3 the axis
TRANSCRIPT
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