Axis determination

Axis Determination Thompson 2

Resources

http://www.blaufuss.org/ECGviewer/indexFrame2.html ems12lead.com


Pathologies

Many different conditions cause axis deviation. Being able to determine whether axis deviation exists, and to what

extent can assist in the interpretation of the 12-lead ECG. This is a commonly overlooked skill that can aid in

assessment and proper treatment. The next few pages are from EMS12lead.com


Why should you learn how to determine the electrical axis?

By Tom Bouthilet

The most common causes of left axis deviation are left anterior fascicular block and Q-waves from inferior MI. So when

I see a left axis deviation it prompts me to consider these conditions. Many times I have caught subtle inferior STEMIs

because the axis was slightly to the left and it prompted me to look at lead aVL for subtle reciprocal changes.


A paced rhythm with a pacing lead in the apex of the right ventricle typically shows LBBB morphology in lead V1 and left

axis deviation. So this prompts me to double-check for a pacemaker pocket on the patient’s chest and consider that the

rhythm may be paced before I decide the patient is showing frequent PVCs or a run of slow VT.


Conversely, it would be very unusual for LBBB or paced rhythm to show LBBB moprhology in lead V1 with a right axis

deviation. That in turn further supports the dx of VT in a patient who happens to have a pacemaker. That helped me

identify a run of VT at a rate of 140 when others called it a “runaway pacemaker.”


A pulmonary disease pattern may pull the axis to the right. It may also cause right atrial enlargement. In addition many

congenital heart defects cause right ventricular hypertrophy with an associated right ventricular strain pattern. So when

you see right axis deviation, tall R-waves in lead V1, and T-wave inversion in the right precordial leads, you know it’s

consistent with the patient’s history and not “anterior ischemia” requiring NTG.


Q-waves from high lateral MI pulls the axis to the right. Left posterior fascicular block is rare as an isolated finding, but

that also pulls the axis to the right. Combine left anterior fascicular block (left axis deviation) or left posterior fascicular

block (right axis deviation) with RBBB morphology in lead V1 and it’s referred to as a “bifascicular pattern”


An extreme right axis deviation (or right superior axis depending on what terminology you prefer) might suggest

incorrect lead placement, electrolyte derangement, or help you rule-in a ventricular rhythm. Never assume that a wide

complex tachycardia is SVT with aberrancy based solely on QRS morphology! Just because it looks like LBBB doesn’t

mean it isn’t VT.


Part 1

The Frontal Plane Axis


Einthoven’s Triangle

Willem Einthoven won the Nobel Prize in

Physiology or Medicine in 1924 for inventing

the string galvanometer; which was the first

EKG. Because Einthoven was German, this is

why electrocardiogram is abbreviated EKG

for “electrokardiogram”—the Dutch spelling.

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 limb

leads to this day.



Electrically, leads I, II, & III form an equilateral triangle.

Einthoven’s Law: I + (-II) + III = 0

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).

Confused? It gets easier!



How it works:

- First take a look at 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, and you come up with

5 mm. 7.5 – 2.5 = 5

- Lead II is essentially monophasic (only goes in one direction—down). So subtract

the depth of the S-wave from zero. 0 – 10 = -10

- Lead III has an R-wave of about 1mm and an S-wave about 16mm. Subtract the

S-wave from the R-wave. 1 – 16 = -15

Lead I = 5mm

Lead II = -10mm

Lead III = -15mm

Plug the numbers in. I + (-II) + III = 0 5 + 10 -15 = 0



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.


Electrical Axis

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).

- The first area to depolarize (1) is the interventricular septum.

- Next, the area around the left and right ventricular apex (2) depolarizes from a

endocardial-to-epicardial direction (inside-out).

- Finally, the lateral walls of the left and right ventricle depolarize (3) and last

the high lateral wall of the left ventricle (4).

Now notice the large 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.


Mean Electrical Vector

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.

+

+

+ A B A

B


Mean Electrical Vector

Now let go back to Einthoven (electrically) Equilateral Triangle. Imagine that the red arrow is the heart’s mean electrical vector.

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.


Hexaxial Reference System

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.


Hexaxial Reference System

We examined how Einthoven was able to refer to leads I, II, and III as Einthoven’s Equilateral

Triangle. For the exact same reasons, we can draw a mathematical representation of leads

aVR, aVL, and aVF that looks symmetrical like the shape above.


The arrows and lead names are placed on the side of the positive electrode. We will be using the Hexaxial Reference System to

determine the mean electrical axis of the 12-lead ECGs.

After learning the Hexaxial Reference System way of determining the mean electrical axis in the frontal plane, we will review an

easier method of obtaining a quick estimate of the hearts electrical axis.

Imagine that the intersection of all those lines is directly in the center of the heart. This explains which area of the heart the leads are

looking at.


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 inferior leads. It should also demonstrate why we call leads

I and aVL the high 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. You will notice that

lead II cuts across the body in a right 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.


Hexaxial Method

The Hexaxial Method will determine the mean QRS axis in the frontal plane.

The conclusion will be within 15 degrees of the exact axis.

5 Easy Steps

Step 1: Determine the equiphasic lead.

Step 2: Find that lead on the diagram.

Step 3: Find the perpendicular lead.

Step 4: Determine if it is positive or negative.

Step 5: Find your Axis.


Using the Hexaxial Reference System:

ECG - 1

For now, we will concentrate only on the first six leads of the 12-lead ECG. These leads make up the frontal plane. We will be using

the Hexaxial Reference System to determine our mean electrical axis in the frontal plane.


Step 1: Find the most equiphasic lead

ECG - 1

The first step in determining the heart’s mean electrical axis in the frontal plane is to find the most equiphasic lead –this basically

means find the lead with QRS complexes that are equally positive & negative.

aVL in ECG – 1 has very small QRS complexes. The smaller a QRS complex is, the more equiphasic it is. The R-wave seems to be

equally as tall as the S-wave is deep.

Step 1


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.

Since we know that, we can say that on ECG – 1, our mean electrical axis is perpendicular to aVL.

+

+

+ A B A

B


Step 2: Find the equiphasic lead on the Hexaxial Reference System.

Step 3: Find the lead perpendicular to the equiphasic lead.

We stated that ECG – 1 shows aVL as the most equiphasic lead. Lead II appears to be perpendicular to aVL. Since we know that aVL

is perpendicular to our QRS axis (mean electrical axis), and lead II is perpendicular to aVL, we can conclude that lead II is inline with

the QRS axis of ECG -1. If you look at lead II on the Hexaxial Reference System, you will see a different number on either end, +60

& -120. The QRS axis is either 60 or -120.

Step 2 Step 3


Step 4: Determine if your inline lead is positive or negative.

ECG - 1

Lead II is obviously positive.

*Notice how lead II has the largest QRS complexes out of the first six leads? This is evidence that we are correct in concluding that

lead II is the most inline lead with the QRS axis

**In case you were wondering, this ECG is a Lateral Wall STEMI, with ST-Elevation in V5, V6, I, & aVL.

Step 4


Step 5: Match your findings to your diagram

Since lead II is positive, the side with the up arrow next to the

Roman numeral is the side with our axis.

The diagram shows + 60º on the positive side of lead II. This

means that our QRS axis is around 60º (give or take 15º).

The normal QRS axis is from 0º to 90º

Think about what that means. It means that if you average all the directions of travel that the electricity in the heart takes during

ventricular depolarization, you would see that the impulse is mostly traveling towards the positive electrode of lead II; which is

normal. This doesn’t mean that the patient isn’t having a cardiac issue, just that their QRS axis is normal.

Step 5


Normal Axis

SouthEast Quadrant

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.


Left Axis Deviation

NorthEast Quadrant

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.

From 0° to -30° is considered physiological left axis deviation.

Pathological left axis deviation is from -30° to -90°.

Most common cause is left anterior fascicular block (LAFB).


Right Axis Deviation

SouthWest Quadrant

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.


Extreme Right Axis Deviation

NorthWest Quadrant

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.

- Called ERAD

- From -90° to -180° QRS in I & aVF are negative

- Check your lead placement!

- Probably ventricular: Idioventricular or Paced rhythm


Cheat Sheet

The cheat sheet above is featured in many ECG publications. It is a useful tool if you want to memorize the different QRS

morphologies. This method does not require the use of the hexaxial diagram.


Lets do another:

ECG – 2



Step 3: Find lead perpendicular to the equiphasic lead.




Answer:

ECG – 2

- The most equiphasic lead is aVR (Don’t let the st-elevation confuse you)

- The lead perpendicular to aVR is lead III

- Lead III is mostly negative

- The hexaxial diagram shows negative lead III at -60 degrees.

-60 degrees indicates Left Axis Deviation (LAD)


The Quadrant Method

Okay, most people aren’t going to memorize the hexaxial diagram, and I doubt they will be carrying the Hexaxial Reference System

around with them. Using the diagram is the best way to find the best estimate of the mean electrical axis. However, there is an easier

way to determine whether axis deviation exists or not.

The quadrant method uses the basics we know about the hexaxial diagram, and allows us to determine axis deviation based on

information provided by just two leads—Lead I and aVF.

- Remember, lead I cuts across the body horizontally, and aVF does the same

thing vertically.

- The positive electrode for lead I is on the left shoulder, at 0 degrees and the

negative electrode is at 180 degrees.

- The positive electrode for aVF is at 90 degrees and the negative is at -90.


The Quadrant Method

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.


The Quadrant Method

Since Lead I has its positive pole on the right side and negative on the left 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.

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.

aVF +


The Quadrant Method

ECG – 3


The Quadrant Method

See what we did?

- Look at Lead I on ECG – 3.

- Lead I is mostly positive. Since we know that means the axis is on the right side of our diagram, we shade the left side.

- Now look at aVF on ECG – 3

- aVF is also positive. Since we know that means the axis is on the bottom, we shade the top.

This leaves us with only one quadrant, the SouthEast corner, which we know is the normal quadrant.

So we don’t have an exact axis, but we know that it is between 0 & 90 degrees, which is normal.


The Quadrant Method

Cheat Sheet


Axis Determination

ECG – 4

To make things easier, the monitor is usually very good at determining the QRS axis on a clean tracing. This one says 50 degrees.


ECG – 4

Lets see how close the two methods are that we learned.

Hexaxial Method:

Step 1: Determine the equiphasic lead…..aVL is most equiphasic


Step 3: Find lead perpendicular to the equiphasic lead…..Lead II

Step 4: Determine if it is positive or negative……Lead II is positive

Step 5: Find your Axis…….60 degrees—pretty close out of 180 possibilities!


ECG – 4

The Quadrant Method tells us that the QRS axis is normal, & a QRS axis of 50 degrees is normal. Both methods work!


Practice

ECG – 5

Use the quadrant method to determine if axis deviation exists. Remember, there are four potential conditions:

Normal – The axis is between 0 to 90 degrees

Left Axis Deviation (LAD) – The axis is between 0 to -90 degrees

Right Axis Deviation (RAD) – The axis is between 90 to 180 degrees

Extreme Right Axis Deviation – The axis is between -90 to 180 degrees


Practice

ECG – 5

ECG – 5 is an example of Left Axis Deviation (LAD).

- Since Lead I is mostly positive, we shade out the

negative (left) side of the diagram.

- Since aVF is mostly negative, we shade the positive

(top) side of the diagram.

- The NorthEast corner is remaining, indicating LAD.


Part 2

The Precordial Axis


The Precordial Axis

Sometimes refered to as “the Z axis”. The remaining six leads of the 12-Lead ECG make up the precordial leads. These leads have an

axis of their own, most often identified by “R-wave progression”. Since determining the exact precordial axis is of little importance,

we will only concentrate on whether it’s normal or abnormal. This is much easier than determining the QRS axis in the frontal plane.


Pathologies

On the right side of the chart above are some common causes of shifts in the precordial axis.

Note that an Anterior MI may cause a late transition, or “poor R-wave progression”. This is important, because minimal ST-

elevation in V2 to V4 without reciprocal changes, with tall R-waves and a short QTc-interval is almost always early repolarization—a

common STE-Mimic. Conversely, the same findings with poor R-wave progression and a longer QTc are very indicative of an

Anterior MI.


Precordial Axis

ECG – 6

To determine if there is an abnormality of the precordial QRS axis, you only have to observe the precordial leads (also called the

“chest leads” or “V leads”). The QRS complexes represent ventricular depolarization (firing of the ventricles to stimulate

contraction). A positive deflection, like an R-wave or an R-prime (secondary R-wave, often seen with Right Bundle Branch Block),

occurs when the impulse is traveling towards the lead being observed. A negative deflection, like a Q-wave or S-wave, occurs when

the impulse is traveling away from the electrode of the lead being observed.


Precordial Axis

This diagram on the right shows a rough representation of where the precordial

electrodes are in relation to the heart. The image on the rights shows us the

sequence of NORMAL ventricular depolarization.


Precordial Axis

ECG – 6

Take a look at lead V1 on ECG – 6

Since V1 has a very small R-wave (which is normal) as its first deflection, it is safe to say that at the beginning of ventricular

depolarization, the impulse is traveling towards the V1 electrode only momentarily. The QRS complex in V1 then transitions into a

deep S-wave, indicating that the impulse travels away from the V1 electrode. This makes since if you consider the image from the

previous page. The intraventricular septum is depolarized first (in the direction of V1), then the impulse travels away from V1.


Precordial Axis

The R-wave usually begins small, or nonexistent in V1 then becomes larger in V2, V3 and so on until V6, where the QRS complex

should be almost completely positive. The transition from a mostly negative QRS complex to mostly positive QRS complex should

occur in either V3 or V4. If the QRS complex stays mostly negative past V4, this is referred to as poor or late R-wave progression,

and is indicative of a clockwise rotation of the precordial QRS axis. Conversely, if the R-wave is prominent in V1, and the QRS

complex is more positive than negative, this is called “early R-wave progression”, or counterclockwise rotation of the precordial axis.

Normal Transition Zone Early R-Wave Progression Late R-Wave Progression


ECG – 7

Take a look at ECG – 7

Notice where the QRS complex becomes more positive than negative in the precordial leads? V4 is mostly negative, and then V5

seems to be more positive. This is an example of late R-wave progression, or “clockwise rotation” of the precordial axis. ECG – 7 is

an example of a Left Bundle Branch Block (LBBB), which is a very common cause of late R-wave progression.

* Did you notice that left axis deviation (LAD) is also present on this 12-lead? LBBB may also cause LAD!


ECG – 8

Now examine ECG – 8

This is an example of early R-wave progression, or a “counterclockwise rotation” of the precordial axis—notice the tall R-waves in

V1? QRS complexes in V1 or V2 that are mostly positive are never normal! ECG – 8 happens to be a Right Bundle Branch Block

(RBBB), which is a common cause of early R-wave progression. Notice that the QRS complex doesn’t appear very wide at first

glance—it was the precordial axis that helped determine that this was a RBBB.

* Another strong indicator of RBBB is terminal S-waves in leads I and V6.

** Note: The frontal plane axis is “indeterminate”, because every complex is equiphasic (equally positive & negative).


ECG – 9

Here you can see how an anterior MI can alter the precordial axis. By far the most common change is late R-wave progression. This

clockwise shift in the precordial axis should always be looked for when tying to determine if a 12-lead ECG represents an anterior

infarct or benign early repolarization (BER). BER will not cause this clockwise rotation of the precordial axis, but an anterior

infarction will almost always cause a deviation.

ECG – 9 also gives us an example of right axis deviation (RAD). There are many common causes of RAD, but a left posterior

fascicular block (LPFB) is the most common. An LPFB can actually result from an infarction.


ECG – 10

This is an example of why an anterior infarction would not have poor R-wave progression. The RBBB present on this 12-lead ECG

causes early R-wave progression, and apparently has more effect on the precordial axis than the anterior infarction.

* This infarction can be noted by the ST-elevation in V1, and the hyperacute T-waves in V2, V3, & V4.


Part 3

Practice 12-Lead ECGs


ECG – 1 ECG – 2


ECG – 3 ECG – 4


ECG – 5 ECG – 6


ECG – 7 ECG – 8


ECG – 9 ECG – 10


ECG – 11 ECG – 12


ECG – 13 ECG – 14


ECG – 15 ECG – 16


ECG – 17 ECG – 18


ECG – 19 ECG - 20


ECG – 21 ECG – 22


ECG – 23 ECG – 24


ECG – 25 ECG – 26

ECG – 27 ECG – 28


ECG – 29 ECG – 30


ECG – 31 ECG – 32


Part 4

Answers & Interpretations


ECG – 1 ECG – 2


ECG – 1 & ECG – 2 These are both examples of Left Ventricular Hypertrophy with a typical Left Ventricular Strain Pattern. Because there is limited

space on prehospital 12-lead print outs, the monitor actually cuts the depth and height of complexes short. This is to keep extra tall or

deep complexes from interfering with other leads. The ST-Elevation present in the right precordial leads (V1, V2, V3) is entirely due

to the LV-Strain pattern. With LV-Strain, you will typically see ST-Elevation in the right precordial leads, and ST-Depression in the

left precordial leads (V4, V5, V6).

"Strain" is a pattern of asymmetric ST segment depression and T wave inversion. LV strain is most commonly seen in one or more

leads that look at the left ventricle (leads I, aVL, V4, V5, V6); less commonly it can be seen in inferior leads.

Axis: Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positive Precordial QRS Axis (“V Leads”): Normal transition, The QRS complex transitions from

mostly negative to mostly positive in the V3, V4 range.

Normal Transition Zone


ECG – 3 ECG – 4


ECG – 5 ECG – 3, ECG – 4, ECG – 5 These are various examples of Left Bundle Branch Block (LBBB). LBBB is most commonly identified by a supraventricular rhythm

(p-waves are present), that is wide (greater than 3 small boxes, 120ms), and has a terminal S-wave in V1.

Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, Lead I is positive & aVF is negative

Precordial QRS Axis (“V Leads”): Late R-wave progression, a.k.a. clockwise rotation of the precordial axis. The QRS complex

transitions after V4.


ECG – 6 ECG – 6 Technically this 12-lead tracing represents a “non-specific intraventricular conduction delay”; which is a fancy way of saying that it

doesn’t fit into a right or left bundle branch block category, but there is a slowing of the impulse between the ventricles. However, in

the prehospital environment, it would not be wrong to call this a left bundle branch block—because the terminal wave in V1 is

negative and it is a wide atrial rhythm. This means that STEMI alert should not be called.

Frontal Plane QRS Axis (Limb Leads): Right Axis Deviation, Lead I is mostly negative & aVF is positive

Precordial QRS Axis (“V Leads”): Normal R-wave progression


ECG – 7 ECG – 8


ECG – 9 ECG – 10


ECG – 7, ECG – 8, ECG – 9, & ECG – 10 These are all examples of Benign Early Repolarization (BER), “Early Repol”. BER is one of the most common reasons for

misdiagnosed STEMI. BER is caused by an elevation of the J-Point due to premature repolarization (recharging) of the ventricles.

Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positive

Precordial QRS Axis (“V Leads”): Normal R-wave progression, ECG – 8 is slightly later to progress than the others.

“Early Repol” Clues

- No reciprocal changes – because an MI often causes st-depression in leads opposite to those with elevation - Asymmetrical T-waves – because an early infarction has hyperactute T-waves (tall, broad, & symmetrical) - Concave ST-elevation – because the presence of convex ST-elevation is almost always an MI - Notched J-points – not always present with early repol, but a GREAT indicator that it is NOT an MI - Normal R-wave progression – because a MI often causes poor R-wave progression (clockwise rotation)


ECG – 11 ECG – 12


ECG – 13 ECG – 11, ECG – 12, & ECG – 13 These are all examples of Acute Pericarditis. Note the widespread ST-Elevation amongst the many leads. PR-depression is also a

common finding with pericarditis. The patient’s symptoms may be the biggest clue; positional pain relief is common.


Precordial QRS Axis (“V Leads”): Normal R-wave progression, Acute Pericarditis does not generally affect the electrical axis.


ECG – 14 ECG – 14 This 12-lead presents as a LBBB vs. Sine-wave. The patient’s history, and presentation should be used come to a solid determination.

A Sine-wave is a sign of significant hyperkalemia, and may only last for minutes before degrading into a lethal arrhythmia. A Sine-

wave is present when there is a straight line from the tip of the S-wave (nadir) to the peak of the T-wave.

Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, Lead I is positive & aVF is negative

Precordial QRS Axis (“V Leads”): Late R-wave progression


ECG – 15 ECG – 15 This 12-lead has a great example of peaked T-waves, indicating hyperkalemia. Note the tall, narrow T-waves in nearly every lead.

The T-waves are actually larger than most of the QRS-complexes. This is a sign of increased potassium.

Frontal Plane QRS Axis (Limb Leads): About 90 degrees, Since Lead I is equiphasic and aVF is perpendicular to Lead I, the QRS axis

is inline with aVF, since the QRS complexes in aVF are positive, and the positive end of aVF is at 90 degrees, that is the axis.



ECG – 16 ECG – 16

This is most likely an early Inferior Wall MI with lateral, and posterior wall extension. If you recall how the coronary anatomy works,

the right coronary artery (RCA) is usually the producer of the posterior descending artery (85% of the time). The right coronary artery

may supply the inferior, posterior, and part of the lateral wall of the heart.

Frontal Plane QRS Axis (Limb Leads): Normal, about 30 degrees



ECG – 17 ECG – 17 This is an example of an Antero-Septal MI, with some lateral wall extension. This is likely due to a proximal occlusion of the Left

Anterior Descending coronary artery (LAD). The LAD, termed “Widow Maker”, supplies predominately the left ventricle.


Precordial QRS Axis (“V Leads”): Late R-wave progression, V4 is equiphasic—it should be mostly positive.


ECG – 18 ECG – 18 This is an example of an extensive Inferior Wall MI (IWMI), with posterior & lateral wall extension. Just like ECG-16, this is

probably due to a proximal RCA occlusion. Since the angle of lead III’s view obtains a better picture of the right ventricle than the

angle of lead II, if lead III has more ST-elevation than lead II it is an indicator of right ventricular infarction.

Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are both positive.

Precordial QRS Axis (“V Leads”): Normal R-wave progression, note that V1 & V2 have developed R-waves (indication of PWMI).


ECG – 19 ECG – 19 This is another example of an Antero-Septal MI. Often, multiple sides of the heart are affected simultaneously. The anterior wall, and

septum are commonly infarcted together. Our knowledge of the precordial axis tells us that leads V3 & V4 were probably reversed

on this patient. This means that V3 on this tracing is actually in the V4 position and visa versa.

Frontal Plane QRS Axis (Limb Leads): Normal, about 0 degrees.

Precordial QRS Axis (“V Leads”): Normal R-wave progression, V3 & V4 misplaced.


ECG - 20 ECG – 20 This is a rare example of an isolated Lateral Wall Infarct. This injury pattern is nearly always due to an occlusion to the Left

Circumflex (LCx).

Frontal Plane QRS Axis (Limb Leads): Normal, about 60 degrees.


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ECG – 21 ECG – 21 This is an example of an Inferior Wall MI, with probable posterior wall extension. Its important to note that since aVR is the most

reciprocal lead to Lead III, it almost always has some form of reciprocal change present with an IWMI. The most common change is

downwardly sloping ST-depression.

Frontal Plane QRS Axis (Limb Leads): Normal, about 90 degrees. Since lead I is equiphasic, the axis is inline with aVF.



By using what we have learned about axis, we can more easily understand

what we are looking at on the 12-Lead ECG. The image to the right has a

few of the leads placed with arrows pointing away from where the positive

electrodes would be placed. This easily explains why leads II, III, & aVF

are the “inferior leads”. It also illustrates why aVL and lead I are the

“high lateral leads”. Also, note how aVL and lead III are nearly opposite

each other. This is the reason that nearly every inferior MI has a

reciprocal change found in aVL. Finally, note the angle of lead III, it has a

near perfect picture of the right ventricle; which is why ST-elevation in

lead III which is greater than ST-elevation in lead II indicates a right-sided

infarction.

Lead III

aVF Lead II

aVL

Lead I


ECG – 22 ECG – 22 This is an example of Wellen’s Phenomenon. Sometimes called Wellen’s warning, syndrome, or sign, this phenomenon is an

indication of an impending anterior infarction. This phenomenon does NOT always occur. Wellen’s may also present as a biphasic

T-wave, usually found in V2.

Frontal Plane QRS Axis (Limb Leads): Normal



ECG – 23 ECG – 23 This is another Antero-Septal Infarct with lateral wall extension (seen best in aVL). Remember that leads aVL & III are the most reciprocal to each other. If you see ST-segment changes in one of these leads, immediately look for inverse changes in the other. As you can see on this ECG, there is STE in aVL, and ST-depression in lead III.

Frontal Plane QRS Axis (Limb Leads): Normal, lead III is mostly negative, meaning that the axis is probably between 0º & -30º


Note: a QS-wave in V2 is always a sign of infarction (new or old). This rule is completely reliant on proper lead placement.


ECG – 24 ECG – 24 This is an Inferior Wall MI with Posterior Wall extension. Notice the hyperacute T-waves in the inferior leads (II, III, & aVF), and

the reciprocal changes in the high lateral leads (I & aVL)? The amount of ST-elevation is significant due to the QRS-complex having

such low voltage.




ECG – 25 ECG – 25 This is another example of an Inferior Wall MI with posterior changes, most likely due to a proximal occlusion of the right coronary

artery (RCA). The RCA is connected to the posterior descending artery in 85% of the population; the left circumflex (LCx) supplies

the PDA in the rest of people.


Precordial QRS Axis (“V Leads”): Normal R-wave progression, its difficult to tell how tall the QRS complexes in V4 are because they

are cut off by the monitor.


ECG – 26 ECG – 26 This ECG is an example of Right Bundle Branch Block (RBBB). RBBB is present

when a wide supraventricular rhythm presents with a positive terminal deflection in V1.

Other findings include appropriate T-wave discordance, and a slurred S-wave in Lead I

and V6.

Frontal Plane QRS Axis (Limb Leads): Indeterminate, all frontal leads are equiphasic.

Precordial QRS Axis (“V Leads”): Early R-wave Progression


Right Bundle Branch Block Explained

The right bundle branch consists of one fascicle. When this

fascicle is blocked, the conduction that normally travels from the

atria is routed away from the right bundle branch and towards the

healthy left bundle branch (1). The conduction travels fast to the

health left bundle branch (2). After the left ventricle is fully

depolarized, the conduction moves slower to depolarize the right

ventricle through cell-to-cell conduction (3).

This is why with a RBBB you will see a terminal R-wave in V1

and terminal S-wave in V6, because the last flow of conduction

moves towards V1 and away from V6.

A Right Bundle Branch block may cause Right Axis Deviation in the frontal plane, because of the S-waves that occur in lead I as a

result of the above-mentioned conduction abnormality. It may also cause early r-wave progression in the precordial axis due to the

larger-than-normal R-wave in V1.

1 2

3

V1

I & V6 +

ECG – 27 ECG – 27 This is an early Antero-Septal MI. This 12-lead doesn’t meet STEMI Alert criteria, but the ST-morphology in V1, hyperacute T-

waves in V2 & V3, and the reciprocal changes in the inferior leads are highly suggestive of MI.

Frontal Plane QRS Axis (Limb Leads): Normal, Leads I & aVF are mostly positive

Precordial QRS Axis (“V Leads”): Normal R-wave Progression

Axis Determination Thompson 103 ECG – 28 ECG – 28 This is an example of Atrial Bigeminy with an Anterior Infarct. Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, about -30º

Precordial QRS Axis (“V Leads”): Normal R-wave Progression Lead II is the most equiphasic, and aVL is perpendicular to lead II. aVL is

positive on the strip above, and the positive end of aVL is at -30 degrees on

the hexaxial reference system.

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Axis Determination Thompson 104 ECG – 29 ECG – 29 This ECG is that of a Right Bundle Branch Block (RBBB) with Antero-Septal Infarction.

Frontal Plane QRS Axis (Limb Leads): Left Axis Deviation, about -30º

Precordial QRS Axis (“V Leads”): Early R-wave Progression, counter-clockwise rotation of precordial axis Early R-wave progression is commonly caused by a right bundle branch block. The left axis deviation on this 12-lead is on the edge

of being considered pathological, and a Left Anterior Fascicular Block (LAFB) is probable. A RBBB in conjunction with a LAFB is

considered a bifascicular block, and alerts us that only a single fascicle is still conducting impulses; the laft posterior fascicle.

Axis Determination Thompson 105 ECG – 30 ECG – 30 This is an example of Global Ischemia.

Frontal Plane QRS Axis (Limb Leads): Physiologic Left Axis Deviation, about 0º

Precordial QRS Axis (“V Leads”): Normal R-wave Progression, it is easier to determine that the QRS complexes in V4 are mostly

positive if you examine the last few complexes.

Remember that lead I is at 0 degrees. This would explain why this tracing has nice tall QRS complexes in lead I.

Axis Determination Thompson 106 ECG – 31 ECG – 31 This is an Anterior Wall Infarct. The STEMI is not obvious, but present in V3 through V6.


Precordial QRS Axis (“V Leads”): Late R-wave Progression, a common finding with an Anterior Wall MI.

Axis Determination Thompson 107 ECG – 32 ECG – 32 This is an example of Reversed Limb Leads. When lead I is negative and aVR is positive, there should be a concern about limb lead

reversal. aVR will almost never be this positively deflected with a supraventricular

rhythm. One of the concerns with not identifying this problem is the misinterpretation of

the 12-lead. This 12-lead looks to have ST-elevation when it is entirely due to the

mislplaced limb leads.

Axis determination

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