What is a cardiac stress test, including its indications, preferred exercise or pharmacologic protocols, contraindications, and interpretation of results?

Cardiac Stress Test Overview

A cardiac stress test evaluates the heart's response to increased workload through exercise or pharmacologic agents, primarily used to diagnose coronary artery disease in symptomatic patients, assess prognosis in known cardiac disease, and evaluate functional capacity.

What It Is

A stress test assesses myocardial oxygen supply-demand mismatch by inducing cardiac stress while monitoring for ischemia through ECG changes, wall motion abnormalities, or perfusion defects. The "ischemic cascade" occurs in sequence: reduced LV compliance → regional wall motion abnormalities → increased LV end-diastolic pressure → ST-segment changes → angina (if it occurs at all) 1.

Primary Indications

• Diagnosis of coronary artery disease in symptomatic patients (chest pain, dyspnea) 2
• Risk stratification in known cardiac disease
• Preoperative evaluation for vascular surgery or patients with active cardiac symptoms before nonemergent noncardiac surgery 2
• Assessment of valvular disease, hypertrophic cardiomyopathy, diastolic function 3
• Evaluation of functional capacity and prognosis in heart failure, cardiomyopathies 4

Testing asymptomatic patients is generally NOT indicated 2. The exception is select deconditioned adults before vigorous exercise programs, though evidence for this practice is limited 2.

Choosing Exercise vs. Pharmacologic Stress

Exercise Stress is First-Line

Exercise-based testing should always be considered before pharmacologic testing 5. Exercise is the only physiological stress, provides the safest option, and yields additional prognostic information including functional capacity, blood pressure response, and heart rate recovery 6, 5.

Exercise modalities:

• Semi-supine bicycle (optimal for continuous imaging) 6
• Treadmill (most common in US)
• Upright bicycle 6

Pharmacologic Stress Indications

Use pharmacologic agents when patients cannot achieve ≥5 METs of exercise 5 due to:

• Deconditioning
• Peripheral vascular disease
• Orthopedic disabilities
• Neurological disease 1

Agent selection:

• Vasodilators (adenosine, dipyridamole, regadenoson): Preferred for perfusion imaging 6, 1

  • Adenosine: 140 μg/kg/min IV, titrate up to 210 μg/kg/min over 6 minutes 6
  • Regadenoson: Fixed 0.4 mg bolus (no weight adjustment), simpler workflow 6
  • Contraindicated in reactive airway disease/bronchospasm 6

• Dobutamine: Preferred for viability assessment and when vasodilators contraindicated 6, 1

  • Increases myocardial oxygen demand through increased contractility, HR, BP 1
  • Target 85% age-predicted max HR 1
  • Atropine may be added if adequate HR not achieved 1

• Pacing: Excellent option in patients with permanent pacemakers (catheter-free, needle-free external programming) 6

Imaging vs. ECG Alone

Add imaging (echocardiography or nuclear perfusion) when:

• Baseline ECG abnormalities (left bundle branch block, resting ST depression >1 mm) 1
• Equivocal or indeterminate exercise ECG results 1
• Women (nuclear imaging preferred modality) 5
• Need to localize ischemia or quantify ischemic burden 1

Imaging is NOT necessary if patients achieve >10 METs on exercise testing 2.

Major Contraindications

Absolute contraindications include:

• Acute MI (within days)
• Unstable angina
• Uncontrolled arrhythmias causing symptoms or hemodynamic compromise
• Symptomatic severe aortic stenosis
• Acute pulmonary embolism or infarction
• Acute myocarditis or pericarditis
• Acute aortic dissection 3

Relative contraindications:

• Known severe coronary stenoses
• Electrolyte abnormalities
• Severe hypertension (>200/110 mmHg)
• Moderate stenotic valvular disease
• High-degree AV block 3

Interpretation

Exercise ECG Criteria

• Positive: ≥1 mm horizontal or downsloping ST depression
• Duke Treadmill Score: Excellent prognostic value for risk stratification 2

High-Risk Features (Require Immediate Attention)

• ST elevation
• Sustained ventricular tachycardia
• Hypotensive response to exercise
• Severe ST depression (>2 mm)
• ST depression in multiple leads
• Prolonged ST depression in recovery 5

Functional Capacity

• <4 METs: High risk; stress testing not indicated before noncardiac surgery 2
• ≥5 METs: Adequate for most activities
• >10 METs: Excellent prognosis; imaging unnecessary 2

Safety and Complications

Overall complication rates are very low:

• MI: <0.02%
• Death: <0.002% 1
• Dobutamine has highest adverse event rate among modalities 3

Mandatory safety requirements:

• Physician with resuscitation expertise must be immediately available 6
• Fully equipped resuscitation trolley with defibrillator 6
• Adequate space to manage cardiac arrest 6
• Nurse present to support the performing cardiologist 6

Special Considerations

Avoid repeat testing in stable patients:

• <2 years post-PCI without new symptoms 2
• <5 years post-CABG without new symptoms 2

COVID-19 era: Pharmacologic testing preferred over exercise to avoid aerosol virus diffusion 6.

Women: Nuclear imaging stress test is preferable due to better diagnostic accuracy 5.