[Is the response to cardiac pacing controlled by central venous temperature physiological?]

Rate responsive cardiac pacemakers are capable of adapting their pacing rate according to metabolic demands in the physical effort and some of the sensors in use even according to such physiological stimuli in which the level of metabolism remains unchanged. Central blood temperature (CVT) could possibly represent a much-needed and searched ideal sensor, which truly reflects physiological processes. In order to verify the response of the thermistor sensor under various physiological conditions, 10 single-chamber VVIR pacemakers Thermos M 02 (Biotronik) were implanted since 1993 through 1995. Our group of patients consisted of 9 men and 1 women. 8 patients had chronic atrial fibrillation with bradycardia and ventricular chronotropic incompetence, 2 patients suffered from the 3rd degree atrioventricular block. The mean age at the time of implant was 62.4 (52-72) years, the mean follow-up period has amounted to 23 (2-32) months. The CVT response to physical exercise was proportional and smooth, especially in the strenuous physical effort. In contrast to some other sensors, CVT exhibited the physiological reaction also in situations in which the metabolic level did not change. It displayed a physiological circadian fluctuation of the pacing rate. Nevertheless, a markedly prolonged reaction time at the onset of physical exercise in the patients who were still "cold" was a shortcoming of this principle. The special sensor lead is a must and only the ventricular pacing is possible. Isolated CVT is not the ideal sensor but it be combined with fast sensors. It will undoubtedly be one of the sensors within the automatic multisensor pacemaker in the forseeable future. (Tab. 1, Fig. 1, Ref. 15.)