1. The 12-Lead ECG
The 12-Lead ECG sees the heart from 12 different views.
Therefore, the 12-Lead ECG helps you see what is happening in different portions of the heart.
The rhythm strip is only 1 of these 12 views.

2. Determination of electrical axis
Revision

3. aVR, aVL, aVF (augmented limb leads)
Summary of Leads
Limb Leads
Precordial Leads
Bipolar
I, II, III
(standard limb leads) -
Unipolar
aVR, aVL, aVF (augmented limb leads)
V1-V6

4. Views of the Heart Some leads get a good view of the:
Anterior portion of the heart
Lateral portion of the heart
Inferior portion of the heart

5. Precordial Leads

6. Precordial Leads

7. Anterior View of the Heart
Remember the anterior portion of the heart is best viewed using leads V1- V4.
Limb Leads
Augmented Leads
Precordial Leads

8. Lateral View of the Heart
So what leads do you think the lateral portion of the heart is best viewed?
Leads I, aVL, and V5- V6
Limb Leads
Augmented Leads
Precordial Leads

9. Inferior View of the Heart
Now how about the inferior portion of the heart?
Leads II, III and aVF
Limb Leads
Augmented Leads
Precordial Leads

10. Rhythm Analysis Step 1: Calculate rate. Step 2: Determine regularity.
Step 3: Assess the P waves.
Step 4: Determine PR interval.
Step 5: Determine QRS duration.
Step 6; Determine electrical axis

11. 12 lead ECG

12. The Axis the normal QRS axis is defined as ranging from -30° to +90°.
-30° to -90° is referred to as a left axis deviation (LAD)
+90° to +180° is referred to as a right axis deviation (RAD)

13. Determining the Axis Predominantly Positive Predominantly Negative
Equiphasic

14. Determination of Axis

15. A quick way to determine the axis
is to look at the QRS complexes in leads I and II.
To summarize:
The normal QRS axis falls between -30o and +90o because ventricular depolarization is leftward and downward.
Left axis deviation occurs when the axis falls between -30o and -90o.
Right axis deviation occurs when the axis falls between +90o and +150o.
Right superior axis deviation occurs when the axis falls between between +150o and -90o.
QRS Complexes
Axis
I II
normal
left axis deviation
right axis deviation
right superior axis deviation

16. Determining the Axis; The Quadrant Approach
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.

17. The Quadrant Approach
1. Examine the QRS complex in leads I and aVF to determine if they are predominantly positive or predominantly negative. The combination should place the axis into one of the 4 quadrants below.

18. The Quadrant Approach
2. In the event that LAD is present, examine lead II to determine if this deviation is pathologic. If the QRS in II is predominantly positive, the LAD is non-pathologic (in other words, the axis is normal). If it is predominantly negative, it is pathologic.

19. Quadrant Approach: Example 1
Negative in I, positive in aVF  RAD

20. Quadrant Approach: Example 2
Positive in I, negative in aVF  Predominantly positive in II 
Normal Axis (non-pathologic LAD)