Cardiac pacemakers stimulate the heart with electrical impulses to maintain a regular heartbeat. Pacemakers are used to treat disorders in which the heart’s electrical conducting system is faulty, such as complete heart block. Some pacemakers produce impulses continually; others send an impulse only when the heart rate falls too low. Defibrillator pacemakers deliver an electric shock to the heart when ventricular fibrillation (rapid, uncoordinated contraction of the lower chambers of the heart) occurs to restore the normal rate and rhythm.
People who have heart failure and whose ECG shows that electrical activity of the heart’s electrical conducting system is very slow may be treated by implantation of a special type of pacemaker called a biventricular pacemaker. This device is inserted and positioned in the same way as a standard pacemaker and similarly has one wire running to the right atrium and another wire running to the right ventricle. A biventricular pacemaker also has a third wire, which runs to the outside surface of the left ventricle. This type of pacemaker delivers an impulse simultaneously to the left and right ventricles, which improves the efficiency of the heart by causing the heart chambers to contract in a more coordinated way (known as resynchronization).
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.