What is the protocol for conducting an exercise stress test (EST) for patients at risk for coronary artery disease (CAD)?

Exercise Stress Test Protocol for Patients at Risk for Coronary Artery Disease

For patients at intermediate risk (15-65% pre-test probability) who can exercise and have an interpretable baseline ECG, standard exercise ECG testing without imaging is the recommended initial diagnostic test. 1

Patient Selection for Standard Exercise ECG

Ideal Candidates (Class I Recommendation)

• Intermediate pre-test probability of CAD (15-65%) with anginal symptoms 1
• Ability to exercise adequately (achieve ≥85% maximum predicted heart rate) 1
• Normal or near-normal baseline ECG without ST-segment abnormalities 1, 2
• Not taking digoxin 1
• No prior coronary revascularization (PCI or CABG) 1

Absolute Contraindications Requiring Imaging Instead

• Baseline ST-segment depression ≥0.1 mV (1 mm) 1
• Baseline ST-segment elevation 3
• Left bundle branch block (LBBB) 1
• Ventricular paced rhythm 1
• Wolff-Parkinson-White syndrome 1
• Left ventricular hypertrophy with strain pattern 1
• Taking digoxin 1

When to Use Stress Imaging as Initial Test

High-Risk Scenarios (Class I for Imaging)

• Pre-test probability 66-85% 1
• Left ventricular ejection fraction <50% without typical angina 1
• Prior revascularization (PCI or CABG) 1
• Uninterpretable baseline ECG due to abnormalities listed above 1

Gender Considerations

• Women have lower sensitivity and specificity with standard exercise ECG 1
• However, a randomized trial showed no incremental benefit of nuclear imaging over standard treadmill testing for clinical outcomes in symptomatic women capable of exercise 1
• Stress echocardiography or nuclear imaging should be considered for women with intermediate-to-high pre-test probability and abnormal baseline ECG 1

Exercise Protocol Selection

Preferred Modality

• Exercise (treadmill or bicycle) is always preferred over pharmacologic stress when the patient can exercise 1
• Treadmill provides higher diagnostic sensitivity than bicycle ergometer 4
• Target duration: 8-12 minutes to maximal capacity 4

Common Protocols

• Bruce protocol is most widely used in North America 4
• Modified protocols with smaller workload increments are preferred for patients with limited exercise capacity or very high fitness levels to achieve the 8-12 minute target 4

Test Endpoints and Interpretation

Adequate Test Requirements

• Achievement of ≥85% maximum predicted heart rate in absence of symptoms or ischemic signs 1
• Maximum predicted heart rate = 220 - age 5

Key Diagnostic Parameters Beyond ECG Changes

• Exercise capacity (METs achieved) - most powerful predictor of risk 1
• Heart rate response and recovery 6
• Blood pressure response 1, 5
• Symptoms during exercise 1
• Workload achieved 1

Positive Test Criteria

• Horizontal or downsloping ST-segment depression ≥1 mm (0.1 mV) 1
• ST-segment elevation in non-Q wave leads 1

Risk Stratification After Testing

Low-Risk Patients (Conservative Management)

• Normal exercise ECG with good exercise capacity 1
• No further imaging required 1
• Medical therapy and risk factor modification 1

High-Risk Patients (Refer to Angiography)

• Significant ischemia at low workload 1
• Extensive ST-segment changes 1
• Hypotensive response to exercise 5
• Poor exercise capacity with ischemic changes 1

Intermediate/Uncertain Risk (Consider Imaging)

• Inconclusive test (failure to achieve 85% maximum heart rate without symptoms/signs) 1
• Equivocal ECG changes 1
• Borderline ST-segment depression (0.05-0.1 mV) 1

Special Populations

Acute Coronary Syndrome Patients

• Low-risk patients: test within 72 hours of presentation 1
• Intermediate-risk patients: test after 2-3 days of clinical stability (minimum 8-12 hours symptom-free) 1
• Submaximal test can be performed before hospital discharge 5
• Full symptom-limited test after 2-3 weeks post-MI 5

Asymptomatic Patients with Risk Factors

• Exercise stress testing may provide valuable prognostic information 5
• Not routinely recommended for screening but can guide risk stratification 1

Common Pitfalls to Avoid

• Never perform standard exercise ECG in patients with baseline ST-segment abnormalities - this leads to uninterpretable results and requires imaging 1, 3
• Do not interpret a "normal" test in patients taking anti-ischemic medications as ruling out significant CAD 1
• Avoid testing patients with unstable symptoms - ensure clinical stability first 1
• Do not rely solely on ST-segment changes - incorporate exercise capacity, hemodynamic response, and symptoms into risk assessment 1, 6
• False-positive rates are higher in women, patients with LVH, electrolyte imbalances, and those on digoxin 1