Ventilatory response to exercise improves risk stratification in patients with chronic heart failure and intermediate functional capacity

Abstract

Background: Peak oxygen consumption (VO2) has an important prognostic role in chronic heart failure (CHF), but its discriminatory power is limited in patients with intermediate exercise capacity (peak VO2 between 10-18 mL/kg/min). Thus, supplementary exertional indexes are greatly needed.

Methods: Six hundred patients with CHF with left ventricular ejection fraction (LVEF) < or = 40% who performed a symptom-limited cardiopulmonary exercise testing were screened and followed up for 780 +/- 450 days.

Results: Eighty-seven patients had major cardiac events (77 cardiac deaths and 10 urgent heart transplantations). Multivariate analysis revealed the rate of increase of minute ventilation per unit of increase of carbon dioxide production (VE/VCO2 slope) (chi2, 79.3, P <.0001), LVEF (chi2, 24.6, P <.0001), and peak VO2 (chi2, 9.4, P <.0001) as independent and additional predictors of major cardiac events. VE/VCO2 slope was the strongest independent predictor of outcome (chi2, 20.9, P =.0001) in patients with intermediate peak VO2 (n = 403), and the best cutoff value was 35 (chi2, 25.8; relative risk = 3.2, 95% CI 2.0-5.1, P <.0001). Total mortality rate was 30% in patients with VE/VCO2 slope > or = 35 (n = 103, 26%) and 10% in those with VE/VCO2 slope <35 (n = 300, 74%) (P <.0001). Patients with VE/VCO2 slope > or = 35 had a similar total mortality rate to those with peak VO2 < or = 10 mL/kg/min (30% vs 37%, P not significant).

Conclusions: A rational and pragmatic risk stratification process with symptom-limited cardiopulmonary exercise testing in CHF should include both peak VO2 and VE/VCO2 slope, the latter index effectively predicting outcome in almost one fourth of patients with intermediate exercise capacity.