The implantable cardioverter / defibrillator is commonly referred to as an ICD. It is a device that continuously monitors the heart rhythm. If it detects an abnormally fast heart rhythm, it either electrically paces the heart very fast or delivers a small electrical shock to the heart to convert the heart rhythm back to normal. The rapid pacing is not felt by the patient but the electrical shock, if used, is felt as a strong jolt in the chest.
The device is normally used for the instantaneous treatment of immediately life threatening heart rhythms (i.e., ventricular tachycardia and ventricular fibrillation) that often can't wait for treatment until an ambulance arrives. Some people are now studying the use of these devices for the treatment of less dangerous heart rhythms as well, such as atrial fibrillation.
ICDs are implanted in patients who have had ventricular fibrillation and patients with high risk ventricular tachycardia. ICDs are also implanted in some patients who have never had any of these abnormal heart rhythms but are felt to be at high risk for having one in the future due to some other heart disease they have.
The device is implanted in an operating room under deep sedation. The procedure typically takes two to three hours and patients are discharged from the hospital on the following day. Older devices were implanted in the abdominal wall but the newer, smaller devices are implanted under the collar bone, similar to a standard pacemaker. Leads run from the device through a vein into the heart. These leads report the heart's electrical activity back to the device and deliver the electrical therapy, if needed. These devices can also act like a standard pacemaker and pace the heart if it ever beats too slow. Some devices also incorporate biventricular pacing to strengthen weak heart muscle.
Like pacemakers, these devices must be continually monitored. An interrogating device placed on the skin overlying the ICD can find out about how the device has been programmed, determine the status of the battery, see if any pacing or shocks were given and the heart rhythm that was treated. The programming of the ICD can be modified as needed to best suit the patient's needs. Routine monitoring will detect a battery that is nearing the end of its lifespan long before it gives out. When this happens, the old device is removed and a new device is implanted. The leads are usually left in place.
If a patient feels a shock, they are generally advised to report it to their physician immediately. Feeling one shock does not necessarily mean that they have to be admitted to a hospital. The patient is generally brought into the office the next working day to interrogate the device. Patients experiencing multiple shocks are often admitted to the hospital, however.
These devices are not perfect. Sometimes they deliver therapy for non-life threatening fast heart rhythms. That is why it always important to interrogate the device after any shocks are felt by the patient. The programming or medications may then be altered based on what type of heart rhythm received the shock.
A special type of pacemaker that stimulates both the left and right ventricles of the heart simultaneously ( a biventricular pacemaker) can reduce symptoms and the need to be rehospitalized in heart failure patients with weak heart muscle who demonstrate slow electrical conduction through the ventricles on their ECG. This is known as cardiac resynchronization therapy. Thses pacemakers are usually combined with implantable defibrillators. Because these pacemakers are specifically designed for patients with heart failure, they may also come with a monitor to detect the amount of fluid in the lungs or the strength of contraction of the heart muscle.
Related topics: Electrical Cardioversion and Pacemaker Implantation
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