Editing Pacemaker (section)

=== Permanent transvenous pacing ===
Permanent pacing with an implantable pacemaker involves transvenous placement of one or more pacing electrodes within a chamber, or chambers, of the heart, while the pacemaker is implanted under the skin below the clavicle. The procedure is performed by incision of a suitable vein into which the electrode [[Lead (electronics)|lead]] is inserted and passed along the vein, through the valve of the heart, until positioned in the chamber. The procedure is facilitated by [[fluoroscopy]] which enables the physician to view the passage of the electrode lead. After satisfactory lodgement of the electrode is confirmed, the opposite end of the electrode lead is connected to the pacemaker generator.

There are three basic types of permanent pacemakers, classified according to the number of [[Heart chamber|chambers]] involved and their basic operating mechanism:<ref name="url_Heart_Rhythm_Society">{{cite web |url=http://www.hrspatients.org/patients/treatments/pacemakers.asp |title=Pacemakers, Patient and Public Information Center : Heart Rhythm Society |archive-url=https://web.archive.org/web/20100619152432/http://hrspatients.org/patients/treatments/pacemakers.asp |archive-date=2010-06-19 |url-status=dead }}</ref>
* ''Single-chamber pacemaker''. In this type, only one pacing lead is placed into a chamber of the heart, either the [[Atrium (heart)|atrium]] or the [[Ventricle (heart)|ventricle]].<ref name="url_Heart_Rhythm_Society" />
* ''Dual-chamber pacemaker''. Here, wires are placed in two chambers of the heart. One lead paces the atrium and one paces the ventricle. This type more closely resembles the natural pacing of the heart by assisting the heart in coordinating the function between the atria and ventricles.<ref name="url_Heart_Rhythm_Society" />
*''Biventricular pacemaker''. This pacemaker has three wires placed in three chambers of the heart. One in the atrium and two in either ventricle. It is more complicated to implant.<ref name="url_Heart_Rhythm_Society" />
* ''Rate-responsive pacemaker''. This pacemaker has sensors that detect changes in the patient's physical activity and automatically adjust the pacing rate to fulfill the body's metabolic needs.<ref name="url_Heart_Rhythm_Society" />

The pacemaker generator is a [[hermetically sealed]] device containing a power source, usually a [[Lithium metal battery|lithium battery]], a sensing amplifier which processes the electrical manifestation of naturally occurring heart beats as sensed by the heart electrodes, the [[computer]] logic for the pacemaker and the output circuitry which delivers the pacing impulse to the electrodes.

Most commonly, the generator is placed below the subcutaneous fat of the chest wall, above the muscles and bones of the chest. However, the placement may vary on a case-by-case basis.

The outer casing of pacemakers is so designed that it will rarely be rejected by the body's [[immune system]]. It is usually made of [[titanium]], which is inert in the body.