EFFECTS OF SENSOR SELECTION ON EXERCISE STROKE VOLUME IN PACEMAKER DEPENDENT PATIENTS

The effects of sensor selection and sensor blending on the cardiovascu lar response to graded exercise was evaluated in 10 patients (age 74 /- 2 yrs; 7 men and 3 women) implanted with a dual sensor rate adaptiv e VVIR pacemaker (Vitatron Topaz(TM) model 515). Patients underwent th ree graded exercise tests (GXT) with sensor programming randomly assig ned. For a given graded exercise test the pacemaker was programmed int o activity sensing (ACT), QT sensing, or dual sensing (ACT = QT). Data were recorded at rest and during each stage of the graded exercise te xt. Oxygen uptake (VO2) was measured continuously using a Q Plex I sys tem. Heart rate (HR), stroke volume (SV), and cardiac output (Qc) were measured by impedance cardiography. Systolic time intervals were calc ulated from simultaneous recordings of the EGG, phonocardiogram, and t he impedance cardiogram. in response to the GXT no differences in peak VO2 were observed across the three sensor settings. Regardless of the sensor setting Qc increased linearly with each increment in VO2. The HR response to ACT only pacing was significantly higher than in the ot her two pacing conditions. During ACT only pacing SV failed to rise in response to exercise. The increased exercise Qc during QT and ACT = Q T pacing were mediated by significant increases in both HR and Sir. Th e QT and dual pacing conditions were also associated with longer diast olic filling times. The data indicate that the mechanisms responsible for the increase Qc during exercise were different for ACT versus ACT = QT or QT sensor-driven pacing.