Normal QRS axis range
May 23, 2022
Source: Cainiu Health
Dr. Tian Hongbo
Introduction
The QRS axis between –30° and +90° falls within the normal range. A negative axis is termed left-axis deviation, whereas a positive axis is termed right-axis deviation. One specific range—referred to as the “northwest axis” or “indeterminate axis”—is sometimes colloquially called the “no-man’s-land” axis. The ECG system used in electrocardiography is based on the hexaxial reference system; however, its clinical significance is limited, primarily serving diagnostic purposes in ECG interpretation. Axis deviation is largely influenced by physiological factors.
The electrical axis—also known as the mean electrical axis—is the average direction (vector) of the heart’s electrical activity. It is one of the parameters assessed in electrocardiography (ECG), defined as the angle formed between the maximum resultant vector of depolarization and repolarization in the frontal plane and the horizontal axis. This includes the mean electrical axes of the P wave, PT segment, QRS complex, and T wave; however, clinically, only the QRS axis is routinely measured. So, what is the normal range for the QRS axis?
Normal Range of the QRS Axis
A QRS axis between –30° and +90° is considered normal. A negative value indicates left axis deviation, whereas a positive value indicates right axis deviation. One specific range—between –90° and –180°—is termed the “indeterminate” or “no-man’s land” axis. The ECG system used in electrocardiography is based on the hexaxial reference system; however, this system holds limited clinical significance, primarily serving diagnostic purposes in ECG interpretation. For instance, right ventricular enlargement commonly causes right axis deviation, reflecting clockwise rotation of the heart; conversely, left ventricular enlargement frequently results in left axis deviation, indicating counterclockwise rotation.
Axis deviation is largely influenced by physiological factors, yet it can also provide valuable diagnostic clues in certain clinical scenarios. For example, in the clinical diagnosis of mitral stenosis, the electrical axis should be normal (within the expected range). If left axis deviation is observed, concomitant mitral regurgitation or aortic valve disease should be considered. In atrial septal defect (ASD), the axis is typically deviated to the right; if left axis deviation occurs together with prolonged PR interval, it suggests primary (ostium primum-type) ASD. A leftward axis deviation of 45° is indicative of left anterior fascicular block.
The above outlines the normal range for the QRS axis. We hope this explanation proves helpful to you!
