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. The shape forms an inverted equilateral triangle with the heart at the center. It is named after

Willem Einthoven Willem Einthoven (21 May 1860 – 29 September 1927) was a Dutch doctor and physiologist. He invented the first practical electrocardiograph (ECG or EKG) in 1895 and received the Nobel Prize in Physiology or Medicine in 1924 for it ("for the di ...

, who theorized its existence. Einthoven used these measuring points, by immersing the hands and foot in pails of salt water, as the contacts for his

string galvanometer A string galvanometer is a sensitive fast-responding measuring instrument that uses a single fine filament of wire suspended in a strong magnetic field to measure small currents. In use, a strong light source is used to illuminate the fine filament ...

, the first practical ECG machine.

Lead placements

* 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. :

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. :

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. :

III = LL - LA

Electrodes may be placed

distally Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

ly on the limb without affecting the recording. The right leg electrode acts to reduce interference, and can be placed anywhere without an effect on the ECG results. Each lead measures the electric field created by the heart during the

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is ess ...

and

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myocyte A muscle cell is also known as a myocyte when referring to either a cardiac muscle cell (cardiomyocyte), or a smooth muscle cell as these are both small cells. A skeletal muscle cell is long and threadlike with many nuclei and is called a muscl ...

s. The electric field can be represented as a vector that changes continuously and can be measured by recording the voltage difference between electrodes.

Using Einthoven's triangle to identify lead misplacements

Einthoven's triangle can be helpful in the identification in incorrect placement of leads. Incorrect placement of leads can lead to error in the recording, which can ultimately lead to misdiagnosis. If the arm electrodes are reversed, lead I changes polarity, causing lead II and lead III to switch. If the right arm electrode is reversed with the leg's electrode, lead II changes polarity, causing lead I to become lead III, and vice versa. Reversal of the left arm and leg causes a change in polarity of lead III and switching of leads I and II.

References

Cardiac electrophysiology Dutch inventions {{circulatory-stub