Exercise Test Predicts Heart Failure Mortality Risk

WINSTON-SALEM, N.C., May 31 -- A simple exercise test measuring the ratio of oxygen consumption to carbon dioxide production can predict mortality risks in systolic heart failure, said researchers here.
In a study comparing patients with either diastolic or systolic heart failure with healthy controls, the relationship of minute ventilation to carbon dioxide production (the VE/VCO2 slope) was significantly higher among patients with systolic heart failure, reported cardiologist Dalane Kitzman, M.D., of Wake Forest, and colleagues, in the May issue of the Journal of Heart Failure.
"This may allow doctors to better assess patient risk, and could help them determine the most appropriate plan of care based on the prognosis of the patient," said Dr. Kitzman.
Although exercise intolerance as measured by oxygen consumption (VO2) has been a standard means for risk stratification and prognosis of patients in heart failure, recent evidence has suggested that the VE/VCO2 slope value is a better predictor for hospitalization, the authors wrote. A slope value greater than 34 is thought to signal an increased risk for death.
"With advances in medical management, survival rates among systolic heart failure patients have improved," they wrote. "In contrast, diastolic heart failure prevalence has increased, yet the survival rate from this disorder has remained unchanged. Therefore, it is important for current and future research to focus not only on potential treatments for diastolic heart failure but also to develop the best method to assess prognosis and risk stratify diastolic heart failure patients."
In a cross-sectional study, the authors enrolled 147 patients -- 59 with diastolic heart failure, 60 with systolic heart failure, and 28 healthy controls -- and asked them to perform a maximal graded exercise test using a bicycle ergometer.
They performed breath-by-breath expired gas analysis using a commercially available system, with on-line computer calculations.
They calculated the VE/VCO2 slope from a regression line of minute ventilation and carbon dioxide production. The statistical analysis included one-way analysis of covariance with a Benferroni post hoc test, and they used Pearson correlations for statistical analysis.
They found that the VE/VCO2 slope was significantly higher in systolic heart failure at 37 ± 8, compared with either diastolic heart failure (34 ± 7, P = 0.03) or controls (32 ± 5, P =0 .002).
There was no significant difference in the slope between patients with diastolic heart failure and healthy controls (P=0.52).
In all, 45% of patients with diastolic heart failure, and 59% of patients with systolic heart failure had a VE/VCO2 slope greater than 34 (the threshold for increased mortality risk), compared with 36% of healthy controls.
VO2 peak was significantly and negatively correlated with VE/VCO2 slope in patients with systolic heart failure patients (r=-0.40, P=0.002), but not in patients with diastolic heart failure patients (r=-0.09, P=0.49) or in controls (r=0.13, P=0.50).
"The finding that VO2 peak is as severely reduced in elderly patients with diastolic heart failure as in those with systolic heart failure, but that VE/VCO2 slope is not significantly increased parallels the findings regarding morbidity and mortality in large population based studies of elderly out-patients with diastolic heart failure," the investigators wrote.
"Specifically, morbidity is similar in diastolic heart failure and systolic heart failure outpatients, paralleling the VO2 peak data, whereas mortality is considerably lower in diastolic heart failure compared to systolic heart failure, paralleling the VE/VCO2 slope data."