What are the types of stress tests, their indications, and contraindications for a patient with suspected coronary artery disease (CAD)?

Types of Stress Tests for Suspected Coronary Artery Disease

For patients with suspected CAD, the choice of stress test depends primarily on pre-test probability of disease, ability to exercise, and baseline ECG interpretability—with exercise-based testing preferred when feasible, and imaging modalities reserved for intermediate-to-high risk patients or those with uninterpretable ECGs. 1

Pre-Test Probability Assessment: The Critical First Step

Before selecting any stress test, you must calculate pre-test probability using the Risk Factor-weighted Clinical Likelihood model incorporating age, sex, symptom type, and cardiovascular risk factors 1. This determines whether testing is even appropriate:

• Very low probability (≤5%): Defer further testing—more harm than benefit from false positives 1
• Low probability (>5-15%): Consider coronary artery calcium scoring first to reclassify patients 1
• Moderate probability (>15-50%): Coronary CTA is recommended as first-line 1
• Moderate-to-high probability (>15-85%): Stress imaging (echo, SPECT, PET, or CMR) is recommended 1
• Very high probability (>85%): Assume CAD is present; proceed directly to risk stratification, not diagnosis 1

Exercise ECG Stress Testing

Indications

• Primary indication: Patients with intermediate pre-test probability (15-65%) who can exercise adequately (≥5 METs), have normal resting ECG, and are not on medications interfering with ECG interpretation 1, 2
• Assessment of exercise tolerance, symptoms, arrhythmias, blood pressure response, and event risk 1
• Evaluating symptom control in patients already on treatment 1, 2

Diagnostic Performance

Exercise ECG has the lowest sensitivity of all stress tests at only 45-50%, though specificity is excellent at 90% 1. This poor sensitivity means it misses half of patients with obstructive CAD 1.

Contraindications

• Absolute: Acute myocardial infarction within 2 days, unstable angina not stabilized by medical therapy, uncontrolled cardiac arrhythmias causing symptoms or hemodynamic compromise, symptomatic severe aortic stenosis, acute pulmonary embolus or infarction, acute myocarditis or pericarditis 3, 4
• Relative: Left main coronary stenosis, moderate stenotic valvular heart disease, severe hypertension (systolic >200 mmHg or diastolic >110 mmHg), electrolyte abnormalities 3, 4

When NOT to Use Exercise ECG

• >0.1 mV ST-segment depression on resting ECG or digitalis use: Not recommended for diagnostic purposes 1
• Left bundle branch block or ventricular pacing: Use pharmacologic stress perfusion imaging instead 2, 5
• Prior revascularization (PCI or CABG): Stress imaging is superior 6

Exercise Stress Echocardiography

Indications

• Intermediate-to-high pre-test probability (>15-85%) in patients who can exercise 1
• Superior to exercise ECG with sensitivity 80-85% 1
• Provides localization of ischemia, assessment of LV function, and quantification of ischemic burden 7

Key Technical Requirements

• Mandatory use of ultrasound contrast (microbubbles) when ≥2 contiguous segments are not visualized to improve diagnostic accuracy 1
• Contrast-enhanced myocardial perfusion imaging during stress echo is recommended to improve accuracy and risk stratification beyond wall motion alone 1

Advantages Over Exercise ECG

A 2017 randomized trial demonstrated exercise stress echo was more efficacious than exercise ECG as initial testing, with 100% positive predictive value for obstructive CAD (9/9 patients) versus only 64% for exercise ECG (9/14 patients), and lower cost (£266 vs £327) 7.

Dobutamine Stress Echocardiography

Indications

• Primary indication: Symptomatic patients unable to exercise adequately due to orthopedic limitations, peripheral vascular disease, severe deconditioning, or inability to achieve ≥5 METs 5
• Not for patients with LBBB or paced rhythm—use vasodilator stress perfusion imaging instead 5

Diagnostic Performance

• Sensitivity: 75-93% (meta-analysis: 80%) 5
• Specificity: 79-92% (meta-analysis: 84%) 5
• Higher sensitivity but slightly lower specificity compared to vasodilator stress echo 5

Prognostic Value

• Normal dobutamine stress echo: <1% annual cardiac death rate over 5 years 5
• Abnormal with multivessel ischemia: 1-3% annual cardiac death rate (10-fold higher risk) 5

Contraindications

• Significant left ventricular outflow tract obstruction, recent myocardial infarction, unstable angina, uncontrolled hypertension, severe hypertension, significant arrhythmias 5

Vasodilator Stress Perfusion Imaging (Adenosine/Dipyridamole SPECT or PET)

Indications

• First-line pharmacologic stress test for LBBB or electronically paced ventricular rhythm, regardless of ability to exercise 2
• Patients unable to exercise adequately 2, 8
• High pre-test probability (66-85%) or LVEF <50% 2
• Prior revascularization with change in anginal pattern 2

Diagnostic Performance

• Vasodilator stress SPECT: Sensitivity 90-91% 1
• Vasodilator stress PET: Sensitivity 81-97% (PET preferred over SPECT when available) 1
• Adenosine SPECT specificity: 64-90% 2

Adenosine Contraindications (FDA Label)

• Absolute contraindications: Second- or third-degree AV block (without functioning pacemaker), sinus node disease/sick sinus syndrome/symptomatic bradycardia (without functioning pacemaker), known or suspected bronchoconstrictive or bronchospastic lung disease (e.g., asthma), known hypersensitivity to adenosine 8
• Warnings: Can cause cardiac arrest, ventricular arrhythmias, myocardial infarction, cerebrovascular accidents (hemorrhagic and ischemic), seizures, severe bronchoconstriction, and significant hypotension 8
• Avoid in patients with symptoms or signs of acute myocardial ischemia 8

Adenosine Dosing

Standard dose: 0.14 mg/kg/min infused over 6 minutes as continuous peripheral IV infusion (total dose 0.84 mg/kg) 8. This produces maximum coronary hyperemia in approximately 95% of cases within 2-3 minutes 8.

Exercise Stress SPECT/PET

When to Choose Exercise Over Pharmacologic Stress

Exercise stress SPECT is preferred over pharmacologic stress when patients can exercise ≥5 METs because exercise capacity alone is one of the strongest independent predictors of mortality, providing critical prognostic data beyond imaging findings 2. Exercise achieves higher physiological stress than pharmacologic agents, translating into superior ischemia detection 2.

Diagnostic Performance

• Exercise SPECT: Sensitivity 73-92%, specificity 70-75% 1, 2
• Exercise PET provides additional quantification of myocardial blood flow 1

Indications

• Intermediate-to-high pre-test probability (>15-85%) in patients capable of adequate exercise 1
• Mandatory measurement of coronary artery calcium score from unenhanced CT (used for attenuation correction) to improve detection of both non-obstructive and obstructive CAD 1

Cardiac Magnetic Resonance (CMR) Perfusion Imaging

Indications

• Intermediate-to-high pre-test probability (>15-85%) to diagnose and quantify myocardial ischemia/scar and estimate risk of major adverse cardiac events 1
• Sensitivity: 67-94% 1
• No radiation exposure—important consideration in young patients 1

Coronary CT Angiography (CCTA)

Indications

• Recommended for low-to-moderate pre-test probability (>5-50%) to diagnose obstructive CAD and estimate risk 1
• Highest sensitivity of all non-invasive tests: 95-99% 1
• Alternative to invasive angiography when another non-invasive test is equivocal or non-diagnostic 1

Contraindications

• Not recommended when extensive coronary calcification, irregular heart rate, significant obesity, inability to cooperate with breath-hold commands, or any condition making good image quality unlikely 1
• Not recommended as routine follow-up test for established CAD 1
• Coronary calcium scoring alone is not recommended to identify obstructive CAD 1

Critical Decision Algorithm

1. Calculate pre-test probability using Risk Factor-weighted Clinical Likelihood model 1
2. If ≤5%: No testing 1
3. If >5-15%: Consider calcium scoring or CCTA 1
4. If >5-50%: CCTA recommended 1
5. If >15-85% AND can exercise with normal ECG: Exercise stress imaging (echo or SPECT/PET preferred over exercise ECG alone due to superior sensitivity) 1, 2
6. If >15-85% AND cannot exercise: Dobutamine stress echo (if no LBBB/pacing) OR vasodilator stress perfusion imaging 2, 5
7. If LBBB or paced rhythm: Vasodilator stress perfusion imaging (adenosine/dipyridamole) regardless of exercise capacity 2, 5
8. If >85%: Assume CAD present; proceed to risk stratification with invasive angiography if considering revascularization 1

Common Pitfalls to Avoid

• Do not perform exercise ECG in patients with baseline ST depression >0.1 mV or on digitalis—it is not recommended for diagnostic purposes 1
• Do not use dobutamine or exercise stress in LBBB/paced rhythm—this causes false-positive septal wall motion abnormalities; use vasodilator stress instead 2, 5
• Do not default to pharmacologic stress in elderly patients based on age alone—if they can exercise ≥5 METs, exercise testing provides superior prognostic information 2
• Do not give adenosine to asthmatics or patients with bronchospastic lung disease—this is an absolute contraindication due to risk of severe bronchoconstriction 8
• Do not order stress testing in very low (≤5%) or very high (>85%) pre-test probability patients for diagnosis—testing causes more harm than benefit from false results 1