ICDs are small automatic devices that can detect and treat arrhythmias in patients with ventricular tachycardia and ventricular fibrillation where the heart beats dangerously fast. While antiarrhythmic drugs may prevent the occurrence of arrhythmias in some patients, ICDs are the only therapy that can terminate an existing arrhythmia once it has started with an internal electrical shock delivered when implanted sensors tell the device there has been an abnormal heart rate. Current ICDs are about the size of a pager and are implanted in the upper chest in a relatively simple surgical procedure that lasts about an hour.
An ICD responds to a fast or irregular heart rate with a range of programmed therapies that can be tailored to your condition. ICDs, like drugs, do not cure the underlying disease that causes an arrhythmia. Instead, the device terminates the arrhythmia and stores a record of the episode for a physician to evaluate later.