Defibrillation

Ventricular fibrillation is a state of cardiac arrhythmia in which theindividual heart muscles contract in a random, uncoordinated way. The heartappears to shiver, and blood circulation ceases. Ventricular fibrillation isfatal unless an electric shock is applied within minutes to restore normal heart contraction. As early as 1899, French physiologists, Jean Louis Prevost and Frederic Battelli were able to stop ventricular fibrillation in a dog by applying an electric shock to the animal's exposed heart. In 1930, William B.Kouwenhoven, an American electrical engineer at Johns Hopkins University, developed with colleagues a closed-chest defibrillator that sent alternating current (AC) electrical shocks to the heart through electrodes placed on a dog'schest. In 1947, Claude Beck, professor of surgery at Case Western Reserve University, first successfully resuscitated a human patient by internal cardiacmassage and electrical defibrillation; American cardiologist Paul Zoll applied AC defibrillator to human patients in 1961; and the direct current (DC) defibrillator introduced by Lown and Neuman in 1962 provided greater reliability and safety.

Defibrillators greatly improved the ability of patients to survive heart surgery, invasive cardiac diagnostic and treatment techniques, and heart attacks,all of which can send the heart into ventricular fibrillation. Since the 1970s, most hospital emergency rooms have been equipped with electric defibrillators, and portable devices have become standard equipment for ambulances. Most recently, automated external defibrillators (AEDs), light-weight, portable,user-friendly devices about the size of a lunch box, can be found at sportsstadiums, hotels and casinos, in coast guard marine vehicles and police cars,and many other places where people gather. These devices can be used by operators with much less training than paramedics, and are intended for use by on-site personnel like fire fighters until paramedics arrive. Sometimes calledthe "smart" defibrillator, they provide audio instructions and visual promptsto walk the operator through the defibrillating process, as well as recording the sequences of events such as when the operator connected the analyzer and pushed the shock button.

An implantable device, called the automatic implantable cardioverter defibrillator (AICD) was invented by Mieczyslaw Mirowski of the Johns HopkinsUniversity Medical School to stop heart arrhythmias. Approved for use by theFood and Drug Administration in October 1985, Mirowski's AICD senses two kinds of abnormal heart rhythms--ventricular fibrillation and ventricular tachycardia--automatically sending an electric shock to the heart to correct the disturbance. As a defibrillator, the device jolts the heart out of ventricular fibrillation; as a cardioverter, it shocks the heart out of an abnormally fastheartbeat called ventricular tachycardia, restoring normal heart rate. Because the AICD requires a heftier power pack than the standard cardiac pacemaker, the battery pack for the AICD is separately implanted in the patient's abdomen. The lithium batteries can deliver 100 =150 shocks during their three-year lifetime. The AICD is a potential lifesaver for the 700,000 people in the United States who survive heart attacks each year and are therefore at risk for potentially fatal arrhythmias. The AICD is also routinely used for patients whose arrhythmias cannot be treated with medication or surgery.

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