# 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.

Axis | Net QRS voltage | |

Lead I | Lead 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 |

aVF | 0 |

III | +30 |

aVL | +60 |

I | +90 |

**Left Axis Deviation**

Lead (Isoelectric QRS) | Axis |

I | -90 |

aVR | -60 |

II | -30 |

aVF | 0 |

**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

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 2 - What is the axis deviation?**

**ECG 3 - What is the axis deviation?**

**ECG 4 - What is the axis deviation?**

**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**

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