A pacemaker is an electronic device that regulates a slow or erratic heartbeat. When your heart is working correctly, its own “natural pacemaker” produces the electrical impulses needed to make your heart beat normally. If this natural pacemaker becomes defective, or if there is a blocked pathway to the heart, you may develop an arrhythmia, meaning your heartbeat may become too fast, too slow, or irregular. Artificial pacemakers are designed to control your heartbeat through a series of rhythmic electrical discharges that help your heart pump properly. While an internal pacemaker is permanent, the external type is temporary.
Implantable Cardioverter Defibrillator (ICD)
ICDs have been very useful in preventing sudden death in patients with known, sustained ventricular tachycardia or fibrillation. Studies have shown that they may have a role in preventing cardiac arrest in high-risk patients who haven’t had but are at risk for, life-threatening ventricular arrhythmias. On an acute basis, a tachycardia, which is an abnormally fast heartbeat (more than 100 beats per minute), could be life-threatening but can be stopped by giving the heart an electric shock or by rapid “overdrive” pacing with an electrode catheter. An implantable device, the ICD, can provide automatic electrical therapy on a chronic basis for patients with recurrent tachycardias or fibrillation.
An ICD is a battery-powered device placed under your skin, beneath the collarbone, that is connected to your heart by one or more wires (leads) and keeps track of your heartbeat. The ICD detects dangerous heart rhythms (arrhythmias) then sends electrical signals that ‘shock’ your heart out of the dangerous rhythms and allow normal rhythms to resume.
The American Heart Association recommends that before a patient is considered to be a candidate for an implanted defibrillator, the arrhythmia in question must be life-threatening. Remediable causes of the arrhythmia must be ruled out.
You can find further information here: The American Heart Association Website