Treadmill Test in Coronary Artery Disease: Indications and Results
Exercise treadmill testing should be the initial diagnostic test for patients with suspected coronary artery disease who have an intermediate pre-test probability (15-65%), can exercise adequately, have a normal resting ECG, and are not taking digoxin. 1
Indications for Treadmill Testing
Primary Indications:
- Diagnosis and risk stratification in patients with:
- Intermediate pre-test probability of CAD (15-65%)
- Normal resting ECG
- Adequate exercise capacity
- Symptoms of chest pain (typical or atypical angina)
Contraindications:
- Resting ECG abnormalities that interfere with interpretation:
- Preexcitation (Wolff-Parkinson-White) syndrome
- Electronically paced ventricular rhythm
1 mm ST depression at rest
- Complete left bundle-branch block 1
- Patients taking digoxin
- Inability to exercise adequately
Alternative Testing Scenarios:
- For patients with abnormal resting ECG or those taking digoxin: Exercise perfusion imaging or exercise echocardiography 1
- For patients unable to exercise: Pharmacological stress testing with dipyridamole, adenosine, or dobutamine 1
- For patients with left bundle-branch block: Dipyridamole or adenosine myocardial perfusion imaging regardless of exercise ability 1
Interpretation of Results
Diagnostic Criteria:
- Positive test: Horizontal or down-sloping ST-segment depression ≥0.1mV (1 mm), persisting for at least 0.06-0.08s after the J-point 1
- Important note: In approximately 15% of patients, diagnostic ST-segment changes appear only during recovery phase 1
Risk Stratification Using Duke Treadmill Score:
The Duke treadmill score is calculated as:
- Exercise time in minutes - (5 × ST deviation in mm) - (4 × treadmill angina index)
Risk categories based on Duke treadmill score:
- Low risk: Score ≥ +5
- Annual mortality rate: 0.25%
- 60% have no significant coronary stenosis 3
- Moderate risk: Score between -10 and +4
- Annual mortality rate: 1.25-2.5%
- High risk: Score ≤ -11
- Annual mortality rate: 5%
- 74% have 3-vessel or left main coronary disease 3
Prognostic Value:
- ST segment depression pattern matters:
- Early onset ischemic changes (first 3 minutes): 86% prevalence of multi-vessel disease
- Prolonged recovery (ST changes persisting >8 minutes): 90% prevalence of multi-vessel disease 4
Special Considerations
Women:
- Exercise ECG has lower sensitivity (61%) and specificity (70%) in women compared to men (72% and 77%, respectively) 1
- Factors affecting accuracy in women:
- More frequent resting ST-T wave changes
- Lower ECG voltage
- Hormonal factors (estrogen, hormone replacement therapy) 1
- Despite lower accuracy, integrating multiple parameters (Duke treadmill score) improves diagnostic value in women 1
Clinical Pitfalls:
- Relying solely on ST-segment changes without considering other parameters leads to inadequate risk assessment 1
- False-positive results are more common with slowly upsloping ST depression (32%) compared to horizontal (15%) or downsloping (1%) patterns 4
- Equivocal results are common (up to 54% in some studies) and may require additional testing with coronary CT angiography 5
Modern Testing Algorithm
- Assess pre-test probability of CAD based on age, sex, and nature of chest pain
- For patients with intermediate pre-test probability (15-65%):
- If normal resting ECG and able to exercise: Exercise treadmill test
- If abnormal resting ECG or unable to exercise: Stress imaging test
- For high Duke treadmill score (≤-11): Consider invasive coronary angiography
- For intermediate Duke treadmill score: Consider additional risk stratification with cardiac imaging
- For low Duke treadmill score (≥+5): Medical management with risk factor modification 1
Remember that coronary CT angiography is increasingly being recommended as first-line for patients with low-intermediate pre-test probability (15-50%), particularly when suitable candidates are available and appropriate technology and expertise exist 6.