Influence of the pacing rate on the atrioventricular conduction time during aerobic and anaerobic exercise: basic concepts for a dromotropically controlled rate responsive pacemaker

Rate-responsive pacing using the atrio-ventricular conduction time: design and test of a new algorithm

The cardio-circulatory system of chronotropic incompetent patients is unable to adapt heart rate adequately to the level of strain. A common therapy is the implantation of a pacemaker that stimulates the heart at a rate derived from a strain related sensor signal. The paper describes a new pacemaker concept that uses a well-defined time interval in the electrogram as a sensor parameter, the atrioventricular conduction time (AVCT). Identification experiments with patients delivered the stationary and dynamic behaviour of AVCT subject to variations in the exercise rate and the pacing frequency. Furthermore, it was demonstrated that AVCT is perturbed by respiratory activity. The new rate-responsive algorithm, which uses the internal model control principle, explicitly takes into account the closed-loop nature of the underlying system. The major design objectives were: extended range of the individual heart rate; effective attenuation of the respiratory-related disturbance; and stability. Seven patients undergoing incremental exercise were paced with this AVCT-based algorithm. The experiments confirmed the suitability of this concept with respect to the design goals. The patients' peak intrinsic heart rate at exercise was 100 +/- 20min(-1). When paced with the AVCT algorithm, the paced heart rate was 126 +/- 12min(-1). The increase was significant (26 +/- 13min(-1); 15 to 53 min(-1)), which clearly demonstrated the potential of this concept to restore chronotropic competence.

[Rate-responsive pacemaker concept: parametric system identification]

The focus of this paper is the design of a rate-responsive pacemaker which uses the atrio-ventricular conduction time (AVCT) as an exertion related sensor signal. AVCT can be easily obtained from an intracardial electrogram. During atrial pacing AVCT shortens with exercise but increases with the stimulation rate. Hence, an AVCT based pacemaker always establishes a closed-loop system. General design rules for an AVCT pacemaker have been developed from our experimental results and a system-theoretical treatment. Topics addressed were the controller gain, uncertainties concerning the dynamics of the AVCT, the attenuation of disturbances, the closed-loop bandwidth and stability.

Rate-responsive pacing based on the atrio-ventricular conduction time

Chronotropic incompetent patients are unable to adapt their heart rate adequately to the level of exertion. One treatment for this disease is a rate-responsive pacemaker that stimulates the heart at a rate proportional to an exertion-related variable derived from an implemented sensor (e.g., ventilation). The atrio-ventricular conduction time (AVCT), which can act as such a sensor, corresponds to a well-defined interval in the intracardial electrogram. The AVCT is coupled to the sympathetic/parasympathetic activity of the autonomous nervous system (dromotropic effect), leading to a shortening of AVCT during exercise. We found that AVCT is also sensitive to the pacing frequency (pf). Hence, an AVCT-based pacemaker always constitutes a closed-loop system. General design rules for an AVCT pacemaker have been developed from our experimental results and a system-theoretical treatment with reasonable assumptions. Problems addressed were uncertainties concerning the AVCT dynamics and disturbances in the signal. The following rules for the controller design have been derived: 1) The controller gain strongly depends on the therapeutic range of the pf, which is set by the medical doctor; 2) the closed-loop bandwidth of the system should be smaller than the respiratory frequency; and 3) a robust control strategy, capable of guaranteeing stability for a certain set of plant models, should be applied.