Willem Einthoven led the study of the electrical currents of the heart by inventing the string galvanometer, which evolved into the modern-day electrocardiogram.
In the late 1800’s, there was substantial research interest in the electrical events that took place in the human body. Scientists studied many organs and systems in the body, including the nerves, eyes, lungs, muscles, and heart. As a result of the lack of necessary technology, this research was very tedious, and the results were frequently inaccurate. Therefore, the development of appropriate instrumentation was as important as the research itself.
The initial work on the electrical activity of the heart (detected from the surface of the body) was conducted by Augustus D. Waller and published in 1887. Many credit Waller with the development of the first electrocardiogram. He used a Lippmann’s capillary electrometer to determine the electrical changes in the heart, recording the changes by placing a series of small tubes on the surface of the body. The tubes contained mercury and sulfuric acid, and as an electrical current passed through them, the mercury expanded and contracted. The images this process produced were projected onto photographic paper, creating the first cardiograph. Despite the contributions Waller made to science, he failed to use his device for any clinical applications. As a result, he did not pursue this area of study.
In the early 1890’s, Willem Einthoven, who became a good friend of Waller, began using the same type of capillary tube to study the electrical currents of the heart. Einthoven also had a difficult time working with the instrument. His laboratory was located in an old wooden building near a cobblestone street, and passing teams of horses pulling heavy wagons would cause his laboratory to vibrate. This vibration affected the capillary tube, causing the cardiographs to be unclear. In his frustration, Einthoven began to modify his laboratory. He removed the floorboards and dug a hole ten to fifteen feet deep. He then lined the walls of the hole with large rocks to stabilize his instrument. When this failed to solve the problem, Einthoven abandoned the Lippmann’s capillary tube, but he did not abandon the idea. Instead, he began to experiment with other instruments.
An early electrocardiographic device that required the patient to immerse both hands and one foot in a salt solution.
In order to continue his research on the electrical currents of the heart, Einthoven began to work with a new device, the d’Arsonval galvanometer. This instrument had a heavy coil of wire suspended between the poles of a horseshoe magnet. Changes in electrical activity would cause the coil to move; however, Einthoven found that the coil was too heavy to record the small electrical changes found in the heart. Therefore, he modified the instrument by replacing the coil with a silver-coated quartz thread (string). He found that he could record the movements by transmitting the deflections through a microscope and projecting them on photographic film. Einthoven called the new instrument the string galvanometer.
Einthoven’s development of the string galvanometer was very important for science. Some have questioned whether the invention was Einthoven’s original idea. In 1897, Clément Ader, a French electrical engineer, reported his development of a device similar to the string galvanometer. Ader was working with telegraph recorders, and he also found a need to replace the slow coil in the galvanometer with a lighter component: a wire. Both scientists needed to make their respective instruments more sensitive, and both chose to use a wire in place of the coil. Yet there were some fundamental differences between the two instruments. The major difference lay in the size of the wire. Ader used a wire that was ten times the diameter of Einthoven’s. It is believed that Ader’s instrument would not have been sensitive enough to detect the electrical currents in the heart. Although Ader developed the concept first, he was not given credit for developing the forerunner to the electrocardiogram because his instrument could not be used for studying the heart.
After developing the string galvanometer, Einthoven began work to validate the string galvanometer with the instrument accepted at the time: the capillary tube. Using both instruments on the same subjects, he made comparisons between the two outputs. He was able to identify the similarities in the wave changes between the two instruments. The waves on tracings from the capillary electrometer had been labeled A, B, C, and D. Einthoven labeled the waves on his galvanometer P, Q, R, S, and T. He changed the labels on the waves because, in geometry, points on curved lines begin with P and points on straight lines begin with A. As the output was obviously a curve, he chose to use a new system. Einthoven’s labels became universally known and continue to be used in electrocardiography.
By 1905, Einthoven had improved the string galvanometer to the point that he could begin using it for clinical studies. In 1906, he had his laboratory connected to the hospital in Leiden by a telephone wire. With this arrangement, he was able to study in his laboratory electrocardiograms that were derived from patients in the hospital located one mile away. With this source of subjects, Einthoven was able to use his galvanometer to study many heart problems. As a result of these studies, Einthoven identified the following heart problems with his galvanometer: blocks in the electrical conduction system of the heart, enlargements of the various chambers of the heart, and premature beats of the heart, including two premature beats in a row. He was also able to study the heart during the administration of cardiac drugs. These studies and studies conducted by other researchers with the string galvanometer added to the knowledge that has made the electrocardiogram an important diagnostic tool.
A major researcher who communicated with Einthoven about the electrocardiogram was Sir Thomas Lewis. Lewis is credited with developing the electrocardiogram into a useful clinical tool. One of his important accomplishments was his identification of atrial fibrillation, the overactive state of the upper chambers of the heart. During World War I, Lewis was involved with studying soldiers’ hearts. He designed a series of graded exercises that he used to test the soldiers’ ability to perform work. Based on the results of this study, he was able to use similar tests to diagnose heart disease and screen recruits who had some heart problems.
Throughout his career, Einthoven was influenced by one of his professors, Johannes Bosscha.
The electrocardiogram was not created in a short period of time. The work of many people over many years was required to produce a workable instrument, and additional years of study were then needed to determine the clinical significance of the instrument’s output. Although the forerunner to the electrocardiogram was first created in 1901, a reliable instrument was not used clinically for several years after that.
As Einthoven published additional studies on the string galvanometer in 1903, 1906, and 1908, greater interest in his instrument was generated around the world. In 1910, one of the instruments, now called the electrocardiograph, was installed in the United States. It was the foundation of a new laboratory for the study of heart disease at The Johns Hopkins University Hospital. The electrocardiograph was used to diagnose various types of heart problem that previously had been very difficult to diagnose.
In 1924, Einthoven visited the United States to discuss the electrocardiograph with researchers and clinicians. Among other lectures, he spoke at Harvard University as part of a lecture series founded in memory of Dr. Edward K. Dunham. During his visit to the United States, Einthoven was awarded the Nobel Prize in Physiology or Medicine.
Through the 1920’s, Einthoven’s instrument included four electrodes, one placed on each limb. One of the electrodes acted as a ground, and the other three could be combined in several ways to make three different leads. These three leads were used to diagnose many heart problems. In the 1930’s, researchers at the University of Michigan, led by Dr. Frank N. Wilson, developed a system that combined the same four electrodes into three new leads. They also added six new electrodes, which created six new leads to make a total of twelve leads. The addition of the nine leads to Einthoven’s three leads significantly improved the diagnostic capabilities of the instrument.
As time passed, the use of the electrocardiogram—or ECG, as it is now known—increased substantially. The major advantage of the ECG is that it can be used to diagnose problems in the heart without incisions or the use of needles. It is relatively painless for the patient. Also, in comparison with other diagnostic techniques, it is relatively inexpensive. Therefore, Einthoven’s invention has resulted in an important diagnostic tool that can be widely used.
Recent developments in the use of the ECG include work in the area of stress testing. Many heart problems are not apparent on the ECG while a patient is idle, so the ECG is used on a patient who is exercising, when the heart is working much harder. The clinician gradually increases the intensity of work the patient is doing (usually walking or running on a treadmill) while monitoring the patient’s heart with the ECG.
The electrocardiogram is a very important diagnostic tool. It is continually being improved, and researchers are constantly examining new applications. Although the electrocardiogram was initially developed at the beginning of the twentieth century, it is still an integral part of the fight against heart disease and other heart problems.
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Barold, S. S. “Willem Einthoven and the Birth of Clinical Electrocardiography a Hundred Years Ago.” Cardiac Electrophysiology Review 7 (January, 2003): 99-104. This article describes Einthoven’s work on the string galvanometer, from its initial development through its establishment as a useful diagnostic tool. -
Barron, S. L. “The Development of the Electrocardiogram in Great Britain.” British Medical Journal 1 (1950): 720-725. This article focuses on how the ECG was developed in Great Britain. The work of Sir Thomas Lewis is an important element in this account, which is directed at an audience with an appropriate science background. -
Burch, George E., and Nicholas P. De Pasquale. A History of Electrocardiography. Chicago: Year Book Medical Publishers, 1964. This book traces the history of the development of the electrocardiogram through the 1960’s. Discusses the work of the major contributors, including Einthoven. Includes a wealth of references. -
Cooper, James K. “Electrocardiography One Hundred Years Ago.” New England Journal of Medicine 315 (August, 1986): 461-464. This article, written in celebration of the one hundredth anniversary of the invention of electrocardiography, discusses the history of electrocardiography, beginning with the contributions of Waller and concluding with the works of Einthoven. Concise and understandable. Includes references. -
Einthoven, Willem. “The String Galvanometer and the Measurement of the Action Currents of the Heart.” Nobel lecture, December 11, 1925. http://nobel prize.org/medicine/laureates/1924/einthoven-lecture .pdf. This is the address that Einthoven gave on the occasion of his receiving the 1924 Nobel Prize in Physiology or Medicine. The Nobel Foundation makes this and other Nobel lectures available online. -
Ershler, Irving. “Willem Einthoven: The Man.” Archives of Internal Medicine 148 (February, 1988): 453-455. This article features the experiences of Dr. George E. Fahr during the years he worked with Einthoven, beginning in 1909. The author obtained much of the information from Fahr while they worked together from 1935 to 1938. Light, easy reading. -
Mehta, Nirav J., and Ijaz A. Khan. “Cardiology’s Ten Greatest Discoveries of the Twentieth Century.” Texas Heart Institute Journal 29, no. 3 (2002): 164-171. This article summarizes the ten cardiologic developments and discoveries of the twentieth century that the authors deem to be most important. Their list includes electrocardiography, preventive cardiology, coronary care units, coronary angioplasty, and open-heart surgery. -
Snellen, H. A. Two Pioneers of Electrocardiography: The Correspondence Between Einthoven and Lewis from 1908-1926. Rotterdam, the Netherlands: Donker Academic Publications, 1983. This book highlights the correspondence between two of the major researchers in electrocardiography. May be too technical for some lay readers.
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