A New Rate-Modulated Pacemaker System Optimized by Combination of Two Sensors ECKHARD ALT, HEINZ THERES, MICHAEL HEINZ, MARKUS MATULA, RUDOLF THILO, and HANS BLOMER From the 1st Medical Clinic, Rechts der Isar Medical Center, Technical University of Munich. ALT, E., ET AL.: A new rate-modulated pacemaker system optimized by combination of two sensors. A new rate-modulated pacemaker system optimized by combination of two sensors is described. The parame- ter body activity and central venous blood temperature control the pacemaker rate. The specijic charac- teristic of each parameter determines its roie within the algorithm. While the motion sensor yields a fast reaction following the onset OT a change of stress intensity, central venous blood temperature corresponds better to body metabolism. An indication of increased exercise from the motion sensor results in an accordingly rapid increase in the pacing rate. Unless this increased exercise is confirmed by an increase in central venous bJood temperature within 2 or 3 minutes, the new motion level will be assumed to he the new baseline motion value and the pace rate will return to a basic pacing rate. Prolonged inappropriate responses are there/ore avoided. Longer lasting exercise, fever and nonphysiological signals are recog- nized and handled safely. Exercise tests with five voJunteers under various conditions showed pacing rate behavior that was close to normal.(PACE, Vol. 11 August 1988} rate-modulated cardiac pacing, temperature pacing, activity pacing Introduction For most patients cardiac pacing is unahle to truly normalize or at least optimize circulatory performance since there are a number of defects inherent in this mode of treatment as it is usually applied today. This is especially reflected by tbe hemodynamic situation of the paced heart in pa- tients with myocardial impairment. The symp- toms of heart failure are often hardly improved by pacing and most individuals remain limited in their exercise capacity.^ The underlying cardiac disease as well as pacing itself must be held re- sponsible for this unfavorable situation. The major defect in contemporary normal nonrate-modulated pacing is the inability ofthese pacemaicers to increase the pacing rate in accor- dance with changing physiological requirements. Address for reprints: Eckhard U. AU, M.D., 1st Medical Clinic Technical University of Munich, Ismaninger Strasse 22, D - 8000 Muchen 80, Federal Republic of Germany. Received June 2, 1987; accepted June 3. 1987. Even so called "physiological pacing with DDD pacemakers" can redress this problem only in those patients who have an adequate rate in- crease of the intrinsic sinus rhythm when they exercise, A considerable number of parameters have been proposed in tbe past as input signals for a rate-modulated pacemaker system.^'^^ The most popular system at present is activity driven rate- modulated pacing.^ This system is simple and reli- able. But since the sensor responds to mechanical forces its relation to body metabolism varies with different kinds of physical activities. It responds rapidly to the onset of exercise, but its rate re- sponse to low or high workload exercise can differ only slightly.^'^^ At sensitive settings the system might be falsely triggered by enviromental noise.^^ Central venous blood temperature as a parameter for adjusting the rate of a rate-modu- lated pacing system has been studied by several groups in recent years.^'^""'^^ The ratio of me- chanical work to heat production is constant (22 ± 4 to 78 ± 4%) in hormonally healthy subjects. Therefore the amount of heat produced when PACE, Vol. 11 August 1988 1119