One form of treatment for a very fast heart rhythm is to surgically implant a device called an implantable cardioverter defibrillator (ICD), about the size of a deck of cards, connected to specially coated wires (leads) in the body. Pioneered more than twenty 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 pattern of beating.

Early models were considerably more bulky and required a much more extensive operation to implant. As you can see, today’s ICDs are small. Although they are light in weight, they have many capabilities which 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 use it for guidance in making decisions about further treatment. These newest ICDs are sometimes called "tiered therapy devices", because they can now provide a whole series of treatments, prescribed by the doctor especially for an individual patient, ranging from the gentlest to a strong jolt according to 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; it’s most uncommon 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 is also ready. Its gentlest treatment for a fast rate is known as antitachycardia pacing, and may be prescribed if the electrophysiologist finds that it’s 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 isn’t effective.

When he or she finds it a useful treatment for a particular patient, the physician can also 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.

Maximum-energy shocks are also available for the physician’s selection, and provide the strongest therapy for a racing heart. When the ICD delivers this therapy, the patient knows it! Below, you can see a picture of the defibrillator at work: at the left, notice that the heart is beating very rapidly. The arrow shows the point where the ICD intervened, delivering the doctor’s prescribed therapy, and to the right of the arrow you’ll notice that the heart rhythm has returned to normal. We hear from people who have experienced it 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. For more information about implantable cardioverter defibrillators, please click here.

Text by Charles L. Witherell, RN, CS, MSN Clinical Nurse Specialist, Cardiac Electrophysiology Service