DELAYED EXERCISE RATE RESPONSE KINETICS DUE TO SENSOR CROSS-CHECKING IN A DUAL SENSOR RATE-ADAPTIVE PACING SYSTEM - THE IMPORTANCE OF INDIVIDUAL SENSOR PROGRAMMING

By cross-checking the relative sensor activation between a nonspecific and specific sensor during extraneous interference, a multisensor rat e adaptive pacemaker may be able to limit inappropriate rate responses . The effects of activity (ACT) sensor programming on rate response ki netics of a QT and ACT dual sensor VVIR pacemaker with sensor cross-ch ecking algorithm were studied in four patients with atrial fibrillatio n and complete heart block. The rate adaptive setting of each sensor w as individually optimized, and an equal rate contribution for the QT a nd ACT sensors (QT = ACT) was used in the dual sensor VVIR mode. Three maximal treadmill exercise tests were performed in random order in th ree different VVIR modes driven by QT only, QT = ACT, and in the dual sensor mode with the most sensitive (low threshold) ACT setting In the two dual sensor modes, the time for onset of rate response (delay tim e) was reduced (both < 15 sec) compared with QT only VVIR mode (233 +/ - 70 sec). However, the time to 50% of rate response in the low ACT th reshold dual sensor mode was delayed compared with to QT = ACT (450 +/ - 110 [95% confidence interval 234-666] vs 311 +/- 103 [109-513]sec, P < 0.05) and was similar to the QT only mode (401 +/- 120 [166-636]sec ). The time to reach 90% of rate response was similar in the three mod es tested. The resting activity counts registered by the ACT sensor we re < 5 and 16 +/- 2 counts/min in the optimally programmed and low thr eshold ACT settings, respectively. This resulted in sensor cross-check ing at rest in the over-programmed dual sensor VVIR mode, thereby limi ting the rate response. Thus, the combined sensor system provides a fa ster initial response to exercise than the QT only sensor. Programming the ACT threshold to low will prevent this faster response because of sensor cross-checking.