What an exercise test can predict
An exercise stress test records the heart’s electrical activity while the patient walks on a treadmill at increasing speed and slope. Narrowed coronary arteries may not supply enough blood at high effort, which shows up as chest pain (angina) or as a shift of the ST segment on the electrocardiogram. The Duke treadmill score, developed by Daniel Mark and colleagues at Duke University in 1987, combines three results of the test into one number that predicts the risk of death.
The formula
DTS = exercise time − 5 × ST deviation − 4 × angina index
- Exercise time is in minutes on the standard Bruce protocol, which raises speed and slope every 3 minutes.
- ST deviation is the largest ST-segment depression or elevation, in millimeters, during or after exercise.
- Angina index: 0 for no angina, 1 for angina that did not stop the test, 2 for angina that ended the test.
A long exercise time pushes the score up. ST changes and angina pull it down.
Worked example
A patient walks 9 minutes, develops 1 mm of ST depression and has chest discomfort that does not stop the test:
DTS = 9 − 5 × 1 − 4 × 1 = 0
A score of 0 falls in the moderate-risk group.
Risk groups
From the original validation in outpatients with suspected coronary disease:
- +5 or more: low risk, annual mortality about 0.25%, and about 99% survival at four years.
- −10 to +4: moderate risk, annual mortality about 1.25%.
- −11 or less: high risk, annual mortality about 5%.
Low-risk patients can usually be managed with medication and lifestyle measures without immediate further tests. Moderate-risk patients often go on to a stress imaging test or CT coronary angiography. High-risk patients are usually referred for invasive coronary angiography.
When the score does not apply
The score was derived with the Bruce protocol and assumes the ECG can be read during exercise. It is less reliable with:
- left bundle branch block, a paced rhythm or Wolff-Parkinson-White pattern;
- more than 1 mm of ST depression at rest;
- digoxin treatment or left ventricular hypertrophy;
- patients who cannot exercise enough to reach a meaningful workload.
It has been validated in both men and women, though the test detects disease less accurately in women. In many centers, imaging tests have replaced the plain exercise ECG as the first test, but the Duke score remains a useful way to read the results when an exercise ECG is done.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.