[Music] hello everyone I'm Olivia from geeky Medics today I'm going to take you through how to interpret an ECG if you haven't already make sure you check out our video about how to record an ECG and subscribe to this channel so you can be notified about new videos in this video we're going to work through a structured approach to ECG inter interpretation at the end of the video we'll work through a case view to test your ECG interpretation skills let's start by discussing the basic principles of an ECG an ECG is used to record the electrical activity of the heart from different angles to identify and locate pathology ECGs are recorded by placing electrodes on the patient these are conductive pads that record the electrical activity of the heart these electrodes create a graphical representation of the heart electrical activity which we refer to as the ECG leads it's worth noting that a 12 lead ECG produces 12 separate graphs on a piece of ECG paper however only 10 physical electrodes are actually attached to the patient to generate the 12 leads here we can see the different components of an ECG cycle p waves represent atrial depolarization or contraction in healthy individuals there should be a p-wave preceding each QRS complex the PR interval begins at the start of the p wve and ends at the beginning of the qwave it represents the time for electrical activity to move between the Atria and the ventricles the QRS complex represents the depolarization or contraction of the ventricles it appears as three closely related waves on the ECG the Q R and S Wave the ST segment is an isoelectric line representing the time between depolarizing ation and repolarization of the ventricles the t-wave represents ventricular repolarization it appears as a small upwards deflection after the QRS complex the QT interval begins at the start of the QRS complex and finishes at the end of the t-wave it represents the time taken for the ventricles to depolarize and then repolarize before beginning ECG interpretation you should always check the following details firstly confirm the name and date of birth of the patient and check this matches the details on the ECG check the date and time that the ECG was performed check the calibration of the ECG you should also understand the clinical context and why the ECG is being performed for example does the patient have any symptoms such as chest pain or breathlessness knowing the clinical context and the indication for performing the ECG will help you in your overall interpretation the first step to our structured approach to ECG interpretation is to calculate the patient's heart rate as a reminder a normal heart rate is between 60 to 100 beats per minute Tachi cardia or a fast heart rate refers to a heart rate that is greater than 100 beats per minute Brady cardia or a slow heart rate refers to a heart rate that is less than 60 beats per minute there are two methods for calculating the heart rate and the choice of these depends on whether the patient has a regular or irregular heart rhythm let's look at the first method using the RR interval this method is suitable for regular rhythms to use this method count the number of large squares within one RR interval next divide 300 by this number to calculate the heart rate in this example there are seven large squares therefore the calculation is 300 / 7 which equals 48 this second method is useful when the heart rhythm is irregular in this situation we can't use the RR interval method as the RR interval will vary to use this method you need to make sure you're dealing with a standard ECG strip which is typically 10 seconds long or 50 large squares count the number of QRS complexes on the Rhythm strip after you've done this multiply the number of QRS complexes by six giving you the number of QRS complexes with within 1 minute in this example we can see we have 11 QRS complexes therefore when we times this by six we get a heart rate of 66 beats per minute as we've mentioned some patients can have regular or irregular heart rhythms irregular rhythms can be either regularly irregular I.E a recurrent pattern of irregularity or irregularly irregular are you completely disorganized an example of this is atrial fib iation to assess whether a rhythm is regular Mark out several consecutive RR intervals on a piece of paper then move them along the Rhythm strip to check if the subsequent intervals are similar here are two examples of irregular heart rhythms let's look first at the top ECG you can see the irregularly irregular rhythm is very disorganized with variable RR intervals this strip shows atrial fibrillation the regularly irregular rhythm is different and there is a recurrent pattern of irregularity these rhythms can be seen with atrio ventricular blocks which we will discuss later in the video Let's look now at the cardiac axis the cardiac axis represents the overall direction of electrical activity as it spreads through the cardiac conduction system in healthy individuals you would expect the cardiac axis to lie between -30° and + 90° before we continue There are some important Concepts to understand firstly whenever the net direction of electrical activity is towards a particular ECG lead you should see a positive deflection in that lead of the ECG whenever the net direction of electrical activity is away from a particular ECG lead you should see a negative deflection in that lead on the ECG so let's apply these Concepts to a normal cardiac axis which is seen in the diagram on this slide in the context of a normal cardiac axis the axis normally lies between -30° and + 90° which you'll see represented by the yellow arrow on the diagram as a result you'll see a positive deflection in lead one and lead two with the most positive deflection being in lead two as it is most closely aligned to the overall direction of electrical spread these are the leads you should pay the closest attention to as if these are both positive the cardiac axis is normal lead three may be slightly positive ISO electric or rarely ever so slightly negative you would expect to see the most negative deflection in AVR due to AVR looking at the heart in the opposite direction so now we understand the normal cardiac axis let's move on and look at when this is abnormal right Axis deviation involves the direction of depolarization being distorted to the right meaning ends up between + 90° and plus 180° on the cardiac axis the most common cause of right Axis deviation is right ventricular hypertrophy extra right ventricular tissue results in a stronger electrical signal being generated by the right side of the heart this causes the deflection in lead one to become negative and the deflection in leads avf and Lead three to be more positive right Axis deviation is commonly associated with conditions which result in the development of right ventricular hypertrophy such as pulmonary hypertension right AIS deviation can however be a normal finding in very tall individuals left axis deviation involves the direction of depolarization being distorted to the left meaning the electrical signal travels between -3° and -90° Lead 1 becomes positive whilst in lead three there is a negative deflection do know however that this is only considered significant if the deflection of lead 2 also becomes negative left axis deviation is usually caused by left ventricular hypertrophy or conduction abnormalities the next step in our ECG interpretation process is to look at the p waves which represent atrial depolarization we need to ask the following questions firstly are p waves present if so is each p-wave followed by a QRS complex next do the p waves look normal check the duration Direction and shape of the p-wave finally if p waves are absent is there any atrial activity as a reminder a Sawtooth Baseline represents flutter waves a chaotic Basel line represents fibrillation waves and finally a flatline represents no atrial activity at all let's now discuss the PR interval in more detail the PR interval should be between 120 and 200 milliseconds that is 3 to five small squares a prolonged PR interval suggests the presence of atrio ventricular delay or an AV block let's look at some examples of Av blocks first deegree AV blocks involves the consistent prolongation of the PR interval defined as being greater than 200 milliseconds this is due to delayed conduction via the atrio ventricular node if we look at the ECG we can see that every p-wave is followed by a QRS complex and there are no dropped complexes this is unlike some other forms of Av block which we'll discuss later first first deegree AV block is common and can often be an incidental finding with patients usually being asymptomatic second degree AV block type 1 is also known as mobitz type 1 AV block or wanky back phenomenon typical ECG findings in mobit type 1 AV block include Progressive prolongation of the PR interval until eventually the Hol impulse is not conducted and the QRS complex is dropped AV noal conduction resumes within the next beat and the sequence of progressive PR interval prolongation and the eventual dropping of a QRS complex repeats itself second deegree AV block type one is usually benign and rarely causes hemodynamic compromise usually no intervention is required if the patient is asymptomatic second deegree AV block type 2 is also known as mobitz type 2 AV block typical ECG findings in mobitz type 2 a block include a consistent PR interval duration with intermittently dropped QRS complexes due to a failure of conduction the intermittent dropping of the QRS complexes typically follows a repeating cycle after every third p-wave in a 3:1 block or after every fourth p-wave in a 4:1 block mid's type 2 AV block is always pathological with the block typically occurring at either the bundle of hiss which occurs in 20% of cases or the bundle branches in 80% of cases patients are at risk of progressing to complete AV block the underlying cause of the AV block therefore should always be investigated third degree or complete AV block occurs when there is no electrical communication between the Atria and ventricles in other words the Atria and the ventricles are functioning independently if the PR interval is shortened this can mean one of two things simply the p-wave originates from somewhere closer to the AV node so the conduction takes less time remember the Sino atrial node is not in a fixed place and some other people's Atria are smaller than others the other reason is that the atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall this accessory pathway can be associated with a Delta wave which we will discuss next this ECG shows a wolf Parkinson White pattern which is typically associated with wolf Parkinson White syndrome in Wolf Parkinson in white an accessory pathway leads to stimulation of the ventricles this accessory pathway enables electrical conduction to bypass the AV node and stimulate the proximal ventricles prematurely we call this preexcitation this in addition to normal electrical conduction through the AV node leads to double excitation of the ventricles on this ECG we can see a shortened PR interval a Delta wave and a widen QRS complex a Delta wave wave is a slurred upstroke of the QRS patients with wolf Parkinson White syndrome are at a risk of developing Tachi arhythmia which are abnormal heart rhythms with a ventricular rate of 100 or more beats per minute let's move on and look at QRS complexes in more detail the QRS complex represents the depolarization of the ventricles when assessing a QRS complex you need to pay attention to the following characteristics firstly look at the width a normal QRS complex should be less than 0.12 seconds or three small squares look at the height to see if there are small complexes or tall complexes small complexes are defined as being less than 5 mm in the limb leads or less than 10 mm in the chest leads tall complexes imply ventricular hypertrophy although this can be due to body habitus such as in tall slim people look at the morphology see if you can see a Delta wave broad QRS complexes occur if there is an abnormal depolarization sequence for example a ventricular ectopic where the impulse spreads slowly Across The myocardium from the focus in The ventricle similarly a bundle branch block results in a broad QRS complex because the impulse gets to one ventricle rapidly down the intrinsic conduction system and then spreads slowly Across The myocardium to the other ventricle let's look at the ECG features of bundle branch block in more detail in both form the Hallmark feature is Broad QRS complexes the William marrow pneumonic can be used to quickly recognize left and right bundle branch blocks by looking at lead V1 and V6 the middle letters of the names help you remember which bundle branch block each name is referring to note the two L's in William in the left bundle branch block and the two RS in Marrow in the right bundle branch block here we can see the characteristic features of right bundle branch block with an rsr Prime pattern in V1 seen as an m shape and a broad swave in V6 seen as a w shape in contrast in left bundle branch block there is a deep swave in V1 which may be notched and seen as a w and a broad m-shaped r-wave in V6 the ST segment is the part of the ECG between the end of the swave and the start of the t-wave in a healthy individual it should be an isoelectric line that is neither elevated nor depressed abnormalities of the ST segment indicate esea or infarction of The myocardium seen in acute coronary syndromes High takeoff or benign early repolarization is a normal variant that causes a lot of angst and confusion as it looks like St elevation here we can see an example of St elevation St elevation is significant when it is greater than 1 mm or one small square in two or more contiguous limb leads or greater than 2 mm in two or more chest leads it is most commonly caused by acute full thickness myocardial infarction also known as a stemi STD depression that is 0.5 mm or greater in two or more contiguous leads indicates myocardial esea this may be seen in an N stemi it's important to understand which leads represent which anatomical territory of the heart as this allows you to localize pathology to a particular heart region for example if there is St elevation in leads V3 and V4 it suggests an anterior myocardial infarction you can then combine this with your anatomical knowledge of the heart's blood supply to determine which artery is likely to be affected t-waves represent the repolarization of the ventricles tall t- waves can be associated with hyperemia or a hyperacute stemi t-wave inversion can represent present normal physiological variation or underlying pathology isolated t-wave inversion in leads AVR and V1 is normal other normal variants include isolated t-wave inversion in leads 3 V2 and V3 new t-wave inversion as compared to a patient's prior ECGs should always be treated as pathological pathological t-wave inversion is often a non-specific sign in the context of acute illness however it can be a more specific sign of conditions such as myocardial lemia or myocarditis U waves are not a common finding the uwave is a greater than 0.5 mm deflection which is seen after the t-wave and best visualized in lead V2 or V3 these become larger the slower the Brady cardia classically U waves are seen in various electrolyte imbalances hypothermia and secondary to anti rythmic therapy such as dexin or amiodarone so this concludes our structured approach to interpreting an ECG once you've interpreted an ECG it's important to document your interpretation in the notes you should include the patient details the time and date the ECG was performed your interpretation of the ECG and your overall impression and plan let's have a look at a case study to put our ECG interpretation skills to the test take a moment now to pause the video and we'll go through the answers afterwards of course remember first of all you'd always be checking the patient details the clinical context as to why you're performing the ECG and making sure that the ECG is calibrated if we look at the rate there are 17 QRS complexes therefore when we times this by six it gives a rate of 102 beats per minute if we look at the Rhythm it is clearly IR regular and there aren't any clear patterns between the RR intervals therefore it's IR regularly irregular if we look at the cardiac axis we can see that lead one and lead two are positive this means it is a normal cardiac axis if we look at calculating the PR interval you'll soon realize that there aren't actually any p waves on this ECG therefore we can't calculate this the QRS is of a normal width and height and there is no abnormal morphology therefore this is normal there is no evidence of St elevation on this ECG the t- waves are also normal with no evidence of tall tented t- waves when we put all of this together the characteristic irregularly irregular rhythm in combination with the lack of p waves indicates a diagnosis of atrial fibrillation congratulations you've come to the end of our guide to ECG interpretation learning to interpret an ECG can be challenging but but following a structured approach can help you to identify pathology for further ECG guidance head over to the geeki Medics website or practice your interpretation skills using our OSI station bank if you liked this video you'll love our textbook the geeki Medics clinical examination guide summarizes all the key examination skills for your practical exams by now at geeky medics.com [Music]