[Measuring intracardiac impedance for determining sympathetic nerve activity in frequency-adjustment electrostimulation--1: Biomedical technical principles].

Modern Pacemaker technology makes it possible to adapt the pacing rate to hemodynamic requirements. The most ambitious approach aims at restoring the physiological closed-loop system by utilizing the information supplied by the Autonomic Nervous System and extracted from myocardial contractile performance. Measurement is accomplished by the impedance method using the stimulating electrode as the measuring electrode. The Ventricular Inotropic Parameter (VIP) has been identified as an ANS-dependent parameter. A special detection algorithm, the Regional Effective Slope Quantity (RQ), with a high ANS sensitivity has been developed specially for the purpose. Rate adaptation is achieved by using an individually-adjustable Inotropic Index (II). The concept has been evaluated in a multicenter study employing a standardized exercise protocol. The clinical results will be presented in Part 2 of this paper.