Implanted defibrillators have become a multibillion dollar business for medical device makers following clinical trials showing that they could save thousands of lives annually among patients with weak or damaged hearts who are at heightened risk of sudden cardiac arrest. They consist of small battery-powered canisters implanted into muscle under the collarbone (usually on the right side for left-handed patients and the left for those who are right-handed), which are connected to the heart by insulated wires known as leads.
The leads are used both to sense when the heart is experiencing a rhythm that requires a shock and to deliver the shock. Defibrillator canisters need to be replaced when batteries are depleted -- currently every four to seven years -- but leads are left in place unless fractures or infections require them to be removed.
Many defibrillators are designed to be multi-purpose devices that can also deliver low-powered stimulation to pace slow-beating hearts or to help the four chambers of the heart contract in more synchronized rhythms.
External defibrillators, which deliver life-saving jolts through paddles applied to the chest, are standard equipment in ambulances and many other emergency response vehicles. In recent years, simpler models of such devices known as automated external defibrillators, or A.E.D.'s, have been placed on commercial aircraft, in offices and schools for public use by citizens who are trained to use them in courses offered by the Red Cross and other groups. In 2004, Philips Medical Systems introduced the first F.D.A. approved A.E.D. for sale to home users.
--Barnaby J. Feder, Dec. 14, 2007
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