How important is Implatable Cardioverter Defibrillator
ICD’s are invaluable for treating patients with VT. These devices can be programmed to deliver different types of therapy for several kinds of VT, such as anti-tachycardia pacing or direct current shocks ranging from 1-40. When a milder treatment fails to convert a tachycardia, the device can proceed to deliver a stronger therapy. The ICD systems include an ICD pulse generator plus one or more leads which have electrodes for sensing cardiac rhythm and for delivery of pacing stimuli or shocks of up to 40 to the heart. The usual current pathway for a shock from the device is between an electrode coil in the RV apex and the can of the pulse generator.
Other electrodes may also be employed in the high voltage shocking circuit, such as a proximal electrode coil situated in the superior vena cava, and less frequently electrodes that are located either on the epicardium or subcutaneously. ICDs can deliver antitachycardia pacing even while charging internal capacitors in preparation for ICD re-examines the heart rate to see if VT is still present. If VT is reconfirmed, a shock is delivered to the heart.
Even ICDs with single leads have algorithms that are able to differentiate SVT from VT, based on the morphology of the intracardiac signal, suddenness of onset, and a ventricular lead, which greatly enhances their capacity to distinguish VT from other rhythms such as atrial fibrillation with rapid response, sinus tachycardia and other forms of SVT. This greatly diminishes the incidence of inappropriate shocks or therapies when the heart rate increases because of SVT rather than VT. Some ICDs offer atrial therapies for treating SVT, atrial flutter and atrial fibrillation, in addition to shocking and pacing therapies for VT.
ICDs can malfunction as a result of lead dislodgement, poor connection between the lead and the pulse generator, lead fracture, or breakdown of insulation of the lead. Rarely, the ICD itself may malfunction because of a flaw in manufacturing. Occasionally, manufacturers have issued recalls or technical warnings and physicians, their patients have had to weigh whether to explants and replace a possibly defective device.