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implantable cardioverter defibrillator





ICD and pacemaker
Comparison of an implantable cardioverter defibrillator and a pacemaker. Figure A shows the location and general size of an implantable cardiac defibrillator in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest. Figure B shows the location and general size of a double-electrode pacemaker in the upper chest. The wires with electrodes on the ends are inserted into the heart through a vein in the upper chest.
An implantable cardioverter defibrillator (ICN) is a small device that automatically administers a form of CPR when a person's heart shows signs that it is about to stop.

An ICD is is placed in the chest or abdomen. It uses electrical pulses or shocks to help control life-threatening, irregular heartbeats, especially those that could lead the heart to suddenly stop beating (sudden cardiac arrest). If the heart stops beating, blood stops flowing to the brain and other vital organs. This usually causes death if it's not treated in minutes.


Overview

A problem with any part of the heart's electrical system process can cause irregular heartbeats called arrhythmias. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. Faulty electrical signaling in the heart causes arrhythmias.

ICDs use electrical pulses or shocks to treat life-threatening arrhythmias that occur in the ventricles (lower chambers of the heart).

When these ventricular arrhythmias occur, the heart can't effectively pump blood, and a person will pass out within seconds and die within minutes if not treated. To prevent death, the condition must be treated right away with an electric shock to the heart. This treatment is called defibrillation.

An ICD has wires with electrodes on the ends that connect to the chambers of your heart. The ICD will continually monitor your heart rhythm. When the device detects that you're having an irregular rhythm in your ventricles, the ICD will use low-energy electrical pulses to restore a normal rhythm. If this doesn't restore your normal heart rhythm, or if your ventricles start to quiver rather than contract strongly, the ICD will switch to high-energy electrical pulses for defibrillation.

Doctors also treat irregular heartbeats with another device called a pacemaker. An ICD is similar to a pacemaker, but there are some differences. Pacemakers can only give off low-energy electrical pulses. They are often used to treat less dangerous heart rhythms, such as those that occur in the upper chambers of your heart. Most new ICDs can act as both pacemakers and ICDs.





Who needs an implantable cardioverter defibrillator?

You may need an implantable cardioverter defibrillator (ICD) if you're at risk for certain life-threatening ventricular arrhythmias, such as ventricles that beat too fast or that quiver. For example, you may be considered at high risk for a ventricular arrhythmia if you:
  • Have had a ventricular arrhythmia before
  • Have had a heart attack that has damaged the electrical system in your ventricles
An ICD is often recommended for people who have survived sudden cardiac arrest.

Your doctor may recommend an ICD if he or she sees signs of a ventricular arrhythmia (or heart damage that would make one likely) on the following tests.


Electrocardiogram

This simple and painless test detects and records the electrical activity of the heart. An EKG (electrocardiogram) shows how fast the heart is beating and the heart's rhythm (steady or irregular). It also records the strength and timing of electrical signals as they pass through each part of the heart.


Holter monitor

A Holter monitor, also called an ambulatory EKG, records the electrical signals of your heart for a full 24- or 48-hour period. You wear small patches called electrodes on your chest that are connected by wires to a small, portable recorder. The recorder can be clipped to a belt, kept in a pocket, or hung around your neck.

During the 24 or 48 hours, you do your usual daily activities and keep a notebook, writing down any symptoms you have and the time they occur. You then return both the recorder and the notebook to your doctor to read the results. Your doctor can see how your heart was beating at the time you had symptoms.

The purpose of a Holter monitor is to record heart signals during typical daily activities and while sleeping, and to find heart problems that may occur for only a few minutes out of the day. Also, the Holter monitor can pick up irregular heartbeats that don't cause symptoms, but are important to treat.


Echocardiogram

This test uses sound waves to create a moving picture of your heart. An echocardiogram provides information about the size and shape of your heart and how well your heart chambers and valves are working. The test also can identify areas of poor blood flow to the heart, areas of heart muscle that aren't contracting normally, and injury to the heart muscle caused by poor blood flow.


Electrophysiology study

For an electrophysiology study, your doctor threads a catheter (a small, flexible tube) from a blood vessel in your arm or leg up to your heart. Through the catheter, your doctor gives you certain medicines and electrically stimulates your heart to see how your heart's electrical system responds. The electrical stimulation helps to find where the heart 's electrical system is damaged.


Stress test

Some heart problems are easier to diagnose when your heart is working harder and beating faster than when it's at rest. During stress testing, you exercise (or are given medicine if you are unable to exercise) to make your heart work harder and beat faster while heart tests, such as an EKG or echocardiogram, are performed.


How does an implantable cardioverter defibrillator work?

An implantable cardioverter defibrillator (ICD) has wires with electrodes on the ends that connect to one or more of your heart's chambers. These wires monitor your heart rhythm. They also deliver high- or low-energy electrical pulses to the heart when it beats abnormally.

Single-chamber ICDs have wires that connect to one or both of your ventricles. These ICDs correct faulty electrical signaling within the ventricles. Dual-chamber ICDs have wires that connect to both an upper heart chamber (atrium) and a ventricle. These ICDs correct faulty electrical signaling between the two chambers.

The wires on an ICD connect to a small metal box implanted in your chest or abdomen that contains a battery, pulse generator, and computer. The computer triggers the ICD's pulse generator to send electrical pulses when it detects irregular rhythms. Wires carry these pulses to the heart.

The ICD also can record the heart's electrical activity and heart rhythms. The recordings can help your doctor fine-tune the programming of your ICD so it works better to correct irregular heartbeats.

Whether you receive a single-chamber or dual-chamber ICD is based on your heart's pumping abilities, structural defects, and the type of irregular heartbeats you've had. Whichever type of ICD you receive, it will be programmed to respond to the type of irregular heart rhythm you're most likely to have.


What to expect during implantable cardioverter defibrillator surgery

Placing an implantable cardioverter defibrillator (ICD) requires minor surgery, which is usually done in a hospital. You will be given medicine right before the surgery that will help you relax and may make you fall asleep. Your doctor will give you a local anesthetic so you won't feel anything in the area where he or she puts the ICD.

First, your doctor will thread the ICD wires through a vein to the correct location in your heart. An X-ray "movie" of the wires as they pass through your vein and into your heart will help your doctor place the wires. Once the wires are in place, your doctor will make a small cut into the skin of your chest or abdomen. He or she will then slip the generator/battery box part of the ICD through the cut and place it just under your skin.

Once in place, your doctor will test your ICD. You will be given medicine to help you sleep during this testing so you don't feel any electrical pulses. Then your doctor will sew up the cut. The entire surgery takes a few hours.


What to expect after implantable cardioverter defibrillator surgery?

Expect to stay in the hospital 1 to 2 days so your heartbeat can be monitored and your doctor can make sure your implantable cardioverter defibrillator (ICD) is working properly. You may need to arrange for a ride home from the hospital. Check with your doctor about whether you can drive after the procedure.

For a few days to weeks after surgery, you may have pain, swelling, or tenderness in the area where your ICD was placed. The pain is usually mild, and over-the-counter medicines can help relieve it. Consult with your doctor before taking any pain medicines. Your doctor also may ask you to avoid any vigorous activities and heavy lifting for about a month. Most people return to normal activities within a few days of having ICD surgery.


What are the risks of having an implantable cardioverter defibrillator?

The most common problem with implantable cardioverter defibrillators (ICDs) is that they give pulses when they aren't needed. Pulses delivered too often or at the wrong time can damage the heart or trigger an irregular heartbeat. They also can be painful and emotionally upsetting. If this occurs, your doctor can reprogram the ICD or prescribe medicines so the pulses occur less often.

Although rare, some risks are linked to the ICD surgery, including:
  • Swelling, bruising, or infection in the area where the ICD was placed
  • Bleeding from the site where the ICD was placed
  • Blood vessel, heart, or nerve damage
  • A collapsed lung
  • A bad reaction to the medicine used to make you sleep during the surgery
People with an ICD may be at increased risk of developing heart failure. Heart failure is when your heart can't pump enough blood throughout the body. It's not known for sure whether an ICD increases the risk of heart failure or whether heart failure is just more common in people who need an ICD.

There also is the rare risk that your ICD won't work correctly. This will prevent your ICD from correcting irregular heart rhythms. If your ICD malfunctions, your doctor may be able to reprogram it. If that doesn't work, the ICD may need to be replaced.


How will an implantable cardioverter defibrillator affect my lifestyle?

The low-energy electrical pulses your implantable cardioverter defibrillator (ICD) gives off aren't painful. You may not notice them,or you may feel a fluttering in your chest.

The high-energy pulses your ICD gives last only a second and feel like a thumping or painful kick in the chest, depending on their strength. Your doctor may give you medicine to lower the number of irregular heartbeats you have. This will reduce the number of high-energy pulses sent to your heart. Such medicines include amiodarone or sotalol and beta blockers.

Your doctor may want you to call his or her office or come in within 24 hours of getting a strong shock from your ICD. See your doctor or go to an emergency room right away if you get many strong pulses within a short time.


Devices that can disrupt implantable cardioverter defibrillator functions

Once you have an ICD, you have to avoid close or prolonged contact with electrical devices or devices that have strong magnetic fields. Devices that can interfere with an ICD include:
  • Cell phones
  • iPods
  • Appliances, such as microwave ovens
  • High-tension wires
  • Metal detectors
  • Industrial welders
  • Electrical generators
These devices can disrupt the electrical signaling of your ICD and stop it from working properly. You may not be able to tell whether your ICD has been affected. How likely a device is to disrupt your ICD depends on how long you're exposed to it and how close it is to your ICD.

To be on the safe side, some experts recommend not putting your cell phone or iPod in a shirt pocket over your ICD (if they are turned on). You may want to hold your cell phone up to the ear that's opposite the site where your ICD was implanted. If you strap your iPod to your arm while listening to it, put it on the arm farthest from your ICD.

You can still use household appliances, but avoid close and prolonged exposure, as it may interfere with your ICD.

You can walk through security system metal detectors at your normal pace. Someone can check you with a metal detector wand as long as it isn't held for too long over your ICD site. You should avoid sitting or standing close to a security system metal detector.

Stay at least 2 feet away from industrial welders or electrical generators.

Some medical procedures also can disrupt your ICD. These procedures include:
  • Magnetic resonance imaging (also called MRI)
  • Shock-wave lithotripsy to get rid of kidney stones
  • Electrocauterization to stop bleeding during surgery
Let all of your doctors, dentists, and medical technicians know that you have an ICD. You also should notify airport screeners. Your doctor can give you a card that states what kind of ICD you have. Carry this card in your wallet.


Maintaining daily activities


Physical activity

In most cases, having an ICD won't limit you from taking part in sports and exercise, including strenuous activities. You may need to avoid full-contact sports, such as football. Such contact could damage your ICD or shake loose the wires in your heart. Ask your doctor how much and what kinds of physical activity are safe for you.


Driving

An ICD will not prevent you from driving. However, your doctor may ask you not to drive until you have gone 6 months without fainting. Some people may still faint even with an ICD.


Followup

Your doctor will want to check your ICD regularly. Over time, your ICD may stop working properly because:
  • Its wires get dislodged or broken
  • Its battery fails
  • Your heart disease progresses
  • Other devices have disrupted its electrical signaling
To check your ICD, your doctor may ask you to come in for an office visit several times a year. Some ICD functions can be checked remotely through a telephone call or a computer connection to the Internet. Your doctor also may ask you to have an EKG (electrocardiogram) to check for changes in the electrical activity of your heart.


Battery replacement

ICD batteries last between 5 and 7 years. Your doctor will replace the generator along with the battery before the battery begins to run down.

Replacing the generator/battery is less involved surgery than the original surgery to implant the ICD. The wires of your ICD also may need to be replaced eventually. Your doctor can tell you whether you need to replace your ICD or its wires.


What are the benefits of having an implantable cardioverter defibrillator?

An ICD is very effective in detecting and stopping certain deadly heart rhythms. An ICD can be more effective than drug therapy in preventing sudden cardiac arrest, depending on the cause of the arrest. Although an ICD can't cure heart disease, it can lower the risk of dying by up to 50 percent in some patients who have heart disease.


Related categories

   • HEART TOPICS
   • HEALTH AND DISEASE

Source: U.S. National Heart, Lung and Blood Institute