Variations in electrical heart axis

The electrical axis of the heart is the mean direction of the cardiac impulse during ventricular depolarization. The QRS complex, which represents ventricular depolarization, is used for the determination of the electrical heart axis. The term, electrical heart axis, usually refers to the electrical axis in the frontal plane as measured by the limb leads.

Normally, the vector representing the heart axis originates from the AV node, where ventricular activation is initiated, and points towards the left ventricle.

Content on this page requires a newer version of Adobe Flash Player.

Get Adobe Flash player

Click here to enlarge

This is because the more massive left ventricle dominates the process of ventricular depolarization. Many factors may alter the electrical heart axis including:

Anatomic factors:

  • Abnormal anatomic position of the heart in the thoracic cavity (such as in dextrocardia)
  • Abnormal thoracic anatomy
  • Abnormal position of the diaphragm (such as in obesity, pregnancy, ascites)

Cardiopulmonary pathology:

  • Prior myocardial infarction
  • Recent ischemia
  • Pulmonary embolism
  • Pulmonary obstructive disease
  • Myocardial hypertrophy
  • Dilated cardiomyopathy
  • Conduction abnormalities

Click here to read about variations of the elecrical heart axis.