An electrocardiogram (ECG) is a noninvasive test used in the examination of heart disease. Abbreviated from the German Elektrokardiogramm (EKG), this test records the electrical activity of the heart in the form of a continuous strip graph.
In the 19th century, it was discovered that the human heart generated electricity. British physiologist, Augustus Waller of St Mary's Hospital in Paddington (London), was the first man to systematically approach the heart from an electrical viewpoint. In 1887, he published the first human electrocardiogram, which was recorded with a capillary electrometer from Thomas Goswell.
The breakthrough came in 1893 when Willem Einthoven of Leiden (The Netherlands) introduced the term ‘electrocardiogram’ at a conference of the Dutch Medical Association. In 1901, Einthoven invented a galvanometer for creating electrocardiograms using a fine quartz string coated in silver. This new equipment was more responsive than the capillary electrometer that Waller used. In 1902, he prepared the first electrocardiogram recorded on a string galvanometer and assigned the letters P, Q, R, S and T to the various deflections. In 1924, Einthoven won the Nobel Prize for physiology for his discovery.
ECG is now one of the most important tools in cardiac electrophysiology. It measures the rate and promptness of heartbeats as well as the size and position of the chambers, the presence of any hurt to the heart, and the effects of drugs or devices used to regulate the heart, like a pacemaker.
To make an electrocardiogram, 10 ECG leads (electrodes) are attached to each extremity and to 6 pre-defined points on the neck, on the arm and legs, and over the heart, while the patient lies flat on a bed. The skin is coated with a small amount of gel that permits the electrical signals of the heart to be more easily transmitted to the leads. Velcro straps are small suction cups attached to the ECG leads. This painless test continues for about 5 minutes and the results are traced on graph paper.
During ECG tracing, it is essential to be relaxed and relatively warm, because any motion, including muscle tremors such as shivering, will change the recording. Other factors affecting ECG results are movement or faulty position of the leads, disproportion of electrolytes in blood (such as too much or too little calcium, potassium, magnesium or sodium), and low body temperature.
The major advantages of this test are that it is painless, noninvasive, safe, inexpensive, and easy to perform. Besides, the machines are readily available in most medical facilities. But, ECG does not produce an exact diagnosis for all time. It can often be normal or nearly normal despite a serious heart problem, including undiagnosed coronary artery disease, and this is known as false negative results.
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