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The Mysterious Human Heart The Mysterious Human Heart border=
A Series by David Grubin


Anatomy of a Pacemaker
This photo of the Microny K SR pacemaker shows the small scale of the technology
Some pacemakers, like the Microny K SR shown here,
are incredibly compact.

Photo courtesy of St. Jude Medical, Inc.
A pacing system includes an artificial pacemaker, one or two insulated wires called leads, and a programming device that remains on the outside of the body. Together, these components can be used to ensure that a person's heart maintains a healthy rate by constantly monitoring and -- if necessary -- intervening in the heart's electrical impulses. Most of today's pacemakers are demand pacemakers, meaning they only become active when they detect that the heart rate has moved outside the range considered safe.

The pacemaker is a small, metal (usually titanium) case surgically implanted in the shoulder area that contains electronic circuitry and a battery. The pacemaker's circuitry is like a tiny computer; it transforms the power from the battery into tiny, controlled electrical pulses. At the top of the metal container is a connector block, where the pacing lead attaches through a connector pin.

The lead body is very flexible, so the movement of the body does not disturb it. In an endocardial lead, the most common, the lead is inserted through a vein and guided into the right ventricle or right atrium. In an epicardial lead, most often used in children to accommodate their growing bodies, the lead is attached to the outside of the heart. A small fixation mechanism holds the lead to the heart tissue. At the very tip of the lead is at least one electrode, which delivers the electrical energy from the pacemaker into the heart tissue. The lead can also deliver information about the heart's rhythm back to the pacemaker.

At a check-up, the doctor at the clinic or hospital will use a programming device, sometimes called a programmer/recorder/monitor (PRM), to receive information about how the pacemaker or the heart itself is functioning. The programming device communicates with the pacemaker via radio waves from a wand held over the site where the pacemaker is implanted. The PRM sends instructions to the pacemaker about how often to deliver an electrical pulse.


Funding is provided by Medtronic, AstraZeneca, and Mars, Incorporated - makers of CocoaVia. Additional funding is provided by the Fannie E. Rippel Foundation. A co-production of David Grubin Productions, Thirteen/WNET New York and WETA Washington, D.C.
Medtronic AsrtaZeneca MARS Thirteen/WNET NEW YORK