What is the recommended initial diagnostic step for patients with suspected angina, specifically regarding exercise testing?

Exercise Testing for Suspected Angina

Exercise ECG testing using the Bruce protocol with Duke treadmill score should be the initial diagnostic test for patients with suspected stable angina who can exercise, have a normal resting ECG, and are not taking digoxin. 1

Initial Patient Assessment

Before proceeding to exercise testing, obtain:

• 12-lead resting ECG in all patients with chest pain to identify baseline abnormalities and assess for acute ischemia 1, 2
• Resting transthoracic echocardiography to exclude alternative causes of angina, identify regional wall motion abnormalities, measure left ventricular ejection fraction for risk stratification, and evaluate diastolic function 1
• Basic laboratory tests including complete blood count, fasting glucose/HbA1c, lipid profile, serum creatinine, and cardiac biomarkers to exclude acute myocardial injury 2

When Exercise ECG is Recommended

Exercise ECG is the preferred initial test when patients meet ALL of the following criteria 1:

• Able to exercise adequately (can achieve 85% maximum predicted heart rate)
• Normal baseline ECG or minimal abnormalities (<1 mm ST depression)
• Not taking digoxin (causes false-positive ST changes)
• Intermediate to high pretest probability of CAD (15-85% based on age, sex, and symptom characteristics) 1
• Clinically stable without features of unstable angina 3

The test provides critical prognostic information beyond diagnosis, including exercise capacity, blood pressure response, arrhythmias, and symptom reproduction 1.

Absolute Contraindications to Exercise ECG

Exercise ECG testing is not recommended and should be replaced with stress imaging when the following ECG abnormalities are present 1:

• Complete left bundle branch block (produces false-positive septal defects)
• Electronically paced ventricular rhythm
• Wolff-Parkinson-White syndrome (preexcitation pattern)
• >1 mm ST-segment depression at rest
• Unstable angina or acute coronary syndrome (high-risk features require immediate angiography, not stress testing) 3

Duke Treadmill Score for Risk Stratification

When exercise ECG is performed, calculate the Duke treadmill score 1:

Formula: Exercise time (minutes) − (5 × ST deviation in mm) − (4 if angina occurs) − (8 if angina causes test termination)

Risk categories:

• Low risk (score ≥5): 4-year survival 99%, annual mortality 0.25%
• Moderate risk (score −10 to +4): Intermediate prognosis
• High risk (score ≤−10): 4-year survival 79%, annual mortality 5%

This scoring system is well-validated for both inpatients and outpatients, and performs equally in men and women, though it has limited accuracy in patients >75 years old 1.

When to Use Stress Imaging Instead

Stress imaging (nuclear perfusion or echocardiography) should be the initial test in the following scenarios 1:

• Baseline ECG abnormalities that prevent accurate interpretation (as listed above)
• Unable to exercise due to orthopedic, neurologic, or other physical limitations
• Previous coronary revascularization (PCI or CABG) with new or worsening symptoms 1
• High pretest probability (66-85%) or left ventricular ejection fraction <50% without typical angina 1
• Taking digoxin (causes ST-segment changes independent of ischemia) 1

Exercise stress testing with imaging is preferred over pharmacologic stress whenever the patient can exercise adequately 1.

Special Considerations for Unstable Angina

For patients with low-risk unstable angina who have stabilized 3:

• Wait minimum 8-12 hours after being free of active ischemic or heart failure symptoms before stress testing 1, 3
• Exercise ECG can be performed within 72 hours of presentation in outpatient low-risk patients 1
• Intermediate-risk patients should wait 2-3 days after stabilization before testing 1
• High-risk patients should proceed directly to coronary angiography without stress testing 3

Limited evidence shows only 0.5% death or MI rate within 24 hours of exercise testing in stabilized unstable angina patients 1.

Alternative Diagnostic Pathways

Non-invasive functional imaging or coronary CT angiography is recommended as the initial test when obstructive CAD cannot be excluded by clinical assessment alone 1. The 2019 ESC guidelines have elevated coronary CTA and stress imaging to equal footing with exercise ECG, with test selection based on clinical likelihood, local expertise, and availability 1.

However, coronary CTA is not recommended when extensive coronary calcification, irregular heart rate, significant obesity, or inability to cooperate with breath-hold commands makes good image quality unlikely 1.

Common Pitfalls

• False-positive rates are higher in women with exercise ECG, though a recent randomized trial showed no incremental benefit of nuclear imaging over standard exercise testing for clinical outcomes in symptomatic women who could exercise 1
• Do not perform exercise ECG in patients taking digoxin or with significant baseline ST depression, as interpretation is unreliable 1
• Recognize that a "normal" exercise ECG on anti-ischemic medications does not rule out significant coronary disease 1
• Avoid routine periodic exercise testing in patients with no change in clinical status and low-risk findings on initial evaluation 1