Effect of Biventricular Pacing on the Exercise Pathophysiology of Heart Failure

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 ( V˙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 V˙o2 < 11.6 mL/min/kg, AT < 7.6 mL/min/kg, peak O2 pulse < 12.0 mL/beat, and minute ventilation/ V˙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.