Behavior of a respiratory driven pacemaker and direct respiratory measurements

In 10 patients with a mean age of 76 +/- 8 years, a rate responsive pacemaker (Meta-MV, Telectronics) was implanted in the left pectoral site. An exercise test was performed in SSI ("adaptive") mode, allowing the device to measure the changes in thoracic impedance. The "slope number" at maximal exercise was chosen to program the pacemaker for a second exercise test in rate responsive mode. Direct measurements of respiratory rate and minute volume were correlated with the pacing rate. After 1 minute of exercise, pacing rate increased by 6% and it decreased smoothly after maximal exercise. The programmed maximal rate was reached at the maximum exercise level in six patients. During 24-hour Holter recording, the mean maximal pacing rate was 103 +/- 18 beats/min. For individual patients, a good correlation of pacing rate with respiratory rate (r = 0.757), oxygen consumption (r = 0.731), and minute volume (r = 0.800) was observed. The data from the entire group showed a highly significant correlation of changes in pacing rate and in respiratory parameters for different levels of exercise and recovery. In a subgroup of five patients, the slope numbers at maximal exercise were reproducible after 10 months. It was concluded that minute volume and its changes were recognized in a reliable way by the Meta-MV pacemaker.