Usefulness of the predicted percentage ventilatory efficiency for carbon dioxide output during exercise in patients with chronic heart failure.

The ventilatory efficiency for carbon dioxide output ([Formula: see text]CO 2 ) during exercise, as measured by the minute ventilation vs. [Formula: see text]CO 2 slope ([Formula: see text]E vs. [Formula: see text]CO 2 slope), is a powerful prognostic index in patients with chronic heart failure (CHF). This measurement is higher in women than in men, and it increases with age. This study aimed to investigate the usefulness of the predicted value of the percentage [Formula: see text]E vs. [Formula: see text]CO 2 slope (%[Formula: see text]E vs. [Formula: see text]CO 2 slope) as a prognostic index in patients with CHF. A total of 320 patients with CHF and a left ventricular ejection fraction (LVEF) < 45% (male, 85.6%; mean age, 64.6 years) who underwent symptom-limited cardiopulmonary exercise tests using a cycle ergometer were included in the study. The %[Formula: see text]E vs. [Formula: see text]CO 2 was calculated using predictive formulae based on age and sex. Cardiovascular-related death was defined as the primary endpoint. The mean follow-up duration was 7.5 ± 3.3 years. Of 101 patients who died during the study period, 75 experienced cardiovascular-related deaths. The average [Formula: see text]E vs. [Formula: see text]CO 2 slope was 32.8 ± 8.0, and the average %[Formula: see text]E vs. [Formula: see text]CO 2 slope was 119.6 ± 28.2%. The cumulative incidence of cardiovascular-related death after 10 years of follow-up were 44.7% (95% CI 34.4-54.6%) in patients with %[Formula: see text]E vs. [Formula: see text]CO 2 slope > 120 and 15.0% (95% CI 9.4-21.8%) in patients with %[Formula: see text]E vs. [Formula: see text]CO 2 slope ≤ 120. The multivariate Cox regression analysis indicated that a %[Formula: see text]E vs. [Formula: see text]CO 2 slope > 120 was an independent predictor of cardiovascular-related death (adjusted hazard ratio, 3.24; 95% confidence interval 1.65-6.67; p < 0.01). The %[Formula: see text]E vs. [Formula: see text]CO 2 slope can be used for risk stratification in patients with CHF and an LVEF < 45%.