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Effect of Biventricular Pacing on the Exercise Pathophysiology of Heart Failure^*

Karlman Wasserman, MD, PhD; Xing-Guo Sun, MD and James E. Hansen, MD, FCCP

^* From the Department of Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA. Source Investigators and Investigational Centers for the study are listed in the ^Appendix.

Corresponding author: Karlman Wasserman, MD, PhD, Department of Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson St, Torrance, CA 90502; e-mail: kwasserman{at}labiomed.org

Abstract

Background: Biventricular pacing (BVP) is used for cardiac resynchronization therapy in wide-QRS-complex heart failure. We sought to quantify the effect of BVP on the exercise pathophysiology of heart failure patients.

Methods: Using cardiopulmonary exercise testing, we analyzed exercise data for a multicenter study sponsored by St. Jude Medical. Patients had pacemaker electrodes implanted in both ventricles in the standard manner and were randomized by St. Jude before exercise testing. Exercise measurements included peak oxygen uptake (O₂), peak O₂ pulse, anaerobic threshold (AT), and ventilatory equivalent for CO₂ (reflecting change in peak exercise cardiac output, stroke volume, maximal sustainable exercise capacity, and ventilation-perfusion mismatching, respectively) at baseline and at a 6-month follow-up. The studies included progressively and uniformly increasing work rate to maximum tolerance. The investigators were blinded both to sponsor-controlled randomization and pacemaker status. There were 239 paired 6-month studies, as follows: 47 studies served as the control with the pacemaker off (ie, the BVP-OFF group); and 192 patients received pacing (ie, the BVP-ON group).

Results: The BVP-ON group significantly improved in all exercise parameters in contrast to the control group (p < 0.0001). When baseline measurements for the BVP-ON group were ranked in quintiles, only patients in the three functionally worst quintiles improved significantly at 6 months (peak O₂ < 11.6 mL/min/kg, AT < 7.6 mL/min/kg, peak O₂ pulse < 12.0 mL/beat, and minute ventilation/CO₂ ratio at AT > 38.1) [p < 0.01 to < 0.0001].

Conclusion: BVP benefited aerobic function and ventilation-perfusion mismatching most in those patients with the greatest physiologic impairment.

Key Words: anaerobic threshold • biventricular pacing • cardiopulmonary exercise testing • cardiac resynchronization therapy • heart failure • oxygen transport • peak O₂ pulse • peak O₂ • ventilatory efficiency