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OVERVIEW — It is estimated that 200,000 to 400,000 people die suddenly every year in the United States; the majority die as a result of heart rhythm abnormalities (arrhythmias) known as ventricular tachycardia (VT) or ventricular fibrillation (VF). These heart rhythm disorders can be deadly because they arise from the ventricles, which are the lower pumping chambers of the heart. Heart rhythm disorders such as atrial fibrillation that arise from the upper chambers of the heart (the atria) are rarely life threatening.
Cardiac arrest, also known as sudden cardiac death, occurs when an abnormal and very rapid heart rhythm such as VT or VF prevents the heart from pumping normally to deliver blood to the brain and other vital organs. This is different from a heart attack, also known as a myocardial infarction, which occurs when a blood vessel is partially or completely blocked, preventing blood flow to the heart, causing heart muscle to die. Although a cardiac arrest is not the same as a heart attack, 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. The only treatment for a cardiac arrest is a shock to the heart, or defibrillation. When a person has a cardiac arrest outside of the hospital, a paramedic can use an external defibrillator, or a bystander can use an automatic external defibrillator (AED) to deliver a shock to the heart. Unfortunately, the likelihood of surviving an out of hospital cardiac arrest is less than 10 percent. For patients who are at an increased risk of having a cardiac arrest, a permanent implantable cardioverter-defibrillator (ICD), sometimes referred to simply as a defibrillator, can be implanted so that a shock can be quickly delivered if it is ever needed. An ICD is a battery-powered device that constantly monitors the heart rhythm and delivers a shock if the rate becomes very fast, and significantly improves the chances of survival in people at high risk for these arrhythmias. Having an ICD does not prevent the abnormal rhythm from occurring, but it rapidly detects and treats the abnormality, restoring a normal heart rhythm.
WHAT DOES AN ICD DO? — Modern ICDs are sophisticated devices that are able to perform two general functions: record the heart's activity and treat dangerous ventricular arrhythmias with a shock. Most defibrillators also work as a pacemaker, should marked slowing of heart rate occur, and can deliver antitachycardia pacing should VT occur to terminate it without delivering a shock. Some ICDs have multiple pacing leads to deliver cardiac resynchronization therapy (CRT) to treat heart failure. (See 'Pacemaker' below and 'Cardiac resynchronization' below.)
Treat ventricular arrhythmias — The primary purpose of an ICD is 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. Some patients require additional therapy to prevent arrhythmias from occurring, including catheter ablation procedures and antiarrhythmic medications. (See "Patient education: Catheter ablation for abnormal heartbeats (Beyond the Basics)".)
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. Most of the time, however, a shock for a dangerous arrhythmia is delivered after the patient has lost consciousness, and is therefore unable to feel the shock. It is important to understand that if you receive a shock from an implantable defibrillator, it will not cause harm to anyone else who might be touching you.
Anti-tachycardia pacing is an alternative method of stopping ventricular arrhythmias and is available in most ICDs. 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 200 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 200 to 220 beats per minute), or as a rescue therapy if anti-tachycardia pacing fails.
ICDs attempt to distinguish between different fast arrhythmias, such as atrial fibrillation and VT. This is important because atrial fibrillation causes a rapid heart rate, but is generally not life-threatening and rarely requires a shock. Unfortunately, however, patients can still receive inappropriate shocks from their ICD. (See "Patient education: Atrial fibrillation (Beyond the Basics)".)
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, or when the information is delivered during a remote home monitoring transmission, enabling the health care provider to monitor any underlying conditions causing abnormal heart rhythms. This allows the provider to properly treat the patient's heart rhythm disorders. The ICD does not record all of the heartbeats because that would drain the battery, but is programmed in a way to record certain types of episodes based on your medical condition.
Pacemaker — In addition to treating dangerous rapid arrhythmias, most modern ICDs also have the ability to function as a standard cardiac pacemaker and treat slow heart rhythms, also called bradycardias. However, standard pacemakers do not perform the key function of an ICD, which is to deliver a shock. (See "Patient education: Pacemakers (Beyond the Basics)".)
Combination therapy — As mentioned above, a health care 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 and catheter ablation procedures. However, antiarrhythmic drugs and procedures are not 100 percent effective in preventing VT, VF, and sudden death, so they are generally used together with an ICD. (See "Patient education: Catheter ablation for abnormal heartbeats (Beyond the Basics)".)
WHO SHOULD CONSIDER AN ICD? — In general, patients who are at a high risk of having a cardiac arrest 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, cardiomyopathy, congenital heart disease, and/or advanced heart failure).
People who have a combination of risk factors may be referred for additional tests, including an invasive 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 (picture 1) – 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) (figure 1). The longevity of the ICD is defined by the length of life of the battery (usually 6 to 12 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 entire ICD generator (but not usually the leads) must be replaced when the batteries are drained, as the batteries themselves cannot be replaced separately. The leads usually last for several years.
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 three leads will be placed inside the heart (figure 2). 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. A third lead is implanted when cardiac resynchronization therapy is planned. (See 'Cardiac resynchronization' below.)
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 clinician may trigger the heart to beat rapidly, and then use the ICD to deliver a shock to the heart and stop the rapid beating; this is usually done one to five times to make sure the ICD functions properly. The procedure takes about 30 to 90 minutes to complete. A chest x-ray is performed after the procedure to be sure the leads are in the proper position and that the lung has not been injured or collapsed during the procedure.
Patients usually 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 an electrocardiogram (ECG). CRT can relieve heart failure symptoms by synchronizing the contraction of the left ventricle so that the heart functions more efficiently. To deliver CRT, a third lead is placed into a vein behind the heart and positioned to pace the left ventricle.
The subcutaneous ICD — A newer type of ICD that is placed entirely under the skin is also available. The subcutaneous ICD (S-ICD) is placed with no leads inside the heart. The device itself is placed under the skin along the rib cage below the left axilla, or armpit, rather than in the standard location near the collarbone (picture 2). The lead that is connected to the device is tunneled under the skin along the left side of the sternum rather than inside the heart. The advantages of the S-ICD are that it is not associated with any of the immediate or long-term complications related to placing a lead into the heart through a blood vessel, such as perforation of the heart and collapse of the lung (immediate) or blood vessel narrowing (long-term). Additionally, if an infection occurs, the risk of an infection is lower since the infection will not go directly into the bloodstream or the heart itself. The disadvantages of the S-ICD include its large size and its inability to provide pacing for slow heart rates, cardiac resynchronization therapy, or anti-tachycardia pacing. The device appears safe and effective in all types of patients who need an ICD.
COMPLICATIONS — As with any therapy, complications can occur with the placement or use of an ICD. Before the ICD is placed, the cardiologist 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 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.
●Dislodgement of a defibrillator lead occurs in about 1 percent of patients, and is usually managed by repositioning the lead within the heart. Dislodgment of other leads, such as those implanted for a cardiac resynchronization therapy, can occur at higher rates.
●The risk of death from implantation of a defibrillator is less than 1 in 1000.
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. When a new lead is implanted, the old lead can either be abandoned or extracted.
●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 have been several ICD leads and devices that have been 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. Monitoring is needed to make sure the device continues to work correctly. In general, your team will evaluate the ICD’s battery life, recordings of arrhythmias, and settings. Monitoring occurs at clinic visits or from home.
●Monitoring in clinic is done with a "wand" that is placed over your device. A special computer receives this data and displays your device’s battery life, settings, and a description of any arrhythmias. This computer can also be used to make programming changes to your device. In this way, your device can be painlessly examined for important findings, and its settings can be changed.
●Monitoring from home can also be performed. Home monitoring requires you to use a bedside transmitter or mobile phone application to send data to your team. This type of monitoring only requires that you be near the bedside transmitter (usually nightly) or your phone and does not require you to use a "wand." Your team will help you obtain and operate the remote monitoring equipment or software. Once your remote system is working, your ICD will automatically send information to your team at scheduled intervals or if an arrhythmia occurs. In addition, you can have your remote monitor send ICD information whenever you want. For example, if you faint, you can ask your device to transmit information to your team ahead of schedule. Home monitoring is not a replacement for your healthcare team. If you believe you had an abnormal heart rhythm, shock, or device problem, you should contact the physician or nurse in the device clinic.
Battery life — Your ICD will need to be replaced before its lithium battery is completely out of power. Regular monitoring helps to determine the ideal time for replacement. The batteries in an ICD typically last 6 to 12 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 the existing leads.
After a shock is delivered — If a person experiences a shock from their ICD, they are advised to immediately notify their doctor. If a person experiences a shock after hours, they can call their provider’s office and ask for the provider on call. However, the patient should call 911 or go to the closest emergency room if they receive more than one shock, lose consciousness with the shock, or have other severe symptoms such as chest pain before or after the shock. Also, because most arrhythmias require only one shock to return the heart rhythm to normal, anyone who has frequent or clusters of shocks must be urgently evaluated, usually at 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.
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, although if the person did not pass out from the shock, many experts limit driving for only one to three months. Commercial drivers who have experienced an ICD shock may be prohibited from driving 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. The device manufacturers can provide additional resources related to sources of electromagnetic interference in the work environment.
Cellular phones — People with an ICD or pacemaker should know that items with strong magnetic fields (eg, a cellular phone with a magnet that can be used for wireless charging [iPhone 12, iPhone 13], magnetic accessories such as certain "smart watches") can affect the function of the device if they are nearby. Cell phones without strong magnets are unlikely to cause problems with pacemakers or defibrillators.
If you have an ICD or pacemaker, the safest strategy is to use your cell phone at the ear on the side opposite the cardiac device. When you are carrying your cell phone, keep it in a pocket or bag below your waist. If you’re not sure whether your phone or watch is likely to cause problems with your cardiac device, check with the manufacturer or your doctor.
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 unless there are no alternative imaging options. However, an MRI can safely be performed if absolutely needed when certain protocols are followed and patients are monitored closely. In addition, most modern ICDs that are currently being implanted have been designed to be MRI-compatible and pose very low risk. Extracorporeal shock wave lithotripsy, often performed as a treatment for kidney stones, and radiation therapy for cancer can interfere with an ICD, and the device should be reprogrammed for these procedures. 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 health care 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 health care 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 clinician. This is a painless procedure that can be achieved with the same specialized computer programmer that is used for routine checks.
WHERE TO GET MORE INFORMATION — Your health care provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/contents/table-of-contents/patient-information). Related topics for patients, as well as selected articles written for health care professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient education: Implantable cardioverter-defibrillators (The Basics)
Patient education: Pacemakers (The Basics)
Patient education: Wolff-Parkinson-White syndrome (The Basics)
Patient education: Cardiac resynchronization therapy (The Basics)
Patient education: Sudden cardiac arrest (The Basics)
Patient education: Ventricular fibrillation (The Basics)
Patient education: Hypertrophic cardiomyopathy in children (The Basics)
Patient education: Time to stop driving? (The Basics)
Patient education: Long QT syndrome (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient education: Atrial fibrillation (Beyond the Basics)
Patient education: Pacemakers (Beyond the Basics)
Patient education: High cholesterol and lipid treatment options (Beyond the Basics)
Patient education: Catheter ablation for abnormal heartbeats (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Cardiac implantable electronic device interactions with electromagnetic fields in the nonhospital environment
Implantable cardioverter-defibrillators: Overview of indications, components, and functions
Implantable cardioverter-defibrillators: Optimal programming
Cardiac implantable electronic devices: Long-term complications
Cardiac implantable electronic devices: Patient follow-up
Infections involving cardiac implantable electronic devices: Epidemiology, microbiology, clinical manifestations, and diagnosis
Ventricular arrhythmias: Overview in patients with heart failure and cardiomyopathy
Secondary prevention of sudden cardiac death in heart failure and cardiomyopathy
Primary prevention of sudden cardiac death in patients with cardiomyopathy and heart failure with reduced LVEF
Brugada syndrome: Prognosis, management, and approach to screening
Cardiac implantable electronic devices: Periprocedural complications
The following organizations also provide reliable health information.
●National Library of Medicine
(medlineplus.gov/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
●Heart Rhythm Society
[1-4]
ACKNOWLEDGMENT — The author would like to thank Jessica Charron, NP, for her valuable input on this review.
