Development of a ventilatory classification system in patients with heart failure

BACKGROUND - Ventilatory efficiency, commonly assessed by the minute ventilation (V̇E)-carbon dioxide production (V̇CO2) slope, is a powerful prognostic marker in the heart failure population. The purpose of the present study is to refine the prognostic power of the V̇E/V̇CO 2 slope by developing a ventilatory class system that correlates V̇E/V̇CO2 cut points to cardiac-related events. METHODS AND RESULTS - Four hundred forty-eight subjects diagnosed with heart failure were included in this analysis. The V̇E/V̇CO2 slope was determined via cardiopulmonary exercise testing. Subjects were tracked for major cardiac events (mortality, transplantation, or left ventricular assist device implantation) for 2 years after cardiopulmonary exercise testing. There were 81 cardiac-related events (64 deaths, 10 heart transplants, and 7 left ventricular assist device implantations) during the 2-year tracking period. Receiver operating characteristic curve analysis revealed the overall V̇E/V̇CO2 slope classification scheme was significant (area under the curve: 0.78 [95% CI, 0.73 to 0.83], P<0.001). On the basis of test sensitivity and specificity, the following ventilatory class system was developed: (1) ventilatory class (VC) I: ≤29; (2) VC II: 30.0 to 35.9; (3) VC III: 36.0 to 44.9; and (4) VC IV: ≥45.0. The numbers of subjects in VCs I through IV were 144, 149, 112, and 43, respectively. Kaplan-Meier analysis revealed event-free survival for subjects in VC I, II, III, and IV was 97.2%, 85.2%, 72.3%, and 44.2%, respectively (log-rank 86.8; P<0.001). CONCLUSIONS - A multiple-level classificatory system based on exercise V̇E/V̇CO 2 slope stratifies the burden of risk for the entire spectrum of heart failure severity. Application of this classification is therefore proposed to improve clinical decision making in heart failure.