Normal and Abnormal Heart Axis
- Normal (intermediate) heart axis vector points between -30° and +90° (yellow)
- Right Axis Deviation vector points between +90° and +180° (green)
- Left Axis Deviation vector points between -30° and -90° (red)
- Extreme Axis Deviation vector points between -90° and +180° (blue)
Normal (intermediate) Heart Axis
- If positive leads (I, aVF)
- Then the vector points to the lower left quadrant (0° to 90°) and the axis is normal
- If Lead I is positive and aVF is negative
- Then the vector points to the upper left quadrant (0° to -90°)
- Lead aVL (-30°) is the boundary
- between normal axis and left axis deviation
- Lead II is perpendicular to lead aVL
- According to biphasic QRS in lead II, it is determined whether it is a normal axis or left axis deviation