Duke Exercise Stress Test Score Interpretation
The Duke treadmill score (DTS) is the most widely used and validated method to assess risk and prognosis in patients with suspected ischemic heart disease, with scores categorized as low risk (≥5), intermediate risk (-10 to 4), and high risk (≤-11) corresponding to annual mortality rates of 0.25%, intermediate risk, and 5% respectively. 1
Calculation of the Duke Treadmill Score
The Duke treadmill score is calculated using the following formula:
- DTS = Exercise time in minutes - (5 × ST-segment deviation in mm) - (4 × Angina index)
- Where the angina index is:
- 0 if no angina occurs during the test
- 4 if angina occurs during the test
- 8 if angina is the reason for stopping the test
Risk Stratification Based on Duke Treadmill Score
| Risk Category | DTS Value | Annual Mortality Rate | 4-Year Survival Rate |
|---|---|---|---|
| Low Risk | ≥ 5 | 0.25% | 99% |
| Intermediate Risk | -10 to 4 | 1-3% | ~95% |
| High Risk | ≤ -11 | 5% | 79% |
Clinical Implications of DTS Categories
Low Risk (DTS ≥ 5)
- Represents approximately 62-66% of outpatients with suspected coronary artery disease 1
- Annual mortality rate of only 0.25%
- Typically associated with:
- Good exercise capacity
- Minimal or no ST-segment depression
- No exercise-induced angina
- Further cardiac testing generally not required unless clinical suspicion remains high
Intermediate Risk (DTS -10 to 4)
- Represents approximately 30-34% of patients
- Annual mortality rate between 1-3%
- May benefit from additional risk stratification with imaging studies:
- Exercise or pharmacologic stress imaging (nuclear or echocardiography)
- Particularly useful when there is either impaired functional capacity or abnormal heart rate recovery, but not both 1
High Risk (DTS ≤ -11)
- Represents approximately 4% of patients
- Annual mortality rate of 5%
- Associated with:
- Poor exercise capacity
- Significant ST-segment depression
- Exercise-limiting angina
- Consideration for coronary angiography is appropriate
- High likelihood of severe coronary artery disease (74% have 3-vessel or left main disease) 2
Diagnostic Value of the Duke Treadmill Score
Beyond its prognostic value, the DTS also provides diagnostic information:
- Low-risk patients (DTS ≥ 5): 60% have no significant coronary stenosis, 16% have single-vessel disease 2
- High-risk patients (DTS < -11): 74% have 3-vessel or left main coronary disease 2
Special Considerations
- Gender differences: The score performs equally well in both men and women, though preliminary data suggests some differences in interpretation may be needed 1, 3
- Age limitations: The score may not work as well in elderly patients, particularly those over 75 years of age 1
- Medication effects: Beta-blockers and other anti-ischemic drugs should ideally be withheld for 4-5 half-lives (about 48 hours) before testing to avoid masking ischemic changes 1
- Inability to exercise: The inability to perform an exercise test is itself a strong negative prognostic factor 1
When Additional Imaging Is Recommended
While the DTS is valuable, additional imaging may be warranted in specific situations:
- Patients with uninterpretable baseline ECG (left bundle branch block, ventricular pacing, LV hypertrophy, digitalis use, resting ST abnormalities) 1
- Patients with equivocal exercise results or intermediate DTS 1
- Patients with prior revascularization and significant change in anginal pattern 1
The Duke treadmill score remains a powerful tool for risk stratification in patients with suspected coronary artery disease, providing valuable prognostic information that guides clinical decision-making and helps determine the need for additional testing or intervention.