The implantable cardioverter defibrillator, or ICD, is an electronic device usually placed under the collarbone, preferably on the left side of the body to help patients who are at risk for life-threatening heart rhythms.
These rhythms include ventricular tachycardia, in which the ventricles, the heart's main pumping chambers, beat abnormally fast, and ventricular fibrillation,which is an electrically disorganized state resulting in a completely ineffective mechanical heartbeat and “cardiac arrest”.
Without the normal heartbeat being restored, death can result after 4 to 6 minutes of cardiac arrest.
In use for the treatment of life-threatening ventricular arrhythmias since 1980, an ICD consists of a generator and a lead, which connects the generator to the heart. Smaller than a pager, the generator is a smooth, lightweight titanium case containing a tiny computer and a battery. It tracks and records heart rhythms and sends electrical pulses and shocks to the heart when needed. It also records the pulses and shocks the defibrillation device has sent to the heart. It stores this information, which helps the physician determine if the defibrillator is working appropriately.
The lead that links the generator to the heart is placed through a vein into the heart. The lead helps the generator keep track of the heart rhythm and carries pulses and shocks from the generator to the heart. The device can also function like a standard pacemaker, pacing the heart if it ever beats too slowly, or to deliver a special pacing therapy called “biventricular pacing”, which is appropriate for certain heart failure patients.
In recent years, ICDs have become smaller and more sophisticated. The original generators were implanted in the abdominal wall, and required surgery to open the chest. Today, like pacemakers, ICDs can almost always be placed under the collarbone. The batteries usually lasts 3 to 7 years, after which the ICD generator is replaced.
How an ICD Works?
An ICD works in one or more of the following ways to help the heartbeat return to normal:
- Antitachycardia pacing: The defibrillator sends out a series of pulses to override a fast rhythm, which may feel like fluttering in the chest, or may not be felt at all.
- Defibrillation: If the defibrillator senses a very fast and irregular rhythm, it quickly sends a shock to the heart to override the fast rhythm. The shock typically feels like a strong kick to the chest.
- Bradycardia pacing: A defibrillator's main job is to slow a fast heart rhythm, but sometimes, the heart may beat too slowly, which is called bradycardia. The defibrillator may then provide pacing assistance to keep the heart rate from staying too low.
The ICD can be programmed in an electrophysiology lab or at the bedside using an external programming device. The physician can choose a heart rate cutoff, the point at which the device considers the heart rate abnormal, and program the types of therapies.
It is now generally accepted, based on clinical trials, that ICDs are superior to drugs for the treatment of patients who have survived a life-threatening arrhythmia, as well as for certain patients who are identified as being at very high risk of such arrhythmias. In particular, patients with heart failure caused by poor heart muscle function, whether or not they have had a prior heart attack, can be expected to live longer with an ICD implanted for protection against cardiac arrest.
ICDs are not perfect. For example, sometimes they deliver therapy for non-life-threatening arrhythmias or fast heart rates caused by exercise. In this situation the device may need to be reprogrammed. Also, sometimes patients feel the sensation of a shock when one has not occurred. These episodes, which are relatively common when drifting off to sleep, are called phantom shock episodes. They may be related to muscle contractions that occur as the person begins to fall asleep.
Before the Procedure
Patients are typically instructed not to eat or drink anything for approximately 6 to 12 hours before an ICD is implanted. The physician will advise the patient about whether or not daily medications should be taken the morning of the procedure. In most cases, anticoagulant medications, such as warfarin (Coumadin), are withheld a few days before the procedure to reduce the risk of bleeding during the implantation.
What to Expect
Placing an ICD is a minor surgical procedure performed by a cardiologist who has advanced training and experience in device implantation. Sedation, rather than general anesthesia, is usually used so the patient can sleep through the procedure.
The procedure generally takes place in an operating room or in a heart catheterization laboratory designed for electrophysiology procedures. The chest is cleansed with a special antibacterial soap. An intravenous (IV) line will be placed to provide fluids, the sedative, and an antibiotic. Sometimes another line, inserted in an artery, may be used to monitor blood pressure and the oxygen level in the blood during the procedure. The patient will also be connected to a number of machines, which will monitor heart rate and electrical activity. An X-ray tube is positioned over the chest to allow the physician to see the leads on the x ray screen as they are guided into the heart.
The physician will begin the procedure by making a small incision under the collarbone. The physician then creates a “pocket” under the skin or muscle into which the generator will be placed. The lead is placed into the vein (“subclavian vein”) than runs just under the collarbone, and then guided to the heart using X-ray imaging. All of the procedural work is done from this small incision. The lead tip attaches to the heart muscle, and the other end is attached to the generator. In some ICD systems two or even three leads are placed in the heart. The generator is programmed and then is placed under the skin in the “pocket”. The incision is then closed and covered with a sterile dressing. The procedure can take from 1 to 4 hours to complete. Patients are usually kept in the hospital overnight.
After the Procedure. Precautions and Care.
Depending on the procedure, the patient will remain in the hospital overnight or be discharged the same day. While in the hospital, the patient's heart will be monitored to make sure the defibrillator is working properly. The physician may order a chest x ray to check the patient's lungs and the position of the device and leads. In addition the patient may also have the ICD tested in an electrophysiology lab and have the programming customized, if necessary.
Before leaving the hospital, the patient will receive instructions about care at home. Pain medication may be prescribed, because pain and stiffness usually occur around the incision and last for a week or so.
The patient is also scheduled for a 15- to 20-minute checkup every 2 to 4 months. The ICD records every event or episode that occurs and what it did to treat the event. During the checkup visit, a programming machine will be placed over the ICD to see if the device has detected or treated any abnormal heart rhythms. The battery will also be checked at this time. Additionally, a home monitoring device may also be available to allow the patient to download information from their device. Some ICDs can be continuously monitored without requiring the patient to actively download. Home monitoring can be very useful to analyze what has happened when a patient thinks they have been shocked, without needing to leave the house.
The patient will also receive an information card that should be carried at all times. The card contains important information should the patient need medical care, including:
- The patient's name, address, and telephone number;
- The name and telephone number of the physician who prescribed the ICD;
- The type of defibrillator; and
- The date of implantation.
Once home, it is important to check the incision area every day and call the physician if there are any signs of infection. The patient should notify the physician immediately if any of the following occur:
- Drainage around the site
- Fever of more than 100 degrees Fahrenheit
- Tenderness, swelling, or redness at or around the incision
- Twitching chest muscles
- Increasing pain around the ICD
- Bleeding from the incision
- Arm swelling on the side of the incision site
The patient may experience numbness or fullness in the area where the ICD has been implanted, which is normal. One should not place any ointments on the incision site. The incision site should be kept clean and dry until instructed that it is safe to get it wet (usually 3-7 days after the procedure).
Patients can usually resume most daily activities, although they should avoid:
- Strenuous activities for a couple of weeks;
- Raising the arms above the head on the side of the body where the device is implanted for 2 to 6 weeks to prevent the defibrillator and leads from dislodging or shifting, according to what the physician has instructed; and
- Manipulating or playing with the ICD, even after fully healed.
It is usually recommended that people who have received an ICD not drive for a period of time after their procedure. The duration of this restriction is dependent on factors that are individual to each patient. Patients who have undergone defibrillator implantation should also refer to their state law regarding any driving restrictions. Restrictions are typically more stringent for commercial driving.
Should a patient feel symptoms of an arrhythmia, such as fluttering in the chest, lightheadedness, or dizziness, he or she will be advised to stay calm and find a place to sit or lie down. If possible, the patient should have someone stay with him or her. If a shock is needed, it will feel like a thump or a strong kick to the chest. It is safe to touch someone whose ICD has delivered a shock.
If the patient feels well enough after receiving the shock, it is not necessary to seek emergency medical attention; however, patients should call their doctor within 24 hours of ICD intervention. Patients should seek emergency medical attention if:
- Symptoms are still felt after the shock
- Symptoms recur after a short while
- Two or more shocks in a row are felt
- Symptoms do not go away but no shock is felt
The ICD may set off walk-through metal detectors in airports and stores, but they will not harm it. It is very important, however, that patients avoid contact with hand-held security wands, such as those used in airports, because they have magnets in them, which can disrupt the ICD. They can be avoided if the patient shows the card containing the ICD details to the security personnel.
Patients may also want to wear a medical alert identification bracelet or necklace, which identifies the heart problem and indicates that the patient has an ICD. Also, patients should know their rate cutoff, which is the heart rate at which the ICD begins treatment. Other physicians or emergency medical personnel may need this number.
Most household appliances and tools should not harm the ICD, including shielded microwave ovens, computers, hair dryers, power tools, radios, televisions, cordless telephones, electric blankets, and fax machines. Patients should avoid close contact with the following devices because they may have strong electrical or magnetic fields that can alter the ICD programmed settings:
- Large electrical transformers
- Welding equipment
- Auto ignition systems
- Large electrical generators
- Power plants
- Magnetic resonance imaging (MRI) machines
- Stereo speakers
- Antennas used in ham or CB radios
Cellular phones should be held to the ear farthest from the ICD. Patients should never carry cell phones in a breast pocket, even when the phones are turned off. In stores with an anti-theft device at the door, patients should simply walk through without lingering.
Batteries usually last 3 to 7 years, and the physician will know in advance when the battery needs to be replaced. When replacement becomes necessary, the patient will be admitted to the hospital. The ICD will then be removed, the lead tested, and a new device implanted. Leads need to be replaced less often than batteries. If this becomes necessary, the patient will undergo a procedure similar to the first implantation. If the ICD programming needs to be changed, this can be done from outside the body.
Defibrillator implantation is a relatively simple, low-risk procedure. However, complications, although rare, can occur. Patients having a defibrillator implanted are at risk for the following complications:
- Infection at the incision site
- Nerve damage at the incision site
- Blood clots or air bubbles in the vein
- Tearing of the vein or artery wall
- Punctured heart or lung.
There are also times when the device company will detect a flaw that may result in the issuance of an advisory to patients and physicians, or “recall”. While these events are very infrequent, they do occur, and therefore it is important to continue to have the device checked in accordance with the physician’s recommendations