The basic law of ECG, specifically concerning the standard limb leads, is known as Einthoven's law.
Understanding Einthoven's Law
Einthoven's law describes the mathematical relationship between the voltages recorded by the three standard bipolar limb leads (Lead I, Lead II, and Lead III) in an electrocardiogram (ECG). It is based on the electrical principles governing closed circuits.
The Principle from Physics
According to the reference provided:
According to Kirchhoff's law, the sum of the voltage gains and voltage drops in a closed circuit is equal to zero.
This fundamental principle from physics, specifically Kirchhoff's voltage law, is applied to understand the relationship between the limb leads in Einthoven's triangle – an imaginary equilateral triangle formed by connecting the points representing the right arm, left arm, and left leg. The heart is considered to be at the center of this triangle.
The Relationship Between Leads
Applying Kirchhoff's law to the circuit formed by the limb leads, Einthoven's law states the following crucial relationship at any given instant in the cardiac cycle:
Lead II = Lead I + Lead III
This means that the electrical potential difference measured by Lead II (between the right arm and the left leg) is equal to the sum of the potential difference measured by Lead I (between the right arm and the left arm) and Lead III (between the left arm and the left leg).
Significance
This law is fundamental to understanding the standard 12-lead ECG and is used to:
- Verify the proper placement of electrodes for the standard limb leads.
- Detect potential errors or artifacts in the recording.
- Provide a foundational understanding of how electrical activity is measured from different perspectives on the body surface.
In essence, Einthoven's law provides a reliable mathematical check for the consistency of the electrical signals recorded by the standard limb leads based on established physics principles.
