IMPLANTABLE CARDIOVERTER DEFIBRILLATORS

Introduction

Your heart is a muscular organ that pumps blood to all parts of your body to provide them with oxygen and nutrients. The normal heart is about the size of your clenched fist and sits directly underneath your breastbone. It pumps about 5 liters (approximately 5 quarts) of blood throughout the body each minute, which equals about 75 gallons or 285 liters of blood each day. This is accomplished by rhythmic relaxation and contraction of the heart. Each such cycle is called a "heart beat." Number of heart beats occurring per minute is called the "heart rate". An average person at rest has a heart rate of about 70 beats per minute.

If the heart beats too slow, then it may not pump enough blood for the needs of the body. As the heart rate gets faster, more and more blood is pumped, but at very fast heart rates (above 150 to 180) there is not enough time for the heart to fill in between beats and the output of the heart falls off drastically. In fact at extremely fast heart rates, the heart may effectively pump no blood, causing the person to faint or even die. This is the most common form of "Cardiac arrest". Much less commonly cardiac arrest occurs because of the heart actually slowing and stopping.

So, rapid heart beat can be as or even more troublesome than slow heart beat.

The heart is divided up into four sections, called chambers. The two upper chambers are called the Atria, designated as left and right, and the two lower chambers are called the Ventricles, again designated as left and right. During a heart beat, the atria contract to squeeze blood into the ventricles below them, and then the ventricles pump that blood out into the body.

Normal heart beat arises in the "natural pacemaker" of the heart termed the Sinoatrial (SA) node and conducts throughout the four chambers of the heart using specialized conduction fibers illustrated in the figure, producing a coordinated and efficient heart beat. In contrast, rapid heart beat may arise in any portion of the heart muscle. Depending upon it's site of origin, it may not have access to the specialized conduction system and hence may travel through the heart muscle in a haphazard way making the contraction of the heart in-coordinated and inefficient, reducing pump function even further.

Rapid heart beat arising from the lower chambers (ventricles) is usually very inefficient and commonly produces cardiac arrest. It can be rapidly fatal unless treated quickly by applying an electric shock to the chest such as by using "Paddles" as is often seen in the movies. The "Paddles" are the business end of a "Defibrillator".

What is a Defibrillator

A defibrillator is an electrical device designed to deliver an electric shock to the heart. It provides the quickest and usually the most effective way to treat cardiac arrest: Applying a large DC electric current to the heart extinguishes all abnormal electrical circuits and provides the "natural pacemaker" an opportunity to take control again. This process is called defibrillation.

What is an Implantable Cardioverter Defibrillator (ICD)?

An ICD is a miniaturized defibrillator that runs on a battery and is prepared specially for implantation inside the body. All defibrillators include a built-in single or dual chamber pacemaker. Hence, an ICD is usually able to treat both fast and slow heart rhythms. It continuously "watches" over the rhythm of your heart. If your own heart rhythm becomes slow, the ICD uses its pacemaker to keep the heart rate at the preprogrammed rate. If your heart beat becomes abnormally fast, the ICD gives you an electrical jolt which feels like a kick in the chest, but restores the heart rhythm back to normal.

An ICD system is made up of three parts:

1. The generator, a smooth, lightweight case containing a tiny computer and a battery, which all the electrical functionality of the ICD;
2. The connector or header, which is the part of the generator where the leads are attached; and
3. The leads, which are wires covered in soft, flexible plastic that are inserted into the heart to help the generator watch the heart and carry out the ICD functions.

Why would I need an ICD?

ICDs are used to treat abnormally fast heart beat arising from the lower chambers of the heart. These rhythm abnormalities commonly occur in patients with history of previous myocardial infarction (heart attack) and reduced pumping function. The two most such rhythms are Ventricular Tachycardia (VT) and Ventricular Fibrillation (VF).

Ventricular Tachycardia (VT) occurs when heart muscle cells become locked into a circuit and send out signals that make the lower chambers of the heart beat too quickly. As explained above, when the ventricles are beating too fast and are not in time with the upper chambers of the heart, they do not fill properly and hence don’t pump out enough blood to support the needs of the body. Depending upon the heart rate and the strength of the heart, VT may result in fainting without warning or other symptoms such as:

• Palpitations: a fluttering feeling in your chest
• Dizziness or lightheadedness
• Fainting
• Weakness
• Warm, flushed feeling
• Diaphoresis: breaking out in a cold sweat

Regardless of the level of consciousness experienced, ventricular tachycardia must be dealt with expeditiously, or it may deteriorate into ventricular fibrillation (VF), an even more life-threatening condition.                   

In ventricular fibrillation (VF), the cardiac electrical activity becomes completely haphazard and disorganized, and the heart beats so fast and irregularly that it actually quivers rather than pumps. No blood is being pumped from the heart into the body. This is called cardiac arrest or sudden cardiac death. Loss of consciousness is immediate, and immediate CardioPulmonary Resuscitation (CPR) must be started with defibrillation as soon as possible. Emergency medical teams are trained to provide electrical defibrillation, using an external defibrillator. As noted above, the defibrillator gives a strong electrical shock to the chest through the paddles that are applied to the bare chest wall. The electric shock is transmitted through the chest to the heart. It stops all erratic electrical activity and allow a normal rhythm to return, in effect - restarting the heart.

In case of cardiac arrest, survival depends upon availability of effective CPR and defibrillation within a few minutes. Otherwise, irreversible brain damage or death may occur. In urban areas, where ambulances cannot get to the victims of cardiac arrest soon enough, chance of survival from cardiac arrest is less than 5%. Overall survival of out-of-hospital cardiac arrest victims in the United States is about 10%. It was because of these reasons that the implantable cardioverter defibrillator (ICD) was developed. It is implanted inside the body and in case of cardiac arrest it delivers the required electric shock within a few seconds, achieving a success and survival rate of 99% in patients with uncomplicated cardiac arrest.

What can an ICD do

An ICD is capable of doing much more than its primary function of providing defibrillation shocks in case of cardiac arrest. It is in effect a heart rhythm management system. Not only that it can provide defibrillation but also it includes complete pacemaker functionality. It provides many means or recording heart rate statistics and even actual electrograms from inside the heart, assisting your physicians in the analysis of your heart rhythms.

The ICD tailors the treatment to the kind of heart rhythm abnormality detected: If VT is detected, your ICD may simply deliver small, rapid paced beats (antitachycardia pacing). Thus by pacing faster than the VT, it overrides the heart’s abnormal rhythm. When pacing stops, the heart rhythm returns to normal.

If antitachycardia pacing is unsuccessful, the ICD can cardiovert the heart, which means it delivers one or more small shocks timed to your heart rhythm to stop the VT and return your heart rhythm to normal. These shocks may feel like small thumps in the chest.                  

If the ICD detects VF, or if the above measures fail to terminate VT, it will perform automatic defibrillation: The ICD sends out a strong electric shock to stop the irregular rhythm and restart the electrical system. This shock feels like a kick in the chest and can even throw some patients off balance. Although the jolt may be uncomfortable, it is very short lived and does not cause any damage. In some patients, fainting sets in so quickly that they do not feel the shock. They simply wake up a few seconds later.

Sometimes after a shock, or even otherwise, the heart beats too slowly (bradycardia). Most ICDs have pacemaker capabilities, and when programmed, can pace the heart until it can maintain a normal rate on its own.

Implanting the ICD

Pre-procedure

The implantation of an ICD is a fairly simple surgical procedure that can be performed in the operating room or in the cardiac catheterization lab. When the decision to implant an ICD is made, you will receive pre-procedure instructions similar to the following:

1. Do not have anything to eat or drink for 6 hours before your procedure.
2. If you are a diabetic you may be instructed to reduce or not take your insulin or other diabetic medicine on the day of the procedure to avoid low blood sugar.
3. You may be asked stop taking aspirin or other blood thinners several days prior to the procedure to avoid unnecessary bleeding.
4. Blood tests may be required on the day of the procedure or before it.
5. Usually you will be asked to arrive in the hospital on the morning of the procedure several hours before the procedure so that you can be adequately prepared to undergo the surgery. After the procedure usual hospital stay is one day.

During the procedure                                                                                    

ICDs used to implanted in the abdomen because of their large size. Now they have become relatively much smaller so that in most patients they can be comfortable implanted in under the skin in the upper part of the chest.

Immediately before your procedure, the skin area just beneath your shoulder and above the breast will be cleansed with special soap and may be shaved to remove excess hair. A mild sedative may be given to you to help you relax.

The procedure may take 1 to 2 hours to complete. It is usually done under local anesthesia, which means that the area where the ICD will be implanted will be numbed with an injection. You should not feel any pain during the procedure, and should inform the doctor or staff if you are having pain so that more medication may be given. An incision is made in the skin under the collarbone and a "pocket" is formed under the skin and in front of the muscle in the upper chest for the ICD generator to rest in. The lead or leads are then threaded through a major vein in your upper chest and into your heart with the help of x-ray monitors. Their position inside your heart is determined by electrical measurements. Once the leads are in place, they are hooked to the generator, which is then inserted into the pocket that has been made. The ICD settings are programmed. The ICD is then tested by inducing abnormal heart rhythm and allowing the ICD to automatically detect and correct this rhythm. After assuring normal ICD function, the incision is closed and a sterile dressing is placed over the incision.

In some cases, the generator is placed in the abdominal region. The procedure remains the same, the only difference being that the lead is threaded under the skin to the generator in the abdomen.

In rare cases, an ICD may be implanted during an open chest procedure. This may be done during other heart surgery while another heart problem is being corrected, or it may be necessary if the leads will not be able to be placed through the veins. Also, the lead can be attached to the outside of the heart if necessary. The generator in this procedure is placed in the abdomen region.

After the procedure

While in the hospital, your vital signs will be checked frequently, and your heart’s signal will be checked to make sure that the ICD is functioning correctly. Your incision will also be checked for bleeding or swelling. Pain medication will be available to make you more comfortable. It is important to tell the nurse if you feel any unusual symptoms such as hiccups that won’t go away, dizziness or chest pain. It’s normal to have some stiffness and pain to the area around the incision for about a week or so. In order to give the leads a chance to secure themselves in your vein and heart, do not lift the arm on the side the device was implanted above your shoulder.

• It will be a few days before you can go back to your daily activities, and you should take it easy with the arm on the side of implantation for several weeks. Your doctor will tell you when it is okay to go back to work.
• Do not lift your arm over your head for at least three weeks.
• Treat the insertion site with care. Avoid getting the incision site wet for about a week. This will help reduce the chances of infection.
• The bandage is usually taken off before you are discharged from the hospital. Small steri-strips (tapes) remain applied. These should be left in place until your doctor takes them off.
• Avoid vigorous exercise such as heavy lifting, running, or contact sports for six weeks.
• Monitor your temperature and insertion site, and notify your doctor if you develop a temperature or notice swelling, bleeding, redness, or drainage from your insertion site, or if you feel any of the symptoms you had before the ICD was implanted.

Risks of ICD Implantation

ICD implantation is a safe procedure. Procedural complications are rare, but do occur. These include but are not limited to:

• 5% chance of bleeding or severe bruising at the insertion site.
• 1% chance of puncture of lung puncture while obtaining access into the veins. The lung when punctured can deflate like a balloon. This usually requires insertion of a tube in the side of the chest to reinflate the lung. The lung then heals up in five to seven days.
• 1% chance of puncture of heart muscle. This may require specific treatment.
• 1% chance of infection.
• Other risks may apply, depending upon your general condition and other medical conditions that you might have.

Some discomfort is usual at the implant site. However, this is usually easily controllable with simple pain killers.

Follow-up: Caring for your ICD

You will have a follow-up visit in the doctor’s office about one week after your procedure to check the insertion site and monitor for any problems.

At three months, you will have another doctor’s visit to check the ICD’s settings and readjust them to better help your heart and maximize battery life.

Currently the ICDs cannot be checked over the phone like pacemakers. Hence periodic checks in the physicians office are required, usually every two to three months, to ensure continued normal ICD function. During these checks the data collected by the ICD is retrieved, battery status is checked and lead integrity is assessed. If you do not receive an ICD shock for a long time, a more comprehensive ICD check in the hospital may be required. During hospital checks, abnormal rhythms are induced and the response of the ICD to this is observed. If the ICD correctly detects the occurrence of the abnormality and appropriately corrects it, that is proof of continued normal function of the entire system.

ICD batteries usually last for 4 to 6 years before they need to be replaced. Because the battery is sealed inside the generator, replacing the battery requires that the entire generator be replaced. This procedure is more simple than the implantation procedure. The pocket where the generator sits is opened, the old generator is removed from the pocket and detached from the leads, the new generator is hooked to the leads and placed into the pocket, and the incision is closed. This is usually an outpatient procedure and does not require hospital admission. If the leads wear out and need to be replaced, a procedure similar to your original one will be needed. There is a small chance that the ICD can fail, but with the advances in ICD technology in recent years, the chance is remote. If your ICD were to fail, you may not feel any symptoms, until a cardiac arrest occurs which is then not treated appropriately by the malfunctioning device. Hence it is vitally important to undergo the required periodic ICD checks to keep the ICD in good functioning order so that it will be available to you if and when you should need it.

Your incision should heal completely in about two to three months. Continue to treat the insertion site with care. Don’t play with the ICD under your skin. You may feel some numbness or fullness in the area around the ICD for a few months that resolves as you become accustomed to the ICD.

Living with an ICD

1. Your ICD is registered with the manufacturer at the time of implant. You will be given an ID card which contains important information about your ICD before being discharged from the hospital. A printed card containing the same information will arrive in the mail in a few weeks. Keep this card in your wallet and show it to any doctor, dentist, or other medical professional you visit. You should carry it with you at all times to alert emergency personnel.
2. Your ICD is a metallic device and it may set off security devices such as those found in airports or libraries, and you may need to show your registration card to the security personnel.
3. Contact sports and other activities such as racquetball should be avoided due to the risk of bumping your ICD. However the ICD does not prevent you from exercising regularly. Your doctor can recommend an exercise program, if needed.
4. Most home appliances will not interfere with your ICD’s signal provided these are kept at least six inches away from the ICD. These include electric drills, electric blankets, hair dryers, electric shavers, heating pads, metal detectors, microwave ovens, TV transmitters and remote control TV changers.
5. Avoid being close to very strong magnets, such as MRI equipment, heavy duty electrical equipment, radio-transmitting towers, ham radios, certain surgical instruments, and cellular phones.
6. Use of therapeutic magnets such as those for treating arthritis or muscle aches, etc. does not interfere with ICD function if the magnet stays at least six inches away from the device. Magnet mattress pads should not be used because these can deactivate your ICD.
7. Generally it is not possible to undergo an MRI test if you have an implanted ICD, because MRI uses a very strong magnetic field to obtain images. This magnetic field can dislodge your ICD.
8. Cellular phones, CB radios and ham radios can sometimes interfere with the function of some ICDs. Cellular phone and CB radio antennas must remain at least six inches away from the ICD. Hence do not carry a cellular phone in your chest pocket, even when it is turned off. When using a cellular phone, hold it to the ear farthest from the ICD generator. Ham radio antenna should remain at least six feet away from the ICD.
9. Do not stand over the open hood of a running car as the engine generates a strong electrical field.

Driving

The ICD is effective therapy for terminating ventricular arrhythmias and preventing sudden cardiac death. However, despite its effectiveness, identifying the appropriate time (if any) for the patient to return to driving is difficult because of many reasons:

• Successful termination of the arrhythmia by ICDs usually takes 20 to 60 seconds and sometimes may take even longer. Patients may experience severe symptoms or may even faint during this time depending upon the mechanism of arrhythmia, the heart rate, and the status of the underlying heart function.
• Occurrence of one's ventricular arrhythmia occurs almost randomly is difficult to predict.
• Initial ICD therapy may worsen the arrhythmia causing fainting before further steps of ICD therapy finally correct the arrhythmia.
• ICD shock therapy may cause discomfort and could frighten or startle a patient, which could lead to loss of control of a vehicle when driving, even in the absence of symptoms due to the arrhythmia.

Although the decision to allow driving needs to be considered individually for each patient, the following guidelines are generally followed:

• For patients who receive an ICD for ventricular fibrillation (VF), commercial driving is prohibited permanently. Personal driving may be allowed after six months, if no recurrence of initial symptoms occurs and any ICD shocks received are well tolerated.
• For patients who receive an ICD for ventricular tachycardia (VT), commercial driving may be allowed in some circumstances after a period of six months to two years. Personal driving may be allowed after six months, if no recurrence of initial symptoms occurs and any ICD shocks received are well tolerated.
• There are many exceptions to above guidelines and each patient's individual condition will determine the final recommendation.

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Cardiology Associates provides a complete ICD follow-up clinic.

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