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 patients benefit from rate-adaptive pacing in terms of improvement in maximum performance and aerobic capacity. Methods: Thirty patients with implanted accelerometer-driven, rate-adaptive pacemakers underwent a standardized, ergospirometrically and maximally symptoms=limited cardiopulmonary exercise (CPX) stress test with both rate-adaptive and fixed-rate stimulation in a randomized order. The patients were divided into three groups depending on the intrinsic heart rate achieved during maximum workload: group 1 achieved less than or equal to 90 beats per minute (bpm), group 2 achieved 90 to less than or equal to 110 bpm, and group 3 achieved >110 bpm. Results: Group 1 demonstrated a significant increase (p less than or equal to 0.01) in maximum oxygen uptake from 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, oxygen uptake significantly increased (p less than or equal to 0.01) from 11.8+/-2.7 mL/kg/min to 15.7+/-5 mL/kg/min (+33.1%). Group 2 patients showed an increase in maximum oxygen uptake from 23.3+/-5.4 mL/kg/min to 25.3+/-4.9 mL/kg/min (+8.5%, p less than or equal to 0.05) as well as 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 to 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 enabled a stress-oriented heart rate increase and an age- and gender-dependent adequate matching of maximum performance. The benefit from a rate-adaptive system to the patient increases as his or her chronotropic reserve limitation became more pronounced.