Age-adjusted Modification of the Duke Treadmill Score Nomogram

Amir H. Sadrzadeh Rafie, MD; Frederick E. Dewey, BA; Jonathan Myers, PhD; Victor F. Froelicher, MD

Disclosures

Am Heart J. 2008;155(6):1033-1038. 

In This Article

Abstract and Introduction

Background: The Duke Treadmill Score (DTS) is an established clinical tool for risk stratification of patients referred for exercise testing, but it does not consider age. We aimed to determine if age could improve the prognostic power of the DTS and if so, to modify the DTS nomogram to include age.
Methods: Of 1,959 patients referred for exercise testing from 1997 to 2006, 1,759 male veterans (age range 23-86 years) remained after exclusion of female and patients with heart failure. Cardiovascular mortality was the main outcome considered.
Results: Cox survival analysis was performed entering age and the DTS; both were significant (P ≤ .002) with similar Wald Z values (5.4 and -3.1) and regression coefficients but opposite signs. The score: age-DTS yielded an area under the receiver operating characteristic curve of 0.80 compared with 0.76 for the DTS (P < .001). Using this equation, a nomogram was constructed by adding age to the original DTS nomogram. The point at which the age-DTS line intersects the drawing line from the DTS to the corresponding value for age indicates average annual cardiovascular (CV) mortality adjusted for age. For a DTS associated with a 2.5% annual CV mortality, an age of 30 compared with 70 decreased CV risk by a factor of 10 to less than 0.2% (P < .05, log-rank test).
Conclusions: We propose an age-adjusted DTS nomogram that improves the prognostic estimates of average annual CV mortality over the DTS alone. This nomogram requires external validation and extension to women.

The standard exercise test remains a well-established tool to evaluate prognosis in patients with known or suspected coronary artery disease. For the past several years, clinical investigators have attempted to enhance the ability of the exercise test to predict cardiovascular deaths by identifying the most important prognostic variables and deriving scores for risk stratification.[1,2,3,4,5,6,7,8,9,10,11,12,13] The most thoroughly investigated of these is the Duke Treadmill Score (DTS), which is based on duration of exercise, ST-segment depression, and exercise-induced angina.[12,13] The DTS can be considered the culmination of years of clinical research that explored this subject often with conflicting results.[12,14,15] This score was originally derived from an inpatient population of patients with an average age of 49 years who had suspected coronary artery disease and underwent catheterization. Later, it was validated by the same investigators in an outpatient population of asymptomatic patients with an average age of 54, in whom it was demonstrated that the DTS has greater prognostic power than the clinical assessment.[13] Further studies examined the value of the widely recommended DTS for risk stratification of different patient populations including the elderly patients.[16,17]

Age is well recognized as a powerful predictor of outcomes in the setting of cardiovascular disease. Differences in age of the subjects can explain differences in the studies using exercise testing to predict prognosis.[18] Although age is a powerful prognostic factor for cardiovascular mortality, it was not included in the DTS because of the narrow age range in the populations originally studied.

We conducted the current study to determine if age could improve the prognostic power of the DTS and if so, to modify the DTS nomogram to include age.

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