Peak exercise oxygen uptake (peak VO₂) and ventilation to CO₂ production (VE/VCO₂) slope are established prognostic indicators in patients with chronic heart failure (CHF). A high VE/VCO₂ slope, however, does not take into account the level of physical performance as expressed by peak VO₂. We hypothesized that the prognostic value of a high VE/VCO₂ slope may be improved by normalization for peak VO₂ (VE/VCO₂/VO₂).

One hundred patients with CHF underwent pulmonary function tests at rest (spirometry and lung diffusion capacity) and maximal cardiopulmonary exercise testing. The prognostic value of VE/VCO₂ slope, peak VO₂ and VE/VCO₂/VO₂ was probed prospectively.

Twenty-one patients died from cardiac reasons during a mean follow-up of 26 ± 19 months. Nonsurvivors, compared to survivors, showed a lower peak VO₂ (13.6 ± 4.0 vs 17.5 ± 4.1 mL · min⁻¹ · kg⁻¹, P < .01) and a steeper VE/VCO₂ slope (43 ± 11 vs 31.6 ± 5.0, P < .01). Nonetheless, in patients whose VE/VCO₂ slope exceeded 34 (upper normal limit), there was no correlation with peak VO₂ (r = −35, P = not significant). Interestingly 35% of them showed a normal exercise performance (peak VO₂ ≥18 mL · min⁻¹ · kg⁻¹). At multivariate analysis, the VE/VCO₂ slope showed a prognostic power stronger than that of peak VO₂; however, the VE/VCO₂/VO₂ index retained a prognostic power greater than that of both VE/VCO₂ slope and peak VO₂. A VE/VCO₂/VO₂ ≥2.4 signaled cases at higher risk.

Discrepancies between VE/VCO₂ slope and peak VO₂ may generate uncertainty. Normalization of the former by the latter improves outcome prediction and may be considered a simple and effective way for maximizing the clinical applicability of these 2 indicators.