Variations in the electrical heart axis

The normal electrical axis of the heart is situated between -30 degrees (negative 30 degrees) and +90 degrees (positive 90 degrees) with respect to the horizontal line. Variations in electrical heart axis can be classified as left axis deviation, right axis deviation or extreme right axis deviation.

  • Left axis deviation or left heart axis: the electrical heart axis is between -30 degrees (negative 30 degrees) and -90 degrees (negative 90 degrees) with respect to the horizontal line.
  • Right axis deviation or right heart axis: the electrical heart axis is between +90 degrees (positive 90 degrees) and 180 degrees (positive 180 degrees) with respect to the horizontal line.
  • Extreme right axis deviation (also known as the northwest axis): the electrical heart axis is between +180 degrees (positive 180 degrees) and -90 degrees (negative 90 degrees) with respect to the horizontal line.

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Causes of left axis deviation include:

  • Left ventricular hypertrophy (the left ventricle is enlarged and generates more electrical activity, so the heart axis is “pulled” to the left)
  • Inferior myocardial infarction
  • Elevated diaphragm (such as in ascites and obesity)
  • Wolff-Parkinson-White syndrome with a right-sided accessory pathway
  • Chronic obstructive pulmonary disease
  • Left bundle branch block or LBBB (Note that in patients with LBBB, left axis deviation, normal axis, and to a lesser extent right axis deviation can also be encountered)
  • Left anterior fascicular block (LAFB)

Causes of right axis deviation include:

  • Right ventricular hypertrophy (the right ventricle is enlarged and generates more electrical activity, so the heart axis is “pulled” to the right)
  • Loss of tissue of the left ventricle (e.g. as caused by lateral myocardial infarction)
  • Wolff-Parkinson-White syndrome with a left-sided accessory pathway
  • Left posterior fascicular block
  • May be a normal finding in children
  • Dextrocardia
  • Chronic obstructive pulmonary disease
  • Pulmonary embolism (Due to the obstruction in the pulmonary artery the right ventricle has to generate higher pressures to pump blood into the pulmonary artery. This results in greater electrical activity of the right ventricle and right axis deviation.)