An implantable cardioverter-defibrillator (ICD) is a pager-sized device placed in the chest to reduce the risk of sudden cardiac death if the lower chambers of the heart (ventricles) go into a dangerous rhythm and stop beating effectively (cardiac arrest). An ICD might be needed if you have a dangerously fast heartbeat (ventricular tachycardia) or a chaotic heartbeat that keeps your heart from supplying enough blood to the rest of your body (ventricular fibrillation). This problem might manifest as a passing out episode or aborted sudden cardiac death. ICDs are also implanted as a preventive measure in patient who have never suffered these events but have been deemed to be at significant risk of sudden cardiac death. Commonly these are patients with severe weakness of the heart muscle (cardiomyopathy), patient with significant heart muscle damage from previous heart attack, inherited life threatening arrhythmia disorders.
ICDs detect and stop life threatening abnormal heart arrhythmias. The device continuously monitors the heart rhythm and delivers electrical pulses to restore a normal heart rhythm when necessary. These devices are 99 percent effective in stopping life-threatening abnormal heart rhythms and are the most successful option to treat ventricular fibrillation (VF), the major cause of sudden cardiac arrest (SCA). An ICD differs from a pacemaker — another implantable device used to help control abnormal heart rhythms. Most ICDs can act as pacemakers, but pacemakers without ICD capabilities cannot deliver the electric shock to abort sudden cardiac death in the setting of ventricular tachycardia or ventricular fibrillation.