Prognostic power of ventilatory responses during submaximal exercise in patients with chronic heart disease

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 ((V) over dot O-2,). 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 (V) over dot O-2, the ratio of the increase in (V) over dot O-2 to the increase in work rate (WR) [(V) over dot O-2/DeltaWR], and the ratio of the increase in minute ventilation (V) over dot E to the increase in carbon dioxide output ((V) over dot O-2,) [Delta(V) over dot E/Delta(V) over dot O-2]. Results: After 1,899 +/- 495 days of follow-up (mean +/- SD), 33 cardiovascular-related deaths occurred. Nonsurvivors achieved lower peak (V) over dot O-2, lower (V) over dot O-2/DeltaWR, and higher Delta(V) over dot E/Delta(V) over dot CO2 compared to the survivors. In the univariate Cox proportional hazards analysis, peak (V) over dot O-2, (V) O-2/DeltaWR, and Delta(V) over dot E/Delta(V) over dot CO2 were found to be significant prognostic indexes of survival. However, multivariate analysis revealed (V) over dot O-2/DeltaWR as an independent predictor of mortality and Delta(V) over dot E/delta(V) over dot CO2 as a slightly weaker predictor. In this analysis, the prognostic power of peak (V) over dot O-2 was insignificant. Conclusion: Submaximal respiratory gas indexes are very likely to be more sensitive than peak (V) over dot O-2 for predicting poor survival in ambulatory patients with chronic heart disease.