Implantable Cardioverter Defibrillators (ICDs) are pacemaker-like devices that continuously monitor the heart's rhythm, and deliver life-saving shocks if a dangerous heart rhythm is detected. If you have survived a heart attack that affected your heart's pumping ability, or have other problems with the heart's electrical system, your physician may refer you to an electrophysiologist to determine if you are at risk for sudden cardiac death (SCD). ICDs can significantly improve survival in certain groups of patients who are at high risk of ventricular fibrillation (VF), the heart rhythm disorder that causes SCD.   VF is a deadly heart rhythm disorder that is the primary cause of cardiac arrest, or sudden cardiac death (SCD). In VF, the electrical signals that coordinate the heart muscle become rapid and chaotic. The lower chambers of the heart, the ventricles, begin to quiver and can no longer pump blood to the brain, lungs and other parts of the body. Unless an immediate emergency shock is delivered to the heart, death occurs within minutes.

ICDs are 99 percent effective in preventing cardiac arrest.

  ICDs also have the ability to act as pacemakers for too-slow heart rates and can be modified to provide resynchronization therapy for people with heart failure.

How ICDs Work

The "pager sized" ICD contains a battery, a microprocessor and related circuits. It is connected to wires called "leads". The system is implanted in the chest, near the collarbone, where it automatically monitors the heart rate to detect and correct abnormal rhythms. The device can act as a pacemaker when it detects a too-slow heart beat (bradycardia). When a life-threatening arrhythmia is detected, the ICD delivers a controlled electrical shock through the leads to restore the heart's normal rhythm and prevent sudden cardiac death. Modern ICDs keep a record of the heart's activity when an abnormal heart rhythm occurs. With this information, the electrophysiologist can study the heart's activity and ask about other symptoms that may have occurred. Sometimes the ICD can be programmed to "pace" the heart to restore its natural rhythm and avoid the need for a shock from the ICD. Pacing signals from the ICD are not feel by the patient.

Implanting an ICD

The surgery to implant an ICD is similar to a pacemaker procedure. The wires, or leads, are positioned in the lower right chamber, or ventricle, of the heart and, when needed -- in the upper right chamber, or atrium. A space or "pocket" is formed under the skin near the patient's collarbone and the ICD is inserted and connected to the leads. Electrophysiology tests are performed while the patient is still asleep to be sure the device correctly monitors the heartbeat and delivers an appropriate shock when it detects a life-threatening rhythm.

During surgery to implant an ICD, electrophysiologists monitor the patient's heart while tests are done to make sure that the device is working properly, and will shock the heart's rhythm back to normal if a life-threatening rhythm disorder is detected.

Risks and Complications

All surgical procedures have some risks, depending on the nature of the patient's condition and his or her overall health. The likelihood of complications from ICD implantation is low - from 97 percent to 99 percent of all procedures are performed without any complications. Most complications that do occur will get better on their own, or can be treated without lasting effects, such as infection, bleeding and bruising. Sometimes, a second procedure is required to reposition the leads from the ICD.

Complications are rare with ICD surgery. Always discuss the possibility of complications with your doctor before surgery.

After ICD Surgery

Usually, patients can return home after one night in the hospital and resume normal activities within a few days, depending on the health of the individual. It is not unusual for ICD patients and their families to feel anxiety, fear, and depression. After all, an ICD is a reminder that the individual may experience a deadly heart rhythm that comes on without warning. It is important to learn all you can about your condition and how your ICD works before your surgery. Do not hesitate to ask questions about anything that concerns you before and after the procedure, and be sure to speak up if you don't understand the answers. Many healthcare centers have support groups, educational seminars and other meeting for patients with ICDs and their families or caregivers. Regular visits to your doctor and/or ICD clinic are an important part of your treatment. Modern ICD devices have an electronic memory that records the electrical patterns of the heart whenever an arrhythmia occurs. During your visits, the physician reviews this record and checks the battery of your ICD to be certain it has a normal amount of energy. Be sure to tell your doctor or other caregiver about any physical or mental symptoms, and discuss available treatments.

In 2001, the nation's Vice President, Richard Cheney, was tested by an electrophysiologist who determined he was at risk of cardiac arrest, and implanted an ICD.The ICD protects the Vice President from ventricular fibrillation, the deadly heart rhythm disorder that causes sudden cardiac death. More

Many Americans have both coronary artery disease (the primary cause of heart attack) and a heart rhythm disorder. They are at particular risk for sudden cardiac death and may be candidates for ICDs, even though they have no noticeable symptoms of an abnormal heart rhythm. Patients who have had a previous heart attack are advised to consult a cardiologist or electrophysiologist to see if they are potentially at high risk. If an individual has a reduction in heart pumping function (an abnormally low ejection fraction, or EF) and/ or a potentially deadly heart rhythm is detected, the person should be seen by an electrophysiologist. An electrophysiologist is a cardiologist who specializes in the electrical system of the heart and in diagnosing and treating heart rhythm disorders.

Who is a Candidate for an ICD?

Representatives of the North American Society of Pacing and Electrophysiology (NASPE) along with The American College of Cardiology and the American Heart Association have developed guidelines to help physicians and patients decide whether an ICD is the best treatment for an individual at risk for SCD. For example, it is agreed that ICD therapy will benefit:

Cardiac arrest, or sudden cardiac death (SCD) is NOT a heart attack, but a prior heart attack can put someone at risk.

Individuals who have suffered a prior cardiac arrest or who experience spontaneous, sustained episodes of a too-rapid heartbeat called ventricular tachycardia (VT) that is not self-correcting, especially if they also have episodes of unexplained fainting Certain patients with an ejection fraction of less than 35-40 percent and documented episodes of ventricular tachycardia that are self-correcting and cause no adverse symptoms.

 

More recently, the MADIT II trial found that people who have survived a myocardial infarction (heart attack) and who have an ejection fraction of 35 or below may benefit from ICDs, even if they have no known episodes of ventricular tachycardia or other dangerous heart rhythm disorders.

Are You a Heart Attack Survivor? There are 800,000 new heart attacks each year and 7 million heart attack survivors in the U.S. Implantable cardioverter defibrillators signivicantly reduce the risk of SCD in survivors who have a substantial decrease in heart function.

Ejection Fraction: the Number One Predictor of Risk Ejection fraction (EF) is the proportion, or fraction, of blood pumped out of your heart with each beat. A normal heart pumps out a little more than half the heart's volume of blood with each beat. A normal EF is 55 percent or higher.Your doctor can order tests to measure your EF, such as: An echocardiogram, or ECHO, is a simple and painless test in which soundwaves are used to create a moving picture of the heart and measure its pumping ability. A nuclear medicine test called radionuclide ventriculography (also called the "fast pass" technique or Multiple-Gated Acquisition Scanning - MUGA) also is used to measure EF. A small amount of dye is injected into a vein. A special camera is used to trace radioactive particles called isotopes in the dye. How quickly the isotopes are pumped out of the heart and travel through the body is a measure of EF, and of how well your heart is pumping. The isotopes quickly lose their radioactivity and are passed from the body without harm to the patient.

Clinical Trials: Scientific Studies Comparing ICDs with Other Treatments to Prevent Sudden Cardiac Death

Large clinical trials have shown that ICDs can decrease deaths by as much as 75 percent compared with conventional medical care. A number of clinical trials - some still in progress - have studied whether ICDs are more successful than drug treatments in preventing sudden cardiac death in certain groups of high risk patients.

In all trials for which results have been reported, the death rate was significantly lower in patients who received ICDs. The improvement in survival was so significant that some studies were stopped early so that all patients could have the option of receiving ICD therapy.

Primary Prevention Trials study individuals who are at high risk for the dangerous heart rhythm disorders that cause sudden cardiac death.

• Multicenter Automatic Defibrillator Implantation (MADIT) Trial. Patients in the study had coronary artery disease, an ejection fraction of less than 35 percent and documented episodes of ventricular tachycardia that were self-correcting and caused no adverse symptoms. The patients underwent electrophysiology study. If they had an inducible arrhythmia, they were divided into two groups: one received conventional drug therapy, and one received ICD therapy.

Results: The death rate from any cause among patients who did not have an ICD was as high as 39 percent, but much lower (16 percent) in the group of patients with ICDs.

• Multicenter Unsustained Tachycardia Trial (MUSTT). The study included more than 2,000 patients who had coronary artery disease (blocked blood vessels to the heart), an ejection fraction of 40 percent or less, and episodes of ventricular tachycardia - an abnormally rapid heartbeat - that stopped on their own and caused no adverse symptoms. Treatment decisions were based on whether sustained VT (VT that does not stop on its own) could be induced during an electrophysiology study.

Results: A significant reduction in the rate of sudden cardiac death (approximately 75 percent) was seen in patients with inducible VT who were treated with ICDs. No improvement in survival was seen in patients who took medications alone.  

• Multi-center Automatic Defibrillator Implantation Trial (MADIT II). MADIT II was a prospective, randomized, multi-center study that enrolled more than 1,200 patients in 71 centers in the United States and in five European centers. The trial studied whether ICDs improve survival when compared with drug therapy alone in heart attack survivors with moderate impairment (an ejection fraction of 35 or below) of the left ventricle, the heart's main pumping chamber.

Results: An independent review panel stopped the study in November 2001 when it was shown that ICDs reduced deaths by 30 percent compared to medications alone.   Secondary Prevention Trials study individuals who have had episodes of life-threatening arrhythmias that do not go away on their own, or who have survived cardiac arrest.

• Antiarrhythmics vs. Implantable Defibrillators (AVID) Trial. ICDs were compared with medications in patients with a history of documented life-threatening arrhythmias.

Results: Of more than 1,000 patients studied, nearly one-quarter who were taking anti-arrhythmic drugs died, compared with only 16 percent who had an ICD. Overall, The ICD group experienced a 39 percent reduction in deaths in the first year, with a 27 percent and 31 percent reduction in years two and three.

The benefit of ICDs in this group of patients was so significant that the AVID study was terminated early so that all patients would have the option of ICD therapy.

In two similar studies (the Canadian Implantable Defibrillator Study (CIDs) and the Cardiac Arrest Study Hamburg (CASH), ICD therapy significantly reduced sudden cardiac deaths compared with conventional drug therapy in patients who had survived a prior episode of cardiac arrest.