Coronary Flow Reserve Test: Purpose, Test Details & Results

Coronary artery disease (CAD) remains a leading cause of illness and death worldwide. Diagnosing and evaluating its severity accurately is crucial for guiding treatment and improving outcomes. The coronary flow reserve (CFR) test is a powerful tool that helps clinicians assess the functional impact of coronary artery blockages beyond what anatomical imaging can show. This article takes an in-depth look at the purpose, procedures, and interpretation of the coronary flow reserve test, ensuring you understand why this test matters and what its results mean for your heart health.

Purpose of Coronary Flow Reserve Test

The coronary flow reserve test is designed to assess how well blood can flow through the coronary arteries under both resting and stressed (maximally vasodilated) conditions. Unlike traditional imaging, which focuses on the physical narrowing of arteries, the CFR test measures the true physiological impact of those narrowings, offering a more complete picture of heart health.

Why Functional Assessment Matters

Blockages in coronary arteries can limit blood supply to the heart muscle, especially during periods of stress or exertion. However, not all blockages visible on an angiogram are functionally significant. The coronary flow reserve test quantifies how much blood flow can increase above the resting state when the heart needs it most, such as during exercise or stress. A low CFR suggests that the artery cannot deliver enough blood, indicating a functionally significant blockage that may require intervention 1,3,5,8.

Risk Stratification and Outcomes

CFR provides important prognostic information. Research shows that patients with a low CFR face significantly higher risks of cardiac events, including heart attacks and death, compared to those with normal flow reserve. This information directly influences treatment strategies, such as the need for medications, angioplasty, or bypass surgery 2,6,10. By incorporating CFR into risk assessment models, clinicians can reclassify patients more accurately and ensure the right people get the right care.

Beyond the Obvious: Microvascular Health

Coronary artery disease is not always about large, visible blockages. Sometimes, the smaller arteries (microvasculature) are affected, impairing blood flow even when major vessels appear normal. CFR testing can detect these subtle changes, enabling earlier diagnosis and treatment—even before disease is visible on an angiogram 2,7.

Coronary Flow Reserve Test Details

Understanding how the CFR test is performed—and the different methods available—can help patients prepare for the procedure and appreciate the science behind it. The test can be done invasively during a cardiac catheterization, or noninvasively using advanced imaging techniques.

Invasive CFR Measurement

• How it Works: During a cardiac catheterization, a thin wire with a pressure or flow sensor is threaded into the coronary artery. Medications such as adenosine are administered to induce maximal vasodilation (to simulate stress or exercise).
• What’s Measured: The ratio of blood flow during maximal vasodilation (hyperemia) to resting blood flow is calculated. This is the coronary flow reserve (CFR). A related metric, fractional flow reserve (FFR), is calculated from pressure differences across a coronary narrowing 1,3,7,8.
• Advantages: Provides lesion-specific information and can be performed during diagnostic angiography. Highly accurate for determining the need for interventions.
• Limitations: Invasive, with small but real risks related to catheterization.

Noninvasive CFR Measurement

• Techniques:
  • PET (Positron Emission Tomography): Uses radioisotopes to quantify myocardial blood flow at rest and stress. Highly accurate in assessing both global and regional CFR 2.
  • CT Angiography (with FFR-CT): Advanced software can simulate blood flow and pressure, estimating FFR noninvasively 6,10.
  • Doppler Ultrasound: Sometimes used to measure flow velocity in coronary arteries.
• Advantages: No need for cardiac catheterization; can assess the entire coronary circulation, including microvasculature.
• Limitations: Availability, need for specialized equipment, and sometimes lower resolution for very small vessels.

Key Metrics Explained

• CFR (Coronary Flow Reserve): The ratio of maximal (stress-induced) to resting coronary blood flow. A normal CFR is generally >2.0; values below this suggest impaired blood flow 4,7.
• FFR (Fractional Flow Reserve): The ratio of maximal blood flow in a diseased artery to the flow in a normal artery. An FFR <0.75-0.80 is considered significant for ischemia and guides revascularization decisions 1,3,8,9.

Coronary Flow Reserve Test Results & Follow-Up

The results of a coronary flow reserve test provide actionable insights that help guide clinical decisions. Understanding what the numbers mean—and what steps may follow—is crucial for both patients and clinicians.

What Do the Results Mean?

• Normal CFR (usually >2.0) or FFR (>0.80): Indicates that the coronary artery can supply enough blood to meet the demands of the heart, even under stress. This suggests a low risk of ischemia and future cardiac events. Medical management and risk factor control are typically sufficient 1,2,8,9.
• Abnormal CFR (<2.0) or FFR (≤0.75–0.80): Suggests a functionally significant blockage that limits blood flow during stress. These patients have a higher risk for symptoms and events and may benefit from revascularization (angioplasty or bypass surgery) in addition to medication 1,2,3,6,8,9.
• Borderline Results: Sometimes, the results fall into a gray area. In these cases, physicians may recommend additional tests, close monitoring, or integrating CFR/FFR data with other clinical findings to make an informed decision 1,4,9.

Follow-Up and Clinical Decision-Making

• Tailored Treatment: CFR and FFR results are used in combination with symptoms, risk factors, and other test results to personalize therapy.
• Avoiding Unnecessary Procedures: Integrating CFR/FFR into clinical workflows reduces unnecessary invasive procedures by accurately identifying which patients do not need revascularization 6,10.
• Prognostic Value: Patients with impaired CFR have a higher risk of adverse cardiac events and may require more aggressive management and follow-up 2.

Examples from Research

• In patients with moderate coronary stenosis, an FFR <0.75 was strongly associated with reversible myocardial ischemia on noninvasive tests and improved after revascularization. In contrast, those with FFR ≥0.75 rarely showed ischemia and did well with medical therapy alone 1.
• Large studies using noninvasive PET-based CFR demonstrated that impaired flow reserve is linked with a 5.6-fold increase in cardiac mortality, underlining the critical value of this measurement for risk stratification 2.
• Noninvasive FFR-CT has been shown to improve diagnostic accuracy and reduce unnecessary invasive angiography, changing the management pathway for many patients 6,10.

Conclusion

The coronary flow reserve test is a cornerstone of modern heart disease evaluation, bridging the gap between anatomical imaging and true functional assessment. By providing a clear measure of how well blood flows through both large and small coronary vessels, it empowers clinicians to make better-informed decisions and tailor treatments to each patient’s unique needs.

Key takeaways:

• CFR tests measure the heart’s ability to increase blood flow when needed, revealing the true impact of coronary artery blockages.
• They provide critical information for risk assessment, guiding decisions about medication, angioplasty, or surgery.
• Both invasive and noninvasive methods are available, each with specific strengths and use cases.
• Results from CFR testing help avoid unnecessary procedures and ensure patients with significant disease get timely treatment.
• Impaired CFR is a strong predictor of cardiac risk and highlights the need for ongoing management and follow-up.

Whether you are a patient, clinician, or simply someone interested in cardiovascular health, understanding the coronary flow reserve test can lead to better outcomes and a healthier heart.