Evidence Base for Pacemaker Mode Selection

Abstract

The development of implantable technology for cardiac rhythm management remains one of the seminal achievements of the second half of the 20th century. The modern era of cardiac pacing began in 1958, when Elmqvist and Senning1 implanted the first cardiac pacemaker by thoracotomy in a human, and Furman and Robinson2 implanted the first endocardial lead. The focus of development of cardiac pacing has changed over the last several decades. In the 1950s through 1970s, the emphasis was on the development of more reliable power sources and leads. By the end of the 1970s, the power source problems had been largely overcome, and efforts focused on mimicking the normal physiology of cardiac contraction. In the 1980s, in the United States, the focus on normal physiology led to the nearly universal application of dual-chamber pacing to restore atrioventricular (AV) synchrony in patients with sinus rhythm. As sensor technology improved in the 1980s and 1990s,3,4 the same physiological focus spurred the advent and generalization of sensor-driven, rate-modulated pacing to restore chronotropic competence. By the early 1990s, there were lessons from physiology and an emerging body of evidence from observational epidemiological studies.5,6 Indeed, some pacemaker physicians believed that randomized trials in pacing might not be necessary to demonstrate incremental gains in prevention of clinical events and improvement of quality of life with atrial-based pacing.7 It is certainly true that for many hypotheses, randomized trials are neither necessary nor desirable. For example, it would have been unethical to conduct randomized trials of cardiac pacing for the treatment of Stokes-Adams-Morgagni attacks because the benefit was so large.8 As a result of the evolution of progressively more sophisticated technologies, the most plausible effect sizes have become small to moderate, or between a 15% and 30% relative reduction in risk. Such effects, …