The Duke treadmill score in assessing the prognosis of patients tested with bicycle ergometer
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Introduction: The Duke Treadmill Score (DTS) is a weighted index combining treadmill exercise time, maximum ST-segment deviation and exercise-induced angina (DTS = Exercise time – [5 x Max ST-deviation)] – [4 x Angina index]). DTS is one of the most widely studied and clinically used prognostic parameter in treadmill exercise testing, albeit the prognostic capability of DTS independently of its components has not been adequately studied. There are no previous studies on the prognostic value of DTS from standard bicycle ergometer.
Purpose: The aim of this study was to assess the prognostic usefulness of DTS among patients undergoing standard bicycle ergometer testing in two different populations.
Methods: A total of 3936 patients (2371 men) in the Finnish Cardiovascular Study (FINCAVAS) and 2683 men in the Kuopio Ischemic Heart Disease study (KIHD) underwent a standard bicycle ergometer test. DTS was formed with ST-segment deviation and angina pectoris data as appropriate and by converting metabolic equivalents of task (METs) to standard treadmill exercise time.
Results: In FINCAVAS, during a median 6.3-year (interquartile range, IQR, 4.5–8.2) follow-up period, 180 patients (4.6%) suffered the primary endpoint, cardiovascular (CV) mortality. In KIHD, 562 patients (21.0%) died from CV causes during the median follow-up of 24.1 (IQR 18.0–26.2) years. Using Cox regression, DTS was predictive of CV death in both study populations as a continuous variable after adjustment with age, sex, body mass index, current smoking, history of coronary heart disease, diabetes and usage of β-blockers (FINCAVAS; HR 1.03, 95% CI 1.01–1.06, p=0.004 and KIHD; HR 1.04, 95% CI 1.03–1.06, p<0.001). As a three-category-variable, DTS was still predictive of CV death (FINCAVAS; adjusted HR 3.15 for lowest and highest tertile, 95% CI 1.83–5.42, p<0.000 and KIHD; adjusted HR 1.71, 95% CI 1.34–2.18, p<0.000). However, after adjusting for the individual components of DTS (METs, ST-segment deviation and exercise-induced angina), DTS was not associated with CV mortality in either study populations (FINCAVAS; adjusted HR 1.15, 95% CI 0.60–2.19, p=0.672 and KIHD; adjusted HR 0.90, 95% CI 0.68–1.20, p=0.466). Exercise capacity as METs was the only DTS component significantly predicting CV mortality in both study populations (p<0.001).
Conclusions: The Duke Treadmill Score seemed to be predictive of CV death for patients who underwent bicycle exercise test in two different populations. However, when adjusted with its components, the predictive power of DTS disappeared, as METs proved to be a superior predictor. Future treadmill-based research should also elucidate the role of DTS independent of its components, particularly exercise capacity.