In the late 1700s medical researchers learned that muscles produce tiny electric impulses now known as "action potentials." Italian biophysicist, Carlo Matteucci (1811-1868), identified action potentials in a pigeon's heart in 1843and, in 1856, German scientists Rudolf Albert von Kölliker (1817-1905)and Heinrich Müller (1820-1864) recorded these electric currents from afrog's heart. Reasoning that these recordings could reveal irregularities and, hence, heart disease, researchers attempted to develop accurate measuring devices. The French physiologist, Augustus Waller (1856-1922), found that cardiac currents could be recorded by placing surface electrodes on the body. In1887, Waller developed a capillary electrometer--tubes of mercury that rose and fell with the changes in heart muscle current--which, however, was imprecise and difficult to use. So Dutch physiologist Willem Einthoven set out to design an improved apparatus. In 1903 he described the result, his string galvanometer consisting of a thin, silver-coated quartz stretched between the poles of a As the heart's electric impulse flowed through, the wire was deflectedand motion was magnified and projected onto moving photographic film. The extreme sensitivity of the device, which weighed 600 lbs (272.4 kg), allowed itto detect the tiny cardiac currents very accurately. Einthoven called his machine the electrocardiograph and the recorded electrical impulses an electrocardiogram. He devised the standard positioning of the electrodes and described the regular heart waves and the triangle used to interpret electrocardiograms. Through clinical studies, Einthoven identified a number of heart problemswith his galvanometer. Einthoven won the Nobel Prize in 1924 for inventing the ECG. In 1942, Emanuel Goldberger added three augmented limb leads to Einthoven's three limb leads and the six chest leads making the 12-lead electrocardiogram that is used today, and English physician Sir Thomas Lewis (1881-1945) established the electrocardiogram as a standard clinical tool.

With refinements in instrumentation and technique, electrocardiography becameone of the most useful diagnostic tools in medicine. This highly accurate, easy to interpret, and relatively inexpensive device permits diagnosis of heart conditions without needle or incision and even portable devices are now available: the "HeartMirror," weighing only 3.3 lbs (1.5 kg) operates on four AANiCad batteries and will record 12 selectable leads. Housed in a carrying case, it is ideal for a physician's office. The "HeartVision" portable emergency device weighing only 13.4 oz (380 gr.) and using four AA batteries, fits into a pocket. Four built-in emergency electrodes eliminate contact leads--thedevice is simply placed on a patient's chest and displays the reading on a liquid crystal display (LCD). It also stores the reading, which can be printedout later on an analog ECG recorder or personal computer.

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