Pacing can be instituted for many reasons: in the case of slow ventricular rate (bradycardia, heartblock) or rapid ventricular rate (atrial fibrillation or atrial flutter) or when dangerous arrhythmias are noted when the EKG is monitored.
The first pacemaker was designed and built by the Canadian electrical engineer John Hopps in 1950, a substantial external device it was somewhat crude and also painful to the patient in use. A number of inventors, including Paul Zoll, made smaller but still bulky devices in the following years. The first true implantable pacemaker was completed in 1958 by the American Wilson Greatbatch, who made the first transistorized device. He had patented the idea some five years earlier.
The first implantation into a human was made in 1958 by a Swedish team using a pacemaker invented by Rune Elmqvist and Åke Senning. The device failed after three hours.
Devices constructed by Greatbatch began being implanted 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.
The first American-made nuclear powered pacemaker was developed and implanted at Newark Beth Israel Medical Center in Newark, New Jersey.
When first invented, pacemakers controlled only the rate of speed at which the heart's two largest chambers, the ventricless, beat.
More recently, pacemakers which control not only the ventricles but the atria as well have become common. 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.
Sometimes devices resembling pacemakers, called ICDs (implantable cardioverter/defibrillators] are implanted. These devices have the ability of sensing dangerous rhythm disturbances and then shocking the heart back into a normal rhythm.