Cardiac Pacemaker

A pacemaker is a medical device designed to regulate the beating of the heart. The purpose of an artificial pacemaker is to stimulate the heart when either the heart's native pacemaker is not fast enough or if there are blocks in the heart's electrical conduction system preventing the propagation of electrical impulses from the native pacemaker to the lower chambers of the heart, known as the ventricles.

Modern pacemakers usually have multiple functions. The most basic form listens to the heart's native electrical rhythm, and if the device doesn't sense any electrical activity within a certain time period, the device will stimulate the vetricles of heart with a set amount of energy, measured in joules. The more complex forms include the ability to sense and/or stimulate both the the atrial and ventricular chambers.

When first invented, pacemakers controlled only the rate at which the heart's two largest chambers, the ventricles, beat.  Many advancements have been made to enhance the control of the pacemaker once implanted. Many of these enhancements have been made possible by the transition to microprocessor controlled pacemakers. Pacemakers that control not only the ventricles but the atria as well have become common. Pacemakers that control both the atria and ventricles are called dual-chamber pacemakers. Although these dual-chamber models are usually more expensive, timing the contractions of the atria to precede that of the ventricles improves the pumping efficiency of the heart and can be useful in congestive heart failure.

...More at Wikipedia

Related Links:

• US National Library of Medicine

Recent Hope Cube Blog Entries For Cardiac Pacemaker