same distance if you don't have calipers you could use some paper then look at the rate of those p waves count the p waves within that six second strip then multiply by 10 and this is the atrial rate the atrial rate should be around 60 to 100 beats per minute for normal sinus rhythm then the resemblance how do they look do they resemble a p wave how a p wave should look because there should be only one p wave in front of every qrs complex so is that happening are all the p waves identical and how they're round pointing up and are they less than 0.12 seconds less than three squares so look at the p wave and count those squares underneath then apply the three r's to the qrs complex look at the regularity of the qrs complex are the qrs complexes occurring at the same regularity as the consecutive qrs complexes within that strip this represents ventricular you can do this by taking your calipers just how you did with the p waves and going from r wave to r wave both the atrial and ventricular rhythm the regularity should be regular in order for it to be normal sinus rhythm and that shows that it's originating in the sa node then look at the ray of that qrs complex within that six second strip and count those complexes and multiply by 10 this is the ventricular rate and the atrial rate and the ventricular rate should be the same around 60 to 100 beats per minute for normal sinus rhythm and lastly resemblance how do they look do they look like qrs complexes is there one present after each p wave they don't measure any more than .12 seconds so less than three boxes then look at your t wave it should come after the qrs complex be round in the upright position in most leads and then find the extras within the pqrs t complex those intervals and segments so look at the pr interval measure it again it starts at the beginning of the p wave and extends to the beginning of the qrs complex it should be 0.12 2.20 seconds and the measurement should be uniform throughout that strip then look at the st segment it starts at the end of the s wave and stops at the beginning of the t way it should be flat no elevation or depression and then lastly look at the qt interval which starts at the beginning of the qrs complex and ends at the end of the t wave confirm that it measures between 0.35 to 0.44 seconds so now let's analyze this rhythm using those questions that we just went over so i have a six second strip here and the first thing what we want to look at are those p waves so we're going to look at the three r's of the p waves the regularity we're going to start at the first p wave and we're going to take our calipers we're going to put one point of our calipers on that p wave and then we're going to stretch the other part out so it touches the next p wave and then what we're going to do is just go down through the strip and make sure they're all they have the same distance within them so here we go making sure that they line up and so far they have the same distance okay they are regular next we're going to look at the rate so what we're going to do since we have a 6 second strip we are going to count the p waves and then multiply by 10 and that's our atrial rate so 1 2 3 4 5 6 seven eight eight times ten is eighty so we have an atrial rate of eighty now let's look at the resemblance do these resemble p waves and they do they are round they're upright there's only one p wave in front of a qrs complex and their duration let's make sure that they're less than 0.12 seconds so we're just going to take our calipers measure at the beginning of that p wave and at the end of the p wave and it's about two and a half boxes so we get point one zero seconds and then just to confirm that measurement just go throughout all the other p waves and just make sure that they all line up with that measurement now let's look at the qrs complexes the three are so first regularity so just like with the p waves we're going to take one end of our calipers put it on the r wave of the qrs and then put it on the other r wave of the qrs and then just track it down through the strip making sure that they line up together and that they are regular and so far they look regular and they are regular next let's count the rate so count each qrs complex and then multiply by 10 so we have one two three four five six seven eight so eight times ten is eighty so we have a ventricular rate of 80 just like the atrial rate and then lastly the resemblance do these resemble qrs complexes are they where they're supposed to be you're supposed to have one qrs complex after each p wave they do and they look like qrs complexes and let's measure them so what we're going to do is we're going to measure at the beginning of the qrs complex to the end right here with our calipers and when you measure it out and you count the boxes you get two and a half boxes which is about .10 and then just go down through the strip and just measure to just confirm then look at the t waves make sure there's a t wave present after every qrs complex and that it looks like a t wave it's where it's supposed to be it's upright and then lastly we want to look at the extras so let's look at that pr interval and again you measure that by going at the beginning of the p wave to the beginning of the qrs complex and measure out the boxes here we have about three and a half boxes so it's 0.14 seconds and then you just want to go throughout your strip and you just want to measure that and make sure that all your pr intervals line up to be that same measurement then you want to take a look at the qt interval and again that was found at the beginning of the qrs complex to the end of the t wave and you just want to count the boxes from there to there here we have about nine boxes so that gives us 0.36 seconds and just track that down all throughout the strip and just confirm you have that throughout and then lastly we just want to look at the st segment and make sure that the st segment which again is found at the end of the qrs complex to the beginning of the t wave just making sure that this area is flat it's not elevated or depressed more than one millimeter and here that is not so with all those questions that we just answered whenever we look at this rhythm it meets all the criteria for normal sinus rhythm with a rate of 80 beats per minute okay so that wraps up this video and if you'd like to watch more videos in this series you can access the link in the youtube description below