A defibrillator is used to restore a normal heart rhythm by delivering an electrical shock to the heart when the heartbeat is dangerously fast due to ventricular tachycardia or ventricular fibrillation. Either of these conditions can be life-threatening, possibly causing the heart to abruptly cease pumping blood to the body (cardiac arrest), leading to sudden cardiac death.

At one point, defibrillators were used only by physicians in a hospital. However, recent technological advances have allowed people with minimal medical training to use automatic external defibrillators (AEDs) in an emergency when medical professionals are not present. Studies have shown that use of public access defibrillators (PADs) within moments of collapse significantly raises the survival rate from cardiac arrest and increases the likelihood of a meaningful recovery. Based  on these studies, the American Heart Association has endorsed the use of PADs. 

For patients suffering from chronic arrhythmias involving ventricular tachycardia or ventricular fibrillation, or certain patients at high risk of suffering from one of these conditions, there is a type of defibrillator that can be surgically implanted in a patient’s chest. This implantable cardioverter defibrillator (ICD) monitors for and, if necessary, corrects an abnormally fast or “quivering” heartbeat at the first sign of a problem.

A defibrillator is used to restore a normal heart rhythm by delivering an electrical shock to the heart when the heartbeat is dangerously fast due to ventricular tachycardia or ventricular fibrillation. Although few deaths are recorded as caused by ventricular fibrillation, it is the actual cause of death in most cases of coronary artery disease. Patients who have coronary artery disease or have suffered from a previous heart attack are more likely to go into cardiac arrest, a condition in which the heart stops pumping blood suddenly and circulation ceases. Cardiac arrest is also known as sudden cardiac death.

It is estimated that sudden cardiac death claims more than 330,000 people every year outside of hospitals. Other patients at high risk of arrhythmias requiring defibrillation include those with cardiomyopathy, long QT syndrome, arrhythmogenic right ventricular dysplasia and survivors of sudden cardiac death.

Defibrillation works by delivering a strong jolt of electricity to the heart. This is often enough to "restart" the heart's automatic pumping action, restoring blood flow to the body. Some defibrillators are external (e.g., defibrillator paddles in an emergency room), while some may be implanted in the patient’s chest (e.g., an implantable defibrillator). Although the devices range in size and appearance, their goal is the same: to convert an unhealthy cardiac rhythm to a more normal rhythm.

There are three basic types of defibrillators:

A manual defibrillator, or defibrillator paddles, are used by physicians to deliver high intensity electrical charges to patients in ventricular fibrillation or cardiac arrest, restoring normal heart rhythm and restarting the flow of blood. Many popular television programs demonstrate emergency personnel loudly stating, “Clear!” before using the defibrillator paddles. This is done because anyone touching the person about to receive the shock may receive a shock himself or herself.

Manual defibrillators are also used in non-emergency situations in a procedure called elective cardioversion. In this procedure, lower levels of electricity are used to restore normal heart patterns in patients with non-emergency arrhythmias (e.g., atrial fibrillation). Cardioversion is the term doctors use to describe the delivery of a shock that is carefully timed to the waveform of the heartbeat, usually under controlled circumstances. This contrasts with defibrillation, which can occur at any point in the cardiac cycle and is usually performed under emergency circumstances.

Automatic external defibrillators (AEDs) are external devices that can be used by minimally trained laypersons in emergency situations. They are designed to read the heart rhythm patterns of the patient, signal if defibrillation is necessary, then deliver the appropriate electrical shock.  This significantly reduces the amount of training needed for their effective use and allows people with minimal training to perform defibrillation in emergency situations with little risk of additional injury to the patient.

The operator needs to do only four things:

The AED reads the patient’s heart rhythms to determine if a “treatable rhythm” exists. At the moment of collapse, most rhythms are treatable – but this becomes less likely as more time passes. If the patient does not have a “treatable rhythm,” the AED will not discharge the electrical shock.

Both the AED and cardiopulmonary resuscitation (CPR) are techniques that can be used in emergencies when someone has gone into cardiac arrest – an often-fatal condition in which the person loses consciousness as a result of the heart abruptly ceasing to pump blood to the body. Although CPR is a vital life-sustaining tool, it cannot restore the heart rhythm of the patient – defibrillation can. Research has consistently demonstrated that early defibrillation greatly increases the survival rate of patients in cardiac arrest.

Automatic defibrillation attempts should begin as quickly as possible after the onset of cardiac arrest. With each minute that passes, the chance for survival or significant recovery decreases, which is why many healthcare professionals advocate the widespread availability and use of AEDs.

Indeed, AEDs have become more common in ambulances and fire rescue vehicles, as well as public places, such as stadiums, airports, shopping malls, health clubs and golf courses. All U.S. airlines are now required to carry AEDs on all domestic and international flights.

An implantable cardioverter defibrillator (ICD) is a device that is implanted in a patient’s chest and can be programmed to monitor for and, if necessary, correct an abnormal heart rhythm (arrhythmia). If the heartbeat gets too fast (ventricular tachycardia) the ICD will stimulate the heart to restore a normal rhythm (anti-tachycardia pacing). In potentially fatal cases where the heart no longer beats but merely “quivers” or fibrillates (ventricular fibrillation) the ICD can deliver an electric shock (defibrillation) to “reset” the heartbeat.

The ICD has an electronic memory that a physician can retrieve during follow up visits or even by telephone (transtelephonic monitoring). The memory stores information such as:

An ICD is similar in many respects to a pacemaker, which is another type of device that corrects an abnormal heart rhythm. However, pacemakers are usually chosen to correct a heart rhythm that is too slow (bradycardia), whereas ICDs are commonly used to detect and correct a heart rhythm that is too fast (ventricular tachycardia). Pacemakers cannot deliver the high energy electrical shock required for defibrillation. However, ICDs can be programmed to function as a pacemaker, and combination devices are available to detect and treat multiple heart rhythm problems in the same patient.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to defibrillation:

1. Am I at risk for ventricular tachycardia or ventricular fibrillation? What do these conditions feel like?
   
   
2. Should I learn how to use an AED?
   
   
3. Where can I learn how to use an AED?
   
   
4. Do I need an implantable cardioverter defibrillator?
   
   
5. Do arrhythmias run in families?
   
   
6. Besides defibrillation, if I'm at risk for an arrhythmia, should I be on medication?
   
   
7. Are there are any lifestyle changes I can make, such as diet or exercise, that will reduce my risk of suffering an arrhythmia?
   
   
8. How common are arrhythmias?
   
   
9. Does an ICD hurt when it discharges?
   
   
10. Is it dangerous to receive a shock from a defibrillator if I don't need it?