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ECG Axis

Author: Dr. Subrahmanyam Karuturi, MD

 

  • Axis refers to the direction of the movement of depolarization, which spreads throughout the heart to stimulate the myocardium to contract.

 

  • Normal values
    • P wave: 0 to 75 degrees
    • QRS complex: -30 to 90 degress
    • T wave: QRS-T angle <45 degrees frontal or <60 degrees precordial
       
  • Lookout Method - General Determination of Electrical Axis (Frontal Plane)
    • Check if QRS is positive or negative in lead I and avF.
AxisNet QRS voltage
 Lead ILead aVF
Normal axis (0 to +90)++
   
Left Axis (-30 to -90)+-
   
Right Axis (>100)-+
   
Right Superior Axis (-90 to +180) or Indeterminate Axis or Extreme Right Axis or North West Axis--
+ represents positive net QRS voltage
- represents negative net QRS voltage

 

 

 

  • Isolectric Lead Method - Axis in Degrees
    • Identify the lead where QRS is most isoelectric. (Isoelectric QRS has equal positive and negative deflections)
    • When the heart electrical forces are moving in the direction perpendicular to the lead, then the QRS will be isoelectric in that lead
    • So the axis approximates the direction of the lead perpendicular to the isoelectric lead if the QRS is positive in the perpendicular lead
    • Ex: If lead II is isoelectric (+60 degrees), then look at aVL (+150 degrees). If the QRS complexes are positive in aVL, then the axis is approximately +150 degrees. More examples in the following tables.

 

 

Fig : Hexaxial Reference System for ECG Axis.

 

Normal Axis

Lead (Isoelectric QRS)Axis
aVF0
III+30
aVL+60
I+90

Left Axis Deviation

Lead (Isoelectric QRS)Axis
I-90
aVR-60
II-30
aVF0

Right Axis Deviation

Lead (Isoelectric QRS)Axis
aVF+180
II+150
aVR+120
I+90

Right Superior Axis or Indeterminate Axis or Extreme Right Axis Deviation or North West Axis

Lead (Isoelectric QRS)Axis
I-90
aVL-120
III-150
aVF-180

 

 

  • Axis rotation
    • It is the axis of the heart in the horizontal plane (the precordial leads)
    • Normal range
      • Isoelectric QRS in V3 and V4
    • Rightward rotation or Counterclockwise rotation
      • Isoelectric QRS in V1 and V2
    • Leftward rotation or Clockwise rotation
      • Isoelectric QRS in V5 and V6

 

  • Remember
    • Axis deviation is in the coronal plane. (limb leads)
    • Aix rotation is in the horizontal plane. (precordial leads)

 

Normal Axis

 

 

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

Example : In the above ECG, Axis interpretation by Lookout Method - Lead I Positive, Lead aVF Positive , So Normal Axis (0 to +90 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead aVL and you can see Lead II (+60 degrees)  is the perpendicular lead for aVL in the Hexaxial reference system. So the axis deviation is approximately +60 degrees.

 

Left Axis Deviation

 

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

Example : In the above ECG, Axis interpretation by Lookout Method - Lead I Positive & Lead aVF - Negative, So Left Axis Deviation (-30 to -90 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead aVR and you can see Lead III (-60 degrees)  is the perpendicular lead for aVR in the Hexaxial reference system. So the axis deviation is approximately -60 degrees.

 

Differential Diagnosis of Left Axis Deviation

  • LVH
  • LBBB
  • Inferior wall MI
  • Ostium primum ASD
  • Chronic lung disease
  • Hyperkalemia
  • Left anterior fascicular block
     

 

Right Axis Deviation
 

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

Example : In the above ECG, Axis interpretation by Lookout Method - Lead I Negative & Lead aVF Positive, So Right Axis Deviation (>100 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead aVR and you can see Lead III (+120 degrees)  is the perpendicular lead for aVR in the Hexaxial reference system. So the axis deviation is approximately +120 degrees.

 

Differential Diagnosis of Right Axis Deviation

  • Lateral wall MI
  • Left posterior fascicular block
  • Dextrocardia
  • Lead Reversal
  • Ostium Secundum ASD
  • Pulmonary Embolus
  • Vertical Heart
  • RVH
     

 

Extreme Right Axis or Indeterminate Axis Deviation or North West Axis

 

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

Example : In the above ECG, Axis interpretation by Lookout Method - Lead I Negative & Lead aVF Negative, So Extreme Right Axis Deviation or Indeterminate Axis.(-90 to +180 degrees)

 

Differential Diagnosis of Extreme Right Axis or Indeterminate Axis Deviation or North West Axis

  • Apical MI
  • Ventricular tachycardia
  • Hyperkalemia
  • Right Ventricular Hypertrophy

 

Practice ECGs

 

ECG 1 - What is the axis deviation?

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

 

 

ECG 2 - What is the axis deviation?

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

 

 

ECG 3 - What is the axis deviation?

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

 

 

ECG 4 - What is the axis deviation?

ECG Source : Nathanson L A, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians.  http:// ecg.bidmc.harvard.edu

 

 

 

 

 

Answers

  • ECG 1 - Axis interpretation by Lookout Method - Lead I Positive & Lead aVF Negative, So Left Axis Deviation (-30 to -90 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead II and you can see Lead aVL (-30 degrees)  is the perpendicular lead for II in the Hexaxial reference system. So the axis deviation is approximately -30 degrees.

 

  • ECG 2 - Axis interpretation by Lookout Method - Lead I Positive & Lead aVF Negative, So Left Axis Deviation (-30 to -90 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead II and you can see Lead aVL (-30 degrees)  is the perpendicular lead for II in the Hexaxial reference system. So the axis deviation is approximately -30 degrees.

 

  • ECG 3 - Axis interpretation by Lookout Method - Lead I Positive & Lead aVF Positive, So Normal Axis (0 to +90 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead aVL and you can see Lead II (+60 degrees)  is the perpendicular lead for aVL in the Hexaxial reference system. So the axis deviation is approximately +60 degrees.

 

  • ECG 4 - Axis interpretation by Lookout Method - Lead I Positive & Lead aVF Positive, So Normal Axis (0 to +90 degrees). Isoelectric Lead Method - QRS is most isoelectric in lead III and you can see Lead aVR (+30 degrees)  is the perpendicular lead for III in the Hexaxial reference system. So the axis deviation is approximately +30 degrees.

 

References

  1. Lewis K, Handal K. Sensible Analysis of the 12-Lead ECG. Delmar Learning, 2000.
  2. Wagner, GS. Marriott’s Practical Electrocardiography (11th edition), Lippincott Williams & Wilkins 2007.
  3. Phibbs, BP. Advanced ECG: Boards and Beyond (2nd Edition), Saunders Elsevier 2006.