Rate-responsive pacing based on sympathetic activity.

Modern pacemaker technology makes the adaptation of pacing rate to haemodynamic requirements possible. The most ambitious approach aims at restoration of the physiological closed-loop system by utilising the information that is supplied by the autonomic nervous system (ANS) and extracted from myocardial contractile performance. Measurement is accomplished by the impedance method, with the stimulation electrode as measuring electrode. The ventricular inotropic parameter (VIP) has been identified as an ANS-dependent parameter. A special detection algorithm RQ (regional effective slope quantity) with high ANS sensitivity has been developed. Rate adaptation has been achieved by using an individually adjustable inotropic index (II). The concept has been evaluated in a multicentre study employing a standardised exercise protocol. The results in patients with AV block demonstrate the excellent agreement between the spontaneous sinus rhythm and the ANS-controlled stimulation rate during different forms of exercise. Measurement of mean arterial blood pressure (MABP) supports the physiological approach to adapting the pacing rate to different kinds of haemodynamic challenge.