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In 1901, in a historic first, Willem Einthoven invented electrocardiography using a string galvanometer. He assigned the letters P, Q, R, S, and T to the major deflections and described electrocardiographic features of a number of cardiovascular disorders. Water pots that he initially used to record electrical signals from the skin were replaced with patchy electrodes later. These electrodes detect tiny electrical currents arising from the heart muscle during cardiac cycles. The tiny currents are amplified, filtered, and displayed to produce electrocardiographic recordings. The P wave is generated by depolarization of atria. The PR interval represents the duration of atrioventricular conduction, the QRS complex is produced by depolarization of both ventricles, and the ST-T wave reflects ventricular repolarization. Electrocardiography is essential to diagnose myocardial ischemia and various rhythm disorders. It has expanded its scope to include long-term monitoring, exercise tests, signal averaged electrocardiography, electrophysiologic studies, and three-dimensional electrocardiographic mapping system. Owing to these advances, electrocardiography now plays a critical role not only in diagnosis but also in the therapeutic fields of cardiac disease.
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