Why the contraindications are what they are

Read the list as mechanisms

Contraindication tables are long, but they shrink once you ask three questions about any test. What does the stress do to the body? What does the imaging need in order to be readable? What does the test inject or emit? Almost every entry answers one of these, so a condition you have never memorised can usually be reasoned out.

The tool uses five level words, and the differences matter. Contraindicated means a source lists the condition as a contraindication. Not feasible means the test cannot be done as intended, such as exercise in someone who cannot exercise. Nondiagnostic means the test can be done but the result cannot be interpreted. Caution marks a cautionary (relative) issue. Preferred means a source points toward a particular stressor or test for this patient. The 2026 ASNC (American Society of Nuclear Cardiology) guideline makes the same split between absolute contraindications and what it now calls cautionary conditions, which call for an individual risk-benefit judgement Duvall et al., 2026, Highlights of major changes Duvall et al., 2026, Tables 3 and 4.

Vasodilators act outside the coronary arteries

Regadenoson, adenosine and dipyridamole all dilate the coronary arteries through the adenosine A2A receptor Duvall et al., 2026, Regadenoson stress, Mechanism of action. Adenosine, and dipyridamole indirectly, also activate other adenosine receptors, which accounts for heart block at the AV (atrioventricular) node, low blood pressure and bronchospasm Duvall et al., 2026, Side effects/adverse events of adenosine Duvall et al., 2026, Side effects/adverse events of dipyridamole. Regadenoson is more selective for the coronary receptor Duvall et al., 2026, Regadenoson stress, Mechanism of action. The guideline applies its airway and AV-node precautions to the vasodilators as a group Duvall et al., 2026, Reactive airway disease Duvall et al., 2026, Conduction disease/AV block. Most of the vasodilator list follows from this.

• Airways. Ongoing wheezing or a recent exacerbation contraindicates all three vasodilators Duvall et al., 2026, Table 3. Stable asthma or COPD (chronic obstructive pulmonary disease) is different: regadenoson can be given safely, with bronchodilators and aminophylline available Duvall et al., 2026, Reactive airway disease. The 2021 chest pain guideline lists any known or suspected bronchospastic disease Gulati et al., 2021, Table 5. The tool follows the narrower 2026 wording: contraindicated when active, caution when quiescent. For active wheezing or an acute exacerbation, the guideline suggests considering dobutamine or delaying the test until the airway disease is stable Duvall et al., 2026, Reactive airway disease.
• Brain. A seizure within the last 6 months contraindicates regadenoson and adenosine, and is a caution for dipyridamole. The guideline suggests exercise or dobutamine instead Duvall et al., 2026, Seizure risk and management.
• AV node. Mobitz type 2 block, third-degree block or symptomatic bradycardia without a functioning pacemaker contraindicate vasodilators, while Mobitz type 1 (Wenckebach) and sick sinus syndrome are generally acceptable Duvall et al., 2026, Conduction disease/AV block.

Caffeine and other adenosine blockers

Caffeine blocks the receptor that vasodilators rely on. The result can be a weak stress and a falsely reassuring scan Duvall et al., 2026, Caffeine. The guideline recommends 24 hours without caffeine and requires at least 12 Duvall et al., 2026, Caffeine; intake within 12 hours is a contraindication and within 24 hours a caution Duvall et al., 2026, Tables 3 and 4. The 2023 multimodality criteria and the chest pain guideline use the same 12-hour cut-off Winchester et al., 2023, Table A footnote Gulati et al., 2021, Table 5. Dobutamine does not depend on adenosine receptors Duvall et al., 2026, Caffeine, and the guideline suggests considering it when caffeine has been taken recently Duvall et al., 2026, Regadenoson stress, Indications. Rescheduling is the other option.

Dipyridamole causes the opposite problem. Use within the last 48 hours is a contraindication to regadenoson and adenosine Duvall et al., 2026, Table 3, and so is ongoing oral dipyridamole, because it can exaggerate and potentiate their effects. Intravenous dipyridamole is then the stress agent of choice, with dobutamine second-line Duvall et al., 2026, Oral dipyridamole.

Dobutamine: faster, harder, riskier

Dobutamine stimulates beta-1 receptors, raising heart rate and contractility Pellikka et al., 2020, Table 2. Its contraindications are conditions in which a faster, harder beat is dangerous: hypertrophic obstructive cardiomyopathy or other significant outflow obstruction, prior ventricular tachycardia, poorly rate-controlled atrial fibrillation or flutter, acute left ventricular thrombus, and a symptomatic or severely enlarged aortic aneurysm Duvall et al., 2026, Table 3. Frequent premature ventricular contractions and nonsustained ventricular tachycardia are cautions Duvall et al., 2026, Table 4, and the 2021 chest pain guideline lists a high risk of arrhythmia from QT prolongation for exercise ECG and for stress echo Gulati et al., 2021, Table 5.

A beta-blocker at more than a minimal dose blunts the response rather than making dobutamine unsafe, so it is a caution Duvall et al., 2026, Table 4. Atropine is often added to reach the target heart rate Pellikka et al., 2020, Section III.b, so its contraindications, such as narrow-angle glaucoma, matter too Gulati et al., 2021, Table 5.

Conduction patterns and paced rhythms

These cause two separate problems.

The ECG cannot be read. With resting ST abnormalities, digoxin, left bundle branch block (LBBB), a Wolff-Parkinson-White pattern or ventricular pacing, an exercise ECG alone cannot diagnose ischemia, though it can still measure exercise capacity Gulati et al., 2021, Table 5. The tool labels this nondiagnostic. For LBBB and paced rhythm the ASNC guideline states that a stress imaging modality is required to assess ischemia Duvall et al., 2026, Left bundle branch block and ventricular-paced rhythm.

The images can mislead. With LBBB or ventricular pacing, a resting septal perfusion defect gets more prominent as the heart rate rises. Exercise or dobutamine can therefore produce a false reversible defect in the left anterior descending territory, while vasodilators raise the heart rate only modestly. The guideline recommends vasodilator stress without exercise for perfusion imaging, and PET over SPECT because the artifact is more common with SPECT Duvall et al., 2026, Left bundle branch block and ventricular-paced rhythm. The echo guideline prefers stress echo to SPECT in symptomatic LBBB because of its specificity Pellikka et al., 2020, Table 12.

Obstruction and the aorta

Exercise and dobutamine raise heart rate, contractility and blood pressure, which increases wall stress Duvall et al., 2026, Aortic aneurysm. Symptomatic severe aortic stenosis contraindicates every kind of stress, because valve replacement is recommended and an invasive angiogram is warranted instead Duvall et al., 2026, Aortic stenosis. Asymptomatic severe stenosis is a caution, with testing at sites that have emergency resources Duvall et al., 2026, Aortic stenosis.

For aortic aneurysm the worry is expansion or rupture. Symptomatic aneurysms contraindicate all stress, a severely enlarged one contraindicates exercise and dobutamine, and for an unrepaired aneurysm risks and benefits are weighed, with vasodilators preferred Duvall et al., 2026, Aortic aneurysm. Acute left ventricular thrombus and acute deep vein thrombosis rule out exercise; vasodilator stress is then appropriate even in patients who can exercise Duvall et al., 2026, Exercise stress, Indications.

Safe to test, hard to image

Some limits are about image quality, not safety. Echo suffers from limited acoustic windows in COPD, obesity and breast implants Winchester et al., 2023, Table A; an ultrasound enhancing agent is recommended when two or more contiguous segments or a coronary territory cannot be seen Pellikka et al., 2020, Section II.c. SPECT can underestimate disease through attenuation and motion artifacts Winchester et al., 2023, Table A, and the ASNC guideline recommends PET over SPECT in obesity Duvall et al., 2026, Obesity.

Coronary CT angiography (CCTA) needs a patient who can follow breath-hold instructions Gulati et al., 2021, Table 5, and quality falls with high or irregular heart rates, severe calcification and morbid obesity Winchester et al., 2023, Table A. Arrhythmia and artifacts can make stress MRI, SPECT or PET inconclusive Winchester et al., 2023, Table B.

Contrast, devices and radiation

• Iodinated contrast (CCTA, invasive angiography): the chest pain guideline lists allergy to iodinated contrast as a CCTA contraindication, and renal impairment, as defined by local protocols, is also listed Gulati et al., 2021, Table 5; the tool applies both to iodinated contrast in general and shows the renal limit as a caution. Kidney disease does not restrict vasodilator stress itself Duvall et al., 2026, Chronic kidney disease and end-stage renal disease.
• Gadolinium (stress MRI): a GFR below 30 mL/min/1.73 m² is listed as a contraindication Gulati et al., 2021, Table 5. SCMR cites nephrogenic systemic sclerosis and brain retention, and advises the lowest adequate dose and noncontrast techniques where possible Kramer et al., 2020, Safety considerations. The tool shows GFR 30 to 59 and dialysis as cautions.
• Devices and the scanner: a device not safe for MRI, or significant claustrophobia, contraindicates stress MRI Gulati et al., 2021, Table 5. SCMR advises generally not scanning devices implanted under 6 weeks ago or abandoned or epicardial leads, and following manufacturer rules for MR-conditional devices Kramer et al., 2020, Imaging patients with cardiac devices.
• Radiation and pregnancy: ionizing radiation should generally be avoided in pregnancy, and tests without radiation such as echo or MRI considered Gulati et al., 2021, Section 3.3; the guideline words it as “generally avoided”. For low-risk premenopausal women, testing without radiation or no testing should be considered Winchester et al., 2023, Assumptions, item 25.

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