Clinical performance of automatic closed-loop stimulation systems.
Inos pacemakers use contraction dynamics to regulate the pacing rate according to the Closed-Loop Stimulation (CLS) principle. The physician can program only the lower and upper rate limits, while the internal rate responsive parameters are continually adjusted to changing patient conditions. Seventy-two patients with sinus node disease were enrolled in the multicenter Rate Behavior of the Pacing System Inos (2) CLS during Daily Life (RAPID) study to evaluate the appropriateness of CLS rates during daily activities and the long-term stability of the system. The pacemakers clearly differentiated between climbing stairs, descending stairs, and slow walking, with the corresponding peak rates of 104 +/- 18, 95 +/- 15, and 88 +/- 11 beats/min, respectively (P < 0.001 for any pair of activities). The peak CLS rate during the color-word test was significantly higher than that at rest (80 +/- 8 vs 67 +/- 7 beats/min, P = 0.002). The 24-hour heart rate trends retrieved from the pacemaker memory at 3, 6, and 12 months after implantation appeared appropriate in all patients except for two whose pacing rates were occasionally too fast during the night. Mean diurnal and nocturnal rates determined at 3-month, 6-month, and 12-month examinations fluctuated only slightly, from 74.6-75.3 beats/min (diurnal,P = NS) and from 67.0-68.1 beats/min (nocturnal,P = NS), indicating a satisfactory long-term stability of the system. The incidence of atrial pacing events during the entire follow-up was 82 +/- 18%. A 6.5-8.3 beats/min difference, on average, between day and night (P < 0.001)and distinction between different daily activities seem to evidence sensitivity of the automatic CLS-driven pacemakers to physiological demands despite minimum programming requirements.