OVERVIEW

It is estimated that 200,000 to 400,000 people die suddenly in the United States; the majority die as a result of heart rhythm abnormalities known as ventricular tachycardia (VT) or ventricular fibrillation (VF). An implantable cardioverter-defibrillator (ICD) is a battery-powered device that significantly improves the chances of survival in people at high risk for these arrhythmias.

Cardiac arrest, also known as sudden cardiac death, occurs when an abnormal heart rhythm prevents the heart from working normally to deliver blood the brain and other vital organs. A heart attack occurs when a blood vessel is partially or completely blocked, preventing blood flow to the heart, causing heart muscle to die. Cardiac arrest is not the same as a heart attack, although a person can be at a higher risk for cardiac arrest during or after a heart attack.

These dangerous arrhythmias often occur without warning and can be fatal within minutes, making them difficult or impossible to treat with conventional methods. Having an ICD does not prevent the abnormal rhythm from occurring, but it rapidly detects and treats the abnormality, restoring a normal heart rhythm before the event becomes life-threatening.

WHAT DOES AN ICD DO?

Modern ICDs are sophisticated devices that are able to perform three general functions: treat dangerous ventricular arrhythmias, record the heart's activity, and work as a pacemaker. Older devices may not have all of these capacities.

Treat ventricular arrhythmias — The primary functions of an ICD are to treat potentially fatal ventricular arrhythmias (VT and VF). The ICD is highly effective in the treatment of these arrhythmias, and studies have demonstrated that people who have or who are at risk for these arrhythmias survive longer with an ICD. The ICD does not prevent arrhythmias from occurring, but the ICD can stop an arrhythmia that develops, often saving the patient's life.

The ICD treats an arrhythmia in one of three ways:

• Cardioversion
• Defibrillation
• Anti-tachycardia pacing

Cardioversion and defibrillation are both forms of high-energy shocks that stop dangerous arrhythmias and restore a normal heart rhythm. If the patient is conscious (awake) at the time of the shock, it is painful and usually described as feeling like a kick in the chest.

Anti-tachycardia pacing is an alternative method of stopping ventricular arrhythmias. It involves delivering a short series (eg, 5 to 10) of paced beats. This is not painful and may be unnoticed by the patient, although some patients may feel a brief burst of palpitations. Anti-tachycardia pacing can be very effective for some slower ventricular arrhythmias (eg, 150 to 180 beats per minute), and is often programmed as the initial therapy for these arrhythmias. High-energy shocks are often programmed as the initial therapy for very fast rhythms (eg, more than 180 to 200 beats per minute) or as a rescue therapy if anti-tachycardia pacing fails.

ICDs can usually distinguish between different arrhythmias, such as atrial fibrillation and VT. This is important because atrial fibrillation causes a rapid heart rate but does not always require a shock. (See "Patient information: Atrial fibrillation".)

Record the heart's activity — A record of the heart's activity is kept by the ICD. The record can be retrieved during an office visit, enabling the healthcare provider to monitor any underlying conditions causing abnormal heart rhythms. This allows the provider to make adjustments to ICD programming and recommend or change other treatment measures (eg, antiarrhythmic medications).

Pacemaker — In addition to treating dangerous rapid arrhythmias, all modern ICDs also have the ability to function as a standard cardiac pacemaker. However, pacemakers do not perform the functions of an ICD. (See "Patient information: Pacemakers".)

Combination therapy — A healthcare provider may recommend the use of an additional treatment for some people with ICDs, depending upon the frequency of the arrhythmia, the underlying cause, the type of device used, and other factors.

Additional therapies may include antiarrhythmic drugs, lipid lowering medications, and catheter ablation. However, antiarrhythmic drugs provide incomplete protection from VT, VF, and sudden death, and are never used alone; an ICD is the only available treatment option to stop VT/VF. (See "Patient information: High cholesterol treatment options" and "Patient information: Radiofrequency catheter ablation".)

WHO SHOULD CONSIDER AN ICD?

Specific recommendations have been established regarding the use of ICD therapy. The reasons for using an ICD have expanded as more groups of patients have been shown to benefit from ICD therapy. Categories of patients in whom an ICD is recommended include the following:

• Patients who have experienced one or more episodes of spontaneous, sustained VT or VF (if it is not due to a transient or reversible cause).
• Certain patients who have not had prior episodes of VT or VF, but are at high-risk for one of these arrhythmias. The estimated risk for these arrhythmias is based upon a combination of several risk factors (for example, prior heart attacks, severely reduced heart function, and/or advanced heart failure).

People who have a combination of risk factors may be referred for an additional test, called an electrophysiology study, to determine if an ICD is necessary.

PARTS OF AN ICD

An ICD is approximately the size of a pager. The main parts include:

• The ICD — The ICD is powered by a battery and generates an electrical shock. It is also called the battery, device, or pulse generator. It is a single unit that is usually inserted into a "pocket" created under the skin (or muscle) in the chest below the collarbone (in the pectoral region). The longevity of the ICD is defined by the length of life of the battery (usually three to five years).
• The leads — Flexible, insulated wires, or leads, monitor the electrical impulses and report the heart's electrical activity back to the ICD. These leads deliver electrical charges from the generator to the heart muscle when needed. During implantation, the ICD leads are passed through a vein into the heart.

The leads are connected to the ICD. When the ICD reaches the end of battery life and is replaced, the original leads are usually left in place and connected to the new device. The leads may last for 20 years or more.

PROCEDURE

In most cases, an ICD is inserted after the person is given a sedative and a local anesthetic (numbing medication) is injected into the skin. Some patients will be given general anesthesia, which is used to induce sleep while the procedure is performed.

The surgery involves making an incision below one of the collarbones. The leads will be placed into the heart through the vein that runs next to the collarbone. Up to two leads will be placed inside the heart (figure 1). One lead will be placed in the ventricle (bottom chamber) and one may be placed in the atrium (top chamber), on the right side of heart.

During the operation, routine electrical measurements of the heart will be made to be sure that the leads are positioned correctly. After the leads are in place, they are connected to the ICD. The device will be placed under the skin in the upper chest. The physician may trigger the heart to beat rapidly, then use the ICD to deliver a shock to the heart and stop the rapid beating; this is done two to five times to make sure the ICD functions properly. The procedure takes about 15 to 25 minutes to complete. A chest x-ray is performed after the procedure to be sure the leads are in the proper position.

Patients will usually need to stay in the hospital overnight. The first follow-up appointment to check the incision is usually one to two weeks after the surgery.

Cardiac resynchronization — An increasingly common therapy that

is being used in conjunction with ICD implantation is cardiac resynchronization therapy (CRT). This treatment may be recommended for certain people with advanced heart failure and a widened QRS interval on electrocardiogram. CRT can relieve heart failure symptoms by synchronizing the contraction of the left ventricle so that the heart functions more efficiently.

COMPLICATIONS

As with any therapy, complications can occur with the placement or use of an ICD. Before the ICD is placed, the surgeon will discuss the possible complications and specific risks.

Complications can be divided into those that can occur around the time of surgery, and those that can occur well after surgery. The following list describes the most common complications.

Surgical risks

• Collapse of the lung (pneumothorax) occurs in about 1 percent of cases and can usually be treated by inserting a chest tube.
• Perforation of the heart, causing a collection of blood to develop within the sac around the heart (pericardial effusion or tamponade). This occurs in less than 1 percent of cases and can usually be treated by placing a drain in the sac around the heart.
• Bleeding can occur under the skin around the defibrillator and can require drainage. The risk of this complication is higher for patients who take blood thinners (eg, warfarin/Coumadin or aspirin) or have a tendency to bleed easily.
• The risk of infection is about 1 percent. Because the defibrillator is a foreign material, the entire system must usually be removed if an infection occurs. Removal is relatively easy if the device was recently implanted. If an infection occurs several months or years after implantation, there can be significant risk of removal of the device because the leads can become scarred to the blood vessels and the heart.
• Lead movement occurs in about 1 percent of patients, and is usually managed by repositioning the lead within the heart.
• The risk of death from implantation of a modern defibrillator is less than 1 in 500.

Long-term risks

• Infection or erosion of the device. In most cases, the entire system must be removed.
• Lead failure. The leads are the weakest part of the ICD system, and the mechanical stresses on the leads can lead to breakage of the wires within the leads or in the insulation surrounding the leads.
• Inappropriate detection and subsequent delivery of a shock (see 'After a shock is delivered' below).
• Premature battery depletion or device failure. Although ICD systems are extremely reliable, they are like any other piece of electronic equipment and can occasionally fail without warning.

There has been an increase in the number of devices found to have significant problems after manufacturing and placement. In many cases, the problem is too rare to justify replacing every single device. However, in some cases, the device must be replaced. The primary risk of replacement is infection.

The decision to replace the device depends on many factors, including the type and likelihood of device failure, the risk to the individual patient if failure were to occur, the risk of replacement, and the patient's preference. Manufacturers, doctor groups, and the federal government are paying increased attention to surveillance of ICDs after implantation as a result of the numbers of device failures.

LIVING WITH AN ICD

Monitoring — People with ICDs require monitoring throughout their lifetime, generally every three to six months. The device can be painlessly examined with a programmer that is placed on the area of the chest where the ICD is located. ICD manufacturers have developed technology to allow patients to have this evaluation from their home using the internet or over the telephone. Information stored on the device can be reviewed to determine the remaining battery life, lead stability and function, programmed settings, assess pacing and shocks provided, and obtain data concerning the type of rhythm disturbances treated.

Monitoring of the battery life allows time for the device to be replaced before it stops functioning. The ICD is usually powered by lithium batteries, which last approximately three to five years. Replacing the ICD usually requires a simple procedure in which a repeat incision is made, the older ICD is removed, and a new ICD is implanted and joined with existing leads.

Modern ICDs are able to continuously record the electrical activity of heart muscle and record the date and time of each episode and store graphs from such events. This data helps the provider to monitor and diagnose underlying conditions responsible for arrhythmias and to make programming changes if needed.

After a shock is delivered — If a person experiences a shock from their ICD, they are advised to immediately notify their doctor. Also, because most arrhythmias require only one shock to return the heart rhythm to normal, anyone who has frequent or clusters of shocks is admitted to the hospital to investigate the cause. In some cases, programming and/or medications may need to be adjusted; less commonly, a malfunctioning lead may be detected.

Fear of the ICD — Many patients describe the shocks from an ICD as severe and painful; however, most patients are willing to tolerate them because they are lifesaving. Some people feel anxious or depressed because they fear ICD shock or device failure. Supportive therapies (eg, relaxation and cognitive behavioral therapies) and support groups may be helpful in reducing anxiety. (See "Patient information: Anxiety in adults".)

Driving restrictions — After placement of an ICD, or after the ICD administers a shock, many states require the person to stop driving for a period of time. Because VT and VF usually cause the person to pass out and lose control of the car if driving, it is important to follow your heart specialist's recommendation as well as the law. These laws are intended to protect the patient as well as others on the road.

Although the laws vary within the United States and other countries, most experts recommend the following:

• Driving is not recommended for one week after the ICD is implanted.
• Driving is not recommended for six months after an ICD administers a shock. Commercial drivers may be prohibited from driving after a shock for a lifetime.

Avoiding electromagnetic interference — Since reliable ICD functioning depends upon proper sensing of the electrical activity of the heart, it is important to avoid electromagnetic interference from external sources.

Telephones — It is unlikely that wireless communication devices, such as cellular telephones or wireless home telephones, will interfere with ICD functioning. However, it is recommended that patients not carry or place cellular phones within 15 centimeters (6 inches) of the ICD.

Household appliances — Manufacturers do not recommend any special precautions when using common household appliances, such as televisions, radios, toasters, microwave ovens, and electric blankets.

Security systems — Electromagnetic security systems can be located in the workplace, airports, courthouses, or other high-security areas. Exposure to this type of security system has been shown to cause interference in some cases. Interference may be related to the duration of exposure and/or the distance between the ICD and the security device.

Experts advise that people with ICDs be aware of the location of security systems, move through them at a normal pace, and avoid standing too close. In other words, "Don't linger, don't lean."

External electrical equipment — The use of ICDs in certain workplaces, such as near welding equipment or motor-generator systems, has not been shown to cause problems in the functioning of the ICD. However, because interference remains a concern, experts recommend that patients remain at least two feet from external electrical equipment, verify that the equipment is properly grounded, and wear insulated gloves when using electrical devices.

During medical tests or procedures — Although standard x-rays, computed tomography (CT) scans, and fluoroscopy do not interfere with the ICD, certain other procedures may interfere. This includes magnetic resonance imaging (MRI), which should be avoided completely. Extracorporeal shock wave lithotripsy, often performed as a treatment for kidney stones, can damage an ICD, and the device should be turned off during this procedure. ICD function may also be altered during transcutaneous muscle or nerve stimulation (TENS), sometimes used for pain management.

Thus, patients should inform all doctors, dentists, and other healthcare team members about their ICD to discuss the benefits, risks, and alternatives of any planned procedure. Patients should carry or wear a medical identification bracelet or necklace in case of an emergency situation in which the patient cannot speak.

Pregnancy — Women who have an ICD placed are generally able to become pregnant and carry the pregnancy to term without any increased risk of shocks or harm to the fetus. However, if the woman has underlying heart disease or other health problems, she should speak with her healthcare provider before becoming pregnant to discuss the risks, possible need to change medications, and plans for care during pregnancy.

End of life — If a person with an ICD is near death, either due to heart failure or another condition, he or she may choose to have the ICD turned off so that it does not deliver a shock. This decision should be discussed in advance, if possible, and should include the patient, family, and physician.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

This article will be updated as needed every four months on our web site (www.uptodate.com/patients).

Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient level information

Patient information: Atrial fibrillation
Patient information: Pacemakers
Patient information: High cholesterol treatment options
Patient information: Radiofrequency catheter ablation
Patient information: Anxiety in adults

Professional level information

Brugada syndrome and sudden cardiac arrest
Cardiac device interactions with electromagnetic fields
Driving restrictions in patients with an implantable cardioverter-defibrillator
General principles of the implantable cardioverter-defibrillator
Implantable cardioverter-defibrillators: Clinical trials of primary prevention of sudden cardiac death
Implantable cardioverter-defibrillators: Clinical trials of secondary prevention of sudden cardiac death
Implantable cardioverter-defibrillators: Complications
Implantable cardioverter-defibrillators: Patient follow-up
Infection of cardiac pacemakers and implantable cardioverter-defibrillators
Pacemaker and implantable cardioverter-defibrillator lead removal
Role of implantable cardioverter-defibrillators for the primary prevention of sudden cardiac death after myocardial infarction
Role of implantable cardioverter-defibrillators for the secondary prevention of sudden cardiac death
Ventricular arrhythmias in heart failure and cardiomyopathy

The following organizations also provide reliable health information.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/pacemakersandimplantabledefibrillators.html, available in Spanish)

• National Heart, Lung, and Blood Institute

      (www.nhlbi.nih.gov/health/dci/Diseases/icd/icd_whatis.html, available in Spanish)

• American Heart Association

      (www.americanheart.org/presenter.jhtml?identifier=11227)

• Heart Rhythm Society

      (www.hrsonline.org)

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ACKNOWLEDGMENT

We are saddened by the untimely death of Morton F Arnsdorf, MD, MACC, who passed away in June 2010. UpToDate wishes to acknowledge Dr. Arnsdorf's many contributions to cardiology, in particular, his work as our Editor-in-Chief and Section Editor for Cardiac Arrhythmias.