ECG AXIS
Normal: QRS up in lead 1, 2, and aVF (-30° - +90°)
Normal: QRS up in lead 1, and lead 2; down in aVF (-30° - +60°)
LAD:
Beyond -30°
QRS up in lead 1, down in aVF, and lead 2 (S > R in lead II)
Etiologies: LVH, LBBB, inferior MI, elevated diaphragm, WPW
RAD :
Beyond +90
QRS down in lead 1, and up in aVF (S > R in lead I)
Etiologies: RVH, RBBB, PE, COPD, lateral MI, WPW, septal defects.
Extreme or far RAD: QRS down in both leads 1 and aVF.