ECG (Electrocardiogram) EKG Lesson

so do you know why you get a basic you see do you know where you get pqrst you know about pqrs - yes yes so in a normal ECG you're going to go to pee just like this that would be kind of a normal ECG cycle woman so the p is that wave there the Q is this bit where it goes down yeah there's a line along there called the isoelectric line so that's kind of the isoelectric line there where everything goes below and comes back - so we've got P the Q is the bit that goes down Q R the bit that goes down here is the S so collectively we've got the QRS complex together then this wave here is the T wave so we've got a p q r s t in that order and what's actually happening is individual myocardial cells when they're at rest are electrically negative on the inside so the negative inside and they're positive outside in this state we say that the cell is polarized it has two poles like a battery a positive and a negative pole so this cell is polarized so a negative inside a positive outside now muscles pretty stupid is not like nerve cells that are clever it has to be told when it's time to contract so when it's time for a muscle to contract electrical signals will change the polarity across the cell membrane of the individual myocardial cells and they'll become positive inside and negative outside so ions charged atoms will alter their distribution across the membrane reversing the polarity inside the cell and outside so in this state the cell was polarized when the polarity changes we say the cell is depolarized so in this state the cell is depolarized it is depolarized and when a muscle cell depolarizes in health it will contract so this will be associated with contraction the depolarization it will contract but if a cell will only contract when it depolarizes this process here would be depolarization if a cell will only contract when it depolarizes and it needs to contract again in point eight of a second for the next cardiac cycle can you see if it's going to contract when it depolarizes and it's already depolarized in order to depolarize again it must first repolarize so first of all has to repolarize that process is called repolarization so the P wave is the electrical activity as detected on the surface of the body that occurs as a result of atrial myocardial depolarization it's the depolarization of the atria in other words is when the atria contract so the P wave is atrial contraction then the QRS complex represents the depolarization of the ventricular myocardium so the QRS complex is the electrical activity as detected on the surface of the body that occurs as a result of ventricular myocardium depolarization that's why we get a QRS in other words in health the qrs means that the ventricles are contracting it's not actually the ventricular contraction we see what we actually see is the electrical stimulus the electrical depolarization which causes the contraction of the ventricles that's what we actually see and then the T wave is everything is the ventricular myocardium repolarizing going back to normal so the T wave is the electrical activity as detected on the surface of the body that occurs as a result of ventricular myocardial repolarization the ventricles going back to normal and the electrical activity that initiates this is generated in an area in the right atrium called the sinoatrial node or the pacemaker of the heart that's where this rhythm comes from now that rhythm is modified by external sympathetic and parasympathetic stimulation from sympathetic nerves and from the parasympathetic nerve that supplies the heart also what is the name of the parasympathetic nerve that supplies the heart big isn't it is it well there's the vagus nerve what number cranial nerve is that okay and why is it called the vagus nerve what does vagus mean when bored yes long hmm it's very long no doesn't mean that as very weak impulse no doesn't mean that if legal at all that doesn't mean them come on I don't want to stress Simon I've told him you're clever students which of course you are you doing very well Vegas is from an old Latin word that means vagrant and a vagrant is like a they wander around yeah so Vegas actually means the wandering nerve yeah so it wanders down from the wanders down to the mouth then it goes down to the heart then it goes down to the stomach then he goes down to the intestine I just kind of wanders around the body that's why it's called the vagus nerve and that's good anyway the vagus nerve the sympathetic in the power center that it can influence heart rate the actual sinoatrial node has an intrinsic contractile rate of about 90 beats per minute actually 19 depolarization is a minute so most of the time is being slowed down so Simon's heart rate there was about 72 that's because his vagus nerve was inhibiting the rate of contraction of his sinoatrial node this lesson we're not going to do about the way the impulses go through the heart but we are going to notice that this rhythm is generated in the sinus node therefore it's called a sinus rhythm that's normal this is why we call it a sinus rhythm so what is a sinus rhythm well it has a P QRS and a T in the right order and it's fairly regular that is what a sinus rhythm is and to have a proper sinus rhythm the rate must be between 60 and 100 beats per minute so physiologically a sinus rhythm is described as a pqrst in the right order fairly regular with a rate between 60 and 100 beats per minute now if you have a pqrst in the right order and it's fairly regular but the rate is less than 60 beats per minute that can still be a physiological rhythm for example if someone's very fit they might always have a slow heart rate or when you asleep your heart rate can go slow that's called a sinus bradycardia it's normal sinus bradycardia is not can be normal but it's considered slow over the rate is below 60 so sinus bradycardia has a pqrst in the right order and it's regular and the less than 60 sinus rhythm as a pqrst in the right order and it's fairly regular in the range of 60 to 100 if you've got a pqrst in the right order and it's regular that the rate is over 100 again that can be physiological if you go running that will happen if you're excited or trade or an emergency situation that will happen and we call that a sinus tachycardia so they're the three normal sinus rhythms yeah okay how can we distinguish which ones is physiological and which one is pathologic okay well let's take let's take an example of that one example of that is the cardiac arrest rhythms which are obviously going to be pathological so it's worth learning three or four cardiac arrest rhythms so that the foot the foot the first cardiac arrest rhythm the most common one what's the most common form of cardiac arrest hmm assisted is a relatively rare form of cardiac arrest you do see it in trauma especially if someone's X and related very low on blood you can see it but you don't know Lisa sometimes you see asystole in coronary care situations but not that common ventricular fibrillation is the most common and this looks like this so there's polar polarization and depolarization but the ventricles are just doing this to put you hands together like this all right this is ventricular fibrillation gone otherwise we'll forget try you'll forget otherwise because you've got to choose the junior students this and that's a fairly coarse ventricular fibrillation and you can see what it's doing car near the whole thing's fibrillating and of course that's associated with no cardiac output but over time this tends to become fine unlike this you get a fine ventricular fibrillation so this is course ventricular fibrillation once I'm doing the action please of course ventricular fibrillation this is fine ventricular fibrillation yeah it's not moving as much yeah and clinically it's important to note because it's very easy if someone's in fibrillation can you see you need to defibrillate get it right make sure the isle ventricular fibrillation they'll also be unconscious and will have no pulse fine ventricular fibrillation is harder to shock them very often you might need to oxygenate them you might need to give CPR you might even need to give some adrenaline to course of the ventricular fibrillation to make it more shockable that's right that's the most common cardiac arrest rhythm then the pollicis for the fine one is poorer than the Nath one correctly but in Indian good coronary care situation that is manageable in a hospital resuscitation situation you would expect to be able to revert that cases there will not be a clear regular QRS complex absolutely not absolutely not ventricular fibrillation is a completely chaotic rhythm there will be no discernible organized rhythm what's happening is multiple areas of the myocardium are depolarizing chaotically and irregularly and you get no coordinated contraction so to get coordinated contraction with the normal QRS the ventricles have to be doing this I do that one that's pumping the blood out know if they're doing that can you see they're not doing that yeah that's why it's a cardiac arrest situation now there's another situation that can be a cardiac arrest situation and yeah that looks like this ventricular tachycardia now sometimes the patient with this is unconscious other times they might not be now this responds superb early to defibrillation you got to make sure the patients unconscious first there's not very nice getting 2,000 volts or 3,000 volts through your chest when you're awake and ventricular tachycardia is going to be well this is sinus rhythm isn't it this is ventricular tachycardia there's no time for the ventricles to fill up so there's no cardiac out very little cardiac the patient why have a blood pressure of 30 or something but it's not good and if this isn't treated pretty soon it will change into this this isn't reason it will change into this always the reason the reason is usually an ectopic electrical focus in the myocardium which is generating impulses so there's a pathological lesion in the ventricular myocardium that's generating electrical impulses more quickly than the impulses are coming from the sinoatrial node so it's taking over it's what we call an ectopic electrical focus ectopic means something is in the wrong place like an ectopic pregnancy is in the fallopian tubes isn't it it's in the wrong place so if there's a pathological electrical focus in the ventricular myocardium that can start generating waves of depolarization the rest of the ventricle will try and copy it will move across the ventricular myocardium which is a physiological corner sense idiom and the whole thing will start contracting pathological so normally the most common in my experience of this and this in deed is areas of our normal electrical activity in the myocardium caused by usually caused by myocardial infarction and myocardial infarction of course is caused by coronary arteriogram BOCES which is usually caused by unstable depolarized not depolarized d destabilized at the moment as plaques and a third row matters plaques is caused by bad diet smoking and all the things that we don't do because we're clean living it's also genetic there so anyone can get it right another cause of cardiac arrest is asystole now a means without systole means cardiac contraction so this is a normal rhythm that's sinus rhythm this is course ventricular fibrillation this is fine ventricular fibrillation this is ventricular tachycardia this is asystole watch really carefully when we bury people the Radian asystole unless of course you've got it wrong that is a death rhythm and ventricular fibrillation we'll eventually this will become finer and finer until it becomes asystole actually so eventually all of us will end up in a system I hope it's a long long time but eventually we're all going to go into asystole and clinically this is hard to room this is hard to revert you need to treat the causes of asystole so in trauma for example if it's caused by exsanguination it's caused by an acute hypovolemia we need to get some fluid into them pretty quick and then try and restart the heart we need to do CPR to oxygenate the myocardium in the brain we often need to give adrenaline because the only chance of getting a patient back from asystole is to get them back into a ventricular fibrillation we have to irritate the myocardium enough to get it back into ventricular fibrillation then we can shock them and it doesn't happen very often usually this is irreversible having said that I think I did get one patient back from asystole once but maybe it wasn't asystole maybe it was just a very fine maybe it was just a very fine ventricular fibrillation so there are examples of cardiac arrest rhythms now a normal ECG as we've seen has got the P Q R s and the T wave that's normal but with a 12-lead ECG there's two very useful things the 12-lead ECG can shows one is it can show us if an area of myocardium is infarcted that would be a st-elevation myocardial infarction STEMI an ST elevation myocardial infarction now that happens as the name implies there is ST elevation and what this means is that we have a pea-sized fit the section between thee and that's the s and the T there that fit is elevated like that so this bit here is the area of elevation and the area of elevation will vary depending on the position in the myocardium that is involved in so we've got a 12-lead ECG from that we can work out where abouts in the myocardium the infarction is whether it's an inferior myocardial infarction and anterior lateral myocardial infarction or whatever it is the ECG just can reveal there's a presence of SDE and I cannot accurately which part of the heart no no it can accurately tell which part of the heart it is I know by the leads that the St elevation occurs in so remember we said that you're looking at the heart from different directions AVR AVL AVF one two three one two one two three four five six so you're looking at the half and lots of different directions now it takes a bit of practice but the reason this works is any electrical activity which is moving towards an electrode goes up and any electrical activity which is moving away from the electrode goes down so if you look at the different leads you can work out which part of the myocardium is affected I'm not going to tell you how to do it just know because this is just a quick lesson but you can do that so we're looking for ST elevation which indicates infarction now the other common thing we see is ischemic changes yeah ischemic changes and with ischemic changes very often we get ST depression and you can actually get this this with none st-elevation myocardial infarctions where you get schema carriers in the heart or if someone's got stable angina and we put them on a treadmill to exercise them if we can actually induce the ischemia in the myocardium then you can see the St elevation at the time so the patient's complaining of chest pains you know I've got chest pain then immediately do a 12-lead ECG if that chest pain was caused by ischemia it will diagnose the ischemia because you'll see the ST depression in the relevant leads of the ucg but the ST elevation will only be there when there is active ischemia the rest of the time you won't see it and what we see is as normal we have a p q r s t what you see with ischemia is the limbs like this goes up this goes down too far like that and this fit here represents the depression so an ECG where there's infarction will look like this that would be a function st-elevation ischemia will look like this as st depression there are the two most basic things to learn when you're interpreting 12 lead ECGs so rhythms it's very good to look for is there pqrst S or R is a cardiac arrest rhythm there's many other ISM rhythms as well of course another common one that we see is atrial fibrillation atrial fibrillation the AP atria fibrillating that the ventricles aren't what we see is we see the atrial fibrillation there and then we just get irregular QRS complexes it's an irregular rhythm and we get an irregular pulse as the atria fibrillate it's not sinus rhythm because there's no P wave because the atria fibrillating they can't generate a pure wave it's not sinus rhythm because it's not regular it's irregular there's no pqrst in the right order and regular there is a QRS there was the QRS the patient would be in cardiac arrest but there's no P and the QRS the PQRS don't follow in a logical order in fact there is no pre-web so what you need to do is practice lots of normal ECG xin each other look at normal rhythms and then when you do abnormal ones you'll see that the abnormal ones are different and with a bit of practicing workout we're in the heart the ischemia or the infarction is occurring I however when doing CPR how you get normal normal way right if you do CPR you won't get a normal wave on the cardiac monitor what you'll actually see on what what let's you see on the you see G is is a bit of a mess you'll get a lot of integral electrical interference on the ECG and you'll also probably be able to see the underlying rhythm that the heart is in but what you will get with CPR is you've got the vertebrae there you've got the sternum on top and you're squashing the heart in between that means the heart contracts and then is able to relax again so if you're doing good CPR you won't get a pqrst rhythm but what you will get is a cardiac output so if you're doing good CPR you will get a carotid pulse and you will get a femoral pulse but it's caused by the compression of the heart between the sternum and the thoracic vertebral column you don't get the normal electrical activity because the patient's actually electrically they're in a cardiac arrest just like the cardiac monitor will just show electrical interference yeah that's all it will show there is that there is another cardiac arrest rhythm where you actually get a rhythm that looks normal because sometimes the electrical activity in the heart can carry on but there will be no Associated cardiac output again this this tends to happen in a severe hemorrhage it does happen in some cardio coronary care situations as well that's called pulseless electrical activity where you get the electrical activity with no pulse so when we were assessing patients what we've got to do is always compare the ECG with the way the patient looks and with the patient's pulse you've always got to take them together the ECG is not a way of assessing patients it's only a little bit of a way of assessing patient it's only part of the whole clinical picture most important thing in assessing a coronary patient is the color of their face how alert they are what kind of pulse got then this is a little bit of help as well but it's not a substitute for your clinical judgment the most important thing you can learn as your clinical judgment machines are only for fun they help a little bit but there are there is no palace for PE there is no know with pulseless electrical activity there is no pulse but there is a pqrst why because you are getting depolarization of the myocardium as normal but because the myocardium is diseased or hypoxic or hypo profused it's just sitting there doing nothing the muscle is unable to respond to the electrical activity and again that's quite dangerous the rest rhythm if someone's impulses electric activity you've got to treat the underlying cause of the pulses lit electrical activity treated basically as in asystole hope you can get them back into ventricular fibrillation and only then can you shock them but again it's often associated with the poor prognosis but because it happens quite a lot in trauma and it's often young people we make exhaustive efforts to try and get them back again so we'll give them blood transfusions we'll give them fluid we'll give them CPR we'll give them adrenalin and we'll try and shock them that's the worst what they used to do in the old days I think it was in the Korean War I think it was in the Korean War when someone's heart stopped you stir after open the chest and put the hand in and squeeze the heart then someone thought oh why do we have to do that why can't we just squash it between the sternum and the vertebrae and that's when CPI was invented yeah phaedra strength lesions of result Wendy's just opened somebody chasm well opening the chest is associated with many complications but but no know that the major vessels of the mediastinum you can grab the heart without without compressing the major vessels in the mediastinum that can be done that can be done but we'll do that as an advanced floor we're going to do that today but it can't it can't be done on gel CPR no more questions is good alight questions gone yeah is the entry all myocardial depolarizations be seen in the ECG programs absolutely absolutely the reason you're getting the ECG is because of the myocardial depolarization a trio a trio depolarize yes the P wave is atrial depolarization is the rate real repolarization yes that's what you meant to ask isn't it it's money other particular less content absolutely yeah the answer is yes you do get one but it occurs just here like that and you don't see it because the phrase is so that's the atrial depolarization that's the atrial repolarization it's a very good question it's a very good question you knew the answer already but the question is a good one why don't you see atrial repolarization and the answer is it's there that's when it occurs so you don't see it because the QRS is going on at the time what we say is that the repolarization wave of the atrial myocardium is buried in the QRS complex so you don't see it the tachycardia off of the ventricles is a series also three a QRS complex be seen in ventricular tachycardia these are QRS complexes that they are but they're described as web and complexes they are wide they're early and they are bizarre they are not physiological QRS complexes and there is no time for effective ventricular filling so they're associated with a significantly reduced cardiac output this patient will either go into immediate cardiogenic shock or they will actually be unconscious actually the unconscious is good because if you shock them the first time you shop this reverts back into sinus rhythm this is the easiest one to treat if they're still awake you have to sedate them and then shock them that's the safest way to do it anyone thankful patient if mi the P wave and QRS compounds will also change no mi if it's a nun st-elevation myocardial infarction this will look normal or show a schema changes if it's an ST elevation myocardial infarction you'll get the ST elevation so that will alter the shape of the QRS complex but you're still going to get more if you don't get one that means the heart's not contracting that means you have no cardiac output that means you have no blood pressure and that by definition if you got zero blood pressure by definition that will become a cardiac arrest situation usually we have one atopic focus or just they go okay yeah you can get you can get ectopic beats in a normal ECG and that can be a physiological ectopic focus which gives off an ectopic beat sometimes we call them ventricular back topics and in older people they become more common and in coronary care situations we describe those as being normal it will only become abnormal if you had a few together and the patient might become acutely hypotensive but to get a few ectopic beats from time to time especially in older people we consider that normal many many people do it so the if you get 160 65 year olds you put them all on an ECG quite a lot of them are going to have some ventricular rec topics but most of the time the patient won't be aware of it so we'll count them as normal it only becomes abnormal if it's caused by some cardiac pathology we're more concerned if there's a lot of younger people that could be a feature of some some cardiac disease so is it true that Mir sociated my primary my first-degree and second-degree Harbach well heart blocks can occur whenever there is disruption to the internal electrical conducting system of the heart so as you know normally you've got the sinoatrial node the internodal tracts you've got the atrial ventricular node the atrioventricular bundle which used to be called the bundle of his-- the right and left bundle branches and the Purkinje fibers now an ischemic heart disease it's quite possible that the blood supply to an area of myocardium which contains part of the conducting fibers could be in ischemic or infarcted that means that the electrical conducting system is going to be blocked at a particular point and that's what gives rise to heart block now if you go and work in coronary care you actually learn that there's three grades of heart block there's grade one type one type two and type three the first one grade one heart block is just a prolonged interval between the p-wave and the start of the QRS complex but then you get two types of second-degree heart block and one type of third-degree heart block but they're all caused by physiological disruption to the internal electrical conducting system of the heart which is blocking the normal flow of impulses from the sinoatrial node all the way down to the Purkinje fibers that actually innovates the ventricular myocardium and then it is usually irreversible sometimes they get better you'd like to get full recovery if you can thrombus do quick percutaneous coronary artery or revascularisation so it depends how quick you are in your coronary care situation you can get the physiology back again sometimes in the days after you can get a degree of recovery if the conducting pathway is not actually infarcted other times if the severe heart block we have to go in and do cardiac pacing and in cardiac pacing we normally pass an electrical wire into the area of the cardiac apex down the bottom and electrically pace it artificially but that that would be a last resort so the key thing with ischemic heart disease is to give thrombolysis or PCI as quickly as you can and prevent the areas of myocardium which contain the conducting tissues from infarct in the first place you've got to be quick just do whatever is quickest if you can do PCI quick do it it was going to take off an hour to set up PCI thumb belies them if you can do it in two minutes doesn't always happen doesn't always happen give some aspirin yeah if you do it in three minutes is better that will improve the prognosis it's how quick you can do it good half past eleven already one more question yep okay sauce s the elevator mi the graph is elevated the ST segment is elevated so that would be ST elevation mi yes is it because the myocardial is unable to it's a very good question what you're asking is why does an infarction generate an area of St elevation that's what you're asking right the answer is quite complicated the answer is that if an area of myocardium is infarcted there's not going to be any electrical activity in that area so what you're actually seeing when you look through that direction is the opposite wall of the heart so the heart's got two walls like that normally the ECG would be seeing that wall but now you have a dead bit in that wall there's a dead bit so there's no electrical activity there so what you're actually seeing is the other wall it's the activity in the other wall what we say is an infarction is an electrical window you're actually looking straight through it to the other wall so the reason you actually get the St elevation is not actually it doesn't actually come from the infarcted area it comes from the fact that the infarcted area is an electrical window and you see straight through that to other functioning areas of the myocardium there's a very good question thank you very good question it was the last one though yeah okay right Simon's going to talk to you now again that you get those video

Channel: Dr. John Campbell

Views: 179,243

Rating: 4.936564 out of 5

Keywords: ECG, heart, electrocardiogram, cardiac, medical education, EKG

Id: LVzgwQwBIW4

Length: 38min 7sec (2287 seconds)

Published: Tue Jul 16 2013