ECG Interpretation Made Easy (Learn How to Interpret an ECG in 13 Minutes)

foreign [Music] of an electrocardiogram known as an ECG or EKG is a skill in medicine that is often overlooked in this video I'll provide a systematic approach to help you read them more confidently the basics to remember are that each component of the ECG represents electrical activity within the heart corresponding to different points in the cardiac cycle for example the P wave represents atrial depolarization and we will look at each of these points in more detail as part of the interpretation a normal 12 lead ECG is taken by using four limb electrodes and six chest electrodes each lead gives a slightly different view of the heart with a positive deflection when the activity is towards that electrode and negative when it is away from it leads 1 AVL V5 and V6 look at the lateral part of the heart 2 3 and avf the inferior part and V1 to V4 give a septal and anterior View the first step is to ensure the correct patient information the date and the calibration of the machine the date and time are especially important because you may be looking at one of a series of ECGs looking for changes over time the calibration is normally 25 millimeters per second and 10 millimeters per millivolt if these settings are adjusted before the ECG is taken it can look completely different so you need to check it before you start interpreting once they are confirmed I start by looking at the axis because it is so easy to overlook the overall direction of the electrical activity gives the axis and is normally between -30 and 90 degrees it could be normal deviated to the left or to the right or extremely deviated a quick way to assess it is the quadrant method that allows you to quickly place the axis in one of the four quad just by looking at Lead 1 and avf if both the positive the axis must be in the lower right quadrant therefore normal if Lead 1 is negative and avf is positive there is right access deviation if both the negative there is Extreme axis deviation the only one needing a further step is if Lead 1 is positive and avf is negative then the axis is in the upper right quadrant and to distinguish left axis deviation from normal you can look at lead two if it is negative the axis is deviated to the left axis deviation can occur in many different conditions and is not specific but looking at it first can alert you early that there could be further abnormalities next we look at the rate each small square is one millimeter in width on the standard speed of 25 millimeters per second the small squares on the paper represent 40 milliseconds and five of these together form bigger squares therefore with 200 milliseconds each that means five of these big squares make up one second so if one beat happens every five big squares that's one beat in one second so 60 beats in a minute a shortcut is to divide 300 by the number of large squares between each QRS to get the approximate ventricular rate this is easy if the rhythm is regular if it's not then instead count the number of QRS complexes over 10 seconds then multiply it by 6 forget the number of beats in one minute the normal rate is 60 to 100 beats per minute with rates below that being called bradycardia and above that being tachycardia that brings us nicely to Rhythm which basically means do the Beats fall at regular intervals to evaluate this look at the gap between the QRS complexes known as the RR interval is it the same size each time or does it change this is more obvious at normal heart rates but can be tricky to distinguish at very low or very high heart rates if the gap between beats changes throughout the ECG then the rhythm is irregular but the story doesn't end there the irregularity can be present with no clear pattern known as irregularly irregular like atrial fibrillation or regularly irregular such as in some second-degree heart blocks looking at the QRS complexes evaluates the ventricular Rhythm but it's also important to evaluate the atrial rate and the communication between the Atria and the ventricles which is why I also include the P wave and PR interval when looking at the Rhythm the P wave represents atrial depolarization the normal P wave should be positive in lead 2 have a duration of less than 120 milliseconds an amplitude of less than 2.5 millimeters and each P wave should be followed by a QRS complex some abnormalities can include an increased duration or amplitude of the P wave that may indicate left or right atrial dilatation respectively or the absence of p waves entirely such as in atrial fibrillation the electrical activity then normally passes through the Atria ventricular node just before being conducted down into the ventricles and causing ventricular depolarization and contraction the PR interval is the time between atrial depolarization and ventricular depolarization and is measured from the start of the P wave to the start of the QRS complex its normal duration is between 120 and 200 milliseconds a prolongation indicates slowing of the conduction between the Atria and ventricles for example a first degree AV block a shortening may suggest a condition with an accessory pathway like wolf Parkinson White a variable PR interval suggests other forms of atrioventricular blocks I'll leave a link to a video dedicated to Heart blocks here next up is the morphology of the remaining components of the ECG there is the QRS complex itself which represents ventricular depolarization and is generally divided into narrow or widened normally the electrical activity moves quickly through the conduction system and goes more slowly through the muscle tissue narrow complexes generally suggest the origin of that beat is supraventricular while a wider QRS suggests either the activity is originating in the ventricles or there is a block in the conduction system carrying the electrical signal to one of the ventricles and so to get to the other side must go through The myocardium the latter is why left and right bundle branch blocks have a wide QRS morphology and pacemakers will also traditionally have a morphology similar to left bundle branch block here is a comparison of left and right bundle branch blocks and an easy way to remember the morphology of each is the mnemonic William marrow the voltage of the QRS complexes can also indicate pathology classically large amplitudes in the precordial leads May point to left ventricular hypertrophy while alternating amplitudes could indicate pericardial effusion Q waves are the first negative deflection in the QRS the r wave is a following upwards deflection and S is any negative deflection following that pathological Q waves are defined as Q waves greater than 25 percent of the QRS complex with a width greater than 40 milliseconds they can indicate previous ischemia there should be progression from V1 to V6 where the S Wave is initially greater than the r wave but then at around V3 or V4 the r wave becomes greater than the S Wave poor progression can also indicate previous ischemia the ST segment is next representing the interval between ventricular depolarization and repolarization it extends from the end of the S Wave to the start of the T wave this is a famous part of the ECG as elevation of this segment May indicate an st elevation myocardial infarction as well as other conditions like pericarditis in cases of St elevation it's important to look for reciprocal changes in opposite leads for example St elevation in anterior or lateral leads may have reciprocal St depressions in the inferior leads depressions of this portion generally is an abnormal finding that can also indicate ischemia it's worth noting that it's difficult to interpret the ST segment in people with bundle branch blocks therefore more specific criteria are needed another feature to be aware of is the jpoint which is where the S wave ends and the ST segment begins as it can be raised causing the appearance of St elevation this is also known as benign early repolarization and tends to happen in people under the age of 60. it's also likely to be present in multiple leads not corresponding to a specific territory and will not have reciprocal changes and will not change over time as you would expect with acute ischemia T waves indicate repolarization of the ventricles and can be described as tall flat inverted or even biphasic in most cases they will be positive and concordant with the QRS complex but in cases where they are negative they are known as t-wave inversions this is normal in V1 AVR and Lead 3 and can also persist from childhood in some people in V2 and V3 inverted T waves in the absence of St changes can indicate a historic ischemic event the classic example of tall T waves is hyperkalemia and biphasic T waves meaning T waves that have both a positive and negative components are usually due to ischemia or hypokalemia the interval between the start of the Q wave and the end of the T wave is the QT interval and it represents the time taken from the start of ventricular depolarization to the end of repolarization it gets shorter with faster heart rates and longer with slower heart rates so it needs to be corrected for the heart rate for interpretation classically this is using bezet's formula its normal value is generally above 360 milliseconds and less than 440 milliseconds in males or less than 460 milliseconds in females it's important to remember this as prolongation can predispose to potentially lethal arrhythmias like ventricular tachycardia or torsads U waves are other waves that occasionally appear after the T waves most commonly as a result of electrolyte imbalances or hypothermia using all of this information you can categorize the ECG tachycardia is generally divided into broad or narrow complex and then further into regular or irregular bradycardia can be divided based on the presence or absence of p waves then further into if every P wave is followed by a QRS complex or not this is not an exhaustive list but covers some general arrhythmias overall the ACG is a snapshot of the activity of the heart at the time it was captured therefore it needs to be correlated with the history of how the patient presented and why the ECG was indicated in the first place you also need to consider changes over time for example in myocardial ischemia another good example is syncope or palpitations due to an arrhythmia unless the patient's heart was in an arrhythmia at the time of the ECG it won't necessarily be seen therefore longer monitoring with a halter monitor may be used for further reading and practice I would recommend using the Life in the Fast Lane website which is the main reference for this video as they have a comprehensive resource to improve your ECG reading skills

Channel: Rhesus Medicine

Views: 228,236

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Id: u1m3HKW1VqU

Length: 13min 7sec (787 seconds)

Published: Tue Apr 11 2023