QRS Axis

Aka: QRS Axis, EKG Axis, Electrocardiogram Axis

1. See Also
   1. Electrocardiogram
   2. Cardiac Electrophysiology Anatomy
   3. Left Axis Deviation
   4. Right Axis Deviation
2. Interpretation: Axis Determination (Method 1)
   1. Images: EKG Axis
      1. 
   2. Check lead I (0 degrees)
      1. QRS positive (predominately up)
         1. Vector points to patient's Left
         2. Correlates with right half of axis circle (12:00 to 6:00 on clockface)
      2. QRS negative (predominately down)
         1. Vector points to patient's Right (6:00 to 12:00 on clockface)
         2. Correlates with left half of axis circle (always Right Axis Deviation)
   3. Check lead aVF (90 degrees)
      1. QRS positive (predominately up)
         1. Vector points to bottom half of axis circle (3:00 to 9:00 on clockface)
      2. QRS negative (predominately down)
         1. Vector points to upper half of axis circle (Left Axis Deviation if -30 to -90 degrees, or 12:00 to 2:00)
   4. Interpretation
      1. Indeterminate: Extreme Right Axis Deviation
         1. Lead I: Negative QRS
         2. Lead aVF: Negative QRS
      2. Right Axis Deviation
         1. Lead I: Negative QRS
         2. Lead aVF: Positive QRS
      3. Normal range
         1. Lead I: Positive QRS
         2. Lead aVF: Positive QRS
      4. Left Axis Deviation
         1. Lead I: Positive QRS
         2. Lead aVF: Negative QRS (normal if -30 to 0 degrees, 2:00 to 3:00 on clockface)
3. Interpretation: Axis Determination (Method 2)
   1. Select Isoelectric lead from limb and augmented leads
      1. Isoelectric lead averages to baseline
      2. Positive deflection equals negative deflection
   2. Identify isoelectric lead on axis circle
      1. Lead with most symmetric voltage (as much positive QRS voltage as negative QRS voltage)
      2. Choose lead that is perpendicular to isoelectric lead
   3. Use Lead I and aVF to determine quadrant
      1. Read perpendicular lead's degrees off axis circle
   4. Extreme Right Axis Deviation (-90 to -180, negative in lead I and negative in lead avF)
      1. Most Isoelectric I (avF is perpendicular): -90 (12:00)
      2. Most Isoelectric avL (II is perpendicular): -120 (11:00)
      3. Most Isoelectric III (avR is perpendicular): -150 (10:00)
      4. Most Isoelectric avF (I is perpendicular): -180 (9:00)
   5. Right Axis Deviation (+180 to +90, negative in lead I and positive in lead avF)
      1. Most Isoelectric avF (I is perpendicular): +180 (9:00)
      2. Most Isoelectric II (avL is perpendicular): +150 (8:00)
      3. Most Isoelectric avR (III is perpendicular): +120 (7:00)
      4. Most Isoelectric I (avF is perpendicular): +90 (6:00)
   6. 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)
   7. Normal Axis (+90 to -30, positive in lead I and positive in lead avF)
      1. Most Isoelectric avF (I is perpendicular): 0 (3:00)
      2. Most Isoelectric III (avR is perpendicular): +30 (4:00)
      3. Most Isoelectric avL (II is perpendicular): +60 (5:00)
      4. Most Isoelectric I (avF is perpendicular): +90 (6:00)