Comparison of VE/VCO2 Slope in Older Systolic and Diastolic Heart Failure Patients and Age-Matched Healthy Controls

Abstract

Oxygen consumption (VO2) has previously been used for prognosis and risk stratification in patients with heart failure. Furthermore, it has been reported that there is no difference in peak oxygen consumption between systolic and diastolic heart failure patients. More recent research has introduced VE/VCO2 slope as a prognostic measure, but these reports have been limited to systolic heart failure patients only. Risk of mortality has been shown to increase when VE/VCO2 slope values are greater than 34. PURPOSE: To cross-sectionally examine VE/VCO2 slope in systolic and diastolic heart failure populations as well as age-matched healthy controls. METHODS: Symptom limited graded exercise tests were conducted on 147 patients (59 diastolic heart failure, 60 systolic heart failure, 28 controls) using a bicycle ergometer protocol that started at 12 watts and progressed to 25 watts after two minutes. The stages continued to increase by 25 watt increments every three minutes until maximal effort was achieved. Breath-by-breath expired gas analysis was performed using a commercially available system with on-line computer calculations. VE/VCO2 slope was calculated from a regression line of minute ventilation and carbon dioxide production. One way analysis of variance with a Bonferroni post hoc test and Pearson correlations were used for statistical analysis. RESULTS: VE/VCO2 slope was significantly higher in systolic heart failure patients when compared to both diastolic heart failure patients (37.3 ± 7.5 vs. 34.1 ± 6.5, p=0.03) and controls (37.3 ± 7.5 vs. 32.1 ± 4.6, p=0.002). No significant difference was observed between diastolic heart failure and healthy controls (34.1 ± 6.5 vs. 32.1 ± 4.6, p=0.52). Furthermore, we observed that 45% of DHF and 59% had a VE/VCO2 slope greater than 34. Additional analysis resulted in significant correlations between VO2 and VE/VCO2 slope in systolic heart failure patients (r=−0.40, p=0.002), however, there was no significant relationship in diastolic heart failure patients (r=−0.09, p=0.49) or in controls (r=0.13, p=0.50). CONCLUSION: VE/VCO2 slope is significantly higher in patients with systolic heart failure compared to diastolic heart failure and healthy controls. While this study did not address prognosis, the findings are consistent with the belief that mortality rates are greater in SHF than DHF, and VE/VCO2 slope is useful in predicting this risk.