Background: The slope of the relationship between ventilation and carbon dioxide production (VE/VCO2 slope), obtained during symptom-limited ramp exercise testing, reflects exercise ventilatory efficiency. Importantly, the VE/VCO2 slope is related to prognosis in patients with congestive heart failure (CHF). The aim of the present study was to determine the relationship between the institution of beta-blockers, carvedilol or metoprolol, and the VE/VCO2 slope during exercise in patients with CHF.
Methods and results: Fifty-seven patients with New York Heart Association functional class II or III with a radionuclide left ventricular ejection fraction (LVEF) of less than 40% received carvedilol or metoprolol in a randomized fashion. The VE/VCO2 slope, LVEF and plasma brain natriuretic peptide (BNP) concentration were determined before and after 16 weeks of treatment. LVEF improved (p<0.01), but the VE/VCO2 slope and BNP did not. A significant improvement in the VE/VCO2 slope was observed in patients with LVEF <29% or BNP >63 pg/ml (respective baseline median values) (p<0.05, p<0.05). In patients with BNP >63 pg/ml, the improvement effect on the VE/VCO2 slope with carvedilol was significantly greater than that with metoprolol (p<0.05) and a significant improvement in the VE/VCO2 slope was observed only in those who took carvedilol (p<0.01).
Conclusions: The VE/VCO2 slope was not improved after beta-blocker therapy in any of the patients. However, it did improve in patients with a lower LVEF or higher BNP level at baseline, and carvedilol was more effective than metoprolol in improving the VE/VCO2 slope in patients with higher BNP levels at baseline.