For those who are at high risk of the deadliest forms of arrhythmias – ventricular tachycardia and ventricular fibrillation – an internal “shocking” device may provide the best defense against sudden cardiac arrest. Such a device, known as an implantable cardioverter defibrillator (ICD), is considered effective in fighting cardiac arrest over 90 percent of the time, an astounding success for a condition that few survived as recently as 15 years ago.

Implantable cardioverter defibrillators (ICDs) are small devices, about the size of a pager, that are placed below the collarbone. Via wires, or leads, these devices continuously monitor the heart’s rhythm. If the heart beats too quickly, the ventricles will not have enough time to fill with blood and will not effectively pump blood to the rest of the body. Left unchecked, the rapid heartbeat could cause death. To intervene, the ICD issues a lifesaving jolt of electricity to restore the heart’s normal rhythm and prevent sudden cardiac death.

ICDs also can act as pacemakers when a heart beat that is too slow (bradycardia) is detected.

Most ICDs keep a record of the heart’s activity when an abnormal heart rhythm occurs. With this information, the electrophysiologist, nurse practitioner or electrophysiology nurse who is a specialist in arrhythmias, 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 impulse from the ICD are not felt by the patient; shocks are felt, and have been described as a kick in the chest.


Common Questions About ICDs


What is an ICD?

ICDs are pacemaker-like devices that continuously monitor the heart rhythm, and deliver life-saving shocks if a dangerous heart rhythm is detected. They can significantly improve survival in certain groups of patients with heart failure who are at high risk of ventricular fibrillation (VF).

ICD devices have an electronic memory that records the electrical patterns of the heart whenever an abnormal heart beat, or arrhythmia occurs. This record is available for review during regular checkups and home monitoring reviews by the nurse or physician, who can monitor the frequency and severity of problems in the heart’s electrical conduction system that may lead to cardiac arrest or other serious heart disorders.


Can an ICD Prevent a Heart Attack?

No! An ICD cannot prevent a heart attack, which is different from sudden cardiac arrest. A heart attack, or myocardial infarction (MI), is a “plumbing problem” caused by clogged or blocked blood vessels that reduce or block the normal supply of oxygen-rich blood to the heart. Without oxygen, heart muscle dies. An area of dead muscle is called an “infarct.” Although a heart attack and SCD are separate conditions, they are related. Often, the damage done by a prior heart attack is an underlying cause of SCD.

SCD is the result of an “electrical problem” in the conduction system that regulates the normal, rhythmic contractions of the heart muscle that pumps blood throughout the body. In SCD, the electrical signals that regulate the pumping action of the lower chambers of the heart (ventricles) suddenly and without warning become rapid and chaotic. When the rhythmic contractions of the ventricles stop, the heart can’t pump blood. The brain is starved of oxygen, and the individual loses consciousness in seconds. The heart cannot recover on its own from VF. Unless immediate emergency help is available, death follows in minutes.


How Does an ICD Differ from a Pacemaker?

Both an ICD and a pacemaker are devices that are implanted under the skin and connected to wires, or leads, that are placed in the heart. Both continuously monitor the heart to detect changes in its natural rhythm. A pacemaker, however, is used to detect a too-slow heart rate (bradycardia). When it senses that the rhythm is too slow, it sends an electrical signal to stimulate (pace) the heart so it continues its normal electrical beat. The electrical signal that is sent from the pacemaker is strong enough to stimulate the heart to beat, but not strong enough for the patient to feel. An ICD, on the other hand, detects a too-rapid or chaotic heartbeat and delivers a stronger electrical shock to restore the heart to its natural beat. ICDs also act as pacemakers.

How Can an ICD Help a Patient Who Has Suffered a Heart Attack?

The damage done by a heart attack, or MI, can affect the heart’s electrical system and its ability to pump blood effectively. The damaged heart muscle that results from a heart attack may give rise to abnormal electrical signals that sometimes cause deadly heart rhythms, which the ICD detects and corrects.

The most common underlying problem seen in victims of SCD is coronary artery disease. This is a condition in which the arteries that supply blood to the heart are narrowed or blocked, usually due to arteriosclerosis (sometimes called “hardening of the arteries”). In this disease, a fatty substance called “plaque” builds up in the blood vessels, and can affect the normal flow of blood to the heart and other parts of the body.


Can I use a microwave oven or other appliances if I have an ICD?

Yes, normal household appliances and wood working tools will not cause interference. You should avoid strong magnetic fields and large magnets, antennas, arc welders, and industrial equipment. If you work near industrial equipment, discuss your specific situation with your physician or nurse.

Can I use a cellular phone?

Yes, with these general guidelines:
  • Hold the phone to the ear on the side of the body opposite of the implanted device.
  • Do not carry the phone in the ON position in a breast pocket over or within 6 inches of the ICD.
  • Maintain a minimum of 6 inches between the ICD and the phone.

Are security systems and airports a problem?

Walk normally through theft detector systems. Carry your ID card with you at all times. Show the airport security people the card, and ask to be hand searched.

Can an ICD patient drive a car?

Many physicians recommend no driving for 6 months after implantation of an ICD, or after a shock. Commercial drivers may be restricted from driving. Discuss this issue with your physician to maintain your safety as well as that of others.

What do I do when I receive a shock?

If one shock occurs and recovery is immediate, a call to the device clinic may be reassuring for the patient as well as the family. However, if one or more than one shock occur without rapid recovery, 911 emergency services should be called. If CPR and other lifesaving activities are needed, they should be started immediately.

How does it feel?

Fast pacing therapy may feel like a flutter or palpitation in the chest, or nothing at all. The shocks may feel like a sudden painful kick in the chest. It occurs in an instant and then is gone. If a blackout occurs, the shock may not be felt. Someone touching the patient may feel a small muscle jerk. It will not harm them.

How and when is the battery replaced?

The battery check at each visit will determine when the ICD should be replaced. The electronic circuitry as well as the battery are sealed inside the ICD. When replacement time arrives the lead(s) will be tested and then a new ICD is attached to the lead(s). Usually the original lead(s) are reused.

How Effective Are ICDs?

Studies of ICDs show they are 99 percent effective in detecting and stopping deadly heart rhythm disorders. In clinical trials, ICDs have been shown to be the most successful therapy to prevent sudden cardiac death in certain groups of high-risk patients.

Who is a Candidate for an ICD?

The American College of Cardiology and the American Heart Association, along with representatives of the Heart Rhythm Society, 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 is of benefit for:
  • Secondary Prevention. This includes individuals who have suffered a prior cardiac arrest or who experience spontaneous, sustained episodes of ventricular tachycardia (VT) that is not self-correcting), especially if they also have episodes of unexplained fainting. VT is a too-rapid heartbeat that can lead to VF.
  • Primary Prevention. This is treatment for patients who have never experienced the deadly heart rhythm disorders that lead to SCD, but have significant risk factors for the conditions. This includes certain patients with an ejection fraction of less than 35 percent and documented episodes of VT that are self-correcting and cause no adverse symptoms, but in whom sustained VT can be induced during the electrophysiology study. Ejection fraction is a measure of the amount of blood pumped out of the heart with each beat. An ejection fraction below 55 is considered abnormal. Vice President Cheney’s ICD is for primary prevention