14 June 2009

Electrocardiogram

The invention: Device for analyzing the electrical currents of the human heart. The people behind the invention: Willem Einthoven (1860-1927), a Dutch physiologist and winner of the 1924 Nobel Prize in Physiology or Medicine Augustus D. Waller (1856-1922), a German physician and researcher Sir Thomas Lewis (1881-1945), an English physiologist Horse Vibrations In the late 1800’s, there was substantial research interest in the electrical activity that took place in the human body. Researchers studied many organs and systems in the body, including the nerves, eyes, lungs, muscles, and heart. Because of a lack of available technology, this research was tedious and frequently inaccurate. Therefore, the development of the 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 him with the development of the first electrocardiogram. Waller used a Lippmann’s capillary electrometer (named for its inventor, the French physicist Gabriel- Jonas Lippmann) to determine the electrical charges in the heart and called his recording a “cardiograph.” The recording was made by placing a series of small tubes on the surface of the body. The tubes contained mercury and sulfuric acid. As an electrical current passed through the tubes, the mercury would expand and contract. The resulting images were projected onto photographic paper to produce the first cardiograph. Yet Waller had only limited sucess with the device and eventually abandoned it. 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. Teams of horses pulling heavy wagons would pass by and cause his laboratory to vibrate. This vibration affected the capillary tube, causing the cardiograph to be unclear. In his frustration, Einthoven began to modify his laboratory. He removed the floorboards and dug a hole some ten to fifteen feet deep. He lined the walls with large rocks to stabilize his instrument. When this failed to solve the problem, Einthoven, too, abandoned the Lippmann’s capillary tube. Yet Einthoven did not abandon the idea, and he began to experiment with other instruments. Electrocardiographs over the Phone 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 (named for its inventor, the French biophysicist Arsène d’Arsonval). 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). The movements could be recorded by transmitting the deflections through a microscope and projecting them on photographic film. Einthoven called the new instrument the “string galvanometer.” In developing his string galvanomter, Einthoven was influenced by the work of one of his teachers, Johannes Bosscha. In the 1850’s, Bosscha had published a study describing the technical complexities of measuring very small amounts of electricity. He proposed the idea that a galvanometer modified with a needle hanging from a silk thread would be more sensitive in measuring the tiny electric currents of the heart. 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, Einthoven was able to study in his laboratory electrocardiograms derived from patients in the hospital, which was located a 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: blocks in the electrical conduction system of the heart; premature beats of the heart, including two premature beats in a row; and enlargements of the various chambers of the heart. He was also able to study how the heart behaved during the administration of cardiac drugs.A major researcher who communicated with Einthoven about the electrocardiogram was Sir Thomas Lewis, who is credited with developing the electrocardiogram into a useful clinical tool. One of Lewis’s 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, which he used to test the soldiers’ ability to perform work. From this study, Lewis was able to use similar tests to diagnose heart disease and to screen recruits who had heart problems. Impact 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, the instrument, 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 Johns Hopkins University. As time passed, the use of the electrocardiogram—or “EKG,” as it is familiarly known—increased substantially. The major advantage of the EKG 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; in comparison with other diagnostic techniques, moreover, it is relatively inexpensive. Recent developments in the use of the EKG have been in the area of stress testing. Since many heart problems are more evident during exercise, when the heart is working harder, EKGs are often given to patients as they exercise, generally on a treadmill. The clinician gradually increases the intensity of work the patient is doing while monitoring the patient’s heart. The use of stress testing has helped to make the EKG an even more valuable diagnostic tool.