Pacemakers

What Pacemakers Do

The heart's "natural" pacemaker is called the sinoatrial (SA) node or sinus node. It's a small mass of specialized cells in the top of the heart's right atrium (upper chamber). It makes the electrical impulses that cause your heart to beat.

A chamber of the heart contracts when an electrical impulse moves across it. For the heart to beat properly, the signal must travel down a specific path to reach the ventricles, the heart's lower (pumping) chambers.

The natural pacemaker may be defective, causing the heartbeat to be too fast, too slow or irregular. The heart's electrical pathways also may be blocked.

Pacemakers (or "artificial pacemaker", so as not to be confused with the heart's natural 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.

How Pacemakers Do It

The first external pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950. A substantial external device, it was somewhat crude and painful to the patient in use. A number of inventors, including Paul Zoll, made smaller but still bulky external devices in the following years. The pacemakers built in the late 1950s were bulky, relied on external electrodes, and had to be plugged into a wall outlet. External electric shocks were frequently too traumatic for young heart block patients, and the AC-operated pacemaker could fail during a power blackout.

An "artificial pacemaker" is a small, battery-operated device that helps the heart beat in a regular rhythm. Some are permanent (internal) and some are temporary (external). They can replace a defective natural pacemaker or blocked pathway.

The first implantation into a human was made in 1958 by a Swedish team using a pacemaker designed by Rune Elmqvist and Åke Senning. The device failed after three hours. A second device was then implanted which lasted for two days. The world's first implantable pacemaker patient, Arne Larsson, survived the first tests and died in 2001 after having received 22 different pacemakers during his lifetime. In February 1960, an improved model relying on better materials was implanted in Montevideo, Uruguay. That device lasted until the patient died of other ailments, 9 months later. The early Swedish-designed devices used rechargeable batteries, which were charged by an induction coil from the outside.

Devices constructed by the American Wilson Greatbatch entered use in humans from April 1960 following extensive animal testing. The first patient lived for a further 18 months. The early devices suffered from battery problems - every patient required an additional operation every 24 months to replace the batteries. Others who contributed significantly to the technological development of the pacemaker in the pioneering years were Bob Anderson of Medtronic Minneapolis, Geoffrey Davies of Devices Ltd in England, Barouh Berkovits and Sheldon Thaler of American Optical, Geoffrey Wickham of Telectronics Australia, Walter Keller of Cordis Corp. of Miami, Hans Thorander who joined previously mentioned Rune Elmquist of Elema-Schonander in Sweden, Janwillem Van den Berg of Holland and Manuel A. Villafaña of Cardiac Pacemakers Inc.

Pacemakers require wires (called leads) to both send the pacing pulses to the heart and sense the intrinsic rhythm of the heart. The first pacemakers required these leads to be placed surgically on the outer surface of the heart. In the mid 1960s, the first transvenous leads were placed. This allowed the placement of pacemakers without opening the thoracic cavity and therefore without the use of general anaesthesia.