Coronary Flow Reserve

The comparison separates the heart's usual coronary blood flow from its vasodilated response. A vasodilator such as adenosine reduces microvascular resistance, allowing hyperemic flow or velocity to be compared with baseline. Because CFR is expressed as a ratio, the result reflects how much additional flow the coronary circulation can recruit, rather than resting flow alone.

A reduced CFR can arise from several levels of coronary disease rather than from one mechanism alone. Potential explanations supported by the measurement include obstructive epicardial disease, diffuse atherosclerosis, and coronary microvascular dysfunction. This broad interpretation matters because an abnormal result may indicate impaired vascular function even when the clinically relevant problem is not limited to a single focal obstruction.

Anatomical imaging identifies coronary structure, whereas CFR supplies a functional assessment of the circulation's ability to augment flow. The two perspectives can therefore answer different clinical questions and strengthen interpretation when considered together. In medicine, this complementary role is particularly useful when symptoms, suspected ischemia, or other test findings do not align clearly with anatomy.

Assessment requires a baseline coronary blood-flow or velocity measurement followed by pharmacologic hyperemia. A vasodilator such as adenosine reduces microvascular resistance, after which hyperemic flow or velocity is measured again. Clinicians calculate CFR by dividing the hyperemic value by the baseline value. This workflow links the numeric result directly to the coronary circulation's reserve response.

Clinicians may consider CFR when evaluating suspected ischemia, especially if symptoms or other test results leave the functional significance of coronary disease uncertain. Because the measurement assesses vascular performance rather than anatomy alone, it can add information to an evaluation that already includes anatomical imaging. Its role is therefore complementary, not a replacement for structural assessment.

Beyond helping characterize suspected ischemia, CFR can contribute to prognostic assessment and clinical decision-making. A reduced value signals limited flow reserve, with possible contributions from epicardial obstruction, diffuse atherosclerosis, or microvascular dysfunction. That information may help clinicians interpret inconclusive findings and guide management, although the ratio must be understood in the context of the patient's broader evaluation.