Cardiac pacemakers are electronic devices that trigger the heart to beat. In simple terms, the typical pacemaker consists of a battery pack, somewhat smaller then a cigarette package, that is surgically implanted under the skin of the chest. The battery is connected to wires leading through the veins of the neck into the heart. A tiny computer next to the battery senses pauses in the pulse and instructs the battery when to fire a charge down the wires to stimulate a cardiac contraction. The computer is programmed to activate at a certain rate if the natural heartbeat slows or stops.
Modern pacemakers are engineering marvels.
They can sense and fire in a variety of ways to stimulate normal cardiac action. In choosing a pacemaker, the surgeon takes into account the patient's particular cardiac abnormality.