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Cardiac pacemakers that provide permanent pacing by using an implantable pacemaker pulse generator. Implantable pacemakers usually consist of a small unit including a pulse generator with electronic circuitry and a battery that senses the cardiac activity and produces the pacing electrical pulses, and external leads with electrodes at the distal tip fixed to the heart (e.g., myocardial or endocardial) that conduct the electrical signals to and from the heart. Pacemakers can use a variety of technologies and implantation positions; the pacing unit is typically implanted in a surgically created pocket inside the abdomen and attached to the cardiac leads. Most pacemakers permit noninvasive reprogramming of pacing parameters following implantation (i.e., multiprogrammable pacemakers), and some dynamically increase or decrease their pacing rate in response to patient physiological activity (i.e., rate-modulated or rate-responsive pacemakers). Implantable pacemakers are mostly used in the permanent treatment of slowed heart rhythms (bradycardia), in certain classes of cardiac arrhythmias, and in other irregular heart rhythms that need permanent pacing treatment. Some pacemakers that do not include leads (known as leadless pacemakers) and can be implanted inside the heart using catheterization procedures are also available.
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