Rate-responsive pacing based on the atrio-ventricular conduction time: Comparison of different algorithms

Rate-responsive pacing based on the atrio-ventricular conduction time is a promising therapy for restoring physiological heart rate control in chronotropic incompetent patients. This paper compares four different algorithms. Three of them had been formulated as patents, but no real test or application has been reported up to now. The fourth was recently published by the authors of this paper. There the steps involved in the development process were stationary and dynamic system identification, control system design and a pilot study with patients. The data obtained were used to formulate a simulation model of the cardiac system by means of which the other algorithms were tested. Test criteria were stability, the attenuation of disturbances and the response time to changes of the exercise rate. None of the three patents worked when being strictly implemented as described. The problems encountered were instability, unusable parameterisations and some questionable adaptation mechanisms. In a redesign we tried to improve the patents, but only in one case would the results obtained justify real use. In the other cases the variability of the pacing frequency was intolerably high.