Abstract 2748: Development of a Ventilatory Classification System for Patients with Heart Failure
Introduction: Ventilatory efficiency has proven to be a strong prognostic marker in the heart failure (HF) population. The definition of a normal vs. abnormal response has most commonly been expressed dichotomously (</≥34). The purpose of the present study is to explore the value of a four-level ventilatory class system based upon cardiac-related events.
Methods: Four hundred and twenty-two subjects (340 male/82 female, 227 ischemic/195 non-ischemic, mean age: 56.9 ±13.1 years) diagnosed with HF participated in this analysis. Mean left ventricular ejection fraction was 33.3 ±12.3%. Subjects were tracked for time to first cardiac-related event (mortality or hospitalization) for two years following cardiopulmonary exercise testing. Receiver operating characteristic curve analysis defined the minute ventilation/carbon dioxide production (VE/VCO2) slope thresholds based upon high sensitivity (≥90%) and specificity (≥90%) as well as an optimal sensitivity/specificity balance.
Results: There were 139 cardiac-related events (113 hospitalizations/26 deaths) during the two-year tracking period. The VE/VCO2 slope classification scheme was significant [area under the curve: 0.77 (95% CI: 0.72– 0.82), p<0.001] and outperformed both the Weber [area under the curve: 0.71 (95% CI: 0.67– 0.75), p<0.001] and NYHA [area under the curve: 0.70 (95% CI: 0.67– 0.75), p<0.001] classification schemes. Based upon test sensitivity and specificity, the following ventilatory class system was developed:
Ventilatory Class A: ≤29.9;
Ventilatory Class B: 30.0–33.9;
Ventilatory Class C: 34–39.9; and
Ventilatory Class D: ≥40.
The number of subjects in Ventilatory Classes A-D was 143, 102, 96 and 81, respectively. Kaplan-Meier analysis revealed event-free survival for subjects in Ventilatory Classes A-D was 90.9%, 70.6%, 52.1% and 38.3%, respectively (Chi-square: 81.5, p<0.001).
Discussion: Current risk models that suggest using a dichotomous stratification for the VE/VCO2 slope (<or≥334) appear to underutilize the power of this prognostic factor. While additional work is required to better define how ventilatory efficiency should be used to stratify risk in patients with HF our research suggests a risk model with four classes is more appropriate.