INTRINSIC HEART-RATE RESPONSE AS A PREDICTOR OF RATE-ADAPTIVE PACING BENEFIT

Objective: More than half of the pacemaker systems now being implanted can be rate adaptively paced. Our objective was to determine which pa tients benefit from rate-adaptive pacing in terms of improvement in ma ximum performance and aerobic capacity. Methods: Thirty patients with implanted accelerometer-driven, rate-adaptive pacemakers underwent a s tandardized, ergospirometrically and maximally symptoms=limited cardio pulmonary exercise (CPX) stress test with both rate-adaptive and fixed -rate stimulation in a randomized order. The patients were divided int o three groups depending on the intrinsic heart rate achieved during m aximum workload: group 1 achieved less than or equal to 90 beats per m inute (bpm), group 2 achieved 90 to less than or equal to 110 bpm, and group 3 achieved >110 bpm. Results: Group 1 demonstrated a significan t increase (p less than or equal to 0.01) in maximum oxygen uptake fro m 16.4+/-5.6 mL/kg/min with fixed-rate pacing to 23.2+/-11.1 mL/kg/min (+41.5%) with rate-adaptive pacing. At the anaerobic threshold, oxyge n uptake significantly increased (p less than or equal to 0.01) from 1 1.8+/-2.7 mL/kg/min to 15.7+/-5 mL/kg/min (+33.1%). Group 2 patients s howed an increase in maximum oxygen uptake from 23.3+/-5.4 mL/kg/min t o 25.3+/-4.9 mL/kg/min (+8.5%, p less than or equal to 0.05) as well a s an increase in oxygen uptake at the anaerobic threshold from 15.9+/- 2.6 mL/kg/min to 18.1+/-2.9 mL/kg/min (+13.8%, p less than or equal to 0.05) with rate-adaptive pacing. Group 3 demonstrated no significant difference between the two pacing methods (from 25.6+/-9.4 mL/kg/min t o 25.9+/-9.3 mL/kg/min and from 15.8+/-5.5 mL/kg/min to 16.3+/-6 mL/kg /min). No difference in maximum oxygen uptake and in oxygen uptake at the anaerobic threshold was evident among the three groups when paced rate adaptively (not significant). Conclusion: The second-generation, accelerometer controlled rate-adaptive pacemakers used in testing enab led a stress-oriented heart rate increase and an age- and gender-depen dent adequate matching of maximum performance. The benefit from a rate -adaptive system to the patient increases as his or her chronotropic r eserve limitation became more pronounced.