Heart Care | Arrhythmia | Implantable Cardioverter Defibrillators

By Charles L. Witherell, clinical nurse specialist, UCSF Cardiac Electrophysiology Service

One form of treatment for a very fast heart rhythm is to surgically implant a device called an implantable cardioverter defibrillator (ICD), which is about the size of a deck of cards, connected to specially coated wires, or leads, in the body. Pioneered more than 20 years ago, these small devices have two parts, a "pulse generator" that makes the electric shock and "leads," the wires that carry the electric shock to the heart. These devices sense when the heart is beating too fast and deliver a brief jolt of energy directly to the heart to restore a normal heartbeat pattern.

Early models were considerably more bulky and required a much more extensive operation to implant. Today's ICDs are small. Although they are lightweight, they have many capabilities that the first models lacked, and their batteries give them a service period often longer than five years. These new models actually store electronic pictures of a patient's heart rhythm and any therapy given, allowing the doctor to retrieve this information in the office and refer to it when making decisions about further treatment. These newest ICDs are sometimes called "tiered therapy devices," because they can provide a whole series of treatments, prescribed by the doctor especially for an individual patient, ranging from the gentlest to a strong jolt depending on the heart rhythm problem. For example, each of these devices contains a pacemaker. Used to prevent a heart from beating too slowly, the built-in pacemaker can be activated by the doctor and remains constantly alert to the patient's heart rate, ready to do its job automatically whenever required. Pacing doesn't produce a sensation, and it is rare for people to be aware of it at all. By the way, pacemakers are often used all by themselves for patients with some rhythm problems.

When the problem is a heartbeat that is too rapid, the ICD also is ready. Its gentlest treatment for a fast rate is known as antitachycardia pacing, and may be prescribed if the electrophysiologist finds that it is effective for a patient's rhythm disturbance. In antitachycardia pacing, the ICD uses a special pacemaker contained within it to control the heart, rather than a shock. It is so gentle that patients are often unaware that it has been used. When choosing this method of treatment, the doctor always instructs the ICD to use a stronger therapy if antitachycardia pacing is not effective.

When useful, the doctor also can program the device to use low-energy shocks to restore the heart rhythm, instead of its most powerful shocks. Again, the doctor always instructs the ICD to become more aggressive if the problem doesn't respond to low-energy shocks. The doctor also can select maximum-energy shocks that provide the strongest therapy for a racing heart. When the ICD delivers this therapy, the patient knows it. People who have experienced it say that it feels exactly like what it is: a powerful shock. This important protection, always standing by and ready for use, gives patients and doctors alike a sense of assurance that help is immediately on call.

To learn more about ICDs, please see FAQ: Implantable Cardioverter Defibrillators.

This information is for educational purposes only and is not intended to replace the advice of your doctor or health care provider. We encourage you to discuss with your doctor any questions or concerns you may have.