Learn · Part 2. The tests · 5 min read
Stress echocardiography
How stress echo compares wall motion at rest and stress, the exercise and dobutamine options, contrast, and the limits of image quality and operator skill.
60-second take
- Stress echo looks for new regional wall motion abnormalities with stress, not for perfusion. It uses no ionizing radiation and no gadolinium.
- Exercise is preferred when the patient can exercise; dobutamine is the usual alternative. Treadmill images must be taken within 1 to 2 minutes of peak exercise.
- An ultrasound enhancing agent is recommended whenever two or more contiguous segments, or a coronary territory, are not well seen.
- Image quality and interpretation skill matter: limited windows, inadequate stress and inexperienced readers all reduce reliability.
- A stress echo that is poor quality or does not reach target heart rate is inconclusive, not normal.
What it is and how it works
Stress echocardiography takes ultrasound pictures of the heart at rest and again under stress, then compares the two. It looks at function, not blood flow directly. A region of heart muscle supplied by a narrowed artery thickens and moves less with stress than it did at rest, or less than the normal walls around it . The term for this is a new regional wall motion abnormality.
The stress options
- Exercise (treadmill or bicycle). This is the preferred stress when the patient can exercise, because it is more physiologic than drug stress and also records exercise capacity . With a treadmill, images are taken at rest and immediately after peak exercise, and they must be captured within 1 to 2 minutes because wall motion can normalize quickly. With a bicycle (upright or supine), images are taken during exercise as well, starting at 25 watts .
- Dobutamine. A preferred alternative when the patient cannot exercise. Graded doses run from 5 up to 40 micrograms per kg per minute in 3-minute stages, with atropine added if the target heart rate is not reached .
- Vasodilator (dipyridamole or adenosine). Less often used. Most labs prefer dobutamine because of its higher sensitivity, unless contrast is used to assess perfusion .
Contrast (ultrasound enhancing agents)
An intravenous microbubble contrast agent outlines the inner border of the left ventricle. The guideline recommends it whenever two or more contiguous segments, or a whole coronary territory, cannot be seen well . It has improved image quality, reader confidence and the feasibility of the test .
There is no ionizing radiation and no gadolinium, which is part of the appeal for many patients .
What you get
Each of the left ventricle’s 16 or 17 segments is scored at rest and at stress on a five-point scale, from normal or hyperkinetic to aneurysmal, and the scores are averaged into a wall motion score index . A good report states the following :
- The number, location and severity of resting and stress wall motion abnormalities, and the ejection fraction and its response to stress.
- How good the images were, and whether contrast was used (agent and dose).
- How adequate the stress was: the percentage of predicted workload for exercise, or whether the target heart rate was reached for dobutamine.
- Heart rate, blood pressure, ECG findings and symptoms at each stage.
- An overall reading: normal, ischemia, a fixed wall motion abnormality (scar), or a combination.
With bicycle or dobutamine stress, images are taken at several stages, so the lab can also see the heart rate at which ischemia first appears, and a wall motion abnormality at a low heart rate or workload usually points to severe stenosis or multivessel disease .
Accuracy and outlook. The prior version of the ASE guideline reported an average sensitivity of 88% and specificity of 83% for detecting coronary stenosis against angiography, and imaging tests are more accurate than the exercise ECG . A normal stress echo carries a benign outlook, with an event rate of 0.9% per year, while extensive and severe abnormalities carry rates up to 6.7% per year . These figures come from different study sets than the numbers quoted for other tests, so do not line them up side by side.
Strengths and limitations
Strengths
- No radiation and no gadolinium, with a favorable cost-benefit balance .
- The same study shows valves, filling pressures, pulmonary pressures and the pericardium, so it can find causes of symptoms other than ischemia .
- Higher specificity than nuclear perfusion imaging in the meta-analyses the guideline reviews, and good specificity in patients with LBBB, where the ASE favors it over SPECT .
- In the meta-analysis the guideline reviews, more sensitive than nuclear perfusion imaging for left main or multivessel disease, because relative perfusion imaging can miss balanced or global ischemia .
Limitations
- Depends on image quality. Limited acoustic windows (COPD, obesity, breast implants) are the limitation the criteria list for echo . Contrast helps, but some patients are hypersensitive to specific agents .
- Visual interpretation is subjective and needs expertise. The guideline notes that interpretation is hard to learn and sets minimum case numbers for trainees and for yearly maintenance .
- The timing is tight after treadmill exercise, and inadequate stress (under 80% of predicted workload, or target heart rate not reached) lowers sensitivity .
- It shows wall motion, not perfusion, unless a special contrast perfusion technique is used, which is not FDA approved and is used at a few experienced centers .
Practical points
| Radiation | None. |
|---|---|
| Contrast | Ultrasound enhancing agent when views are poor. Needs an IV. No iodinated contrast or gadolinium. |
| Stressor | Exercise (treadmill or bicycle), dobutamine, or a vasodilator. |
| Suits | Patients whose resting ECG cannot be interpreted during exercise, including LBBB; people who want to avoid radiation; and patients whose dyspnea needs a look at diastolic function and pressures during exercise . |
| Struggles | Poor acoustic windows (for example in COPD); inability to reach the target stress; reactive airway disease if a vasodilator is chosen . |
| Stop signs | Acute coronary syndromes, severe arrhythmias, malignant hypertension, significant outflow tract obstruction and symptomatic severe aortic stenosis make all stress testing unsafe . |
Beta-blockers. They can keep the heart rate from reaching target with dobutamine. Atropine can be added, and holding the drug for five half-lives is rarely done . If the heart rate falls short and no ischemia is found, the report should say that the test may have missed ischemia .
Wall motion abnormalities can occur without a flow-limiting stenosis, through microvascular disease, endothelial dysfunction, vasospasm, amyloid and apical ballooning syndrome. In a prognostic study, outcomes for patients with false-positive results were similar to those with true-positive results, and the guideline advises intensive risk-factor management and careful follow-up for them . A hypertensive response by itself should not make you doubt a positive study .
Low-dose dobutamine, or low-level exercise, can show contractile reserve in segments that are dysfunctional at rest. Improvement of thickening in segments that are very hypokinetic or akinetic indicates viability . A biphasic pattern, with improvement at low stress and worsening at high stress, improves sensitivity for both viability and ischemia . Compared with perfusion imaging techniques, dobutamine echo has mildly lower sensitivity for viability but better specificity .
Example from the tool
Abnormal ECG
When the resting ECG is abnormal, the exercise ECG may not be interpretable. See how the criteria rate each test in this situation.
- Exercise ECGMay Be Appropriate
- Exercise SPECTAppropriate
- Pharmacologic SPECTAppropriate
- Pharmacologic PETAppropriate
- Exercise echoAppropriate
- Dobutamine echoAppropriate
- Stress CMRAppropriate
- CAC scoreMay Be Appropriate
- CCTAAppropriate
- Invasive angiographyMay Be Appropriate
- No testMay Be Appropriate
Open this scenario in the builder →, or start from a blank one → to describe your own patient.
Try it in the tool
Sources cited on this page
Click a tag for the full reference. All references