Abstract
Objective
To determine which routinely collected exercise test variables most strongly correlate
with survival and to derive a fitness risk score that can be used to predict 10-year
survival.
Patients and Methods
This was a retrospective cohort study of 58,020 adults aged 18 to 96 years who were
free of established heart disease and were referred for an exercise stress test from
January 1, 1991, through May 31, 2009. Demographic, clinical, exercise, and mortality
data were collected on all patients as part of the Henry Ford ExercIse Testing (FIT)
Project. Cox proportional hazards models were used to identify exercise test variables
most predictive of survival. A “FIT Treadmill Score” was then derived from the β coefficients
of the model with the highest survival discrimination.
Results
The median age of the 58,020 participants was 53 years (interquartile range, 45-62
years), and 28,201 (49%) were female. Over a median of 10 years (interquartile range,
8-14 years), 6456 patients (11%) died. After age and sex, peak metabolic equivalents
of task and percentage of maximum predicted heart rate achieved were most highly predictive
of survival (P<.001). Subsequent addition of baseline blood pressure and heart rate, change in vital
signs, double product, and risk factor data did not further improve survival discrimination.
The FIT Treadmill Score, calculated as [percentage of maximum predicted heart rate +
12(metabolic equivalents of task) – 4(age) + 43 if female], ranged from −200 to 200
across the cohort, was near normally distributed, and was found to be highly predictive
of 10-year survival (Harrell C statistic, 0.811).
Conclusion
The FIT Treadmill Score is easily attainable from any standard exercise test and translates
basic treadmill performance measures into a fitness-related mortality risk score.
The FIT Treadmill Score should be validated in external populations.
Abbreviations and Acronyms:
BP (blood pressure), CAD (coronary artery disease), CVD (cardiovascular disease), DTS (Duke Treadmill Score), FIT (Henry Ford Exercise Testing), HFHS (Henry Ford Health System), HR (heart rate), IQR (interquartile range), METs (metabolic equivalents of task), MPHR (maximum predicted heart rate), %MPHR (percentage of MPHR)To read this article in full you will need to make a payment
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