ECG Axis Calculator
The ECG Axis Calculator estimates the heart's electrical axis in degrees using the net amplitudes from Lead I and Lead aVF. This tool helps medical professionals and students quickly identify cardiac axis deviations to assess heart health. Whether you are diagnosing Left Axis Deviation, checking for Right Axis Deviation, or verifying lead placement, this tool provides fast, accurate results.
How Cardiac Electrical Axis Is Calculated
The cardiac electrical axis represents the average direction of the heart's electrical activity during ventricular depolarization. To find this angle, the calculator uses the trigonometric relationship between the vertical and horizontal vectors of the heart.
Axis Angle = arctan(Lead aVF / Lead I)
Where:
- Lead I: Net QRS amplitude (X-axis)
- Lead aVF: Net QRS amplitude (Y-axis)
First, measure the net QRS amplitude in Lead I, which acts as the horizontal component. Second, measure the net amplitude in Lead aVF to serve as the vertical component. These two values create a right triangle that points toward the dominant electrical force. Finally, the calculator uses the arctangent function to determine the precise angle based on these coordinates. This trigonometric method is the gold standard for vector analysis in electrocardiography.
What Your Cardiac Electrical Axis Means
The calculated angle reveals the general direction of electrical flow through the heart muscle. This helps you determine if the electrical conduction system is working normally or if a specific pathology is present.
Normal Axis (-30° to +90°): If your result falls in this range, the electrical current moves normally from the upper right to the lower left. This indicates healthy conduction in most adults, requiring no specific action regarding the axis.
Left Axis Deviation (-30° to -90°): Results in this range often suggest conditions like Left Anterior Fascicular Block (LAFB) or Left Ventricular Hypertrophy (LVH). You should investigate conduction issues or the patient's history of high blood pressure.
Right Axis Deviation (+90° to +180°): This shift may indicate Right Ventricular Hypertrophy (RVH) or chronic lung disease like COPD. Consider checking for pulmonary or structural heart problems.
Important
Extreme axis deviation (-90° to -180°) is rare and often indicates lead misplacement or a ventricular rhythm rather than a physiological axis.
Disclaimer: This tool is for educational and screening purposes only and is not a substitute for professional medical diagnosis. Always consult a qualified healthcare provider for interpretation and treatment.
To ensure accuracy, verify your measurements by checking that Lead I plus Lead III roughly equals Lead II before relying on the calculated angle.