Duke Treadmill Score
The Duke Treadmill Score (DTS) is a validated prognostic index in cardiology that estimates the risk of cardiac death in patients with suspected coronary artery disease (CAD) by analyzing data from an exercise treadmill test. Developed from the Duke Databank for Cardiovascular Disease, it combines three key variables—duration of exercise, extent of ST-segment deviation on electrocardiography, and the severity of exercise-induced angina—to generate a numerical score ranging from -25 (highest risk) to +15 (lowest risk), thereby stratifying patients into low-risk (≥ +5), moderate-risk (-10 to +4), and high-risk (< -10) categories for guiding clinical decisions on further testing or intervention.[1] The DTS was originally derived in 1991 from a retrospective analysis of 2,842 inpatients at Duke University Medical Center who underwent treadmill testing between 1969 and 1980, and prospectively validated in a cohort of 613 outpatients evaluated between 1983 and 1985, demonstrating superior predictive accuracy compared to clinical data alone (receiver-operating characteristic curve area of 0.849 versus 0.798 for four-year survival).[1] In validation studies, low-risk patients achieved a 99% four-year survival rate (annual mortality of 0.25%), moderate-risk patients a 95% rate (1.25% annual mortality), and high-risk patients a 79% rate (5% annual mortality), highlighting its utility in identifying individuals who may safely avoid invasive procedures like coronary angiography.[1] This simple, non-invasive metric has been incorporated into major clinical guidelines, including the 2002 ACC/AHA Guideline Update for Exercise Testing, which endorses its use for risk stratification in symptomatic patients, and remains referenced in the 2023 AHA/ACC Guideline for the Management of Patients With Chronic Coronary Disease as a tool with moderate discriminative ability (c-index of 0.62).[2][3] Despite its established role, the DTS's prognostic value may be limited in certain populations, such as elderly patients over 75 years, where it performs less reliably for predicting cardiac outcomes,[4] and it is most effective when combined with other risk factors like age, sex, and comorbidities in contemporary practice. Overall, the DTS continues to inform exercise stress testing protocols worldwide, promoting efficient resource allocation in CAD evaluation.Overview
Definition
The Duke Treadmill Score (DTS) is a validated composite prognostic index derived from exercise treadmill testing that integrates three key parameters: exercise duration, ST-segment deviation on electrocardiography, and the presence or severity of angina symptoms during the test.[1] This score provides a single numerical value to quantify cardiovascular risk in patients undergoing evaluation for suspected coronary artery disease (CAD).[5] Developed as a non-invasive tool, it simplifies the interpretation of treadmill test results by combining these elements into a prognostic estimate, avoiding reliance on any single metric alone.[6] In clinical practice, the DTS plays a central role in the non-invasive assessment of CAD prognosis, enabling physicians to estimate the likelihood of adverse cardiac events such as myocardial infarction or death based on exercise performance and ischemic responses.[1] It is particularly useful for stratifying patients into risk groups without immediate need for more invasive procedures like angiography, thereby guiding decisions on further management.[7] The score's design emphasizes the prognostic superiority of combined exercise variables over individual ones, enhancing its reliability in outpatient settings.[6] The DTS is named after Duke University Medical Center, where it was formulated and initially validated through large-scale studies of patients with suspected CAD.[1] As a foundational element of exercise treadmill testing—a standard diagnostic modality for eliciting cardiac stress—it has become a widely adopted metric in cardiology for its simplicity and evidence-based predictive power.[5]Purpose
The Duke Treadmill Score (DTS) serves as a prognostic tool primarily designed to stratify patients with suspected coronary artery disease (CAD) into low-, moderate-, or high-risk categories for major cardiac events, such as myocardial infarction or cardiovascular death, over a 4- to 5-year period following exercise treadmill testing.[1] This risk stratification is achieved by integrating key exercise test variables, including exercise duration, ST-segment deviation, and angina index, to provide an objective estimate of long-term survival that outperforms clinical assessment alone.[8] In validation studies of outpatients, low-risk scores (≥ +5) identified 62% of patients with a 99% 4-year survival rate, while high-risk scores (< -10) flagged the 4% at highest risk with only 79% survival.[1] A key advantage of the DTS is its simplicity and cost-effectiveness, as it relies solely on data from standard treadmill exercise testing without requiring additional advanced imaging modalities like echocardiography or nuclear perfusion scans.[1] This allows seamless incorporation into routine clinical workflows, enabling rapid calculation at the bedside using basic arithmetic and offering prognostic insights comparable to more complex multivariable models derived from Cox regression analysis.[1] By distilling multifaceted exercise responses into a single score ranging from -25 (highest risk) to +15 (lowest risk), it facilitates efficient patient evaluation in resource-limited settings.[8] In clinical practice, the DTS guides management decisions for patients with suspected CAD by identifying those who may safely defer invasive procedures, such as coronary angiography, in favor of conservative medical therapy, particularly among low-risk individuals.[1] Conversely, high-risk scores prompt consideration of prompt revascularization or intensified pharmacotherapy to mitigate adverse outcomes.[7] This targeted approach enhances decision-making in chest pain evaluation, reducing unnecessary procedures while prioritizing high-yield interventions.[9]History
Development
The Duke Treadmill Score was developed in the late 1980s at Duke University Medical Center by a team of cardiologists and researchers, including Mark A. Hlatky and Robert M. Califf, as part of efforts to refine risk assessment in patients with suspected coronary artery disease. This work built on the institution's established infrastructure for cardiovascular research, leveraging prospectively collected clinical data to create a standardized prognostic tool. The score emerged from a comprehensive analysis of 2,842 consecutive patients with chest pain who underwent both treadmill exercise testing and cardiac catheterization at Duke University Medical Center; these patients were drawn from the Duke Databank for Cardiovascular Disease, a long-standing registry initiated in 1976 to track outcomes in cardiovascular patients.[10] To ensure robustness, the dataset was randomly divided into two equal groups of approximately 1,421 patients each, with one group used to derive the score via multivariable Cox regression modeling and the other for internal validation. This methodological approach allowed the researchers to identify key exercise-related variables that independently predicted long-term survival. The primary objective was to enhance prognostic accuracy for coronary artery disease outcomes beyond what could be achieved with exercise duration alone, by integrating electrocardiographic (ECG) findings and symptomatic responses observed during treadmill testing. Prior to this, exercise testing primarily relied on total time achieved, but the inclusion of ST-segment deviations and angina indices addressed limitations in isolating high-risk patients, enabling better stratification into low-, moderate-, and high-risk categories based on 5-year survival rates. This development marked a shift toward composite indices in noninvasive cardiology, emphasizing the value of combining physiological and clinical data for improved decision-making.Key Publications
The Duke Treadmill Score was first introduced in a 1987 study published in the Annals of Internal Medicine by Hlatky and colleagues, which developed a multivariable prognostic model using exercise treadmill test variables to predict survival in patients with suspected coronary artery disease.[11] This work, conducted at Duke University, analyzed data from over 2,800 patients and identified exercise duration, ST-segment deviation, and angina as key predictors, forming the basis for a composite score that stratified prognosis more effectively than individual components.[8] A refinement of the score appeared in a 1991 New England Journal of Medicine article by Mark and co-authors, which validated and weighted the formula for estimating 4-year survival rates in outpatients with suspected coronary artery disease.[12] Drawing on a cohort of 613 outpatients, the study demonstrated that the score—calculated as exercise time minus five times the maximum ST-segment deviation minus four times an angina index—provided superior risk stratification compared to clinical data alone, with low-risk patients (score ≥5) showing 99% 4-year survival.[1] Further validation of the score's clinical utility came in a 1998 Circulation study by Shaw and colleagues, which evaluated its role in identifying low-risk patients who could safely avoid diagnostic coronary angiography. In a study of 2,758 patients undergoing exercise testing and cardiac catheterization, the Duke Treadmill Score demonstrated utility in identifying low-risk patients with low prevalence of significant coronary artery disease, supporting its use to reduce unnecessary invasive procedures.[7]Calculation
Formula
The Duke Treadmill Score (DTS) is calculated using the following formula: \text{DTS} = \text{exercise time (minutes on Bruce protocol)} - 5 \times \text{maximum ST-segment deviation (mm)} - 4 \times \text{angina index} where the angina index is defined as 0 for no angina on the treadmill, 1 for nonlimiting angina, and 2 for exercise-limiting angina.[8] The coefficients in the formula (5 for ST-segment deviation and 4 for angina index) were determined through multivariate Cox proportional hazards regression analysis of prognostic factors in a cohort of 2842 patients undergoing treadmill exercise testing, identifying these components as independently predictive of survival after adjusting for clinical and angiographic variables.[8] For example, a patient achieving 8 minutes of exercise time with a maximum ST-segment deviation of 2 mm and exercise-limiting angina (index of 2) would have a DTS of $8 - 5(2) - 4(2) = -10.[8]Component Measurement
The Duke Treadmill Score relies on three key components derived from a standardized exercise treadmill test: exercise time, ST-segment deviation, and angina index. These measurements are obtained during a symptom-limited test, with the Bruce protocol serving as the standard methodology for treadmill progression. Exercise time is recorded as the total duration in minutes from the start of the test until the patient achieves voluntary exhaustion, develops limiting symptoms, or reaches a protocol-defined endpoint such as significant hemodynamic instability. This duration reflects the patient's functional capacity and is measured precisely using the incremental stages of the Bruce protocol, where speed and incline increase every three minutes.[13] ST-segment deviation is assessed via continuous electrocardiographic monitoring and represents the maximum horizontal or downsloping depression (or, less commonly, elevation) in millimeters, measured 60 to 80 milliseconds after the J point. For enhanced sensitivity in detecting ischemia, this is typically evaluated in lead V5, which provides optimal visualization of left ventricular changes, though the maximum value across multiple leads may be considered.[14][15] The angina index is a categorical assessment of chest pain experienced during the test, graded as 0 for no angina, 1 for non-limiting angina that does not interfere with exercise continuation, or 2 for limiting angina that causes the test to be terminated due to severe symptoms. This index is determined prospectively by the supervising clinician based on patient reports and clinical observation at the time of occurrence.[1]Interpretation
Risk Stratification
The Duke Treadmill Score (DTS) enables risk stratification of patients undergoing exercise treadmill testing by categorizing them into low, moderate, or high risk groups based on predefined score thresholds, which correlate with differences in cardiovascular prognosis.[1] This classification helps clinicians identify patients at varying levels of future cardiac event risk without invasive procedures.[7] Patients with a DTS of ≥ +5 are classified as low risk, corresponding to an annual mortality rate of less than 1% (derived from 4-year survival rates of approximately 99% in validation cohorts).[1] Those with scores ranging from -10 to +4 fall into the moderate risk category, with annual mortality rates of 1-3% (based on 4-year survival of about 95%).[1] High risk is assigned to patients with a DTS of ≤ -11, indicating an annual mortality exceeding 3% (from 4-year survival rates around 79%).[1] These thresholds were established from 4-year survival data in original cohorts of over 2,800 inpatients and validated in more than 600 outpatients with suspected coronary artery disease, using multivariate analysis to link score values to cardiac death rates.[1] According to ACC/AHA guidelines, high risk corresponds to predicted average annual cardiovascular mortality >3%. The following table summarizes the risk categories:| Risk Category | DTS Threshold | Annual Mortality Rate | Basis (4-Year Survival) |
|---|---|---|---|
| Low | ≥ +5 | <1% | ~99% |
| Moderate | -10 to +4 | 1-3% | ~95% |
| High | ≤ -11 | >3% | ~79% |