Implantable Cardioverter Defibrillator (ICD)

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Implantable Cardioverter Defibrillator (ICD)

A problem with any part of the heart’s electrical system can cause an arrhythmia. Most arrhythmias are harmless, but some can be serious. ICDs use electrical pulses or shocks to treat life-threatening arrhythmias that occur in the ventricles (the heart’s lower chambers). When ventricular arrhythmias occur, the heart can’t pump blood well. You can pass out within seconds and die within minutes if not treated. To prevent death, the arrhythmia must be treated right away with an electric shock to the heart. This treatment is called defibrillation.

During my career there has been many an occasion where I participated in the cardiac arrest and resuscitation of a patient, often having to apply the “paddles” as part of a team effort to shock a fibrillating (quivering) heart back to a more normal rhythm. Even in a hospital setting this effort often didn’t work. 

Sudden cardiac death is a very different event than the cardiac arrests I just described, and treatment of SCD survivors often very successful. As a surgeon I have been involved with the treatment of SCD from the early surgical ablations, to placing paddles on the outside of the heart, connected to a large and bulky generator that was implanted under the skin of the abdomen, complicated and often risky procedures as part of a team that included an EP specialized cardiologist. Nowadays this has evolved to the final ever smaller devices implanted under de skin on your chest, and capable of far more than just applying a shock.

Sudden cardiac death can be treated and reversed, but emergency action must take place almost immediately. Survival can be as high as 90 percent if treatment is initiated within the first minutes after SCD. The rate decreases by about 10 percent each minute longer. Those who survive have a good long-term outlook.

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What to do

If someone experiences sudden cardiac arrest:

  • Call 9-1-1 or 9-9-9/1-1-2 depending on the country (US, UK) should be dialed immediately
  • Begin to perform CPR . If performed properly, CPR can help save a life, as the procedure keeps blood and oxygen circulating through the body until emergency medical help arrives.
  • Early defibrillation. If a public access defibrillator — also called an AED (Ambulatory External Defibrillator) — is available, defibrillate. In adults, sudden cardiac death is usually related to ventricular fibrillation. Quick defibrillation (delivery of an electrical shock) is necessary to return the heart rhythm to a normal heartbeat. The shorter the time until defibrillation, the greater the chance the patient will survive. It is CPR plus defibrillation that rescues the person.
  • Once emergency personnel arrive, more traditional defibrillation and initiation of medications can be provided. This type of defibrillation is done through an electric shock given to the heart through paddles placed on the chest.
  • Advanced Care. After successful defibrillation, most patients require hospital care to treat and prevent future cardiac problems.

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Automatic external defibrillators (AEDs)

AEDs are defibrillators with computers that are able to recognize ventricular fibrillation (VF), advise the operator that a shock is needed, and deliver the shock. AEDs are designed to be used by a wide range of personnel such as fire department personnel, police officers, lifeguards, flight attendants, security guards, teachers, and even family members of high-risk persons. The goal is to provide access defibrillation when needed as quickly as possible. CPR along with AEDs can dramatically increase survival rates for sudden cardiac death.

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Learning CPR is the largest gift you can give your family and friends. CPR is easy for most adults and teens to learn. It is a technique designed to temporarily circulate oxygenated blood through the body of a person whose heart has stopped. It involves:

  1. Assessing the airway
  2. Breathing for the person
  3. Determining if the person is pulseless and applying pressure to the chest to circulate blood

The A-B-Cs of CPR:

A – airway

B – breathing

C – circulation
(chest compressions)

To learn more about CPR: call the national American Heart Association at 1-800-AHA-USA1, or
go to the American Heart Association Web site at

(From: Risk of sports: do we need a pre-participation screening for competitive and leisure athletes? Domenico Corrado et al, Eur Heart J. 2011 Jan 29)

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An implantable cardiac defibrillator (ICD) is a small device that is implanted in the chest to help correct irregular life threatening heart rhythms (ventricular tachycardia or ventricular fibrillation).  When the heart starts beating abnormally, the ICD delivers an electrical impulse to the heart to shock it back into a normal heart rhythm.  Patients with a weakened heart muscle (congestive heart failure) due to irregular pathways of caused by a heart attack, cardiomyopathy or high blood pressure are at risk for irregular heart rhythms.  Research studies have shown that patients with irregular heart rhythms (ventricular tachycardia, ventricular fibrillation) are less likely to die suddenly after they receive an ICD.  Many of these studies have included mostly men. 

A study published in 2009 found that women with heart failure did not seem to benefit from an ICD implant, as opposed to men who had a 22% lower risk of dying if they had an ICD. Women need to discuss their individual benefits and risks with their physicians to determine the most appropriate treatment.


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. Known as an implantable cardioverter defibrillator (ICD), it 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 electro physiologist, a cardiologist who specializes in arrhythmias, can study the heart’s activity and check for abnormalities 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 signals from the ICD are not felt by the patient; shock signals are, and have been described as a kick in the chest.

Cardiac arrest, or sudden cardiac death (SCD), happens when a heart rhythm disturbance prevents the heart from operating properly and delivering blood to the brain and other vital organs. A heart attack occurs when a partial or complete vessel blockage interferes with the ability of blood to flow to the heart, and heart muscle dies. Cardiac arrest, or sudden cardiac death (SCD), is NOT a heart attack, but a prior heart attack can put someone at risk for SCD.

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.

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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

 Sudden rapid heartbeats originating in the ventricles are the most dangerous arrhythmias. Ventricular tachycardia, a rapid yet steady beat is dangerous in its own right. It can turn into ventricular fibrillation or VF, which is characterized by irregular and chaotic rapid heartbeats. Because the fibrillating heart muscle cannot contract and pump blood to the brain and vital organs, VF is the number one cause of sudden cardiac death. Without immediate emergency treatment of an electric shock to restore normal rhythm, an individual loses consciousness within seconds and dies within minutes.

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