What Is an Implantable Cardioverter-Defibrillator (ICD)?

When your heart rate is too fast for your heart to pump effectively, an implant-able cardioverter-defibrillator (ICD) may be recommended. An ICD is an implantable electronic device that continuously monitors or senses your heart rate. When your ICD senses an abnormal rhythm, it will deliver an electrical shock to your heart to try to stop the fast rhythm. Your physician can also program the ICD to "pace" your heart back to a normal rhythm when it is going too fast. All ICD's have back-up pacing for rhythms that arc too slow.

The implantable defibrillator includes a defibrillator includes a "pulse generator" and "lead(s)." The pulse generator, or battery pack, is approximately half the size of a deck of cards and is implanted beneath the skin of your left chest or abdomen. The pulse generator is connected to the lead system, which is connected to your heart. The leads are insulated flexible wires that can be placed in your heart.

The lead carries a signal from the heart muscle to the pulse generator when your heart beats. When an abnormal heart rhythm is sensed by the pulse generator, the lead will deliver a shock or pacing from the pulse generator back to your heart.

An implantable cardioverter defibrillator (ICD) looks very similar to a pacemaker, except that it is slightly larger. Some devices combine a pacemaker and ICD in one unit for persons who need both functions.

The ICD has another type of treatment for certain fast rhythms called anti-tachycardia pacing (ATP). When ATP is used, a fast pacing impulse is sent to correct the rhythm. After the shock is delivered, a "back-up" pacing mode is used if needed for a short while.

Other related procedures that may be used to assess the heart include: