Basics of ECG Leads - Simplified approach

3. • Understand the basic concept of an ECG lead,
Learning Objectives:
• Know the 12 conventional ECG leads, and the
angles from which each lead views the heart’s
electrical activity,
• Know the proper location of the 10 conventional
ECG electrodes.
• Correlate specific groups of leads with anatomic
regions of the heart.

4. • A lead is a view of the voltage between two points
(known as poles) as a function of time.
• The positive pole for each lead is marked by a
single recording electrode on the body.
• The negative pole for each lead is marked by
either a single recording electrode, or a virtual
electrode known as a “central terminal” which
averages input from multiple other electrodes.
• A lead is not the same as an electrode.
What is a Lead?

7. STANDARD OR
BIPOLAR
LIMB LEADS
(LEAD I, II, III)

8. AUGMENTED OR
UNIPOLAR
LIMB LEADS
(aVR, aVL, aVF)

9. PRECORDIAL LEADS
(V1 – V6)

10. RHYTHM STRIPS
Usually V1, Lead II, V5

11. • Willem Einthoven invented the
first practical ECG in 1903.
• Attached recording electrodes to
the right arm, left arm, and left leg
to create the three standard limb
leads.
Standard Limb Leads
• The right leg is used to ground the
system.
I + III = II
EINTHOVEN’S RULE

12. • To increase the number of directions
from which the heart can be viewed,
the ECG machine also uses a
“central terminal”.
• The central terminal is made by
connecting the right arm, left arm
and eft leg electrodes together.
• This results in a virtual negative
terminal that is composed of the
average of the electrical potentials
from the 3 limbs.
Augmented Limb Leads

13. aVR + aVL + aVF = 0
• The ‘a’ stands for augmented.
• The “V” is listed in any lead that
uses the central terminal.
Augmented Limb Leads

14. aVR + aVL + aVF = 0
The Hexaxial system
I + III = II
EINTHOVEN’S RULE

15. The Hexaxial system

16. The Hexaxial system
III = II - I
aVR = - ½ (I + II)
aVL = I – ½(II)
aVF = II – ½(I)
• Modern ECG
machines only
directly measures
leads I and II, and
calculate the four
others.

17. • There are 6 leads which
examine the heart’s
electrical activity in the
transverse plane.
• The positive pole for
each is at a location on
the anterior or left lateral
chest wall.
• The negative pole for
each is the central
terminal.
• The leads are named V1
– V6.
V1 V2 V3
V4
V5
V6
PRECORDIAL LEADS

18. PRECORDIAL LEADS
V1 V2 V3
V4
V5
V6
POSITION
V1 4th ICS, just right to sternum
V2 4th ICS, just left to sternum
V3 Halfway between V2 and V4
V4 5th ICS, in midclavicular line
V5 Halfway between V4 and V6
V6 5th ICS, in mid axillary line
V
1
V
2
V
3
V
5
V
4
V
6

19. Spatial Relationship between leads
Frontal plane Transverse plane

20. ANATOMICAL CORRELATIONS
Inferior Leads
II, III, aVF
Septal Leads
V1, V2
Anterior Leads
V3, V4
Lateral Leads
I, aVL, V5, V6
No grouping
aVR

21. Inferior Leads
II, III, aVF
No grouping
aVR
Septal Leads
V1 - V2
Lateral Leads
I, aVL, V5-V6
Anterior Leads
V3 – V4