Modern defibrillators incorporate an a.c.-d.c. converter and a capacitor to store energy provided by the mains a.c. electricity or by battery ( Kerb.er...1..9.9.3). A transformer allows selection of voltage potentials. The energy is discharged as a high voltage d.c. shock via electrodes placed on the patient's chest. The electrodes may be in the form of hand-held paddles or large adhesive pre-gelled pads. ECG monitoring via the paddles or electrode leads is used with a manual pulse check to verify the diagnosis and result of defibrillation attempts.
Semi-automatic defibrillators interpret the ECG and advise the operator who activates the discharge button. Automatic external defibrillators interpret the cardiac rhythm before delivering a warning and shock without operator action. The automatic external defibrillator is effective, and their use by lay personnel is being encouraged to overcome the delays inherent in prehospital cardiac arrests. Surgically implanted cardioverter-defibrillators are used for high-risk patients as treatment for recurrent ventricular dysrhythmias. They incorporate a pulse generator inserted under the skin connected to a transvenous lead positioned endocardially. The cardioverter-defibrillator senses, paces, and defibrillates if necessary. Energies delivered range from 5 to 34 J.
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