Lesson 5: Axis Deviation

Lesson 5: Axis Deviation

• Definition: Axis represents the direction of the mean electrical vector in the frontal plane.

• Determining Axis Deviation:

  • Examine Lead I and aVF.

• Axis Categories:

  • Normal Axis:

  • Lead I = +

  • Lead aVF = +

  • Left Axis Deviation:

  • Lead I = +

  • Lead aVF = -

  • Right Axis Deviation:

  • Lead I = -

  • Lead aVF = +

  • Extreme Right Axis Deviation:

  • Lead I = -

  • Lead aVF = -

• Causes of Right Axis Deviation:

  • Chronic Obstructive Pulmonary Disease (COPD)

  • Acute bronchospasm

  • Cor pulmonale

  • Pulmonary embolus

• Causes of Left Axis Deviation:

  • Chronic hypertension

  • Left bundle branch block

  • Aortic stenosis

  • Aortic insufficiency

  • Mitral regurgitation

• Mean Electrical Vector Direction:

  • Toward hypertrophy

  • Away from myocardial infarction

• Key Numbers:

  • Normal axis: between $-30$ and $+90$ degrees

  • Left axis deviation: more negative than $-30$ degrees

  • Right axis deviation: more positive than $90$ degrees

• Remembering the Axis Deviations:

  1. Both Lead I and aVF up ➔ Normal axis.

  2. Lead I down, aVF up ➔ Right axis deviation.

  3. Lead I up, aVF down ➔ Left axis deviation.

  4. Both leads down ➔ Extreme right axis deviation.