Background: Although parameters obtained during submaximal exercise are known to be useful for predicting mortality in cardiac patients, it has been a matter of debate whether the submaximal parameters are superior to peak oxygen uptake (V̇o2). For this purpose, we aimed to determine the best index among exercise variables in predicting long-term mortality in patients with chronic heart disease.
Methods: The study population consisted of 385 consecutive patients with chronic heart disease who performed a symptom-limited incremental exercise test on a cycle ergometer. Breath-by-breath respiratory gas analysis was used to estimate the peak V̇o2, the ratio of the increase in V̇o2 to the increase in work rate (WR) [V̇o2/ΔWR], and the ratio of the increase in minute ventilation V̇e to the increase in carbon dioxide output (V̇co2) [ΔV̇e/ΔV̇co2].
Results: After 1,899 ± 495 days of follow-up (mean ± SD), 33 cardiovascular-related deaths occurred. Nonsurvivors achieved lower peak V̇o2, lower V̇o2/ΔWR, and higher ΔV̇e/ΔV̇co2 compared to the survivors. In the univariate Cox proportional hazards analysis, peak V̇o2, V̇o2/ΔWR, and ΔV̇e/ΔV̇co2 were found to be significant prognostic indexes of survival. However, multivariate analysis revealed V̇o2/ΔWR as an independent predictor of mortality and ΔV̇e/δV̇co2 as a slightly weaker predictor. In this analysis, the prognostic power of peak V̇o2 was insignificant.
Conclusion: Submaximal respiratory gas indexes are very likely to be more sensitive than peak V̇o2 for predicting poor survival in ambulatory patients with chronic heart disease.