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

Background Peak oxygen consumption (Vo(2)) has an important prognostic role in chronic heart failure (CHF), but its discriminatory power is limited in patients with intermediate exercise capacity (peak Vo(2) 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) less than or equal to 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/Vco(2) slope) (x(2), 79.3, P <.000 1), LVEF (x(2), 24.6, P <.000 1), and peak Vo(2) (x(2), 9.4, P <.000 1) as independent and additional predictors of major cardiac events. VE/Vco(2) slope was the strongest independent predictor of outcome (x(2), 20.9, P =.000 1) in patients with intermediate peak Vo(2) (n = 403), and the best cutoff value was 35 (x(2), 25.8; relative risk = 3.2, 95% Cl 2.0-5. 1, P <.000 1). Total mortality rate was 30% in patients with VE/Vco(2) slope greater than or equal to 35 (n = 103, 26%) and 10% in those with VE/Vco(2) slope <35 (n = 300, 74%) (P <.000 1). Patients with VE/Vco(2) slope greater than or equal to 35 had a similar total mortality rate to those with peak Vo(2) less than or equal to 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 Vo(2) and VE/Vco(2) slope, the latter index effectively predicting outcome in almost one fourth of patients with intermediate exercise capacity.