Definition

Automatic implantable cardioverter defibrillators are surgically implanted to prevent sudden cardiac death from malignant ventricular tachyarrhythmias. These are self-contained diagnostic devices that continuously monitor the patient’s heart rate and electrocardiographic activity. They sense potentially lethal ventricular arrhythmias and treat them with electrical discharges. Whereas pacemakers use low-energy impulses measured in microjoules, these defibrillators release an electrical discharge of approximately 30 J after sensing periods of fibrillation lasting approximately 20 seconds. Most devices now can be programmed to reconfirm ventricular tachycardia or ventricular fibrillation after charging to prevent inappropriate shock therapy.