The implantable defibrillator is another device that is designed for electrical stimulation of the heart tissue. It is different from a pacemaker in that it is used to treat patients at risk of recurrent, sustained ventricular tachycardia (abnormally fast heartbeat) or fibrillation (ineffective "quivering" of the heart which can result in cardiac arrest). The defibrillation device is connected to leads positioned either inside your heart or on the heart surface. These leads sense the normal heart rhythm, detect abnormalities and deliver shocks to your heart as needed to return it to a normal rhythm. The internal device is connected to an implanted pulse generator at a separate site. Some models can also be used to supplement heart rate in the event of a slower than normal beat.
In years past, a relatively larger device was implanted during open chest surgery with electrode leads placed directly on the heart surface. The leads were then connected to a wallet-sized generator placed under the skin in the abdomen. About half of all patients who could have benefitted from the treatment were considered poor risks for such major surgery.
Today, a non-surgical approach has increased the number of patients who can be considered for implantation. This technique involves insertion of the electrode wires into the heart by passage through veins leading to the heart with an electrode patch placed just under the skin.