Cardiac Imaging

Which Imaging Study Is Best for Low-to-Intermediate Risk Chest Pain? An ACR-Guided Workflow

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Which Imaging Study Is Best for Low-to-Intermediate Risk Chest Pain? An ACR-Guided Workflow

A 55-year-old patient presents to the observation unit with several hours of intermittent, substernal chest pressure. The pain is atypical, not clearly exertional, and has resolved. An initial electrocardiogram shows no ischemic changes, and the first set of high-sensitivity troponins is negative. Based on a HEART score of 4, you classify their risk for a major adverse cardiac event as low to intermediate. The immediate life-threats seem unlikely, but you need to decide on the right non-invasive test to rule out significant coronary artery disease before discharge. What is the most appropriate initial imaging study?

According to the American College of Radiology (ACR) Appropriateness Criteria, for a patient with chest pain and a low to intermediate probability for acute coronary syndrome (ACS), a transthoracic stress echocardiogram is rated Usually Appropriate. This article provides a detailed clinical workflow for this specific scenario, exploring the rationale, downstream decisions, and common pitfalls.

Who Fits the Low-to-Intermediate Probability ACS Scenario?

This guidance applies to a specific and common patient population, typically encountered in emergency departments, observation units, or outpatient clinics. The key inclusion criteria are:

  • Atypical or Concerning Chest Pain: The patient’s symptoms are concerning enough for a cardiac workup but lack the classic features of unstable angina.
  • Low-to-Intermediate Pre-test Probability: Validated risk scores like the HEART score (typically 4-6) or TIMI score place the patient outside the very-low-risk and high-risk categories.
  • Non-diagnostic Initial Tests: The initial electrocardiogram (ECG) is negative for ST-segment elevation or other dynamic ischemic changes, and initial cardiac biomarkers (e.g., troponin) are within the normal range or non-diagnostic.
  • Hemodynamic Stability: The patient is not in shock, acute heart failure, or experiencing life-threatening arrhythmias.

Conversely, this workflow is not intended for patients with a high probability of ACS. A patient with ongoing ischemic chest pain, positive troponins, or dynamic ECG changes fits the high-probability ACS scenario and often requires urgent cardiology consultation and consideration for direct invasive coronary angiography, bypassing the non-invasive imaging discussed here. It also does not apply to patients where a clear non-cardiac diagnosis (e.g., herpes zoster, chest wall trauma) has been established.

What Diagnoses Are You Working Up in This Scenario?

When ordering imaging for low-to-intermediate risk chest pain, the goal is to differentiate between several potential causes. The differential diagnosis guides the choice of study.

Demand Ischemia from Coronary Artery Disease (CAD): This is the primary concern. The patient may have a stable but significant coronary stenosis that limits blood flow during periods of increased myocardial oxygen demand (stress). A functional stress test is designed specifically to unmask this physiology.

Non-Ischemic Cardiac Conditions: The symptoms could stem from structural heart issues. A comprehensive cardiac imaging study can reveal alternative diagnoses like significant valvular heart disease (e.g., aortic stenosis), hypertrophic cardiomyopathy, or pericardial disease, all of which can present with chest pain.

Non-Obstructive Coronary Plaque: The patient may have atherosclerotic plaque that is not yet flow-limiting but still represents a risk factor for future events. Anatomic imaging can identify this, though its discovery can sometimes lead to diagnostic uncertainty and further testing.

Non-Cardiac Chest Pain: A negative cardiac workup provides reassurance and allows the clinical focus to shift toward more common causes of chest pain, such as gastroesophageal reflux disease (GERD), esophageal spasm, musculoskeletal pain, or anxiety disorders. While imaging does not diagnose these, it is crucial for safely ruling out a life-threatening cardiac cause.

Why Is Stress Echocardiography the Recommended Initial Study for Low-to-Intermediate Risk Chest Pain?

The ACR designates several imaging modalities as Usually Appropriate for this scenario, but transthoracic stress echocardiography offers a unique combination of diagnostic power, safety, and efficiency. It is a functional test that evaluates the heart’s response to stress, either through exercise (treadmill) or pharmacologic agents like dobutamine.

The core rationale is its ability to detect inducible myocardial ischemia. A region of the heart muscle supplied by a significantly narrowed coronary artery will not contract properly under stress, a finding known as a wall motion abnormality. Stress echocardiography has high sensitivity and specificity for detecting these changes, which are a strong indicator of hemodynamically significant CAD. A major advantage of this study is its complete lack of ionizing radiation (0 mSv), making it a safe choice, particularly for younger patients or those who may require future imaging.

Other studies are also rated highly but involve different trade-offs:

  • CTA Coronary Arteries with IV Contrast: Also rated Usually Appropriate. This is an anatomic test that directly visualizes the coronary arteries. It has an excellent negative predictive value, making it a powerful tool to rule out CAD. However, it involves both iodinated contrast and radiation (☢☢☢ 1-10 mSv). It may also identify non-obstructive plaque, which can create ambiguity in management.
  • SPECT or SPECT/CT MPI Rest and Stress: Also rated Usually Appropriate. This is another functional test that assesses myocardial perfusion. It is a well-validated alternative, especially in patients with poor acoustic windows for echocardiography. Its primary drawback is a significantly higher radiation dose (☢☢☢☢ 10-30 mSv).
  • US Echocardiography Transthoracic Resting: Rated May be appropriate. A resting study is insufficient for this workup. While it can identify structural abnormalities or a resting wall motion abnormality from a prior infarct, a normal resting exam does not rule out demand ischemia, which is the central clinical question.

When ordering, ensure the patient is a candidate for the chosen stress modality. If they cannot walk on a treadmill to achieve their target heart rate, a pharmacologic stress agent should be specified.

What’s the Next Step After a Stress Echocardiogram? Downstream Workflow

The results of the stress echocardiogram will guide the subsequent management plan, creating a clear decision tree for the clinician.

If the study is positive for ischemia: The presence of an inducible wall motion abnormality significantly increases the post-test probability of obstructive CAD. The appropriate next step is an urgent or semi-urgent consultation with a cardiologist. This result often leads to consideration for invasive coronary angiography to define the coronary anatomy and plan for potential revascularization (e.g., stenting or bypass surgery).

If the study is negative for ischemia: A normal stress echocardiogram, where the patient achieves an adequate level of stress, is highly reassuring. It indicates a very low short-term risk of a major adverse cardiac event. The patient can typically be discharged safely from the observation unit or emergency department. The clinical focus should then pivot to investigating common non-cardiac causes of chest pain, with follow-up arranged in the outpatient setting.

If the study is indeterminate or equivocal: This can occur due to suboptimal image quality (e.g., in patients with obesity or lung disease) or if the patient fails to reach their target heart rate, limiting the diagnostic value of the test. In this situation, clinical judgment is paramount. If suspicion for CAD remains high, the next step may be another non-invasive test with different technical properties, such as a coronary CTA or a SPECT MPI. In some cases, proceeding directly to invasive angiography may be warranted.

Pitfalls to Avoid (and When to Get Help)

Navigating the workup for low-to-intermediate risk chest pain requires careful risk stratification and test selection. Here are a few common pitfalls to avoid:

  • Mis-stratifying the Patient: Applying this pathway to a high-risk patient (e.g., with rising troponins or dynamic ECG changes) can dangerously delay necessary intervention. Always use a validated risk score and clinical judgment.
  • Ignoring Test Limitations: A stress test is only valid if an adequate level of stress is achieved. A “negative” result in a patient who only reached 70% of their maximum predicted heart rate is not reassuring.
  • Choosing an Anatomic Test When a Functional Question Is Asked: While coronary CTA is an excellent test, it answers a different question (“Is there plaque?”) than a stress test (“Is the plaque causing a blood flow problem?”). Be clear about the clinical question you need answered.

If a patient’s clinical status changes, their pain recurs and becomes more typical for ischemia, or their biomarkers become positive, escalate immediately to a cardiology consultation, as they have now moved into a higher-risk category.

Related ACR Topics and Tools

For a comprehensive overview of all clinical variants related to this topic, please see our parent guide. For tools to help with ordering, protocoling, and discussing imaging with patients, the following resources are available.

Frequently Asked Questions

What if my patient cannot exercise on a treadmill for a stress echo?

If a patient cannot exercise due to arthritis, deconditioning, or other limitations, a pharmacologic stress echocardiogram can be performed. This involves administering an intravenous medication, typically dobutamine, to increase the heart rate and contractility, simulating the effects of exercise. The diagnostic accuracy is comparable to exercise stress testing.

Why not just get a coronary CTA on every low-to-intermediate risk patient?

Coronary CTA is also rated ‘Usually Appropriate’ and is an excellent test, particularly for ruling out coronary artery disease due to its high negative predictive value. However, it involves radiation and IV contrast, and it may reveal non-obstructive plaque that leads to diagnostic uncertainty and potentially more downstream testing. A stress echo, a functional test, directly answers whether any existing plaque is causing a significant blood flow problem, which is often the more clinically relevant question.

Is a coronary artery calcium (CAC) score useful in this acute setting?

A CAC score is rated ‘May be appropriate’ by the ACR for this scenario. While it is a powerful tool for risk stratification in asymptomatic, intermediate-risk outpatients, its utility in the acute or subacute evaluation of chest pain is less established. A score of zero is very reassuring against obstructive CAD, but a positive score doesn’t confirm that the plaque is the cause of the patient’s current symptoms. It is generally considered more of a long-term risk assessment tool.

What if the stress echo is negative but my clinical suspicion for ACS remains high?

No test is perfect. If a patient has a negative stress echo but their symptoms are highly characteristic of angina or continue to evolve, further evaluation is warranted. This is a situation where clinical judgment supersedes the test result. A discussion with a cardiologist is recommended, and next steps could include a different imaging modality like coronary CTA to assess anatomy or proceeding directly to invasive coronary angiography.

Does a normal resting ECG and a negative initial troponin mean I can send the patient home without imaging?

Not necessarily. For very-low-risk patients (e.g., HEART score 0-3), a strategy of serial ECGs and troponins may be sufficient to rule out ACS. However, for the low-to-intermediate risk group (HEART score 4-6), a significant percentage may still have underlying CAD. Non-invasive testing like a stress echo is performed to further stratify this risk before determining that it is safe for the patient to be discharged.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 29, 2026