While pacemakers are used to tread a slow heart beat, ICD's are used to treat rapid heart rhythms. Some common rapid heart rhythms are: Ventricular Tachycardia (VT), Ventricular Fibrillation (VF), and Atrial Fibrillation (A Fib).
A defibrillator is one of three parts of a defibrillation system. (Defibrillator, leads, and a programmer). Two of these parts are placed inside the body. These two parts work together to recognize a rapid heart rhythm, deliver one or more therapies until a normal rhythm is reached, and it stores data about each episode.
When the defibrillator detects that the heart rhythm is too fast, it sends an electric impulse to your heart, which can return your heart to a normal rhythm.
Defibrillators deliver three types of therapies: pacing, cardioversion, and defibrillation:
Pacing: When your heart beats too fast, your device is programmed to send pacing pulses to moderate your rhythm to a normal rate. You usually will not feel these pulses.
Cardioversion: Cardioversion shocks are stronger electric pulses that feel more like a hit to the chest or a "thump." You may feel a little lightheaded or dizzy when this occurs.
Defibrillation: This is a heavy shock when your heart beat becomes unstable or irregular. When this happens, it may cause you to faint. Many people that have had this occur say it feels like a "kick in the chest." This is usually over quickly.