Coronary Function Testing

Coronary flow reserve evaluates how effectively coronary blood flow increases after vasodilation, making it useful for identifying impaired dilation. The index of microvascular resistance provides additional information about resistance within the small coronary vessels. Considering both measures helps clinicians assess different aspects of coronary circulation rather than relying on a single indicator of abnormal blood flow regulation.

Vasodilator medications challenge the ability of the coronary circulation to increase flow, whereas vasoconstrictor medications test its response to narrowing stimuli. Acetylcholine can provoke vasospasm, allowing clinicians to identify an abnormal constrictive response. Comparing these responses helps separate impaired dilation from vasospastic behavior and clarifies the physiological basis of ischemic symptoms.

The test combines pressure and flow measurements with medication challenges to characterize different abnormalities. Findings may indicate disease involving the larger epicardial arteries, impaired regulation in the coronary microcirculation, or provoked vasospasm. This distinction matters because patients can have persistent angina even when an obvious blockage is not present, requiring a more specific explanation for their symptoms.

During cardiac catheterization, clinicians measure coronary pressure and flow under baseline conditions and again after administering vasodilator or vasoconstrictor medications. They may calculate coronary flow reserve and the index of microvascular resistance, while acetylcholine can be used to provoke vasospasm. The sequence compares resting and challenged physiology to reveal abnormalities that an anatomical assessment alone may not show.

It is particularly relevant when patients continue to experience angina or ischemic symptoms despite the absence of an obvious coronary blockage. In that setting, pressure and flow responses can identify impaired microvascular dilation or vasospasm as possible contributors. The added physiological information helps explain symptoms that may remain unresolved after routine evaluation of the larger coronary arteries.

Results provide a physiological classification of the patient’s coronary problem, distinguishing epicardial artery disease, coronary microvascular dysfunction, and vasospastic angina. That classification supports more precise treatment selection than symptom assessment alone. It also gives clinicians a structured way to interpret persistent ischemic symptoms and align management with the abnormal coronary response identified during testing.