Learn · Part 2. The tests · 5 min read
Stress cardiac MRI
Stress perfusion or dobutamine wall motion plus scar imaging, with no radiation but real gadolinium and device questions.
60-second take
- Stress CMR shows wall motion, blood supply to the muscle and scar in one study, using a vasodilator (perfusion) or dobutamine (wall motion).
- It uses no ionizing radiation, but it uses gadolinium. Reduced kidney function, claustrophobia and devices that are not MR-safe are the usual stumbling blocks.
- Arrhythmia and artifacts can make a study inconclusive, and availability and expertise vary between centers.
- Hold caffeine before vasodilator stress, and check device safety and kidney function before booking.
What it is and how it works
Stress cardiac magnetic resonance (stress CMR) uses a strong magnet and radio waves, not X-rays, to picture the heart while it is under stress. One session can show how well the walls move, whether the muscle is getting enough blood, and whether part of it is scarred .
There are two main ways to stress the heart. In vasodilator perfusion imaging, a drug widens the coronary arteries (adenosine, dipyridamole, regadenoson or ATP) and gadolinium contrast is injected at the peak of the effect, so the scanner can watch it wash into the muscle. In dobutamine imaging, a drug speeds the heart and strengthens its beats while the scanner records wall motion at each dose step. The SCMR protocol document notes that vasodilator perfusion testing is performed more often than dobutamine functional testing . Exercise in the scanner room, on a CMR-compatible treadmill or bicycle, is a described alternative to dobutamine .
| Vasodilator perfusion | Dobutamine wall motion | |
|---|---|---|
| What is imaged | First pass of contrast through the muscle | 3 short-axis and 3 long-axis cine views at each dose step; stop for a new wall motion abnormality, a serious side effect or the target heart rate |
| Hold beforehand | Caffeine, theophylline and dipyridamole, ideally 12 to 24 hours | Beta-blockers and nitrates, ideally 12 to 24 hours |
| Not suitable (SCMR list) | Second-degree type 2 or complete AV block, systolic pressure under 90 mm Hg, severe hypertension, sinus bradycardia under 40 bpm, active bronchospasm needing regular inhalers, known drug hypersensitivity | Severe hypertension, unstable angina, severe aortic stenosis, complex arrhythmias including uncontrolled atrial fibrillation, hypertrophic obstructive cardiomyopathy, myocarditis, endocarditis or pericarditis, uncontrolled heart failure |
Scar imaging, called late gadolinium enhancement (LGE), uses the same contrast. After a wait of at least 10 minutes (shorter with lower doses), scarred muscle shows up bright.
What the result tells you
A perfusion defect is a patch of muscle that fills more slowly than its neighbours at peak stress . If there is no scar in the same place, that points to ischemia. If LGE is present, the muscle has already been damaged . Rest images are sometimes added, but the SCMR document notes that rest scanning adds little and can be omitted.
The appropriate use criteria (AUC) put numbers on how much ischemia matters. On stress CMR, moderate to severe ischemia means perfusion defects in 4 or more of 32 subsegments during vasodilator stress, which corresponds to an estimated annual risk of cardiac death or nonfatal myocardial infarction (MI) of 5% or more . In a registry of 2,496 patients with known coronary disease, an abnormal stress CMR carried nearly twice the mortality hazard .
CMR can also assess whether damaged muscle is still viable, and the AUC list viability testing as a CMR strength . For this, the SCMR protocol combines LGE with an optional low-dose dobutamine step that looks for contractile reserve .
Strengths and limitations
Strengths
- No ionizing radiation .
- Wall motion, ischemia and infarction in one study, with the option to quantify myocardial blood flow and to test viability .
- In the CE-MARC 2 trial, CMR and SPECT led to far fewer unnecessary invasive angiograms than standard testing (see Go deeper) .
Limitations
- Claustrophobia, image artifacts and safety questions with metallic devices .
- Artifacts and arrhythmia can make a study inconclusive .
- Needs dedicated equipment (a cardiac coil, ECG gating, an MR-compatible injector) and monitoring with a way to remove the patient from the scanner quickly . Availability and local expertise vary.
Practical points
- Who struggles. Patients with significant claustrophobia, or with an implanted device that is not safe for CMR or that causes artifact, are listed as not suitable . Reduced kidney function matters because of the contrast (below). Poor acoustic windows, a limit the AUC list for echocardiography, are not among the limits they list for CMR .
- Breath-holds and rhythm. Standard images need breath-holds. The SCMR document describes backups for patients who cannot hold their breath or who have irregular rhythms, such as single-shot LGE, free-breathing perfusion and real-time cine imaging .
- Caffeine. Caffeine within the past 12 hours is listed among the reasons not to proceed with vasodilator stress CMR .
- Side effects. Adenosine, ATP and regadenoson may cause flushing, chest pain, palpitations and breathlessness; more severe effects include transient heart block, hypotension or bronchospasm. Regadenoson lasts longer unless reversed, and aminophylline can itself cause arrhythmias .
- Gadolinium. The SCMR document says to keep the dose as low as possible, to consider each agent’s retention characteristics, and to use non-contrast techniques where possible, because of nephrogenic systemic sclerosis and gadolinium retention in the brain . The chest pain guideline lists a glomerular filtration rate below 30 mL/min/1.73 m² as a contraindication to stress CMR, and discourages gadolinium in pregnancy unless it is needed to guide management .
- Devices. Follow manufacturer and institutional guidance. In general, devices implanted within 6 weeks, and abandoned or epicardial leads, are not scanned unless the indication is compelling and consent is informed. The device is usually interrogated before and after the scan, and wideband LGE can reduce artifact from an ICD .
- Time. The sources do not give a total exam time. The protocol builds in waits, such as at least 10 minutes for contrast to wash out between stress and rest perfusion, and a further wait before LGE .
In the SCMR protocol, dobutamine rises in 10 μg/kg/min steps every 3 minutes until the target heart rate (85% of 220 minus age) is reached, with atropine added if the heart rate response is inadequate. Cine views are repeated at each step and reviewed immediately .
A wrinkle in the AUC definitions: mild ischemia is fewer than 4 of 32 subsegments or fewer than 3 of 16 segments, while the moderate-to-severe wall motion threshold is more than 3 of 16 segments, so a result of exactly 3 segments falls between the two definitions .
Two multicenter trials are cited by the chest pain guideline. In CE-MARC 2 (1,202 patients), CMR and SPECT each led to unnecessary invasive angiography in 7.1% to 7.5%, compared with 28.8% with standard testing. In MR-INFORM (918 patients with typical angina and multiple risk factors or a positive exercise ECG), a CMR strategy led to less revascularization than an invasive FFR strategy, with a similar rate of death, MI or target vessel revascularization .
Adding myocardial blood flow reserve to stress CMR can improve diagnostic accuracy and risk stratification in patients with chronic coronary disease, and is reasonable for patients with persistent chest pain and nonobstructive disease .
An example from the tool
Viability is one question where CMR is often considered. Open the scenario below to see how the criteria rate each test, and the reasons.
Example from the tool
Assessment of myocardial viability
- Exercise ECGRarely Appropriate
- Exercise SPECTAppropriate
- Pharmacologic SPECTAppropriate
- Pharmacologic PETAppropriate
- Exercise echoAppropriate
- Dobutamine echoAppropriate
- Stress CMRAppropriate
- CAC scoreRarely Appropriate
- CCTARarely Appropriate
- Invasive angiographyRarely Appropriate
- No testNot applicable
Try the scenario builder → to check the contraindications that apply to your patient.
Try it in the tool
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