Clinical Research
Exercise Testing
External Prognostic Validations and Comparisons of Age- and Gender-Adjusted Exercise Capacity Predictions

https://doi.org/10.1016/j.jacc.2007.08.003Get rights and content
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Objectives

The purpose of this study was to externally validate the prognostic value of age- and gender-based nomograms and categorical definitions of impaired exercise capacity (EC).

Background

Exercise capacity predicts death, but its use in routine clinical practice is hampered by its close correlation with age and gender.

Methods

For a median of 5 years, we followed 22,275 patients without known heart disease who underwent symptom-limited stress testing. Models for predicted or impaired EC were identified by literature search. Gender-specific multivariable proportional hazards models were constructed. Four methods were used to assess validity: Akaike Information Criterion (AIC), right-censored c-index in 100 out-of-bootstrap samples, the Nagelkerke Index R2, and calculation of calibration error in 100 bootstrap samples.

Results

There were 646 and 430 deaths in 13,098 men and 9,177 women, respectively. Of the 7 models tested in men, a model based on a Veterans Affairs cohort (predicted metabolic equivalents [METs] = 18 − [0.15 × age]) had the highest AIC and R2. In women, a model based on the St. James Take Heart Project (predicted METs = 14.7 − [0.13 × age]) performed best. Categorical definitions of fitness performed less well. Even after accounting for age and gender, there was still an important interaction with age, whereby predicted EC was a weaker predictor in older subjects (p for interaction <0.001 in men and 0.003 in women).

Conclusions

Several methods describe EC accounting for age and gender-related differences, but their ability to predict mortality differ. Simple cutoff values fail to fully describe EC’s strong predictive value.

Abbreviations and Acronyms

AIC
Akaike Information Criterion
EC
exercise capacity
MET
metabolic equivalent
VA
Veterans Affairs

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This work was funded by National Institutes of Health grants R01 HL-66004-2, R01 HL-072771-02, P50 HL-77107, and K12 HD049091.