A pacemaker is a small, battery-powered device that emits small electrical currents that stimulate the heart muscle to contract. The pacemaker system consists of a pulse generator and battery, which generate the electrical impulses, and leads or wires that transmit impulse to the myocardium or heart muscle. Pacemakers can be classified according to the number of chambers paced (single or dual chamber) or whether the pacing rate does (rate responsive) or does not respond to the patient’s activity (fixed rate pacemaker).
Why It Is Done
Pacemakers are implanted to treat bradycardia, i.e. heart rates that are so slow the heart does not pump enough blood to meet the body's needs, resulting in symptoms such as fainting, dizziness, weakness or fatigue.  In patients with bradycardia who do not have symptoms, pacemakers can be implanted if the bradycardia is expected to worsen and cause complications in the future.
How Is It Implanted
Pacemaker implantation is done using local anesthesia and some sedation.  The procedure can be performed in a regular operating room suite, cardiac catheterization laboratory or electrophysiology laboratory. The patient’s skin is first cleaned or prepped with an antibiotic solution. The patient is then covered by sterile surgical drapes leaving only the cleaned operative site exposed. After local anesthesia is infiltrated, an incision is made on the skin of the chest. The incision is then enlarged to create a small pocket under the skin.  This is where the pulse generator is placed. A long needle is then used to enter the subclavian vein as it runs underneath the clavicle. The pacemaker leads are usually threaded through this vessel and into the heart. The leads are placed in different parts of the right ventricle and right atrium in order to identify a site through which the myocardium can be stimulated with the least amount of energy.  Within the heart the leads are anchored by either small plastic fins or tines or a short screw that extrudes from the leads tip. For added stability the leads are also sutured to the muscle of the chest wall. The leads are then connected to generator and both then fitted into the pocket. The incision is then sutured closed.
Abraham Salacata, MD, FACC