Learn · Part 2. The tests · 5 min read
Exercise ECG (treadmill test)
What a treadmill test with ECG monitoring tells you, how to read capacity and the Duke score, and when the resting ECG rules it out.
60-second take
- The exercise ECG gives no images. It reports exercise capacity (METs), ST-segment response, blood pressure and heart rate responses, symptoms, and often the Duke treadmill score.
- It needs a patient who can reach about 5 METs and a resting ECG without ST-T abnormalities, LBBB, paced rhythm, pre-excitation or digoxin effect.
- A positive ST response is 1 mm or more of horizontal or downsloping depression 60 to 80 ms after the J point; ST depression does not localize the artery.
- Reported sensitivity and specificity (60% to 77%) are lower than for stress imaging, but capacity and the Duke score give useful prognostic information.
- A negative test after a poor effort is inconclusive, not reassuring.
What it is and how it works
The exercise ECG, also called the treadmill test, asks one question: does the patient develop symptoms, ST-segment changes or an abnormal blood pressure or heart rate response when the heart is made to work harder? Exercise raises the heart’s oxygen demand. If the coronary arteries cannot raise blood flow to match, the mismatch causes ischemia, which can show up as symptoms or ECG changes .
The patient walks on a treadmill (some labs use a bicycle) with a continuous 12-lead ECG and regular blood pressure checks. The test is symptom-limited, so it continues until fatigue, limiting chest pain, marked ischemia or a drop in blood pressure . The Bruce protocol is the standard, with speed and incline rising every 3 minutes. Gentler options (modified Bruce, Naughton) suit people with limited capacity, and ramp protocols are individualized to the patient and aim for 6 to 12 minutes of exercise .
This test gives no images of the heart. It cannot show where ischemia is or how much muscle is affected. It also uses no contrast or radiotracer, and, because nothing is imaged, no ionizing radiation.
What you get
The report combines several pieces of information. Read all of them, not just the ST segments.
Exercise capacity
Capacity is expressed in metabolic equivalents (METs), where 1 MET is 3.5 mL of oxygen per kg per minute. Reaching 10 METs or more is considered a favorable prognostic sign . Expected capacity falls with age and differs by sex, so compare the result with the predicted value, not a fixed number.
| Age | Women: predicted | Women: reduced | Men: predicted | Men: reduced |
|---|---|---|---|---|
| 40 | 9.5 METs | 8.1 | 12.0 METs | 10.2 |
| 60 | 6.9 METs | 5.9 | 9.0 METs | 7.7 |
| 80 | 4.3 METs | 3.7 | 6.0 METs | 5.1 |
Capacity under 5 METs, or failing to complete the first Bruce stage, or not reaching 85% of the age-predicted level, goes with a higher risk of coronary events. Exercising to Bruce stage III or beyond 10 METs with a negative ECG goes with a low risk .
ST-segment response
ST depression is measured 60 to 80 ms after the J point. Horizontal or downsloping depression of 1.0 mm or more is a positive response. Upsloping depression of 1.0 to under 1.5 mm is equivocal, and 1.5 mm or more is positive. ST elevation of more than 1.0 mm is also positive. ST depression does not tell you which artery is involved .
Hemodynamics and symptoms
The report should also describe the blood pressure response, the heart rate response and how fast the heart rate recovers. A fall of 12 beats per minute or less one minute into recovery is abnormal and is predictive of overall mortality .
The Duke treadmill score
The Duke treadmill score folds three findings into one number: Bruce exercise minutes, minus 5 times the millimeters of ST deviation, minus 4 times the angina index (0 for none, 1 for some, 2 for exercise-limiting angina) . Its prognostic value was studied in outpatients with suspected coronary disease . The PET criteria describe a score of +5 or higher as low risk and −10 to +4 as intermediate; lower scores carry higher risk .
| Bruce minutes | ST deviation | Angina | Score | Range |
|---|---|---|---|---|
| 12 | 0 mm | None (0) | 12 − 0 − 0 = +12 | Low risk |
| 9 | 1 mm | None (0) | 9 − 5 − 0 = +4 | Intermediate |
| 6 | 2 mm | Some (1) | 6 − 10 − 4 = −8 | Intermediate |
Strengths and limitations
Strengths
- Lowest-cost test used in the diagnostic evaluation, apart from calcium scoring , and widely available .
- Gives prognostic information on functional capacity, blood pressure and heart rate responses, and symptom reproduction .
- In chronic coronary disease with symptoms that persist despite medical therapy, it can show whether the symptoms fit angina, how severe they are, and what capacity the patient has, which helps with decisions about management and cardiac rehabilitation .
- Serious events are uncommon. Reported rates are 5 to 10 sudden cardiac deaths per 100,000 tests and about 1 myocardial infarction per 2,500 tests .
Limitations
- Less accurate than stress imaging: reported sensitivity and specificity range from 60% to 77% .
- No imaging, so no location, extent or ventricular function.
- Needs an interpretable resting ECG and enough exercise capacity (see below).
- A submaximal or equivocal test often leads to a second, imaging test.
Practical points
| Time | Ramp protocols aim for 6 to 12 minutes of exercise; Bruce stages last 3 minutes . |
|---|---|
| Radiation, contrast, tracer | None. |
| Stressor | Exercise only: treadmill, or bicycle ergometer in some labs. |
| Suits | Patients who can reach 5 METs or more, with no disabling comorbidity, and a resting ECG free of ST-T abnormalities . |
| Struggles | Frailty, BMI above 40, peripheral artery disease, COPD or orthopedic limits; and a resting ECG with more than 0.5 mm of ST depression, LVH, paced rhythm, LBBB, Wolff-Parkinson-White pattern or digoxin effect . |
When the resting ECG cannot be used. A stress ECG is called non-diagnostic when exercise changes cannot be told apart from baseline abnormalities: LVH with repolarization changes, baseline ST-T changes of 1 mm or more, LBBB, a wide right bundle branch block, pre-excitation, ventricular pacing, or digoxin . In LBBB or paced rhythm the exercise ECG alone cannot assess ischemia, though it can still measure capacity .
Medicines. Beta-blockers, calcium channel blockers and nitrates lower the sensitivity of stress testing. They are more often held for an initial diagnostic test and often continued when the goal is to judge therapy in known disease . Follow your lab’s instructions.
In an externally validated study cited by the chronic coronary disease guideline, the Duke score alone had a c-index of 0.62 for all-cause death. Adding clinical variables raised it to 0.83 and moved 64% of patients with a low-risk Duke score into the intermediate or high-risk group . A low score is a useful finding, not a verdict.
The 2021 guideline notes that marked ischemia (for example 2.0 mm or more at reduced workloads) or a high Duke score signals higher risk, and that further stress or anatomic testing may help these patients. After a submaximal test or ST depression of 1.0 mm or more, added stress imaging may improve risk detection .
The guideline considers exercise ECG reasonable for intermediate-to-high-risk patients with stable chest pain, an interpretable ECG, no known coronary disease and the ability to reach 5 METs or more . Data also support adding stress imaging after an initial exercise ECG to improve diagnostic accuracy and risk stratification . Economic models suggest that a tiered approach, starting with the exercise ECG and adding imaging selectively, can offset its lower accuracy .
Example from the tool
Prior to cardiac rehabilitation, coronary disease (no new or worsening symptoms)
Here the question is how much exercise a patient can do safely, not where ischemia sits. Compare how the criteria rate each test for that question.
- Exercise ECGAppropriate
- Exercise SPECTMay Be Appropriate
- Pharmacologic SPECTMay Be Appropriate
- Pharmacologic PETRarely Appropriate
- Exercise echoMay Be Appropriate
- Dobutamine echoMay Be Appropriate
- Stress CMRMay Be Appropriate
- CAC scoreRarely Appropriate
- CCTARarely Appropriate
- Invasive angiographyRarely Appropriate
- No testMay Be Appropriate
The PET criteria make the same point from the other side: exercise testing is best for determining exercise capacity, while PET uses pharmacologic stress .
Build a scenario for your patient → to see how the published criteria rate the exercise ECG and the imaging tests for their situation.
Try it in the tool
Sources cited on this page
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