In this lesson I am going to teach you how you can uncover some things if you just dig a little.
In this lesson, we are going to cover the second step of the 6-step method to ECG interpretation. Axis Determination.
Axis determination is a critical skill that may assist you in discovering an underlined pathology.
Einthoven ’s arms and his left leg are immersed in buckets of salt water. At the time, this was the only way to obtain a signal for the electrocardiograph. Even after the invention of the electrode, they continued to be placed on the subject ’s arms and legs. From this configuration, leads I, II, and III were born, and they are called the li mb leads to this day.
I know what you 池 e thinking. This equation is scary. I f I just lost you. Take a deep breath! Everything is going to be okay.What is lead I? It is a dipole, with the negative electrode at the right arm (white electrode) and the positive electrode at the left arm (black electrode).What is lead III? It is a dipole with the negative electrode at the left arm (black electrode) and the positive electrode at the left leg (red electrode). Sometimes I wonder why Einthoven didn ’t call this lead II.
As you can see, when you plug in the measurements, you end up with an electrical value of zero.You can try this trick on virtually any ECG.Because this is true, leads I, II, and III can be represented as an electrically equilateral triangle.
This diagram shows the sequence of ventricular depolarization. As you can see, the first area to depolarize (1) is the interventricular septum, which depolarizes in a left-to-right direction (responsible for the so-called septal Q waves in the lateral leads of a normal 12 lead ECG).
Next, the area around the left and right ventricular apex (2) depolarizes from a endocardial-to-epicardial direction (inside-out). You ’lll notice that there are more arrows near the (2) on the left side of the heart. This is because the left ventricle is more massive than the right ventricle. It has to be more massive because it ’s responsible for circulating blood to the entire body and back. In contrast, the right ventricle is thinner, and attaches to the left ventricle like a pocket, because it only has to circulate blood to the lungs and back. In fact, while the septal wall is shared between the left and right ventricles, if you look at a cross-section of the heart, it ’s really owned and operated by the left ventricle, which has the general appearance of a muscular tube.
Finally, the lateral walls of the left and right ventricle depolarize (3) and last the high lateral wall of the left ventricle (4). This is just to give you a general idea. Obviously we can ’t look at the anterior and posterior walls from a cross section of the frontal plane.
Now notice the large block arrow superimposed over the top of the diagram. This is the heart ’s mean electrical vector. That means if you averaged the millions of electrical vectors created as the ventricles depolarize in any given cardiac cycle, the average direction would be right-to-left, superior-to-inferior (for the normal heart). In the first place, that ’s how the heart is oriented in the chest, but it ’s also because the left side of the heart is more massive. More heart cells depolarizing means a a stronger signal that cancels out the signal coming from the right side of the heart, so the normal QRS axis runs from a right shoulder to left leg direction (very similar to lead II).
When the heart ’s mean electrical vector moves toward a positive electrode, you get an upright complex on the ECG in that lead.When the heart ’s mean electrical vector moves away from a positive electrode, you get a negative complex on the ECG in that lead.When the heart ’s mean electrical vector moves perpendicular to a positive electrode, you get a so-called equiphasic complex. It starts out positive (A) as the mean electrical vector approaches, but ends up negative (B) as the vector passes on by.
Now let go back to Einthoven (electrically) Equilateral Triangle. Imagine that the red arrow is the heart’s mean electrical vector. To help explain what happens next, I ’m going to quote 12 Lead ECG � Art of Interpretation , by Tomas Garcia, MD and Neil Holtz, BS, NREMT-P. In my opinion, this is one of the best 12 lead ECG books you can buy (and no they don pay me to say that). In physics, two vectors (or in this case leads) are equal as long as they are parallel and of the same intensity and polarity. Therefore, we can move the leads [...] to a point passing through the center of the heart, and they will be the same. �
Since this is a critical point that is difficult to understand, I ’m going to take this a step further. I interpret this to mean that lead I sees the mean electrical vector like the diagram to the left. In other words, it sees the heart ’s mean electrical vector relative to its own vector created by its negative and positive electrodes.Likewise, leads II and III see the mean electrical vector relative to their own vectors.
Because this is true, we can take the three vectors (or sides) of Einthoven ’s Triangle and make them intersect in the center. This is the first step in creating our hexaxial reference system.
When leads I, II, and III are drawn this way (as they often are) the arrows and Roman numerals are placed in the position of the positive electrodes.
we examined how Einthoven was able to refer to leads I, II, and III as Einthoven ’s Equilateral Triangle even though anatomically speaking, leads I, II, and III form a scalene triangle on the human body.For the exact same reasons, we can draw a mathematical representation of leads aVR, aVL, and aVF that looks symmetrical like the shape on the right.We have just completed the final 3 spokes of the hexaxial reference system!
When leads I, II, and III are drawn this way (as they often are) the arrows and Roman numerals are placed in the position of the positive electrodes.
Print out the hexaxial reference diagram found in the course content.
Before we break down the finished diagram, let ’s look at the hexaxial reference system laying on top of the patient ’s anterior chest, with the arrows and leads in the position of the positive electrodes.The first thing I would like you to notice is that lead I cuts the body in half horizontally and lead aVF cuts the body in half vertically.The second thing I would like you to notice is that even though leads II, III, and aVF share the same positive electrode, they represent three separate vectors. This diagram should clearly demonstrate why we call them the in ferior leads. It should also demonstrate why we call leads I and aVL the hi gh lateral leads.You will notice that leads III and aVL are on opposite sides of the hexaxial reference system. That ’s why they are two of the most reciprocal leads on the 12 lead ECG. More on that later. Right now I 知 just planting the seed.You will notice that lead II cuts across the body in a Ri ght shoulder-to-left leg direction (white electrode to red electrode) which is the same direction as the heart ’s normal axis. That ’s probably why we were first taught to monitor lead II. It tends to show nice, upright P waves, QRS complexes, and T waves.
For now, we 池 e only worried about the first 6 leads of the 12 lead ECG, because they are the leads that make up the frontal plane and the hexaxial reference system.
For now, we 池 e only worried about the first 6 leads of the 12 lead ECG, because they are the leads that make up the frontal plane and the hexaxial reference system.
Remember. When the heart ’s mean electrical vector (or QRS axis) moves toward a positive electrode, you get an upright complex in that lead. When it moves away from a positive electrode, you get a negative complex in that lead. When it moves perpendicular to a positive electrode, you get an equiphasic (and/or isoelectric) complex in that lead.
We can deduce that this patient ’s QRS axis (in the frontal plane) is moving perpendicular to the positive electrode in lead I. Now, look at your diagram of the hexaxial reference system and find lead I (-180 degrees to 0 degrees). We theorize that this patient ’s QRS axis is moving perpendicular to lead I. So, which lead is perpendicular to lead I? aVF!
Find lead aVF(-90 degrees to +90 degrees). The QRS axis is moving along the same vector as lead aVF. But is it moving toward -90 or toward +90? Go back to the sample ECG. Is the QRS complex positive or negative in lead aVF? It ’s positive! You ’ll also notice that lead aVF shows one of the tallest QRS complex in the frontal plane. Interesting! Now look at the hexaxial reference system again. You ’ll see little downward arrow in front of lead aVF at -90 degrees and a little upward arrow in front of lead aVF at +90 degrees. The positive electrode for lead aVF is at +90.
We ’re only off by 1 degree, in a 360 degree circle! That ’s pretty darned good. Does it always work out that perfect? No. But you can almost always get it within 10 or 15 degrees.
As a review, lead I cuts the hexaxial reference system in half horizontally and lead aVF cuts the hexaxial reference system on half vertically. You can think of this as an x and y axis that divides the hexaxial reference system into quadrants. Hence, you can use leads I and aVF to place the heart ’s electrical axis into one of the four quadrants. This is sometimes called the Quadrant Method for axis determination
Remember that the normal QRS axis goes from a right shoulder-to-left leg direction in most patients. In other words, it tends to point down and to the left, or toward the left inferior quadrant of the hexaxial reference system, which ranges from 0 to +90 degrees . When the QRS axis in the frontal plane is in the normal quadrant, you will have positive QRS complexes in lead I and positive QRS complexes in lead aVF .
When the QRS axis is 0 to -90 degrees , we call it a left axis deviation . This is the left superior quadrant of the hexaxial reference system. When the QRS axis is in the left superior quadrant, you will have positive QRS complexes in lead I and negative QRS complexes in lead aVF .
In reality, the QRS axis can be slightly into the left superior quadrant and still be considered normal. When the axis is between 0 and -30 degrees, it is sometimes referred to as a physiological (as opposed to pathological) left axis deviation. With a physiological left axis deviation , lead II is usually equiphasic (remember that lead II is perpendicular to lead aVL and lead aVL points to -30 degrees on the hexaxial reference system). For a good example of this, see the ECG from Part V. Is this ECG normal? Absolutely not! But the axis is technically normal, even though it extends into the left superior quadrant at -26 degrees.The most common causes of pathological left axis deviation are left anterior fascicular block or Q waves from inferior wall myocardial infarction. Some sources say that left ventricular hypertrophy pulls the axis to the left, and while this seems logical, in most cases patients with left ventricular hypertrophy have a normal QRS axis. Electrolyte derangements and ventricular rhythms may also present with a left axis deviation. Paced rhythms in particular should have a left axis deviation if the pacing lead is in the apex of the right ventricle.
If the QRS axis in the frontal plane is +90 to 180 degrees , it is a right axis deviation . This is the right inferior quadrant of the hexaxial reference system. With a right axis deviation, you will have negative QRS complexes in lead I and positive QRS complexes in lead aVF .A right axis deviation is usually abnormal. It might indicate pulmonary disease, right ventricular hypertrophy, Q waves from lateral wall myocardial infarction, left posterior fascicular block, electrolyte derangement, or tricyclic antidepressant overdose, or a ventricular rhythm.
If the QRS axis is -90 to 180 degrees , something is very wrong (possibly your lead placement). This is the right superior quadrant of the hexaxial reference system, but in various publications it can be called an extreme right axis deviation , an indeterminate axis, or a right shoulder axis. It ’s bad because it means the heart is depolarizing in the wrong direction. With an extreme right axis deviation, you will have negative QRS complexes in lead I and negative QRS complexes in lead aVF
Now that you have learned the hard way to determine the frontal QRS axis within 15 degrees, I will show you a much faster method to determine if the axis is normal, to the left, to the right, or in “no man’s land”.
Remember the quadrants on the hexaxial reference system? Any QRS axis that falls between 0 and 90 degrees is normal, anything from 90 to 180 is deviated to the right, anything from 0 to negative 90 is deviated to the left, and all axis ranging from negative 90 to 180 are in no man’s land, and it is considered extreme right axis deviation.
Well we happen to have two leads that separate these quadrants perfectly. Lead I cuts through the middle horizontally with it’s positive end at the 0 degree side, and its negative end at the 180 degree side. aVF cuts right through the middle vertically with its positive end on the bottom and its negative end up top.
Any positive QRS will have an axis to the right of the aVF line, and any negative QRS in Lead 1 will have an axis left of the aVF line.
Even with all the artifact, we can see that the QRS complexes are positive in lead one.
Since the QRS was positive in lead one, and lead one’s positive end is on the right side of the circle, we know that the frontal QRS axis is in one quadrants on the right. We need to isolate the axis in one quadrant though, so to do that, we will look at aVF.
Since aVF has its positive end on the bottom and its negative end up top, a positive QRS in lead aVF will have a QRS axis in one of the bottom two circles while a negative QRS in aVF would have an axis in one of the top two quadrants.
There is less artifact in aVF, and it is easy to see that the QRS complexes are very positive.
Since the QRS was positive in lead aVF, we know that the frontal QRS axis is in one of the bottom two quadrants. Lets add the information we obtained from lead one to see what quadrant the frontal QRS axis is in.
Looks like our axis is in the southeast quadrant. This is the normal quadrant, so we have a normal QRS axis in the frontal plane.
We found our axis in the normal quadrant.
It is easy to remember the quadrant method, and apply it regularly. Here is a cheat table that should be easy to commit to memory.
Note that there are more arrows within the walls of the left ventricle. This means that the mean impulse tranvels down and then around the heart on the left side.
Lets take a rough look at how the chest leads view the heart. The V-leads are unipolar, so their direction of view comes exactly from the electrode placement. THIS IS WHY PROPER PLACEMENT IS IMPERITIVE!
To demonstrate how the normal precordial axis works, I am going to use a demonstration I learned by reading a book written in 1983, Practical Electrocardiography, 7th edition, by Henry Marriott. His example used a single dipole cell, I’ve replaced that with the truck you see here. Since we know that when the mean impulse is traveling away from the positive electrode of a lead, the QRS is negative and when it is approaching a positive lead, the QRS is positive, lets consider the impulse to have a positively charged front end and a negative li
Now let’s picture a residential rode with six houses
The six houses are our six leads, and the street is the pathway of the cardiac electrical signal
Since V1 is proximal to the beginning of the ventricular conduction pathway, which is our street in the picture, the signal, our truck starts out by almost completely bypassing the V1 house and driving away from it.
The truck started out already past the V1 house, so the QRS is all negative in lead V1. Since the truck only approached the V2 house shortly, there is only a blip of a positive deflection on the QRS.
As the truck passes the V2 house, we see how we get our negative deflection in V2. The truck has a longer was to go to get to V3, so the positive, front-end of the truck is heading towards V3 for a longer duration, which causes V3 to have more of a positive deflection than V2. The lead or area between two leads, where the QRS changes from mostly negative to mostly positive is called the transitional zone. This usually occurs between V3 and V4 because they are in the middle of a normal ventricular conduction pathway.
We can see from the picture that the longer the truck moves away from a house, the more negative a complex will be. For instance, the truck has plenty of road after the V1 house, so V1’s QRS is very negative. The road before the V4 house is longer than V3, so V4 will have a slightly more positive complex.
We can see from the picture that the longer the truck moves away from a house, the more negative a complex will be. For instance, the truck has plenty of road after the V1 house, so V1’s QRS is very negative. The road before the V4 house is longer than V3, so V4 will have a slightly more positive complex and a smaller negative complex because the road after the V4 house is shorter.
Since the V6 house is at the end of the road, we don’t really have any negativity in our QRS complex for V6. All of this is subject to change depending on lead placement, and anything that can alter the ventricular conduction pathway. We have just reviewed where the houses, or leads should be placed in relation to a normal ventricular conduction pathway.
Lets imagine what a partial blockage in the conduction pathway would do. The blockage is represented by a yield sign. Can you imagine the changes that would appear on the ECG?
Lets imagine what a complete redirection of the electrical signal would mean. A whole new conduction pathway would result in significant changes on an ECG. These are common pathologies, and this particular one would result in the signal having to head back towards V1 at the same time it is heading towards V6. This means that V1 could have a much more positive complex than normal. This is similar to what happens in a Right Bundle Branch Block. Lets not get too far off track though… we will come back to that in a later lesson.
Lets review what we know as far as the precordial axis is concerned.
It has some positivity, but is mostly negative.
This is more obvious, V6 is very positive, with only a small S wave.
We can see that V3 is only slightly more negative than it is positive, and V4 is tough to distinguish, but appears equiphasic. We can say that the transition occurs between V3 and V4.
Since V1 is mostly negative, V6 is mostly positive, and the transition zone is between V3 & V4, the precordial axis is normal.
Picture the chest leads in the form of a clock with the V leads in their respected numerical position.
Since with normal physiology, the transition zone is in the area of V3 or V4, lets put an arrow in that direction.
If the transition zone comes early, it is called counterclockwise rotation. This means that the R-wave will be bigger earlier. In fact, there may be no transition at all. Every QRS complex could have much bigger R waves than S waves with early transition.
If there is a late transition, we call this clockwise rotation. This means that most of the precordial leads will have predominately negative QRS complexes. The QRS may never become more positive than it is negative. This means that the R waves will never become taller than the S waves of the QRS complexes amongst the chest leads. This is called poor R-wave progression and could indicate a significant pathology.
Lets take a look at this 12-lead from ECGpedia.org. Is V1 mostly negative and V6 mostly positive? Where is the transition? Also, be mindful that the bottom lead is just Lead 2. This is called Long Lead 2, and this is a common 12-lead ECG format.
Since we don’t have a single precordial lead that has a larger S wave than R wave, this is an example of an Early R-wave transition. The cause in this case appears to be WPW or wolff parkinsons white syndrome. Note the shortened PR interval and delta wave.
With WPW, normal conduction bypasses the AV node, which means it doesn’t pause before beginning to conduct the ventricles. This condition may lead to severe tachycardias. More on it later on.
Lets have a look at this 12-lead. Is V1 mostly negative? Is V6 Mostly positive? Where is the transition zone?
Since V4 is mostly negative, and V5 is almost equiphasic, it looks like the transition zone is somewhere between V4 and V5. In this case, the cause appears to be an acute anterior myocardial infarction. Don’t get ahead of yourself though, we will come back to recognizing heart attacks on 12-leads by the end of the course.
Lets review everything we have learned up to this point. Rate, rhythm, frontal axis, and precordial axis.
First we see if the rhythm is regular. aVL has some nice QRS complexes to use.
The rhythm looks pretty regular, now on to heart rate.
We find a QRS that falls on a bold line. The one by the red arrow looks good. Then we count how many boxes there are between it and the next QRS complex.
Looks like there are three big boxes between the complexes.
We now divide that number from 300. 300 divided by 3 is 100. Since the R to R interval is slightly more than 3 boxes in length, the heart rate for this ECG is a little under 100 bpm.
Now it is time to interpret the rhythm. Do you see P waves?
We’ve got P waves, is the PR-interval normal?
The PR-interval is consistent and shorter than one big box which means we don’t have an AV block.
With a regular rhythm under 100 bpm, present P-waves with a normal PR-interval, we can conclude that we are looking at normal sinus rhythm.
Look at the limb leads. What is the most equiphasic lead?
It is a toss up between lead II and aVF, but if you look closely at aVF, you will note that the ST-segment is elevated, and it causes the R-wave to look slightly smaller than it is. I believe aVF to be the most equiphasic.
Since we know that aVF is equiphasic, and we know that means it is perpendicular to the mean frontal electrical axis, we have to find the lead perpendicular to aVF.
Since we know that aVF is equiphasic, and we know that means it is perpendicular to the mean frontal electrical axis, we have to find the lead perpendicular to aVF.
Lets see if Lead I is positive or negative. It appears to be mostly positive, so lets return to the hexaxial reference system and get our approximate frontal axis.
Since we know that aVF is equiphasic, and we know that means it is perpendicular to the mean frontal electrical axis, we have to find the lead perpendicular to aVF.
Since we know that aVF is equiphasic, and we know that means it is perpendicular to the mean frontal electrical axis, we have to find the lead perpendicular to aVF.
We can now note that the frontal axis is normal, and move on to the precordial axis.
We can now note that the frontal axis is normal, and move on to the precordial axis. Lets take a look. Is V1 mostly negative? No!. V1 has an R-wave that is biggar than its S-wave. V6 appears to be mostly positive, and there is no transition.
You will learn this later on, but this particular finding on this ECG would spark a big suspicion of a posterior wall infarction.
We have a regularly-regular rhythm with an obvious P-wave and persistent PR-interval. Our rate is between 60 and 100, so we can conclude that this is indeed Normal Sinus Rhythm. The QRS duration is greater than 120ms, but this does not change the fact that this is NSR. We will learn what has caused this widening later. Now lets determine the frontal axis.
Instead of searching for the exact axis, lets use the quadrant method on this one. To do this we look at lead I, & aVF.
Remember the quadrants on the hexaxial reference system? Any QRS axis that falls between 0 and 90 degrees is normal, anything from 90 to 180 is deviated to the right, anything from 0 to negative 90 is deviated to the left, and all axis ranging from negative 90 to 180 are in no man’s land, and it is considered extreme right axis deviation.
We find that lead I is predominately positive & aVF is mostly negative. Lets look at our chart to see what that means.
Since lead 1 is positive and aVF is negative, we know that the axis is deviated to the left, but sometimes the axis may be deviated to the left without any underlined pathology. Is this pathological left axis deviation?
The Cheat Sheet tells us that if we have a mostly negative complex in lead 2, we are dealing with pathological left axis deviation.
Lead 2 is obviously negative, this means we are looking at pathological left axis deviation, which means that a LAFB is very likely.
Now lets look for our Z-axis. Is the precordial axis normal, or rotated?
If the transition zone comes early, it is called counterclockwise rotation. This means that the R-wave will be bigger earlier. In fact, there may be no transition at all. Every QRS complex could have much bigger R waves than S waves with early transition.
We could call this counterclockwise rotation. However, this is atypical because of the poor R-wave progression in the rest of the chest leads.
Axis determination is a critical skill that may assist you in discovering an underlined pathology.
This concludes lesson 2. You are now a pro at rate, rhythm, and axis determination. Next we will move on to the next two steps of the 6-step process to 12-lead interpretation, Intervals & Morphology!
Transcript
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12-LeadElectrocardiography a comprehensive course sson2 Le Adam Thompson, EMT-P, A.S.
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Lesson Two• Frontal Axis determination tutorial• Precordial Axis rotation• Pathologies that cause axis deviation
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Objectives• Learn how to determine the frontal axis.• Distinguish between the different causes of axis deviation.• Learn how to identify rotation of the precordial axis.
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Axis Determination• Critical Skill!• Use the hexaxial reference system for the frontal plane.• Identify clockwise or counterclockwise rotation of R-wave progression.
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Pathologies Frontal Plane Axis Precordial Axis ERAD Right Axis Pathological Early Transition Late Transition Deviation Left Axis Counterclockwise Clockwise -90° to 180° Deviation Rotation Rotation 90° to 180° -30° to -90°• Ventricular • May be normal • Pregnancy • Posterior wall • SometimesRhythm • LPFB • LAFB infarction Normal,• Paced Rhythm • RVH especially in • Pulmonary • WPW• Dextrocardia • RBBB women disease • Pulmonary • Anterior MI• Electrolyte • RVH diseasederangement • LVH • RBBB • LBBB • LAFB • WPW • Hyperkalemia • LBBB • Dextrocardia • Q-waves, MI • Lung Disease •Venrticular Rhythm
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Willem Einthoven Won the Nobel Prize in Physiology orMedicine in 1924 for inventing the stringgalvanometer which was the first EKG.
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Einthoven’s Triangle• Electrically, leads I, II, & III form an equilateral triangle.• Einthoven’s Law I + (-II) + III = 0
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Einthoven’s Law• How it works• Lead I – The R wave is about 7 1/2 mm tall. – The S wave is about 2 1/2 mm deep. – Subtract the S wave from the R wave • you come up with 5 mm.
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Einthoven’s Law• Lead I = 5mm• Lead II – It’s essentially a monophasic QS complex. – About -10 mm.
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Einthoven’s Law• Lead I = 5mm• Lead II = -10mm• Lead III – R wave that is about 1 mm high. – The S wave is about 16 mm deep. – Subtract the S wave from the R wave. – -15 mm.
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Einthoven’s Law• Lead I = 5mm• Lead II = -10mm• Lead III = -15mm
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Einthoven’s Law• Lead I = 5mm• Lead II = -10mm• Lead III = -15mm – Plug the numbers in. • I + (-II) + III = 0 • 5 + 10 -15 = 0
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Electrical Axis What is the heart’s electrical axis? Mean vector Cardiac vector 4 1 3 3 2 2The first area to depolarize (1) is the interventricular septum
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Electrical Axis What is the heart’s electrical axis? Mean vector Cardiac vector 4 1 3 3 2 2Next, the area around the left and right ventricular apex (2) depolarizes from a endocardial-to-epicardial direction (inside-out).
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Electrical Axis What is the heart’s electrical axis? Mean vector Cardiac vector 4 1 3 3 2 2Finally, the lateral walls of the left and right ventricledepolarize (3) and last the high lateral wall of the left ventricle (4).
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Electrical Axis What is the heart’s electrical axis? Mean vector Cardiac vector 4 1 3 3 2 2The big arrow is the heart’s mean (average) electricalvector. If you averaged the millions of cardiac vectors, you would get the “mean vector”.
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Mean Electrical Vector + + A B A + BMean vector moves towards positive electrode = positive QRSMean vector moves away from positive electrode = negative QRSMean vector is perpendicular to positive electrode = equiphasic QRS
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Mean Electrical VectorRed arrow is heart’smean electrical vector
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Mean Electrical VectorLead I views the heart’sVector similar to theimage on the left.Leads II & III do the samefrom their angles.
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Hexaxial Reference System QuickTime™ and a mpeg4 decompressor are needed to see this picture.
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Hexaxial Reference System• Lead I cuts through body horizontally• aVF cuts through body vertically• II, III, aVF are inferior• III & aVL are reciprocal
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Axis Determination• Is that too much work?• You’re first time is always the hardest.• The more you do this, the easier it is to do.• Eventually, you won’t need any diagrams.
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Axis DeterminationWhich lead isperpendicular toaVF?
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Axis DeterminationWhich lead isperpendicular toaVF?
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Axis DeterminationIs Lead I positive or negative?
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Axis DeterminationSince Lead I isPositive, theaxis is about 0°
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Axis Deviation• So what is a normal axis?• Why does it matter if an axis is deviated?
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Normal Axis • The normal quadrant for the QRS axis is the Southeast quadrant. • From 0° to 90°
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Left Axis Deviation • From -90° to 90° • This is considered the Northeast quadrant.
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Left Axis Deviation • From 0° to -30° • This is considered physiological left axis deviation • Pathological axis deviation is from -30° to -90° • Most common cause is left anterior fascicular block
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Right Axis Deviation • From 90° to -180° • Negative QRS in Lead I • Positive QRS in aVF – Possible Left Posterior Fascicular Block – Q-Waves from lateral MI – Right Ventricular Hypertrophy – Pulmonary Disease.
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Extreme Right Axis Deviation • Called ERAD • From -90° to -180° • QRS in I, II, & III are negative • Probably ventricular – Idioventricular – Paced rhythm
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Cheat Sheet Normal Physiologic Pathologic Right Axis Extreme Indeterminate Axis Left Left Right Axis Axis 0° to 90° 0° to -30° -30° to -90° 90° to 180° -90° to 180° ?Lead ILead IILead III
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Cheat Sheet Normal Physiologic Pathologic Right Axis Extreme Indeterminate Axis Left Left Right Axis Axis 0° to 90° 0° to -30° -30° to -90° 90° to 180° -90° to 180° ?Lead ILead IILead III
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Pathologies Frontal Plane Axis Precordial Axis ERAD Right Axis Pathological Early Transition Late Transition Deviation Left Axis Counterclockwise Clockwise -90° to 180° Deviation Rotation Rotation 90° to 180° -30° to -90°• Ventricular • May be normal • Pregnancy • Posterior wall • SometimesRhythm • LPFB • LAFB infarction Normal,• Paced Rhythm • Pulmonary • WPW • RVH especially in• Dextrocardia • RBBB women disease • Pulmonary • Anterior MI• Electrolyte • RVH diseasederangement • LVH • RBBB • LBBB • LAFB • WPW • Hyperkalemia • LBBB • Dextrocardia • Q-waves, MI • Lung Disease •Venrticular Rhythm
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Fascicles• Right Bundle Branch – 1 Fascicle• Left Bundle Branch – 2 Fascicles • Left Anterior • Left Posterior
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Fascicular Blocks Left PosteriorFascicular Block Left Anterior Fascicular Block
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Fascicular Block• Bifascicular Block – Right Bundle Branch Block (RBBB) with either: • Left Anterior Fascicular Block (LAFB) • Left Posterior Fascicular Block (LPFB) – Only one fascicle remaining• Trifascicular Block – RBBB with LAFB/LPFB and 1st degree AV Block – May degrade into lethal arrhythmia rapidly
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HR ≈ 75 Normal Sinus PracticeDetermine Rate & Rhythm
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HR ≈ 75 Normal Sinus PracticeDetermine Frontal Axis
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Quadrant Method -90° ERAD LAD180° 0° RAD Normal 90°
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HR ≈ 75 Normal Sinus PracticeDetermine Frontal Axis
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Quadrant Method Lead I aVFNormal Positive (+) Positive (+) RAD Negative (-) Positive (+) LAD Positive (+) Negative (-)ERAD Negative (-) Negative (-)
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Cheat Sheet Normal Physiologic Pathologic Right Axis Extreme Indeterminate Axis Left Left Right Axis Axis 0° to 90° 0° to -30° -30° to -90° 90° to 180° -90° to 180° ?Lead ILead IILead III
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HR ≈ 75 Normal Sinus PracticeDetermine Frontal Axis
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HR ≈ 75 Normal Sinus Pathological Left Axis PracticeDetermine Precordial Axis
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