Left Axis Deviation

Aka: Left Axis Deviation, Left QRS Axis

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II. Definition

  1. Deviation into lead aVL axis (-30 to-90 degrees)
  2. Negative net QRS voltage in lead avF (and lead II)
  3. Positive net QRS voltage in lead I
  4. On a clock face, 2:00 to 12:00 position

III. Interpretation: Based on most isoelectric lead

  1. Images
    1. EKG-Axes.png
  2. Approach
    1. See QRS Axis
    2. Lead with most symmetric voltage (as much positive QRS voltage as negative QRS voltage)
    3. Choose lead that is perpendicular to isoelectric lead and that leads axis is the same as the QRS Axis
  3. Left Axis Deviation (-90 to -30, positive in lead I and negative in lead avF)
    1. Most Isoelectric I (avF is perpendicular): -90 (12:00)
    2. Most Isoelectric avR (III is perpendicular): -60 (1:00)
    3. Most Isoelectric II (avL is perpendicular): -30 (2:00)

IV. Interpretation: Pathologic Left Axis Deviation

  1. Left Posterior Hemiblock (rare due to dual supply)
  2. Left Anterior Hemiblock
    1. QRS Axis more negative than -30 degrees (AVL)
    2. Axis <-30 if Lead II is more negative than positive

V. Causes

  1. Normal variant
  2. Mechanical shift
    1. Ascites
    2. High diaphragm
  3. Left Atrial hypertrophy
  4. Left Bundle Branch Block
  5. Wolf-Parkinson-White Syndrome (WPW Syndrome)
  6. Chronic Obstructive Pulmonary Disease (COPD)
  7. Hyperkalemia
  8. Right ventricular ectopic rhythms

VI. Causes: Non-Causes of Left Axis Deviation

  1. Left Ventricular Hypertrophy is not a deviation cause

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