What is the role of treadmill (exercise) stress test (TMT) in the assessment and management of angina?

Role of Treadmill Stress Test (TMT) in Angina

Exercise treadmill testing serves as the initial diagnostic test for risk stratification in patients with stable angina who can exercise adequately, have a normal baseline ECG, and are not taking digoxin, while also being useful for confirming the diagnosis, assessing symptom severity, and guiding management decisions including medical therapy, revascularization, and cardiac rehabilitation. 1

Primary Diagnostic Role

Initial Risk Stratification

• TMT should be the first-line test for symptomatic patients with intermediate-to-high probability of coronary artery disease (CAD) who meet specific criteria. 1, 2
• The test must be performed using the Bruce protocol with Duke treadmill score calculation for standardized risk assessment. 1, 2
• Duke treadmill score = exercise time (minutes) - (5 × ST deviation in mm) - (4 if angina occurs, 8 if angina causes test termination). 1, 2

Risk Stratification by Duke Score:

• Low risk (score ≥5): 4-year survival 99%, annual mortality 0.25% - these patients can be reassured and managed medically. 1
• Moderate risk (score -10 to +4): intermediate prognosis - requires closer follow-up and optimization of medical therapy. 1
• High risk (score ≤-10): 4-year survival 79%, annual mortality 5% - should proceed to invasive coronary angiography (ICA). 1

Specific Clinical Applications

Confirming Angina Diagnosis

• TMT evaluates the relationship between symptoms and graded exercise stress, helping confirm whether chest pain represents true angina pectoris. 1
• Angina occurring during exercise testing increases diagnostic sensitivity to 85% for true coronary disease, compared to 64% with ST-segment depression alone. 3
• Patients who develop angina during TMT have twice the rate of coronary events (myocardial infarction, angina progression, coronary death) compared to those with ST depression alone. 3

Assessing Symptom Severity and Functional Capacity

• The test determines exercise capacity in metabolic equivalents (METs), which directly correlates with prognosis. 1
• Angina induced at low workload (≤4 METs) carries more than twice the risk of coronary events compared to angina at high workload (8-9 METs). 3
• This information guides decisions about cardiac rehabilitation referral and return-to-work recommendations. 1

Guiding Management Decisions

• TMT results help select between medical therapy optimization, coronary revascularization, or cardiac rehabilitation. 1
• In patients with known obstructive CAD on optimal guideline-directed medical therapy (GDMT), TMT can determine if persistent symptoms represent true angina requiring further intervention. 1

Patient Selection Criteria

Appropriate Candidates:

• Must be able to exercise to at least 85% of maximum predicted heart rate for interpretable results. 2, 4
• Normal baseline ECG without confounding abnormalities. 1, 2
• Not taking digoxin (causes false-positive ST changes). 1, 4
• Physically capable of treadmill walking. 2

Absolute Contraindications:

• Preexcitation (Wolff-Parkinson-White) syndrome - causes baseline ST abnormalities. 1, 2
• Electronically paced ventricular rhythm - prevents ST-segment interpretation. 1
• Complete left bundle branch block - causes false-positive ST changes. 1
• >1 mm ST depression at rest - interferes with exercise-induced ST interpretation. 1, 2
• Left ventricular hypertrophy with strain pattern - causes baseline repolarization abnormalities. 2
• High-risk unstable angina or acute myocardial infarction - requires immediate invasive management. 4

When to Use Stress Imaging Instead of Standard TMT

Baseline ECG Abnormalities:

• If the patient has any of the contraindications listed above, proceed directly to exercise stress imaging (echocardiography or nuclear perfusion) rather than standard TMT. 1, 2
• This maintains the benefits of exercise while adding imaging to overcome ECG interpretation limitations. 1, 2

Inability to Exercise:

• For patients unable to exercise adequately due to physical limitations (arthritis, amputation, severe peripheral vascular disease, severe COPD, general weakness), use pharmacologic stress testing with imaging (adenosine/dipyridamole perfusion imaging or dobutamine echocardiography). 1, 4

Known CAD Requiring Ischemia Localization:

• In patients with established obstructive CAD and persistent stable angina despite GDMT, stress imaging (PET/SPECT, CMR, or echocardiography) is recommended over standard TMT to diagnose myocardial ischemia, estimate risk of major adverse cardiac events (MACE), and guide therapeutic decisions. 1
• When both PET and SPECT are available, PET is preferable due to superior diagnostic accuracy and lower rates of nondiagnostic results. 1

Diagnostic Accuracy and Limitations

Performance Characteristics:

• Standard TMT has 68% sensitivity and 77% specificity for detecting CAD using coronary angiography as the gold standard. 5
• Marked ST-segment depression (≥3 mm) identifies severe coronary disease with 69% having triple-vessel disease and 92% having proximal left anterior descending lesions. 6
• ST/heart rate slope >2.4 mV·beats⁻¹·min⁻¹ is abnormal, with values >6 mV·beats⁻¹·min⁻¹ suggesting three-vessel disease. 2

Common Pitfalls:

• False-negative rate of 17% and false-positive rate of 23% compared to stress myocardial perfusion imaging. 5
• In patients with normal coronary arteries on angiography, 24% still show positive TMT results, limiting its value for predicting coronary anatomy in undiagnosed chest pain. 7
• The Duke treadmill score performs poorly in elderly patients, particularly those >75 years old. 1

Role in Patients with Known CAD

Post-Revascularization:

• TMT can assess functional capacity and symptom-exercise relationships after percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG). 1
• For post-CABG patients with stable chest pain suspected of having myocardial ischemia, stress imaging or coronary CT angiography (CCTA) is more reasonable than standard TMT to evaluate graft stenosis or occlusion. 1

Monitoring Disease Progression:

• TMT should be repeated after significant changes in anginal pattern to reassess risk. 1
• In patients with moderate-to-severe ischemia on stress testing despite GDMT, ICA is recommended for guiding therapeutic decision-making. 1

Safety Profile

Complication Rates:

• 0-6 deaths or cardiac arrests per 10,000 tests. 2
• 2-10 myocardial infarctions per 10,000 tests. 2
• Available data suggest graded exercise testing carries acceptably low risk when conducted according to contemporary guidelines. 2

Special Considerations for Unstable Angina

Timing Restrictions:

• High-risk unstable angina is an absolute contraindication to TMT - these patients require prompt angiography without noninvasive risk stratification. 4, 8
• Low-risk unstable angina patients who have stabilized can undergo TMT when free of ischemic symptoms for minimum 12-24 hours. 4
• Patients must be free of active ischemic symptoms, ST-segment changes, elevated cardiac biomarkers, and heart failure symptoms before testing. 4, 8

Risk-Based Approach:

• High-risk features (persistent pain, ST changes, elevated troponin, heart failure) mandate ICU admission and direct angiography. 8
• Intermediate-risk patients (ST depression ≥1 mm, elevated biomarkers, recurrent angina) require monitored hospital beds and should be free of ischemia for 2-3 days before stress testing. 4, 8
• Low-risk patients can be evaluated in chest pain units with TMT performed within 72 hours if clinically stable. 4, 8