pacemaker, artificial

pacemaker, artificial,

device used to stimulate a rhythmic heartbeat by means of electrical impulses. Implanted in the body when the heart's own electrical conduction system (natural pacemaker) does not function normally, the battery-powered device emits impulses that trigger heart-muscle contraction at a rate that is preset or is determined by demand. The device today may be as small as one inch (2.5 cm) in diameter and weigh as little as 0.5 oz. (14 gm). It is implanted, using local anesthetic, under a flap of skin in the chest or abdomen. One or more electrodes are threaded through a vein from the device to the right side of the heart. First developed in the 1960s, pacemakers originally sent one steady beat to the heart. Modern versions can monitor the heart and activate only when necessary; they are also less sensitive to outside sources of electromagnetic radiationelectromagnetic radiation,
energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an electric field.
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 than earlier versions. Most pacemakers run on lithium batteries, which need to be replaced about every 10 years. See also arrhythmiaarrhythmia
, disturbance in the rate or rhythm of the heartbeat. Various arrhythmias can be symptoms of serious heart disorders; however, they are usually of no medical significance except in the presence of additional symptoms.
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