What is the purpose and procedure of a treadmill test for diagnosing coronary artery disease (CAD)?

Treadmill Test for Diagnosing Coronary Artery Disease (CAD)

The treadmill exercise test is the recommended initial test for risk stratification in patients with suspected coronary artery disease who are able to exercise and have a normal resting ECG. 1

Purpose of Treadmill Testing

• Treadmill exercise testing serves as a diagnostic tool to identify patients with suspected CAD by detecting exercise-induced myocardial ischemia 1
• It helps determine the risk for subsequent coronary events and death (risk stratification) to guide appropriate diagnostic and therapeutic interventions 1
• The test evaluates functional capacity, which is an important predictor of cardiovascular risk 2
• It can confirm whether symptoms are consistent with angina pectoris, assess symptom severity, and evaluate exercise tolerance 1

Procedure of Treadmill Testing

• The Bruce protocol is the most commonly used and validated exercise protocol for treadmill testing 1
• The test involves walking on a treadmill with gradually increasing speed and incline every 3 minutes 1
• During the test, continuous 12-lead ECG monitoring is performed to detect ST-segment changes indicative of myocardial ischemia 1
• Blood pressure and heart rate are monitored throughout the test 1
• The patient exercises until reaching a target heart rate, developing limiting symptoms, or showing significant ECG changes 1

Interpretation and Risk Assessment

• The Duke treadmill score is the most validated method for assessing risk and prognosis from treadmill test results 1, 3
• The Duke treadmill score is calculated as: exercise time in minutes - (5 × ST-segment deviation in mm) - (4 × treadmill angina index) 1
• The treadmill angina index is scored as: 0 for no angina, 1 for non-limiting angina, and 2 for exercise-limiting angina 3
• Risk categories based on Duke treadmill score 1, 3:
  • Low risk (score ≥ +5): 4-year survival rate of 99% (annual mortality 0.25%)
  • Moderate risk (score between -10 and +4)
  • High risk (score ≤ -10): 4-year survival rate of 79% (annual mortality 5%)

Special Considerations for Women

• Exercise ECG has lower sensitivity (61%) and specificity (70%) in women compared to men (72% and 77% respectively) 1
• The diminished accuracy in women is due to more frequent resting ST-T wave changes, lower ECG voltage, and hormonal factors 1
• Despite these limitations, integrating multiple parameters into risk scores like the Duke treadmill score improves accuracy in women 1
• In women with an intermediate Duke treadmill score, additional risk stratification with cardiac imaging is generally recommended 1

Contraindications and Limitations

• Exercise ECG testing is not recommended when the following confounding factors are present on resting ECG 1:
  • Preexcitation (Wolff-Parkinson-White) syndrome
  • Electronically paced ventricular rhythm
  • More than 1 mm of ST depression at rest
  • Complete left bundle-branch block
• Patients taking digoxin should not undergo standard exercise ECG testing due to reduced specificity (73% vs 96% in non-digoxin users) 4
• For patients unable to exercise, pharmacological stress testing with imaging is recommended 1

When to Use Alternative or Additional Testing

• For patients with abnormal resting ECG or those taking digoxin, exercise perfusion imaging or exercise echocardiography is recommended instead of standard exercise ECG 1
• Patients with an intermediate Duke treadmill score should be referred for additional risk stratification with cardiac imaging 1
• For patients with high-risk treadmill scores, coronary angiography is recommended to guide therapeutic decision-making 1
• Combined use of treadmill testing with myocardial perfusion imaging can improve diagnostic accuracy for CAD detection 5

Clinical Significance

• The ability to complete a 9-minute Bruce protocol treadmill exercise is associated with extremely low cardiac risk regardless of ECG findings or symptoms during the test 2
• Treadmill testing can effectively stratify patients with chest pain into those who can be safely discharged and those who require hospital admission 6
• The test provides valuable prognostic information beyond just diagnosis, helping guide management decisions 3