Implantable Cardioverter Defibrillator
What is an Implantable Cardioverter Defibrillator?
An implantable cardioverter defibrillator (ICD) is a small electronic device that is implanted in the chest or abdomen to control abnormal heart rhythm and prevent sudden cardiac arrest. The ICD detects the abnormal heart rhythms and restores a normal heart rhythm by delivering electrical impulses to the heart muscle.
Indications for Implantable Cardioverter Defibrillator
Your doctor may recommend an ICD if you have:
- Had a previous cardiac arrest or ventricular fibrillation or ventricular tachycardia
- Heart conditions such as dilated cardiomyopathy or hypertrophic cardiomyopathy that affect the heart muscle
- An inherited condition such as long QT syndrome, Brigades syndrome and arrythmogenic right ventricular dysplasia
Description of the Implantable Cardioverter Defibrillator
An ICD device contains one or more insulated wires called leads and a defibrillator unit, a small metal box that contains a pulse generator, computer and a battery. The device is connected to the heart muscle through leads with electrodes at their end. The lead thus detects the heart’s electrical activity and also delivers impulses from the device to the heart muscle. There are three different types of ICDs:
- Single chamber ICD: These types of ICDs use a single lead which is placed in the right ventricle heart chamber. Energy is delivered to the right ventricle when required to help it contract normally.
- Dual Chamber ICD: In this type of ICD, the leads are attached in the right atrium and the right ventricle. These ICD’s correct faulty electrical activity between an atrium and a ventricle. Energy is delivered to the right atrium first, and then to the right ventricle to restore a normal rhythm.
- Biventricular ICD: In this type of ICD, there are 3 leads which are placed in the right atrium, the right ventricle, and the left ventricle. This device helps the heart beat in a more balanced way and is specifically effective in patients with heart failure.
Procedure to Implant the Cardioverter Defibrillator
An ICD is usually implanted using the transvenous approach. In this approach, a small incision is made in the chest wall after numbing the area with local anaesthetic. Sedation is also given to the patient. Through this incision, the lead is introduced into a vein to reach the specific chamber of the heart. This is done under guidance of real time X-ray images (fluoroscopy). The lead tip attaches to the heart muscle and the other end is connected to the pulse generator. Once the lead wires are in place, it will be tested for proper placement and functioning through a lead function test called pacing. The pulse generator is usually placed in a pocket created under the skin through the incision in the upper chest. The skin incision will be closed with sutures and a dressing will be applied once the procedure is complete. The whole implantation procedure usually takes between 2 to 4 hours. With the transvenous approach, patients recover faster and are discharged from the hospital in about 24 hours. If the transvenous approach cannot be used, the device is implanted in the pocket underneath the skin in the lower abdomen (epicardial approach). The epicardial approach is done under general anaesthesia and requires a longer recovery time.
After the implantation procedure a chest X-ray is done to check the lungs and the position of the device and the leads. A telemetry monitor and Holter monitor are also connected to the chest with sticky electrode patches to monitor and record the heart rhythm. These monitors are removed before the patient is discharged from the hospital. Then the patient is sent to the device clinic for final device settings. In the device clinic, a small device called a programmer is placed directly over the device to change the device settings and to check its function. An echocardiogram may also be performed as part of your evaluation.
After implantation of an ICD, the patient should be scheduled for regular follow up visits. These follow-up visits are important to monitor the function of the device and change the settings if required. Once implanted, an ICD usually lasts for 3 to 6 years before needing replacement