The effects of long-term β-blockade on the ventilatory responses to exercise in chronic heart failure

Aims: Chronic heart failure (CHF) patients complain of breathlessness and fatigue. Beta-blockers improve symptoms, echocardiograpahic variables and prognosis in CHF, but their effect on exercise capacity remains unclear. The aim of this study was to describe the effects of long-term beta-blocker therapy on metabolic gas exchange variables and ventilation during exercise in CHF patients. Methods: 42 patients with symptomatic heart failure due to left ventricular systolic dysfunction (ejection fraction 33.2 (8.2)) on loop diuretics and angiotensin-converting enzyme inhibitors or angiotensin II antagonists, underwent exercise testing with metabolic gas exchange. They were then initiated onto and uptitrated to the maximum tolerated dose of beta-blockers. After I year of follow-up, patients were invited back for repeat testing. Results: 35 patients attended for repeat exercise testing. Four patients had died, and three had not tolerated beta-blockade. After I year, exercise time was increased (487 (221) vs. 500 (217), p < 0.05), and peak oxygen consumption and V-E/V-CO2 slope were unchanged (20.9 (5.0) vs. 20.0 (5.4), p = 0.15 and 36.7 (8.3) vs. 37.3 (7.8), p = 0.70). Peak ventilation, (61.5 (12.9) vs. 57.1 (13.4), p < 0.05), peak carbon dioxide production (1629 (404) vs. 1496 (375), p < 0.02) and hence respiratory exchange ratio ((1.02 (0.08) vs. 0.98 (0.06) p < 0.02) and p < 0.05) were reduced. Submaximal oxygen consumption and carbon dioxide production were lower at matched workloads. The slope relating symptoms to ventilation (B-org/V-E slope) was less steep following beta-blockade (0.18 (0.09) vs. 0.15 (0.06), p < 0.05). Conclusion: Long term beta-blocker therapy increases exercise time but not peak oxygen consumption, and reduces peak carbon dioxide production. CHF patients are less symptomatic for a given ventilation during exercise following beta-blocker treatment. (c) 2004 European Society of Cardiology. Published by Elsevier B.V All rights reserved.