An ICD is a minicomputer that is implanted under the skin of the upper chest area and is small enough to fit in the palm of your hand. It monitors your heart for fast and potentially dangerous heart rates and delivers therapy in the form of small electrical pulses when it senses a dangerously fast heart rhythm. While helping your heart maintain its rhythm, the ICD also stores information that your doctor can use to program the ICD for the best possible therapy.
Once implanted, the device detects your heart rhythm through one or more thin, flexible insulated wires called leads, which are placed on or inside the heart muscle and attached to the device. The leads transmit your heart rate information to the ICD. When an abnormal heart rhythm occurs, the ICD sends an electric shock to the heart muscle to defibrillate it—or to stop the cycle of rapid beats.
ICDs can provide lower- or higher-energy therapy to treat rhythm disorders, depending on the need. Sometimes the shock is uncomfortable and sometimes it is not. Many patients do not notice the defibrillating shock, while others say it feels like receiving a kick to the chest. Whether you can feel it or not, your ICD is doing its work to respond to a dangerous rhythm disorder.