ABSTRACT
The practical use of an implantable device for delivering a controlled, rhythmic electric stimulus to maintain the heartbeat is relatively recent: cardiac pacemakers have been in clinical use only slightly more than 30 years. Although devices have gotten steadily smaller over this period (from 250 g in 1960 to 25 g today), the technological evolution goes far beyond size alone. Early devices provided only single-chamber, asynchronous, nonprogrammable pacing coupled with questionable reliability and longevity. Today, advanced electronics afford dual-chamber multiprogrammability, diagnostic functions, rate response, data collection, and exceptional reliability, and lithium-iodine power sources extend longevity to upward of 10 years. Continual advances in a number of clinical, scientific, and engineering disciplines have so expanded the use of pacing that it now provides cost-effective benefits to an estimated 350,000 patients worldwide each year.
