Rate adaptive pacing--clinical experience with three different pacing systems.

Physiological stimulation can be achieved by either bifocal or rate responsive pacing. The latter pacemakers adapt the heart rate to physical activity by biological signals. Out of many possible approaches only three pacemaker systems for rate responsive pacing are available: the QT-pacemaker (Tx or Quintech), the respiratory biorate pacemaker, and the activity detecting Activitrax. Our own experiences (8 QT, 6 Biorate, 8 Activitrax pacemakers) and a survey of 95 QT- and 37 Biorate pacemakers from 11 centers are reported. The Biorate pacemaker functions without any problems; its present disadvantage is limited programmability. With the Tx pacemaker failing, frequency adaptation (26%) was found more often in the early series, mostly due to voltage polarization at the tip of the electrode. The Activitrax pacemaker gives satisfactory frequency adaptation, largely depending on the activity of the muscles of the shoulder and pectoral region.