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What Are Implantable Cardioverter Defibrillators?

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

An implantable cardioverter-defibrillator (ICD) is a cardiac device that is used to prevent sudden death by sending an electrical shock to the heart in people with sustained ventricular tachycardia or fibrillation.1-4

It is a small battery-powered device designed to keep track of the heart’s rhythm and is capable of sending an electronic signal to the heart muscle if the rhythm becomes abnormal.1-2 The impulse sent to the heart helps to restore a normal beat in a regular rhythm.1-4 It is an effective tool to reduce the risk of sudden cardiac death (SCD) in the management of severe heart rhythm disorders.2

A healthy heart has its own natural pacemaker. If a change in the heart’s rhythm causes it to beat at a rate that is too fast (tachycardia) or too slow (bradycardia), or irregular (arrhythmia) - the ICD can send a signal to restore a more normal heartbeat.4

An ICD is prescribed for people who are at high risk of serious ventricular rhythm problems.1 It may be recommended if you have had a heart attack with SCD, SCD from ventricular arrhythmias, have Long QT or Brugada syndrome or other conditions, including heart failure.4 Because the ICD continuously monitors the heart rate, it can detect a change that may require a lifesaving signal to be sent to cardiovert the heart and return it to a proper rhythm.4

People with systolic heart failure are at increased risk of sudden cardiac death. Taking medications as prescribed can decrease this risk, but ICD therapy is recommended in patients who are on maximally tolerated guideline-directed medications who have an EF <35% to prevent SCD. They are not recommended in patients who do not have a life-expectancy of > 1 year due to their heart failure or another illness.

ICD insertion

Like a pacemaker, an ICD is commonly inserted through a surgical incision just below the collarbone. It is fitted into a pocket between the skin and the chest muscle.3 The cardiologist guides the attached electrodes (wires) through a vein to position them in the heart. The procedure generally takes 1 hour and is performed under local anesthesia.3

Following the procedure, there may be some limited pain, bruising, or discomfort which should resolve within a few days. There will be restrictions on activities and exercises for about 5 weeks. In order to ensure that the leads do not move after implant, you cannot lift your arm above your shoulder and should avoid lifting anything heavy or perform activities that would place a strain on or near the surgical site. Your healthcare team will give you instructions on what you can expect to feel from your ICD and any precautions you need to take so as not to experience disruptions to the functioning of the ICD.1

How does the ICD work?

Damage to the heart muscle or the natural pacemaker can disrupt the normal heartbeat. The battery-powered ICD can detect any irregularities in the heartbeat and deliver electrical impulses to the heart through the wires placed alongside the heart wall.3 The electrical signals can vary in strength depending on what is needed to correct the rate and rhythm of the heart.2-4

ICDs have a built-in pacemaker component which sends one kind of impulse when the heart beats too slowly. If it is beating too fast or chaotically, it can send a different signal, a defibrillation shock to stop the abnormal rhythm. Some people complain of an uncomfortable “thump” in the chest when the shock is delivered.3 The ICD collects and stores data about the timing and quantity of electrical shocks issued. It also tracks whether the corrected arrhythmia was successfully corrected and the battery status.3

What you need to know

An ICD needs to be periodically evaluated to see how well it is working. This can be done remotely through your telephone line, cellular service or wireless internet network. The information includes battery life, the condition of the leads, and the history of abnormal rhythms. The collected information can help your healthcare team to manage your plan of care.1

Always let your non-cardiac healthcare team know that you have an ICD. Some medical or dental procedures may require precautionary measures.1 An ICD has metal and an electrical impulse so you may set off a metal detector. Always let security know that you have an implanted cardiac device. Some restrictions may apply if you have an ICD. Potentially disruptive devices include those with strong magnetic fields. Magnets in some devices and machinery including those like MRIs used in medical testing which can inhibit pulse generators for ICDs and pacemakers. It is important to avoid close or prolonged contact.4

You should carry a medical ID card in your wallet. It lists important personal information including the type of device, manufacturer, make, model and serial number. It also lists the date of implantation and emergency contact information. This can be helpful in emergency situations. These ID cards are available in different forms including ones that can be downloaded for free from the internet.

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