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This year, over 175,00 pacemakers will be implanted in patients in the United States. These devices are taken almost for granted, yet they are remarkable pieces of equipment.

In the animation above, a pacemaker is being placed. "Leads" which pass electrical charges to and from the heart are inserted into the large vein that runs under the collarbone and advanced to the chambers on the side of the heart that receives venous blood return. In real life, x-ray is used to help guide them. In this illustration, two leads are used, one placed in the upper chamber (right atrium), and the other into the lower chamber (right ventricle). The "pulse generator", which is the brains and contains the batteries used to power the pacemaker, is connected to the leads, and then placed in a "pocket" under the skin near the collarbone, the most common place of insertion of modern pacemakers. The pulse generator then sends energy down the leads which "captures" the heart muscle: that is, causes it to depolarize, illustrated here by turning a blue color. This electrical activity will stimulate the contraction of the heart muscle which is necessary for its pumping action. With two leads in place, the normal activation sequence of atrium first followed by ventricle is maintained.

Today's pacemakers sense the electrical activity which the heart is generating on its own, and only deliver electrical impulses if they are needed. Despite vast and ongoing improvements in technology, the average, or most common pacemakers implanted today is one which simply keeps the heart from beating too slow. It does not correct irregular beating, nor does it prevent the heartbeat from going too fast.
©COPY 1997 HeartPoint    Updated February 1998

To learn more about these modern miracles, read on.


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