top of page
What is a defibrillator?

An implantable cardioverter-defibrillator (AICD) is a small battery-powered device placed in your chest to monitor your heart rhythm and detect irregular heartbeats. An AICD can deliver electric shocks via one or more wires connected to your heart to fix an abnormal heart rhythm.

You might need an AICD if you have a dangerously fast heartbeat (ventricular tachycardia) or a chaotic heartbeat that keeps your heart from supplying enough blood to the rest of your body (ventricular fibrillation). Ventricles are the lower chambers of your heart.


AICD's detect and stop abnormal heartbeats (arrhythmias). The device continuously monitors your heartbeat and delivers electrical pulses to restore a normal heart rhythm when necessary. An AICD differs from a pacemaker — another implantable device used to help control abnormal heart rhythms.

Why it's done

You've likely seen TV shows in which hospital workers "shock" an unconscious person out of cardiac arrest with electrified paddles. An AICD does the same thing only internally and automatically when it detects an abnormal heart rhythm.

An AICD is surgically placed under your skin, usually below your left collarbone. One or more flexible, insulated wires (leads) run from the AICD through your veins to your heart.

Because the AICD constantly monitors for abnormal heart rhythms and instantly tries to correct them, it helps when your heart stops beating (cardiac arrest), even when you are far from the nearest hospital.

How an AICD works

When you have a rapid heartbeat, the wires from your heart to the device transmit signals to the AICD, which sends electrical pulses to regulate your heartbeat. Depending on the problem with your heartbeat, your AICD could be programmed for:

  • Low-energy pacing. You may feel nothing or a painless fluttering in your chest when your AICD responds to mild disruptions in your heartbeat.

  • A higher-energy shock. For more-serious heart rhythm problems, the AICD may deliver a higher-energy shock. This shock can be painful, possibly making you feel as if you've been kicked in the chest. The pain usually lasts only a second, and there shouldn't be discomfort after the shock ends.

Usually, only one shock is needed to restore a normal heartbeat. Sometimes, however, you might have two or more shocks during a 24-hour period.

Having three or more shocks in a short time period is known as an electrical or arrhythmia storm. If you have an electrical storm, you should seek emergency care to see if your AICD is working properly or if you have a problem that's making your heart beat abnormally.

If necessary, the AICD can be adjusted to reduce the number and frequency of shocks. You may need additional medications to make your heart beat regularly and decrease the chance of an AICD storm.

An AICD can also record the heart's activity and variations in rhythm. This information helps your doctor evaluate your heart rhythm problem and, if necessary, reprogram your AICD.

Who needs an AICD

You're a candidate for an AICD if you've had sustained ventricular tachycardia, survived a cardiac arrest or fainted from a ventricular arrhythmia. You might also benefit from an AICD if you have:

  • A history of coronary artery disease and heart attack that has weakened your heart.

  • A heart condition that involves abnormal heart muscle, such as enlarged or thickened heart muscle.

  • An inherited heart defect that makes your heart beat abnormally. These include long QT syndrome, which can cause ventricular fibrillation and death even in young people with no signs or symptoms of heart problems.

  • Other rare conditions that may affect your heart rhythm.


Risks associated with AICD implantation are uncommon but may include:

  • Infection at the implant site

  • Allergic reaction to the medications used during the procedure

  • Swelling, bleeding or bruising where your AICD was implanted

  • Damage to the vein where your AICD leads are placed

  • Bleeding around your heart, which can be life-threatening

  • Blood leaking through the heart valve where the AICD lead is placed

  • Collapsed lung (pneumothorax)

How you prepare

To determine whether you need an AICD, your doctor might perform a variety of diagnostic tests, which may include:

  • Electrocardiography (ECG). This noninvasive test uses sensor pads with wires attached (electrodes) placed on your body to measure your heart's electrical impulses. Your heart's beating pattern offers clues to the type of irregular heartbeat you have.

  • Echocardiography. This non-invasive test uses harmless sound waves that allow your doctor to see your heart without making an incision. During the procedure, a small instrument called a transducer is placed on your chest to collect reflected sound waves (echoes) from your heart and transmit them to a machine that uses the sound wave patterns to compose images of your beating heart on a monitor. These images show how well your heart is functioning and the size and thickness of your heart muscle.

  • Holter monitoring. Also known as an ambulatory electrocardiogram monitor, a Holter monitor records your heart rhythm for 24 hours or longer. Wires from electrodes on your chest go to a battery-operated recording device carried in your pocket or worn on a belt or shoulder strap.

    While wearing the monitor, you'll keep a diary of your activities and symptoms. Your doctor will compare the diary with the electrical recordings and try to figure out the cause of your symptoms.

  • Event recorder. Your doctor might ask you to wear a pager-sized device that records your heart activity for more than 24 hours. Unlike a Holter monitor, it doesn't operate continuously — you turn it on when you feel your heart is beating abnormally.

  • Electrophysiology study (EPS). Electrodes are guided through blood vessels to your heart and used to test the function of your heart's electrical system. This can identify whether you have or might develop heart rhythm problems.

What you can expect

During the procedure

Usually, the procedure to implant an AICD can be performed with numbing medication and a sedative that relaxes you but allows you to remain aware of your surroundings. In some cases, general anesthesia may be used so that you're unconscious for the procedure.

During surgery, one or more flexible, insulated wires (leads) are inserted into veins near your collarbone and guided, with the help of X-ray images, to your heart. The ends of the leads are secured to your heart, while the other ends are attached to the generator, which is usually implanted under the skin beneath your collarbone. The procedure usually takes a few hours.

Once the AICD is in place, your doctor will test it and program it for your heart rhythm problem. Testing the AICD might require speeding up your heart and then shocking it back into normal rhythm.


After the procedure

You'll usually be released on the day of your surgery, once the anesthesia has worn off. You'll need to arrange for a ride home because you won't be able to drive right away.

Because some defibrillators have leads placed through the veins into the heart, you'll need to avoid abrupt movements that raise your left arm above shoulder-height for two to three weeks. This is so the leads don't move until the area has had time to heal. That also means no driving during that time.

If you got a subcutaneous defibrillator, there are no leads placed through the veins, so there aren't any restrictions on driving or lifting your arm above your shoulder.

Treating pain after your procedure

After surgery, you may have some pain in the incision area, which can remain swollen and tender for a few days or weeks. Your doctor might prescribe pain medication.

As your pain lessens, you can take an over-the-counter pain reliever, such as paracetamol. Aspirin and ibuprofen aren't recommended because they may increase your risk of bleeding.

Unless your doctor instructs you to do so, don't take pain medication containing aspirin because it can increase the risk of bleeding.


AICDs have become standard treatment for anyone who has survived cardiac arrest, and they're increasingly used in people at high risk of sudden cardiac arrest. An AICD lowers your risk of sudden death from cardiac arrest more than medication alone.

Although the electrical shocks can be unsettling, they're a sign that the AICD is effectively treating your heart rhythm problem and protecting you from sudden death. Talk to your doctor about how to best care for your AICD.


After the procedure, you'll need to take some precautions to avoid injuries and make sure your AICD works properly.

Short-term precautions
Most short-term precautions involve being careful not to dislodge the leads or the device until healing has occurred.


  • You won’t be able to lift anything with the arm on the side of the AICD greater than 5kg for at least one month after your surgery.

  • For the first month of your recovery, avoid activities like vacuuming, moving the lawn, doing the laundry, pushing a trolley, hanging clothes on the line or reaching for items on the top shelf.

  • You won’t be able to drive until your doctor confirms it is safe.

  • Sex requires about the same amount of energy as walking up two flights of stairs, and you’re generally ready to ease back into this from around week 3 (it’s normal to lose interest in sexual activity for a while; however, like other activities, you should be back to normal at 3 months).

  • You can return to work related activities as soon as your concentration, confidence and physical abilities allow, and most people return to light office work  within 4 weeks and heavy work at 3 months

  • Most people with AICD’s can travel freely. When you’re travelling, have your Medical Device ID Card with you at all times.

Long-term precautions


Problems with your AICD due to electrical interference are rare. Still, take precautions with the following:

  • It's safe to talk on a mobile phone, but avoid placing your phone within about 15 centimeters of your AICD implantation site when the phone is turned on. Although unlikely, your AICD could mistake a mobile phone's signal for a heartbeat and slow your heartbeat, causing symptoms such as sudden fatigue.

  • Security systems. After surgery, you'll receive a card that says you have an AICD. Show your card to airport personnel because the AICD may set off airport security alarms.

    Also, hand-held metal detectors often contain a magnet that can interfere with your AICD. Limit scanning with a hand-held detector to less than 30 seconds over the site of your AICD or make a request for a manual search.

  • Medical equipment. Let doctors, medical technicians and dentists you see know you have an AICD. Some procedures, such as magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and radiofrequency or microwave ablation are not recommended if you have an AICD.

  • Power generators. Stand at least 0.6 meters from welding equipment, high-voltage transformers or motor-generator systems. If you work around such equipment, your doctor can arrange a test in your workplace to see if the equipment affects your AICD.

  • Headphones. Headphones may contain a magnetic substance that can interfere with your AICD. Keep your headphones at least about 15 centimeters from your AICD.

  • Magnets. These might affect your AICD, so it's a good idea to keep magnets at least 15 centimeters from your AICD site.


Devices that pose little or no risk to your AICD include microwave ovens, televisions and remote controls, AM/FM radios, toasters, electric blankets, electric shavers and electric drills, computers, scanners, printers, and GPS devices.

Driving restrictions

If you have an AICD to treat ventricular arrhythmia, driving a vehicle presents a challenge. The combination of arrhythmia and shocks from your AICD can cause fainting, which would be dangerous while you're driving.

Current guidelines discourage driving during the first six months after your procedure if your AICD was implanted due to a previous cardiac arrest or ventricular arrhythmia.

If you have no shocks during this period, you'll likely be able to drive again. But if you then have a shock, with or without fainting, tell your doctor and follow his or her recommendations. In most cases, you'll be discouraged from driving until you've been shock-free for another six months.

If you have an AICD but have no history of life-threatening arrhythmias, you can usually resume driving within a week after your procedure if you've had no shocks. 

You usually can't get a commercial driver's license if you have an AICD.

Battery life

The lithium battery in your AICD can last up to seven years. The battery will be checked during regular checkups, which should occur about every six months. When the battery is nearly out of power, your old shock generator is replaced with a new one during a minor outpatient procedure.

AICDs and end-of-life issues

If you have an AICD and become terminally ill, your AICD will still deliver shocks if it isn't deactivated. Turning off your AICD is an easy procedure, and doing so won't immediately cause your heart to stop. But turning off the device can prevent unwanted shocks and unnecessary suffering.

Talk to your doctor about your wishes. Also talk to family members or another person designated to make medical decisions for you about what you'd like to do in end-of-life care situations.

bottom of page