What is the ideal rate-adaptive sensor for patients with implantable cardioverter defibrillators: lessons from cardiac pacing.

The development of implantable pacemakers in the clinical setting mirrors the implementation of advanced technical possibilities. In the United States, 83% of all pacemakers implanted in 1996 had rate response as a programmable option. A variety of sensors have been proposed and used for rate control. Among today's many concepts, accelerometer-controlled pacing is the most widely used rate-adaptive principle. Although the use of a second sensor is currently of proven benefit for only a limited number of patients, the concept of closed-loop pacing--implementing a negative feedback between pacing rate and the control signal--merits further investigation. This is of special importance in defibrillator patients whose myocardial contractility is generally limited. These patients are most sensitive to pacing rates that are too high for a given metabolic situation. The integration of rate-adaptive pacing into defibrillators is a natural consequence of the technical evolution.