Determination of the electrical axis is especially useful for the diagnosis of the following:

  Left anterior fascicular block (left anterior hemiblock).

  Left posterior fascicular block (left posterior hemiblock).

  Ventricular tachycardia (the deviation of electrical axis by at least 40 degrees to left or

      to right during wide QRS tachycardia supports the diagnosis of VT).

  Right ventricular hypertrophy.




Left axis deviation is observed in

  normal variants.

  left ventricular hypertrophy.

  left anterior fascicular block.

  left bundle branch block.

  some types of ventricular tachycardias.

  some congenital heart diseases (tricuspid atresia, endocardial cushion defect).




Right axis deviation is observed in

  normal variants (may be normal in infants)

  right ventricular hypertrophy

  left posterior fascicular block

  lateral myocardial infarction

  emphysema (the heart assumes a more vertical position when anteroposterior chest diameter increases)

  asthenia

  acute pulmonary embolism

  dextrocardia




Extreme right axis deviation (indeterminate axis, northwest region, no man's land)

  is between -90 and 180 degrees.

 
QRS complexes are negative in leads I and aVF.

  Infants with

            - Ostium primum type atrial septal defect (ASD) or

            - Atrioventricular (AV) canal defect

      may show extreme right axis deviation.