ICD

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General Description

An ICD is an electronic device which is typically implanted in people for dangerous ventricular arrhythmias such as ventricular tachycardia or ventricular fibrillation. For a complete description of these heart rhythms, please see the ventricular tachyarrhythmias section. An ICD can also be implanted in certain patients who have had an episode of passing out (syncope) in conjunction with certain types of heart disease. In most cases, a person needs to undergo an electrophysiology study prior to receiving an ICD (see the Electrophysiology Studies section). Once implanted, the ICD monitors the heart rhythm and is able to terminate an episode of ventricular tachycardia or ventricular fibrillation by either very rapid pacing of the ventricle or by delivering a shock to the heart muscle. The ICD also has the capability to act as a pacemaker and prevent slow heart rhythms by pacing the heart muscle.

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How It Works

The ICD is basically composed of 5 components: the outer metal case, the battery, the circuit board, a capacitor, and the lead(s). [Click here to see a picture of an ICD and here to see a picture of ICD leads]. The lead (or leads, depending on the type of ICD) are insulated wires that travel through the veins into the heart and are connected to the ICD. The lead that is placed into the ventricle contains either one or two coils on it to enable delivery of energy to the heart muscle. [Click here to see a picture of an ICD lead with two coils]. The capacitor is a pair of metal plates which can store an electrical charge. The battery, circuit board, and capacitor are sealed within the metal casing of the ICD. The battery provides the energy to run the circuit board and pace the heart and the circuit board controls the timing and multiple functions of the ICD. The battery also charges the capacitors with energy when a shock is needed. The energy is then released from the capacitors and delivered to the heart muscle via the lead coil(s).

The number of leads (one or two) implanted with the ICD will depend on each individual case. Your physician will decide which type of ICD is best for your clinical situation. Many ICDs are implanted with two leads – one in the upper chamber of the heart (atrium) and one in the lower chamber (ventricle) although in certain patients, an ICD with only one lead is required. ICDs with two leads are called dual-chamber ICDs while those with one lead are called single-chamber ICDs. There are some very recently approved ICDs in use for patients with heart failure that have three leads - one in each ventricle (right and left) and one in the right atrium (these are called biventricular ICDs). Patients need to meet specific criteria to be eligible for a biventricular ICD.

The ICD is set to monitor the heart rhythm at all times. If the heart rate exceeds a set rate (i.e. an arrhythmia occurs), the device can then act to stop the arrhythmia. The ICD can stop an arrhythmia in one of two ways: by rapidly pacing the heart muscle (called overdrive pacing) or by delivering a shock to the heart muscle. It is possible that the overdrive pacing would fail to stop the arrhythmia in which case a shock would need to be delivered to terminate the arrhythmia. The ICD also has the capability to act as a pacemaker and can deliver small electrical impulses through the lead(s) to the heart muscle to cause it to contract (pace). The native heart rhythm and the settings of the pacemaker function in the ICD will determine how often it actually needs to pace the heart muscle. The physician can change the settings of the ICD via a programmer which is a modified computer with a wand that enables non-invasive communication with the ICD. Most ICDs have a rate response function built-in which can be activated by the physician. This function enables the ICD to increase the patient's heart rate if it senses that the patient is engaged in physical activity (i.e. walking, running, etc...). There are multiple other programmable options which can be changed by the physician to optimize the function of the ICD. The next generation of ICDs will also be able to terminate atrial arrhythmias (atrial fibrillation and atrial tachycardia).

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Before the Procedure

You will be told not to eat or drink anything after midnight on the night before the procedure. Follow your physicians’ instructions for taking medications the day of the ICD implant. You will also be required to have certain blood tests drawn at least a few days prior to the procedure. If you are of childbearing age a pregnancy test will also be performed to ensure that you are not pregnant.

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The ICD Implant

After arriving at the electrophysiology laboratory, one of the nurses will assist you in changing into a hospital gown and will place an intravenous to assist us in administering sedation and medications during the procedure. Electrocardiogram electrodes and pads will be placed on your chest and back to monitor your heart rhythm throughout the study. You will be placed onto the procedure table lying flat on your back. You will notice a large camera and video monitors nearby. The x-ray camera will be used to view the location of the ICD leads (insulated wires) that will be placed in your heart. The area around the ICD implant site (usually the left upper chest) will be cleaned carefully by the nurse. Your body will be covered with sterile sheets to prevent any infection during the procedure. The nurse will also administer some sedation through the intravenous to make you comfortable throughout the procedure. Click here to see images of the electrophysiology laboratory and staff at Lenox Hill Hospital.

The physician will inject a small amount of anesthetic into the skin in the upper chest area where the ICD will be placed. You might feel a pinch and some burning during this part of the case but otherwise you shouldn’t feel any other discomfort during the procedure. A small vein in the chest area is located which is used to introduce the lead(s) into the right side of the heart. If this vein is too small for use or not located, a vein underneath the collar bone is used. The physician moves the lead(s) into the heart using x-ray guidance (fluoroscopy). The leads are tested to be sure they are in a stable position and are then secured to the tissue. The leads are then attached to the ICD and the ICD is placed underneath the skin. The wound is then closed by the physician and a dressing placed to maintain a clean area.

The ICD is then tested to ensure that it is capable of reliably stopping a ventricular arrhythmia. This is done twice by inducing an arrhythmia and allowing the ICD to terminate it with a shock. An external defibrillator is available to stop the arrhythmia in the event the ICD does not successfully terminate the arrhythmia. In most cases the ICD has no trouble terminating the arrhythmia. You will be kept in a state of deep sedation for the testing and should have no recall of the event.

The entire procedure can last anywhere from 1½ to 2½ hours depending on each particular case. You will be kept comfortable throughout the procedure. The staff will constantly be monitoring your vital signs throughout the procedure. If you feel any discomfort at any point during the procedure you should tell the staff immediately. Most patients recall little if any of the procedure and are usually very comfortable throughout.

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After the Procedure

You will be asked to lie in bed for 2 to 3 hours after the procedure is finished to allow the sedation to wear off. A bedside chest x-ray might be required. After this time you can get out of bed and walk around if you feel up to it. You will need to monitored in the hospital at least overnight if not for 2 days after the procedure. Changes in medication or re-starting of blood thinning medications might prolong your hospital stay.

You shouldn’t perform any heavy lifting or heavy physical exertion (including sexual intercourse, jogging, weight lifting) for at least 2-3 weeks after the ICD implant. Your physician can recommend which specific forms of exercise you will be allowed to perform. A small bruise (black and blue mark) or small lump can sometimes appear over the ICD implant site, which typically resolves over 2-3 weeks. A large lump or worsening pain at the ICD implant site, swelling in the arm or fever should be reported to your doctor at once.

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Risks:

As with any invasive procedure, there are some risks involved in having an ICD implanted. A small amount of bleeding into the ICD pocket or a localized infection of the ICD wound is possible. There is about a 1% risk of nicking the lung and causing it to partially or fully collapse. Very serious side effects such as damage to the heart muscle wall or blood vessels, blood clots, stroke, and heart attack are rare. Death is very rare. The vast majority of patients undergoing an ICD implant do very well and do not experience any complications. You should speak with your physician regarding these risks and understand them prior to undergoing the implant. 

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