What is an implantable cardioverter defibrillator ( ICD)?
An ICD is a device implanted in the chest to monitor and, if necessary, correct episodes of serious abnormal heart rhythms. There are three parts to an ICD:
- The pulse generator, which is responsible for generating the electric shock, is a small box (from 1 to 2 inches wide and weighing ½ to 3 ounces) that also contains a battery.
- The leads are small wires that carry the shock from the generator to the electrodes. Where your doctor decides to place the leads depends on your particular heart problem.
- The electrodes actually deliver the shock to the heart.
ICDs are most often implanted in the upper chest. Sometimes they are placed beneath the abdominal skin or muscles at the “bikini line” for cosmetic reasons because a small lump can be seen where the ICD has been implanted.9
How does an ICD work?
An ICD works by delivering a small low-energy pulse to the heart that you can't feel, much like that from a pacemaker, in order to “reset” the heart. This process is called cardioversion. In cases where the heartbeat is so rapid that you may die from it, the ICD will also deliver an electric shock, or defibrillation, which can be painful or very uncomfortable. Some people describe the feeling as being kicked in the chest.9 Occasionally, the ICD will deliver a series of shocks if the rhythm problem recurs or if one shock is not enough to correct a serious, prolonged, fast heart rhythm.
Some newer devices are a combination of an ICD and biventricular pacemaker in one unit for people with moderate to severe heart failure. In a normal heart, the right and left ventricles pump together, but if you have heart failure, they do not. The left ventricle then is not able to pump enough blood to the body. This can cause symptoms such as shortness of breath, cough, swelling in the ankles or legs, weight gain, increased urination, fatigue, or rapid or irregular heartbeat. The biventricular pacemaker part of the device treats the delay in heart ventricle contractions by keeping the right and left ventricles pumping together, while the ICD part helps prevent potentially fatal arrhythmias.
Who needs an ICD?
In 2002, ICDs were implanted in 63,000 people in the US, of whom 17% were women.2 ICDs are implanted in people who have survived one or more episodes of ventricular tachycardia, when the heart beats fast due to electrical signals from the ventricles, or ventricular fibrillation, when electrical signals in the ventricles are fired in a very fast, uncontrolled manner, causing the heart to quiver rather than beat and pump blood. ICDs are also implanted as a preventative measure in people at high risk for developing ventricular tachycardia, ventricular fibrillation, or sudden cardiac death.9 You may be at high risk for these problems if you've had a heart attack and the left ventricle of your heart is damaged. People who have both heart disease and a heart rhythm disturbance are good candidates for an ICD. ICDs are usually not implanted in people who have an abnormal rhythm during the first 48 hours after a heart attack; external defibrillators or medication will usually be enough to resolve these early arrhythmias, which are often temporary.10 An arrhythmia that occurs more than 48 hours after a heart attack indicates a possible recurrent rhythm disturbance that may require an ICD to be implanted.
How well do women do after having an ICD implanted?
In women, ICDs for tachycardia (fast heart beat) are less successful at correcting the fast heartbeat and have a higher rate of complications.11 Although an ICD should slow the heart beat, women were 3 times more likely to have their heart rate further increased by ICDs compared with men. In terms of preventing sudden cardiac death, ICDs work equally well in both men and women.12
Can I just take medicine instead of getting an ICD?
Medication is often used to prevent life-threatening ventricular tachycardia and ventricular fibrillation; people at low risk for developing these ventricular arrhythmias are usually treated with medication alone. One study of people who had already had a life-threatening arrhythmia (and were therefore high-risk) found that people who had an ICD implanted were 39% less likely to die after 1 year compared with people treated with medication alone.13 Other research has also indicated that the advantage of ICD use over medication therapy benefits people at highest risk more than people at moderate risk.14 An ICD and medications are frequently used together.
