Also known as an implantable cardioverter defibrillator (ICD), a defibrillator is a small electronic device that is implanted into the chest to monitor heart rhythms continuously.
When the heart begins to beat dangerously and abnormally fast (a condition called arrhythmia), a defibrillator can send electrical impulses that "shock" the heart, causing the heart to beat in a normal rhythm again. In a sense, a defibrillator is always on standby, ready to take life-saving action when necessary.
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Defibrillators are most commonly recommended for patients who suffer from hyperactive or irregular heartbeat in a blood-pumping chamber of the heart (called a ventricle). When a ventricle pumps too quickly, the condition is called ventricular tachycardia. When a ventricle twitches or flutters erratically, the condition is called ventricular fibrillation. Either condition can cause sudden death.
Defibrillator implant is recommended for patients who have experienced irregular, fast heartbeat in the past that results in fainting or sudden cardiac arrest.
How a Defibrillator Works
A defibrillator consists of two components:
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- Leads: Long, thin wires that are directly connected to the heart, to monitor heart rhythms. Most defibrillators have two.
- A pulse generator, which consists of a battery and a small computer that receives signals from the lead. If the computer detects an abnormal rhythm, the battery will deliver an electrical signal back to the lead and into the heart muscle.
A defibrillator is programmed by an electrophysiologist, a cardiac physician who specializes in heart rhythms. The device can be set to restore normal heart rhythm in several ways:
- Anti-tachycardia pacing (ATP), or "overdrive pacing," is a sequence of electrical impulses delivered to the heart when it beats dangerously fast (tachycardia).
- Cardioversion is a low-energy shock delivered at the same time as a heart beat after a sequence of ATP impulses fail to restore normal heart rate.
- Bradycardia pacing is needed when the heart beats too slowly (bradycardia). Electrical impulses will speed the heart rate.
- Defibrillation will stop a severely abnormal heart rhythm by delivering a high-energy shock.
Newer defibrillator models also will record the date and time of a ventricular tachycardia or fibrillation event, as well as note the electrical therapy provided to the heart.
Defibrillator Implant Surgery
Defibrillators are most commonly implanted through small incisions in the skin, near the collarbone. The patient is given a mild sedative, but is kept awake; a local anesthetic is used. An electrophysiologist, a physician who specializes in heart rhythm problems, will perform the procedure.
Using a fluoroscopy machine — which creates moving X-rays — to visualize the chest's interior, an electrophysiologist guides the defibrillator leads through the incisions, into veins, until they reach the heart. There, the tip of each lead is attached to the heart muscle. Next, the leads are connected to the device's pulse generator, which is then placed in a pocket, just beneath the skin in the upper chest.
With the defibrillator in place, the electrophysiologist will perform a series of tests to ensure that device is working properly. An artificially fast heart rhythm might be programmed, simply to ensure that the leads are properly monitoring heart beats, and the pulse generator is sending the appropriate signals to stop the abnormal heart beat. Afterward, the device is programmed to meet the patient's needs.
After Defibrillator Implantation
Following surgery, patients are asked to return to doctor for routine follow-up visits. The first appointment is scheduled within six weeks of the device implant procedure.
During each visit, the defibrillator will be checked by a programmer device, which will indicate:
- Whether the defibrillator is working properly.
- Current settings.
- Whether it has delivered corrective signals to the heart.
- How much energy remains in its battery.
The defibrillator's leads also may be checked. Adjustments can be made to how the defibrillator is programmed, as well.
Depending upon how much electrical shock it delivers, a defibrillator's battery can last anywhere from three to eight years. When the battery's voltage runs low, a new ICD will be implanted. However, the defibrillator's leads most likely will not be replaced.
Defibrillator therapy is part of a larger treatment program, which may include medications, proper nutrition, moderate physical activity and healthy lifestyle choices.