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2-1. How to Measure the QRS Axis

Topics for study:

  1. Introduction
  2. QRS Axis Determination
  3. Examples of QRS Axis

 

Introduction

The frontal plane QRS axis represents only the average direction of ventricular activation in the frontal plane. As such this measure can inform the ECG reader of changes in the sequence of ventricular activation (e.g., left anterior fascicular block), or it can be an indicator of myocardial damage (e.g., inferior myocardial infarction).

In the diagram below the normal range is identified (-30° to +90°). Left axis deviation (i.e., superior and leftward) is defined from -30° to -90°, and right axis deviation (i.e., inferior and rightward) is defined from +90° to +150°.

Click to see causes of abnormal axis (lesson 4).

image ecg_534.gif

QRS Axis Determination

Examples of QRS Axis

Axis in the normal range:
image 02-03

Axis in the left axis deviation (LAD) range:
image 02-04

Axis in the right axis deviation (RAD) range:
image 02-08