Table 2.

Indices of invasive coronary function testing.

	Definition	Abnormal findings	Considerations
Coronary flow reserve (CFR)	Ratio of coronary flow during hyperemia vs rest	Low CFR with no visualized angiographic obstruction may indicate CMD	Cannot be used independently to diagnose CMD because it reflects both epicardial and microvascular disease and is dependent on hemodynamic factors58
Fractional flow reserve (FFR)	Pressure difference proximal and distal to a given stenosis in response to intracoronary dilation with adenosine or papaverine	FFR > 0.80 and CFR ≤ 2.5 is consistent with CMD; FFR < 0.80 and CFR ≤ 2.5 is consistent with epicardial disease alone or mixed epicardial obstruction and CMD.	In comparison to FFR, CFR has greater prognostic value for adverse cardiac events in the absence of obstructive CAD and may be more useful for risk stratification in the setting of suspected CMD.63,64
Index of microvascular resistance (IMR)	Minimal achievable microvascular resistance	IMR ≥ 25 is consistent with CMD	Specific to microcirculation and independent of hemodynamic factors and epicardial stenosis,65 making it a specific and reproducible measure of CMD.66
Acetylcholine (ACh) testing	Injection of intracoronary ACh followed by assessment of coronary artery diameter, ECG changes, and patient symptoms	Reduction of coronary artery diameter <90% with ACh is consistent with endothelial dysfunction; ≥90% is consistent with epicardial vasospasm; ECG changes and symptoms only is consistent with microvascular spasm	Safe method of assessing endothelial dysfunction and coronary vasospasm

CAD, coronary artery disease; CMD, coronary microvascular dysfunction; ECG, electrocardiogram.