Electrocardiograph, instrument used to record the electric impulses generated by the heart with each heartbeat. The graph on which the impulses are recorded is called an electrocardiogram, a cardiogram, or simply an ECG or EKG. Sometimes the electrocardiogram may be displayed for examination on an oscilloscope.

The electrocardiogram is an important aid in diagnosing many heart diseases and has become a routine part of the clinical evaluation of patients for diagnosis and treatment of heart disease. It can alsa help diagnose some diseases that affect the heart, such as botulism, acute rheumatic fever, and Rocky Mountain spotted fever.
History. Electrocardiography dates back to 1787 when the Italian physiologist Luigi Galvani demonstrated that the muscles of the hind limbs of a frog generate electricity. However, it was not until 1843 that Emil Du Bois-Reymond, a physiologist at the University of Berlin, successfully recorded and measured the electricity produced by living tissue.

In 1856 the Swiss histologist Rudolf Albert von Kölliker and the German physiologist Johannes Müller first showed that electrical activity is associated with the heartbeat.

With these developments investigators began constructing instruments to measure the electricity that is generated with the heartbeat. Among these researchers were Du Bois-Reymond and the French physiologists Gabriel Lippmann and Etienne Jules Marey. In 1887 the English physiologist Augustus Waller, using a capillary electrometer, recorded for the first time the electrical impulses generated by the beating human heart. However, his instrument, as well as those developed by others, were too crude and insensitive to produce satisfactory recordings.

In 1900 the Dutch physiologist Willem Einthoven began developing a galvanometer that was sufficiently sensitive, rugged, sirnple, and reliable to record accurately the variations in electrical impulses associated with the human heartbeat. His electrocardiograph, which weighed more than 600 pounds (270 kg), was first described in a preliminary paper in 1901 and more completely described in 1903. For his development of this instrument Einthoven was awarded the 1924 Nobel Prize in physiology or medicine.

Einthoven’s electrocardiograph, witlı some simplifications and modifications, was soon manufactured in quantity and sent to different parts of the world. The first one to reach the Western Hemisphere was mauufactured in Germany and sent in 1909 to the United States. Later it was placed on display at the Tulane Medical School, New Orleans, La.

Modern Developments. As the electrocardiograph evolved, it became smaller and smaller. Today’s portable units may weigh less than 10 pounds (4.5 kg). Electronic amplifiers, telemetering devices, and special recording devices also have been developed. Although they differ in appearance from Einthoven’s apparatus, they are based on the same principles.

One of the most recent innovations in electrocardiography is the transmitting of electrocardiograms by telephone or radio to a cardiologist hundreds of miles away. Attempts are also being made to apply computers to the inteıpretation of electrocardiograms.

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