# Einthoven's triangle

Graphical representation of Einthoven's triangle

Einthoven's triangle is an imaginary formation of three limb leads in a triangle used in electrocardiography, formed by the two shoulders and the pubis.[1] The shape forms an inverted equilateral triangle with the heart at the center that produces zero potential when the voltages are summed. It is named after Willem Einthoven, who theorized its existence.[2]

Einthoven used these measuring points, by immersing the hands and foot in pails of salt water, as the contacts for his string galvanometer, the first practical ECG machine.[3]

• Lead I – This axis goes from shoulder to shoulder, with the negative electrode placed on the right shoulder and the positive electrode placed on the left shoulder. This results in a 0 degree angle of orientation. [4]
${\displaystyle I=LA-RA}$
• Lead II – This axis goes from the right arm to the left leg, with the negative electrode on the shoulder and the positive one on the leg. This results in a +60 degree angle of orientation. [4]
${\displaystyle II=LL-RA}$
• Lead III- This axis goes from the left shoulder (negative electrode) to the right or left leg (positive electrode). This results in a +120 degree angle of orientation. [4]
${\displaystyle III=LL-LA}$

Electrodes may be placed distally or proximally on the limb without affecting the recording.[5] The leg electrode acts as a grounding lead, and either the right or left leg can be used as a grounding lead without an effect on the ECG results.[6]

Each lead measures the electric field created by the heart during the depolarization and repolarization of myocytes. The electric field can be represented as a vector that changes continuously and can be measured by recording the voltage difference between electrodes.[7]