ICD (Implantable Cardioverter Debrillators)

An ICD sends electrical pulses to the heart when rhythms get dangerously out of control, effectively halting racing beats and protecting against Sudden Cardiac Death.

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Almost everyone has seen a physician on television, paddles in hand, yelling “Clear!”, then applying those paddles to the chest of a patient to shock him “back to life”.

As dramatic as the scene may be, defibrillation, or shock, can be the only way to stop certain deadly heart arrhythmias before they kill.

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.

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).

Modern 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 by the 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.


Risk Factors

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 35-40 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.



In the simplest terms, anyone who has had or is at a high risk of having ventricular tachycardia, fibrillation or sudden cardiac arrest is a candidate for an ICD.

Many people have both coronary artery disease (the primary cause of heart attacks) and an arrhythmia (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.

A cardiac arrhythmia specialist should evaluate cardiac patients if they have experienced any of the following:
  • A prior cardiac arrest
  • Ventricular tachycardia (VT) which is an episode of rapid heartbeat originating from the lower chambers of the heart
  • Ventricular fibrillation (VF), which is similar to VT but is characterized by a heartbeat that is too rapid and is irregular or chaotic
  • Ejection fractions of less than 35 to 40 percent. An ejection fraction (EF) is the proportion, or fraction, of blood pumped by the heart with each beat. A normal heart pumps out a little more than half the heart’s volume of blood with each beat, making a normal EF 55 percent or higher
  • Patients at a high risk for sudden cardiac death (SCD) because of an inherited heart abnormality



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.


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