Description
The heart has its own internal electrical system that controls the speed and rhythm of the heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the electrical signal causes the heart to contract and pump blood.
Electrical signals normally begin in a group of cells called the sinus node. As these signals spread from the top to the bottom of the heart, they coordinate the timing of heart cell activity. First, the two upper chambers of the heart, called atria, contract. This contraction squeezes blood into the lower chambers of the heart, which are called ventricles. The ventricles then contract and send blood to the rest of the body. The combined contraction of the atria and ventricles is a heartbeat.
A problem with any part of the 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 the heart rhythm. When the device detects an irregular rhythm in the ventricles, the ICD will use low-energy electrical pulses to restore a normal rhythm. If this doesn't restore normal heart rhythm, or if the 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.
The illustration compares 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 (ICD) is needed if a person is at risk for certain life-threatening ventricular arrhythmias, such as ventricles that beat too fast or that quiver. A person may be considered at high risk for a ventricular arrhythmia if he or she:
An ICD is often recommended for people who have survived sudden cardiac arrest.
A 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 the heart for a full 24- or 48-hour period. The person wears small patches called electrodes on his or her 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, the person performs usual daily activities and keeps a notebook, writing down any symptoms he or she experiences and the time they occur. The person then returns both the recorder and the notebook to the doctor to read the results. The doctor can see how the heart was beating at the time the person 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 the heart. An echocardiogram provides information about the size and shape of the heart and how well the 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, the doctor threads a catheter (a small, flexible tube) from a blood vessel in the arm or leg up to the heart. Through the catheter, the doctor gives certain medicines and electrically stimulates the heart to see how the 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 the heart is working harder and beating faster than when it's at rest. During stress testing, the person exercises (or is given medicine if they are unable to exercise) to make the heart work harder and beat faster while heart tests, such as an EKG or echocardiogram, are performed.
An implantable cardioverter defibrillator (ICD) has wires with electrodes on the ends that connect to one or more of the heart's chambers. These wires monitor the 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 the 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 the 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 the doctor fine-tune the programming of your ICD so it works better to correct irregular heartbeats.
Whether the person receives a single-chamber or dual-chamber ICD is based on that person's heart-pumping abilities, structural defects, and the type of irregular heartbeats he or she has experienced. Whichever type of ICD a person receives, it will be programmed to respond to the type of irregular heart rhythm that person is most likely to have.
Placing an implantable cardioverter defibrillator (ICD) requires minor surgery, which is usually done in a hospital. The person will be given medicine right before the surgery that will help him or her relax and may make the person fall asleep. The doctor will give the person a local anesthetic so he or she won't feel anything in the area where the doctor puts the ICD.
First,the doctor will thread the ICD wires through a vein to the correct location in the heart. An x-ray "movie" of the wires as they pass through the vein and into the heart will help the doctor place the wires. Once the wires are in place, the doctor will make a small cut into the skin of the 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 the skin.
Once in place, the doctor will test the ICD. The person will be given medicine to help him or her sleep during this testing so he or she will not feel any electrical pulses. Then the doctor will sew up the cut. The entire surgery takes a few hours.
Expect to stay in the hospital 1 to 2 days so the heartbeat can be monitored and the doctor can make sure the implantable cardioverter defibrillator (ICD) is working properly. The person may need to arrange for a ride home from the hospital.
For a few days to weeks after surgery, the person may have pain, swelling, or tenderness in the area where the ICD was placed. The pain is usually mild, and over-the-counter medicines can help relieve it. Consult with a doctor before taking any pain medicines. The doctor also may ask the person 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.
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:
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 the ICD won't work correctly. This will prevent the ICD from correcting irregular heart rhythms. If the ICD malfunctions, the doctor may be able to reprogram it. If that doesn't work, the ICD may need to be replaced.
The low-energy electrical pulses the implantable cardioverter defibrillator (ICD) gives off aren't painful. The person may not notice them,or may feel a fluttering in his or her 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. The doctor may prescribe medicine to lower the number of irregular heartbeats. This will reduce the number of high-energy pulses sent to the heart. Such medicines include amiodarone or sotalol and beta blockers.
A doctor may want the person to call his or her office or come in within 24 hours of getting a strong shock from the ICD. A person should see the doctor or go to an emergency room right away if he or she gets many strong pulses within a short time.
Once a person has an ICD, he or she has to avoid close or prolonged contact with electrical devices or devices that have strong magnetic fields. Devices that can interfere with an ICD include:
These devices can disrupt the electrical signaling of the ICD and stop it from working properly. A person may not be able to tell whether the ICD has been affected. How likely a device is to disrupt the ICD depends on how long the person is exposed to it and how close it is to the ICD.
To be on the safe side, some experts recommend not putting a cell phone or iPod in a shirt pocket over the ICD (if they are turned on). The person may want to hold the cell phone up to the ear that's opposite the site where the ICD was implanted. An iPod should be placed on the arm farthest from the ICD.
The person can still use household appliances, but avoid close and prolonged exposure, as it may interfere with the ICD.
The person can walk through security system metal detectors at a normal pace. Someone can check the person with a metal detector wand as long as it isn't held for too long over the ICD site. The person 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 the ICD. These procedures include:
Th eperson should notify all of the doctors, dentists, and medical technicians about his or her ICD. Yje person also should notify airport screeners. The doctor can providea card that states the type of implanted ICD.
Physical Activity
In most cases, having an ICD won't limit the person from taking part in sports and exercise, including strenuous activities. The person may need to avoid full-contact sports, such as football. Such contact could damage the ICD or shake loose the wires in the heart. Ask the doctor how much and what kinds of physical activity are safe.
Driving
An ICD will not prevent the person from driving. However, the doctor may ask the person not to drive until he or she has gone 6 months without fainting. Some people may still faint even with an ICD.
Followup
The doctor will want to check the ICD regularly. Over time, the ICD may stop working properly because:
To check the ICD, the doctor may ask the person 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. The doctor also may ask the person to have an EKG (electrocardiogram) to check for changes in the electrical activity of the heart.
Battery Replacement
ICD batteries last between 5 and 7 years. The 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 the ICD also may need to be replaced eventually.
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.