3 the axis

12-Lead 12-Lead ElectrocardiographyElectrocardiography

a comprehensive course

Adam Thompson, EMT-P, A.S.Adam Thompson, EMT-P, A.S.

The

Axis

Resources

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

The 6-Step Method

• 1. Rate & Rhythm1. Rate & Rhythm

• 2. Axis Determination2. Axis Determination

• 3. Intervals3. Intervals

• 4. Morphology4. Morphology

• 5. STE-Mimics5. STE-Mimics

• 6. Ischemia, Injury, & Infarct6. Ischemia, Injury, & Infarct

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.

Axis Determination

• Critical Skill!• Use the hexaxial reference system for

the frontal plane.• Identify clockwise or counterclockwise

rotation of R-wave progression.

PathologiesFrontal Plane Axis Precordial Axis

ERAD-90 to 180

Right Axis Deviation90 to 180

Pathological Left Axis Deviation-30 to -90

Early TransitionCounterclockwise

Rotation

Late TransitionClockwise Rotation

• Ventricular Rhythm• Paced Rhythm• Dextrocardia• Electrolyte derangement

• May be normal• LPFB• Pulmonary disease• RVH• RBBB• WPW• Dextrocardia•Venrticular Rhythm

• Pregnancy• LAFB• WPW• Pulmonary disease• LBBB• Hyperkalemia• Q-waves, MI

• Posterior wall infarction• RVH• RBBB

• Sometimes Normal, especially in women• Anterior MI• LVH• LAFB• LBBB• Lung Disease

Willem Einthoven

Won the Nobel Prize in Physiology or Medicine in 1924 for inventing the string galvanometer which was the first EKG.

Einthoven’s Triangle

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

• Einthoven’s LawI + (-II) + III = 0

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.

Einthoven’s Law

• Lead I = 5mm

• Lead II– It’s essentially a monophasic

QS complex. – About -10 mm.

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.

Einthoven’s Law

• Lead I = 5mm

• Lead II = -10mm

• Lead III = -15mm

Einthoven’s Law

• Lead I = 5mm

• Lead II = -10mm

• Lead III = -15mm– Plug the numbers in.

• I + (-II) + III = 0• 5 + 10 -15 = 0

Einthoven’s Law

The equilateral triangle

Electrical Axis

What is the heart’s electrical axis?

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

1

3

22

3

4

Mean vector

Cardiac vector

Electrical Axis

What is the heart’s electrical axis?

Next, the area around the left and right ventricular apex (2) depolarizes from a endocardial-to-epicardial direction (inside-out).

1

3

22

3

4

Mean vector

Cardiac vector

Electrical Axis

What is the heart’s electrical axis?

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

ventricle (4).

1

3

22

3

4

Mean vector

Cardiac vector

Electrical Axis

What is the heart’s electrical axis?

The big arrow is the heart’s mean (average) electrical vector. If you averaged the millions of cardiac vectors,

you would get the “mean vector”.

1

3

22

3

4

Mean vector

Cardiac vector

Mean Electrical Vector

+

+

+ A B A

B

Mean vector moves towards positive electrode = positive QRSMean vector moves towards positive electrode = positive QRSMean vector moves away from positive electrode = negative QRSMean vector moves away from positive electrode = negative QRSMean vector is perpendicular to positive electrode = equiphasic QRSMean vector is perpendicular to positive electrode = equiphasic QRS

Mean Electrical Vector

Red arrow is heart’s

mean electrical vector

Mean Electrical Vector

Lead I views the heart’s

Vector similar to the

image on the left.

Leads II & III do the same

from their angles.

Einthoven’s Triangle

=

Hexaxial Reference System

The arrows and lead

names are placed on

the side of the

positive electrode.

I

IIIII

Hexaxial Reference System

The augmented leads provide the other 3 leads of the hexaxial reference system.

Hexaxial Reference System

Hexaxial Reference System

I

IIIII aVF

aVLaVR

I+0°

I-

II+

III-

III+

II-

aVR-

aVR+

aVF+

aVF-

aVL+

aVL-30°

-30°

60°90°120°

150°

+/-180°

-150°

-120°-90° -60°

Hexaxial Reference System

I+0°

I-

II+

III-

III+

II-

aVR-

aVR+

aVF+

aVF-

aVL+

aVL-30°

-30°

60°

90°120°

150°

+/-180°

-150°

-120°

-90°-60°

The Hexaxial Method

We only need to concentrate on the first six leads

The Hexaxial Method

The Hexaxial Method

Step 1: Find the equiphasic lead

I+0°I-

II+

III-

III+

II-

aVR-

aVR+

aVF+

aVF-

aVL+

aVL-

30°

-30°

60°90°120°

150°

+/-180°

-150°

-120°

-90° -60°

Step 4: Is the perpendicular lead positive or negative?

Hexaxial Reference System

Find the most equiphasic lead

Hexaxial Reference System

• When the mean axis is perpendicular to the positive electrode, the QRS is equiphasic.

+

+

+ A B A

B

Hexaxial Reference System

I+0°I-

II+

III-

III+

II-

aVR-

aVR+

aVF+

aVF-

aVL+

aVL-

30°

-30°

60°90°120°

150°

+/-180°

-150°

-120°

-90° -60°

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.

Axis Deviation

• So what is a normal axis?

• Why does it matter if an axis is deviated?

Normal Axis

• The normal quadrant for the QRS axis is the Southeast quadrant.

• From 0 to 90

Left Axis Deviation

• From -90 to 0• This is considered the

Northeast quadrant.

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

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.

Extreme Right Axis Deviation

• Called ERAD• From -90 to -180• QRS in I, II, & III are

negative• Probably ventricular

– Idioventricular– Paced rhythm

Cheat SheetNormal

Axis

0 to 90

Physiologic

Left

0 to -30

Pathologic

Left

-30 to -90

Right Axis

90 to 180

Extreme Right Axis

-90 to 180

Indeterminate

Axis

?

Lead I

Lead II

Lead III

Hexaxial Reference System

I+0°I-

II+

III-

III+

II-

aVR-

aVR+

aVF+

aVF-

aVL+

aVL-

30°

-30°

60°90°120°

150°

+/-180°

-150°

-120°

-90° -60°

Cheat SheetNormal

Axis

0 to 90

Physiologic

Left

0 to -30

Pathologic

Left

-30 to -90

Right Axis

90 to 180

Extreme Right Axis

-90 to 180

Indeterminate

Axis

?

Lead I

Lead II

Lead III

Pathologies

ERAD LAD

RAD Normal

180 0

-90

90

Fascicles

• Right Bundle Branch– 1 Fascicle

• Left Bundle Branch– 2 Fascicles

• Left Anterior• Left Posterior

Fascicular Blocks

Left AnteriorFascicular Block

Left PosteriorFascicular Block

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

END