QUANTITATIVE COMPARISON OF RATE RESPONSE AND OXYGEN-UPTAKE KINETICS BETWEEN DIFFERENT SENSOR MODES IN MULTISENSOR RATE-ADAPTIVE PACING

Although multisensor pacing may mitigate the inadequacy of rate adapta tion in a single sensor system, the clinical role of multisensor drive n rate adaptive pacing remains unclear. The cardiopulmonary performanc e of six patients (mean age 63.5 +/- 10 years) who had undergone the i mplant of combined QT and activity VVIR (Topaz(TM) pacemakers was asse ssed during submaximal and maximal treadmill exercise with the rate re sponse sensor randomly programmed to either single sensor mode, QT and activity (ACT), or dual sensor mode, with equal contribution of QT an d ACT (QT = ACT), The rate of response, the proportionality, oxygen ki netics, and maximal exercise performance of the various sensor modes d uring exercise were measured and compared. The ACT sensor mode ''overp aced'' and the QT and QT = ACT sensor modes ''underpaced'' during the first three quartiles of exercise (p < 0.05). The ACT sensor mode also gave the fastest rate of response with the shortest delay (13 +/- 1.5 sec vs 145 +/- 58 sec and 41 +/- 17 sec, P < 0.05), time to 50% rate response (39 +/- 2.7 sec vs 275 +/- 48 sec and 203 +/- 40 sec, P < 0.0 5), and time to 90% of rare response (107 +/- 21 sec vs 375 +/- 34 sec and 347 +/- 34 sec, P < 0.05) and a smaller oxygen debt (0.87 +/- 0.1 6 L vs 1.10 +/- 0.2 L and 1.07 +/- 0.18 L, P < 0.05) compared to the Q T and QT = ACT sensor modes, respectively. These differences were most significant at low exercise workloads. Thus, different sensor combina tions result in different rate response profiles and oxygen delivery, especially during low level exercise. However, the observed oxygen kin etics difference was workload dependent, and its clinical relevance re mains to be tested. Despite the marked difference in exercise rate pro file and oxygen kinetics, there was no difference in the maximal oxyge n uptake, anaerobic threshold, and exercise duration between the vario us sensor modes during maximal exercise.