Internal Cardioverter Defibrillator (ICD) Implantation
ICD implantation is indicated in those with prior cardiac arrest, ventricular tachycardia, or patients with coronary artery disease and severe left ventricular dysfunction. Several recently published prospective, randomized trials have demonstrated reduced mortality in these patient groups (MADIT, MADIT-2, MUSST, CASH, CIDS, AVID). As with pacemakers, ICD’s can have either single leads or two leads. Current ICD’s have most of the functions of pacemakers and therefore treat slow heart rates or electrical conduction disease. Defibrillators can be programmed to detect abnormally fast heart rhythms and deliver therapeutic electrical impulses. In patients with ventricular tachycardia, an ICD can be programmed to pace the patient’s heart to restore a normal rhythm. This process is called anti-tachycardic pacing and may go completely unnoticed by the patient. If this treatment should fail or if a heart rate that is unacceptably high is detected, the device delivers a high voltage shock to the heart in order to restore a normal rhythm. The patient commonly perceives these shocks, often being described as a kick to the chest with no residual discomfort.
Procedure
Duration of the implantation is 1-2 hours depending on the ease of access, positioning the leads to acquire satisfactory parameters, and testing of the device. Local anesthetic is administered at the implantation site. The most common site for implantation is the left chest wall area just adjacent to the left shoulder. This site has important implications regarding the efficacy of the device.
As with pacemaker implantation, ICD implantation is a sterile procedure. The electrophysiologist scrubs, gowns and gloves. Cutdown cannulation of the cephalic vein and/or percutaneous cannulation of the subclavian vein provides access to the heart. The electrical leads (1-2 depending on the type of device chosen) are placed into the heart under fluoroscopic guidance. The lead parameters are measured externally before being connected to the ICD. Once satisfactory lead positioning and functioning have been achieved, the leads are connected to the ICD and implanted under the skin. The device must be tested for its ability to appropriately detect and deliver a therapeutic shock. This is done by placing the patients under deep anesthesia with the assistance of an anesthesiologist. Ventricular fibrillation is then induced and function of the device is observed. A greater than 10 joules safety margin must be demonstrated. In our laboratory we will usually accept two consecutive successful shocks (with a 5-minute rest between each test) with a 15 joule safety margin to meet this requirement. For example, a device with a maximal output of 30 joules will be tested twice consecutively at 15 joules. Once this level of efficacy has been achieved, the incision is closed and bandaged. As with pacemaker implantation, antibiotic prophylaxis is given for 24 hours post-operatively.
