Electrocardiogram

Most scientific breakthroughs are built upon the incremental discoveries of earlier researchers. The evolution of the method of recording and interpreting cardiac action is a classic example of this principle. In 1794, Aloysio Galvani, a professor of anatomy at the University of Bologna, was dissecting a frog’s leg when he observed a remarkable reaction. Working near an electrostatic machine, Galvani noticed that when his metal scalpel touched an exposed nerve, the frog’s leg contracted. He surmised that electricity was produced by living tissue when stimulated. Galvani’s experiments were confirmed with the discovery of the electromagnet in the early 1800s. Gabriel Lippman introduced a device called the capillary electrometer in 1872. With it, the electrical difference between two wires placed in an exposed living animal’s heart could be measured. Four years later, French physician Etienene-Jules Marey recorded the first permanent photographic record of the electrical activity of an animal’s heart using a modified capillary electrometer. Augustus Waller, a British physiologist, published the first human electrocardiogram in 1887. Since the chest could not be opened for direct recording, he created a pair of electrodes by soaking a pair of chamois in brine. He then strapped the electrodes to the front and back of a patient’s chest and recorded the electrical potential difference. In 1889, William Einthoven, a Dutch physiologist, witnessed Waller’s demonstrations. Motivated by what he had seen, Einthoven was inspired to improve upon Waller’s technique. With the invention of the string galvanometer in 1901, Einthoven made one of the most important contributions to electrocardiography of the 20th century and introduced the term electrocardiogram along the way. With the string galvanometer, electric current flowed from the heart to a thin silver-coated glass thread suspended between two magnets. The fluctuating shadow of the string was projected onto a photographic plate for a permanent record. This device enabled physicians to visually track the electrical function of the beating heart for easy analysis. The string galvanometer superseded the electrometer, which was sluggish and inaccurate, and it refined the clinical diagnosis of angina and myocardial infarction. The original string galvanometer weighed 600 pounds and required two rooms and five technicians to operate. During the next 100 years, engineers made significant improvements in the size and utility of Einthoven’s invention. In 1914, researchers built the first electrocardiogram machine in the United States at Columbia Physicians and Surgeons Hospital in New York City. By 1919, the Cambridge Company of London had developed a machine that weighed only 80 pounds. The electrocardiogram illustrated here was built by the Beck-Lee Company in 1936. It is an office model with a permanent internal string galvanometer; the film still had to be removed and developed to obtain a diagnosis. Shortly after World War II, Beck-Lee introduced a machine with a built in developing tank that produced a permanent electrocardiogram in 4 seconds. Because of the significant impact of his electrocardiograph machine, Einthoven received the Nobel Prize in Medicine in 1924.