Prognostic ability of VE/VCO₂ slope calculations using different exercise test time intervals in subjects with heart failure

The minute ventilation-carbon dioxide production (VE/VCO₂) slope, obtained during exercise testing, possesses prognostic value in heart failure (HF). The VE-VCO₂ relationship is generally linear thereby hypothetically producing similar slope values regardless of the exercise-test time interval used for calculation. This study assesses the ability of the VE/VCO₂ slope, calculated at different time intervals throughout a progressive exercise test, to predict 1-year cardiac-related hospitalization and mortality in subjects with HF. Seventy-two subjects underwent symptom-limited exercise testing with ventilatory expired gas analysis. Mean age and left ventricular ejection fraction for 44 male and 28 female subjects were 51.2 years (ケ 13.0) and 27.0% (ケ 12.3) respectively. The VE/VCO₂ slope was calculated from time 0 to 25, 50, 75 and 100% of exercise time and subsequently used to create five randomly selected VE/VCO₂ slope categories. (The intraclass correlation coefficient found calculation of the VE/VCO₂ slope, when divided into quartiles, to be a reliable measure (alpha = 0.94, P<0.0001). Univariate Cox regression analysis revealed all VE/VCO₂ slope categories (25-100% and random selections) were significant predictors of cardiac-related hospitalization and mortality over a 1-year period. Multivariate Cox regression analysis revealed all VE/VCO₂ slope categories outperformed peak oxygen consumption (VO₂) in predicting hospitalization and mortality at 1 year. Although the different classification schemes were not identical, these results suggest VE/VCO₂ slope maintains prognostic significance regardless of exercise-test time interval. Calculation of VE/VCO₂ slope may therefore still be valuable in subjects putting forth a sub-maximal effort while effort-dependent measures, such as peak VO₂, are not.