Drag the vector around the hexaxial circle and watch how the QRS changes in each limb lead.
+60°−30° to +90°
Normal axis
Most positive: II (+60°) · most isodiphasic: aVL, perpendicular to the axis.
Ranges
Normal axis−30° to +90°
Left axis deviation−30° to −90°
Right axis deviation+90° to +180°
Extreme axis deviation−90° to ±180°
How to read it
The QRS is most positive in the lead aligned with the axis and isodiphasic in the lead perpendicular to it. Find the isodiphasic lead, move to its perpendicular and pick the direction where the QRS is positive.
A tool to support learning and decision-making. The result does not replace clinical evaluation of the patient.
About: Electrical axis explorer
The QRS electrical axis is the mean direction of ventricular depolarization in the frontal plane. It is read on the hexaxial reference system, formed by the six limb leads.
In the explorer you rotate the axis vector and instantly see how the QRS looks in leads I, II, III, aVR, aVL and aVF: a visual way to understand why each lead is positive, negative or isodiphasic.
How to use
Drag the arrow around the hexaxial circle, or use the slider or the angle shortcuts.
With the keyboard, the arrow keys rotate the axis in 5-degree steps (1-degree steps with Shift).
Look at the most positive lead (aligned with the axis) and the most isodiphasic lead (perpendicular to it).
How to interpret
Normal axis: −30° to +90°.
Left axis deviation: −30° to −90°.
Right axis deviation: +90° to +180°.
Extreme axis deviation: −90° to ±180°.
Limitations
The tracings are a teaching model of the QRS for each angle, not patient ECGs. In real tracings, morphology also depends on conduction blocks, chamber enlargement and heart position.
References
Surawicz B, Childers R, Deal BJ, Gettes LS. AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram. Part III: intraventricular conduction disturbances. Circulation. 2009;119(10):e235–40.
