The field of electrophysiology dates back to Italian physician Luigi Galvani, and scientists have known specifically about the heart's electrical activity since 1843, when another Italian doctor, Carlo Matteucci, first noted a cardiac current in a pigeon. The problem came in measuring and recording this faint electrical activity. The first person to accomplish this was British physiologist Augustus Desiré Waller in 1887. Waller used a Lippmann capillary electrometer, a device that featured a tube of mercury, a liquid that conducts electricity. When an electrical current generated from a patient's heart was applied to the tube, it changed the surface tension of the column of mercury, causing the meniscus to shift. This change could then be observed through a microscope and photographed. This measurement technique, though slow and imprecise, made a big impression on one witness at the demonstration — Willem Einthoven — who would soon invent the electrocardiograph.
First, Einthoven worked on clarifying Waller's results, which had registered four distinct points of electrical activity in the heart that he called A, B, C and D. Using a mathematical formula he developed, Einthoven corrected the margin of error inherent in the displacement curve of the mercury column and achieved a more sensitive reading revealing not four, but five points of electrical activity. Einthoven renamed these points P, Q, R, S and T, and they have proved remarkably accurate. They correspond to the electrical excitation of the heart's natural pacemaker (P), the combination of impulses involved in the relaxation of the atria and excitation of the ventricles (Q. R, S), and the relaxation of the ventricles (T). They are still used to describe the advanced readings taken today.
After improving the results that could be achieved with a capillary electrometer, Einthoven set about inventing a different type of machine to record the electrical activity of the heart, one that would be more accurate and less cumbersome to operate. He took a big step forward in 1901 when he invented the string galvanometer. This instrument consisted of a fine quartz string coated in silver that, when suspended in a magnetic field and hit with a beam of light, cast a shadow with its deflections and measured electrical activity more precisely than a capillary electrometer or even the traditional galvanometer. Two years later, by combining this invention with a rotating bicycle wheel (whose spokes interrupted the light at regular intervals to keep time) and a falling glass plate camera to record the galvanometer's deflections, Einthoven invented the first electrocardiograph. His prototype weighed 600 pounds, took five people to operate and required the patient to submerge his arms and legs in vats of conductive saline solution in order to acquire an electrical reading. But the image produced, called an electrokardiogramma in German (which accounts for our abbreviation of EKG), provided an unprecedented opportunity to evaluate the heart's pattern of activity and paved the way for the diagnosis of ailments linked to discrepancies in that pattern.
Many improvements followed. The development of electrodes soon eliminated the need for tubs of saline solution. Einthoven determined that placing a dozen electrodes on specific points of the arms, legs and chest yielded the best readings; his 12 lead standard is still in use today. In 1928, Frank Sanborn introduced a more practical table-top model of the EKG machine that weighed 50 pounds and was powered by a 6-volt automobile battery. In time, printers were able to deliver readings far more quickly than Einthoven's original camera. Today's computer-based models offer unparalleled precision and possibilities for storing and transmitting information.
Whether through the work of others or with his own electrocardiograph design, Einthoven’s steadfast pursuit of an accurate cardiac reading has allowed doctors to record and diagnose heart abnormalities and electrolyte imbalances that had been poorly understood. His calculations, observations and inventions have all weathered the scrutiny of time and have proved remarkably accurate, leading to effective treatments that have saved and enriched countless lives. For his work, Einthoven won the Nobel Prize for Physiology or Medicine in 1924.