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The heart has a natural pacemaker that sends electrical pulses through the heart, regulating the beat and moving blood throughout the body. When the electrical system of the heart is disrupted, a person is said to have an arrhythmia (irregular heart beat). In the United States, more than half of all cardiac deaths are sudden deaths — the abrupt loss of heart function — and more than 80 percent of sudden deaths are caused by an arrhythmia.
An implantable cardioverter defibrillator (ICD) is designed to quickly detect a life-threatening arrhythmia and prevent sudden cardiac death. In January of 2005, Medicare expanded the indications for coverage of ICD services to include more categories of people with heart disease.
Q. What causes cardiac arrest?
Cardiac arrest is the sudden, abrupt loss of heart function. Most cardiac arrests that lead to sudden death occur when the electrical impulses in a diseased heart become rapid (ventricular tachycardia or VT) or chaotic (ventricular fibrillation or VF) or both. The irregular heart rhythm causes the heart to suddenly stop beating.
- Ventricular tachycardia is rapid regular beating of the ventricles, the bottom chambers of the heart. The rapid rate prevents the heart from filling adequately with blood; therefore, less blood is pumped through the body.
- Ventricular fibrillation is rapid irregular beating of the ventricles. The ventricles quiver and are unable to contract or pump blood to the body.
Ventricular arrhythmias impair the pumping ability of the heart and greatly raise the risk of sudden cardiac arrest. These arrhythmias tend to develop in people with (known or unknown) coronary artery disease or heart muscle disease. Most people will die the first time they experience sudden cardiac arrest, which is why prevention is so important.
Sudden cardiac arrest is not a heart attack, which is caused when a blocked blood vessel interrupts the flow of blood to the heart. Heart failure is another cause of cardiac death that occurs when the heart muscle becomes weakened.
Q. What is an implantable cardiac defibrillator (ICD)?
An implantable cardiac defibrillator or ICD is a device that is placed in the body. It recognizes rapid arrhythmias such as VT and VF and corrects them with an electronic shock. First developed in the 1980s, the defibrillator continuously monitors the heart rhythm to prevent sudden cardiac death.
An ICD consists of a pulse generator and a capacitor that can shock the heart, a circuit that tells the ICD when to discharge, and electrodes placed in the heart to sense the rhythm and deliver a shock to the heart muscle. All ICDs also have a built-in pacemaker, which also allows the device to correct heartbeats that are too slow.
An ICD runs on batteries that last for five to seven years. During regular clinic visits, a physician can determine when the device is running low and needs to be replaced.
Q. How can an ICD help?
The defibrillator corrects the heart rhythm by delivering a high-voltage electrical shock, when needed, to restore a normal heartbeat. Sometimes, a person might have a heart rhythm that is too slow. In this case, the pacemaker in the ICD will send a low electrical pulse to the heart to “remind” it to beat.
Q. How is an ICD implanted?
Today’s ICDs are much smaller and lighter than those first in use. They are also easier to implant. In a low-risk, minimally invasive surgical procedure, the pulse generator is surgically implanted under the skin in the upper chest. A wire from the ICD is threaded through the blood vessels to the heart. The procedure takes less than two hours. Following an overnight hospital stay, a person may return home.
Q. For what conditions has an ICD been traditionally used?
An ICD has traditionally been used to prevent recurrence in people who have survived a cardiac arrest. Prior to 2005, the standard indications for using an ICD were to:
- Prevent death in people who have survived a cardiac arrest due to VF, and whose condition is not due to a reversible cause. This is the most serious type of condition that can lead to sudden death.
- Treat people with VT that is not associated with having had a cardiac arrest, but the rapid rhythm places them at high risk.
- Treat people who have severe symptoms (especially fainting spells) that, after a medical evaluation, are thought to have suffered a VF or VT episode.
- Treat people who have familial or inherited conditions that place them at a high risk for cardiac arrest, even though they have not suffered cardiac arrest.
Q. What are the new guidelines for using an ICD?
Today, Medicare has expanded the guidelines for coverage of ICDs to include patients who might have a cardiac arrest, without needing to have symptoms of a ventricular arrhythmia (VF or VT). Basically this means that an ICD can be used in people who have not had serious rhythm problems, but who have a history of heart disease that could lead to rhythm problems.
The expanded guidelines are based on three clinical research trials that found that defibrillators saved lives. The studies involved people with ejection fractions less than 35 percent along with other risk factors.
The ejection fraction is the portion of blood that is pumped out of a filled ventricle as a result of a heartbeat. With each beat, the heart normally ejects about half to two-thirds of the blood that is in the ventricle. This is referred to as the ejection fraction, and it is an indicator of the heart’s health. A normal ejection fraction is 50 percent or higher. A reduced ejection fraction indicates heart disease.
In the studies, it was found that an ICD generally helped patients who had an ejection fraction of:
- Less than 35 percent and who have symptoms due to heart failure
- Less than 30 percent and who had a prior heart attack
The expanded Medicare guidelines now include ICD coverage for people in these two groups.
The expanded Medicare guidelines also include patients who need a biventricular pacemaker to treat symptoms of fatigue and shortness of breath due to congestive heart failure. These pacemakers help to synchronize the ventricles of the heart. About a third of patients with heart failure suffer from severe symptoms of fatigue and shortness of breath, which is caused by this asynchronous contraction of the ventricle. A cardiac resynchronization therapy device (called a biventricular pacemaker) stimulates both heart ventricles to pump in a synchronized way. This maximizes blood flow and immediately improves the person’s symptoms. The device is implanted just like a standard pacemaker with one electrical lead attached to the right ventricle and another on the upper chamber (atrium). But unlike a standard pacemaker, the device has a third lead that stimulates the left ventricle. When it’s turned on, the failing heart synchronizes and pumps more efficiently. A defibrillator and biventricular pacemaker are usually combined into a single device so that the same device also protects from VT and VF like a conventional ICD.
Q. Could I be a candidate for an ICD?
Before considering the implantation of an ICD, it’s important to first use standard treatments for heart disease. To prevent heart disease, we look at the patient’s diet, cholesterol, blood pressure, smoking and other factors. If serious heart disease is found, we focus on ways to remove blockages in the arteries, prescribe medication, manage cholesterol, and perform other treatments. For some people with severe heart disease, however, these options aren’t enough. If they still have congestive heart failure and poor heart function, an ICD may be a good option.
Each person, along with his or her physician, needs to decide if an ICD is right for them. An ICD is implanted as a preventive measure to cardiac arrest, and many factors need to be considered, such as family history and the patient’s heart function (ejection fraction). If the ejection fraction is less than 35 percent, the patient and physician should discuss what can be done to improve it or improve the patient’s symptoms, and if an ICD should play a role in treatment. If you have questions about ICDs, talk to your physician.