Stress Testing Cannot Completely Rule Out Angina
A normal stress test does not completely rule out angina, as it has limitations in sensitivity and specificity for detecting coronary artery disease. 1
Understanding Stress Test Limitations
Diagnostic Accuracy
- Exercise ECG testing has a sensitivity of 70-98% and specificity of 40-90% (with mean values of 85-90% and 70-75% respectively) 1
- False negative results can occur due to:
- Single-vessel disease
- Balanced multi-vessel disease
- Submaximal exercise effort
- Anti-ischemic medications masking results
- Microvascular dysfunction
Types of Stress Tests and Their Limitations
Exercise ECG Testing
- Recommended as initial test for patients with intermediate pre-test probability (15-65%) of coronary artery disease 1
- Not reliable in patients with:
- Left bundle branch block
- Paced rhythm
- Wolff-Parkinson-White syndrome
- Abnormal resting ECG with LV hypertrophy
- Electrolyte imbalance
- Intraventricular conduction abnormalities
- Atrial fibrillation
- Digitalis use 1
Stress Imaging Tests
- Higher sensitivity and specificity than exercise ECG alone
- Recommended when:
- Resting ECG abnormalities are present
- Patient has prior revascularization
- Pre-test probability is 66-85% 1
- Even imaging stress tests can miss:
- Microvascular dysfunction
- Endothelial dysfunction
- Myocardial bridges 2
Clinical Implications
When to Consider Coronary Angiography Despite Normal Stress Test
- Persistent typical angina symptoms despite normal stress test
- High clinical suspicion based on risk factors and symptom characteristics
- High-risk treadmill scores with normal imaging 1
- Symptoms occurring at lower workloads than those achieved during testing
Risk Stratification After Stress Testing
- Low-risk findings: <1% annual cardiac mortality
- Intermediate-risk findings: 1-3% annual cardiac mortality
- High-risk findings: >3% annual cardiac mortality 1
Approach to Patients with Suspected Angina
- Assess pre-test probability based on age, gender, and symptom characteristics
- Select appropriate initial test:
- Exercise ECG for intermediate probability without ECG abnormalities
- Stress imaging for higher probability or ECG abnormalities
- Interpret results in clinical context:
- Negative test with persistent symptoms warrants further evaluation
- Consider coronary angiography for high clinical suspicion despite negative test
Important Caveats
- A "normal" stress test in patients taking anti-ischemic medications does not rule out significant coronary disease 1
- Women may have higher false-negative rates with exercise ECG testing 1
- Up to 20% of patients with angina have no obstructive coronary artery disease but may have endothelial dysfunction, microvascular dysfunction, or myocardial bridges that stress tests may miss 2
- Stress echocardiography has been shown to be more accurate than exercise ECG in patients aged ≥70 years 3
Remember that stress testing is a valuable diagnostic tool, but its limitations must be recognized. Clinical judgment remains essential when evaluating patients with suspected angina, especially when symptoms persist despite a negative stress test.