How it began
Willem Einthoven, a physiologist at Leiden University, worked from 1901 to 1905 on a galvanometer designed specifically to measure and record the electrical activity of the human heart. On March 22, 1905, patients at the Academic Hospital in Leiden were connected by telephone line to the instrument in his laboratory, about 1.5 kilometers away, and the first successful clinical recordings were made. Einthoven called these recordings telecardiograms.
Before it existed
The electrical activity of the heart had been recorded earlier with the Lippmann capillary electrometer, which Augustus Waller used on humans in 1887. The d'Arsonval and Thomson galvanometers were also available at the time. Einthoven set out to build an instrument designed specifically for the heart's electrical activity, and the IEEE milestone record treats his string galvanometer as the start of electrocardiography as a clinical tool.
How it works
A very thin quartz fiber coated with silver, the string, hangs in a strong magnetic field and carries the current picked up from the body. The field pushes the fiber sideways in proportion to the current. An optical system projected the shadow of the moving fiber onto a running sheet of film, which recorded the trace. The first machines were very bulky, weighed about 600 pounds and were complicated to operate.
How it spread
The instrument was manufactured by the Cambridge Scientific Instrument Company in England and by Max Edelmann in Germany, although the agreement with Edelmann ended after 1907. Einthoven remained an adviser to the Cambridge company until 1919. He labeled the successive waves of the recording P, Q, R, S and T and defined three leads using electrodes on the right arm, the left arm and the left foot, conventions that clinicians quickly adopted.
What lasted
In 1924 Einthoven received the Nobel Prize in Physiology or Medicine for his discovery of the mechanism of the electrocardiogram. Electrocardiographs in many later forms became an indispensable part of medical practice. The standard 12-lead electrocardiogram still includes the three Einthoven leads, and his letters for the waves remain in use. IEEE has marked the site in Leiden with a milestone for the string galvanometer.
